diff --git a/clang/tools/clang-scan-deps/ClangScanDeps.cpp b/clang/tools/clang-scan-deps/ClangScanDeps.cpp
@@ -15,6 +15,7 @@
 #include "clang/Tooling/DependencyScanning/DependencyScanningTool.h"
 #include "clang/Tooling/DependencyScanning/DependencyScanningWorker.h"
 #include "clang/Tooling/JSONCompilationDatabase.h"
+#include "clang/Tooling/Tooling.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/CommandLine.h"
@@ -24,6 +25,7 @@
 #include "llvm/Support/LLVMDriver.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/Signals.h"
+#include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/ThreadPool.h"
 #include "llvm/Support/Threading.h"
 #include "llvm/Support/Timer.h"
@@ -795,6 +797,7 @@ getCompilationDatabase(int argc, char **argv, std::string &ErrorMessage) {
 }
 
 int clang_scan_deps_main(int argc, char **argv, const llvm::ToolContext &) {
+  llvm::InitializeAllTargetInfos();
   std::string ErrorMessage;
   std::unique_ptr<tooling::CompilationDatabase> Compilations =
       getCompilationDatabase(argc, argv, ErrorMessage);
@@ -810,6 +813,8 @@ int clang_scan_deps_main(int argc, char **argv, const llvm::ToolContext &) {
   Compilations = expandResponseFiles(std::move(Compilations),
                                      llvm::vfs::getRealFileSystem());
 
+  Compilations = inferTargetAndDriverMode(std::move(Compilations));
+
   // The command options are rewritten to run Clang in preprocessor only mode.
   auto AdjustingCompilations =
       std::make_unique<tooling::ArgumentsAdjustingCompilations>(

diff --git a/compiler-rt/cmake/base-config-ix.cmake b/compiler-rt/cmake/base-config-ix.cmake
@@ -81,6 +81,8 @@ if("${COMPILER_RT_TEST_COMPILER}" MATCHES "clang[+]*$")
   set(COMPILER_RT_TEST_COMPILER_ID Clang)
 elseif("${COMPILER_RT_TEST_COMPILER}" MATCHES "clang.*.exe$")
   set(COMPILER_RT_TEST_COMPILER_ID Clang)
+elseif("${COMPILER_RT_TEST_COMPILER}" MATCHES "cl.exe$")
+  set(COMPILER_RT_TEST_COMPILER_ID MSVC)
 else()
   set(COMPILER_RT_TEST_COMPILER_ID GNU)
 endif()

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_common_interface.inc b/compiler-rt/lib/sanitizer_common/sanitizer_common_interface.inc
@@ -22,6 +22,7 @@ INTERFACE_FUNCTION(__sanitizer_verify_double_ended_contiguous_container)
 INTERFACE_WEAK_FUNCTION(__sanitizer_on_print)
 INTERFACE_WEAK_FUNCTION(__sanitizer_report_error_summary)
 INTERFACE_WEAK_FUNCTION(__sanitizer_sandbox_on_notify)
+INTERFACE_WEAK_FUNCTION(__sanitizer_get_dtls_size)
 // Sanitizer weak hooks
 INTERFACE_WEAK_FUNCTION(__sanitizer_weak_hook_memcmp)
 INTERFACE_WEAK_FUNCTION(__sanitizer_weak_hook_strcmp)

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_interface_internal.h b/compiler-rt/lib/sanitizer_common/sanitizer_interface_internal.h
@@ -49,6 +49,11 @@ __sanitizer_sandbox_on_notify(__sanitizer_sandbox_arguments *args);
 SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE void
 __sanitizer_report_error_summary(const char *error_summary);
 
+// Returns size of dynamically allocated block. This function can be overridden
+// by the client.
+SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE __sanitizer::uptr
+__sanitizer_get_dtls_size(const void *tls_begin);
+
 SANITIZER_INTERFACE_ATTRIBUTE void __sanitizer_cov_dump();
 SANITIZER_INTERFACE_ATTRIBUTE void __sanitizer_dump_coverage(
     const __sanitizer::uptr *pcs, const __sanitizer::uptr len);

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_tls_get_addr.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_tls_get_addr.cpp
@@ -110,15 +110,16 @@ SANITIZER_WEAK_ATTRIBUTE
 const void *__sanitizer_get_allocated_begin(const void *p);
 }
 
-static bool GetDTLSRange(uptr &tls_beg, uptr &tls_size) {
-  const void *start = __sanitizer_get_allocated_begin((void *)tls_beg);
+SANITIZER_INTERFACE_WEAK_DEF(uptr, __sanitizer_get_dtls_size,
+                             const void *tls_begin) {
+  const void *start = __sanitizer_get_allocated_begin(tls_begin);
   if (!start)
-    return false;
-  tls_beg = (uptr)start;
-  tls_size = __sanitizer_get_allocated_size(start);
+    return 0;
+  CHECK_EQ(start, tls_begin);
+  uptr tls_size = __sanitizer_get_allocated_size(start);
   VReport(2, "__tls_get_addr: glibc DTLS suspected; tls={%p,0x%zx}\n",
-          (void *)tls_beg, tls_size);
-  return true;
+          tls_begin, tls_size);
+  return tls_size;
 }
 
 DTLS::DTV *DTLS_on_tls_get_addr(void *arg_void, void *res,
@@ -142,10 +143,12 @@ DTLS::DTV *DTLS_on_tls_get_addr(void *arg_void, void *res,
     // creation.
     VReport(2, "__tls_get_addr: static tls: %p\n", (void *)tls_beg);
     tls_size = 0;
-  } else if (!GetDTLSRange(tls_beg, tls_size)) {
-    VReport(2, "__tls_get_addr: Can't guess glibc version\n");
-    // This may happen inside the DTOR of main thread, so just ignore it.
-    tls_size = 0;
+  } else {
+    tls_size = __sanitizer_get_dtls_size(reinterpret_cast<void *>(tls_beg));
+    if (!tls_size) {
+      VReport(2, "__tls_get_addr: Can't guess glibc version\n");
+      // This may happen inside the DTOR of main thread, so just ignore it.
+    }
   }
   dtv->beg = tls_beg;
   dtv->size = tls_size;
@@ -160,6 +163,9 @@ bool DTLSInDestruction(DTLS *dtls) {
 }
 
 #else
+SANITIZER_INTERFACE_WEAK_DEF(uptr, __sanitizer_get_dtls_size, const void *) {
+  return 0;
+}
 DTLS::DTV *DTLS_on_tls_get_addr(void *arg, void *res,
   unsigned long, unsigned long) { return 0; }
 DTLS *DTLS_Get() { return 0; }

diff --git a/compiler-rt/lib/sanitizer_common/weak_symbols.txt b/compiler-rt/lib/sanitizer_common/weak_symbols.txt
@@ -1,4 +1,5 @@
 ___sanitizer_free_hook
+___sanitizer_get_dtls_size
 ___sanitizer_malloc_hook
 ___sanitizer_report_error_summary
 ___sanitizer_sandbox_on_notify

diff --git a/compiler-rt/test/lit.common.cfg.py b/compiler-rt/test/lit.common.cfg.py
@@ -148,6 +148,9 @@ def push_dynamic_library_lookup_path(config, new_path):
         # requested it because it makes ASan reports more precise.
         config.debug_info_flags.append("-gcodeview")
         config.debug_info_flags.append("-gcolumn-info")
+elif compiler_id == "MSVC":
+    config.debug_info_flags = ["/Z7"]
+    config.cxx_mode_flags = []
 elif compiler_id == "GNU":
     config.cxx_mode_flags = ["-x c++"]
     config.debug_info_flags = ["-g"]

diff --git a/compiler-rt/test/sanitizer_common/TestCases/Linux/tls_get_addr.c b/compiler-rt/test/sanitizer_common/TestCases/Linux/tls_get_addr.c
@@ -0,0 +1,52 @@
+// RUN: %clang -g %s -o %t
+// RUN: %clang -g %s -DBUILD_SO -fPIC -o %t-so.so -shared
+// RUN: %run %t 2>&1 | FileCheck %s
+
+// REQUIRES: glibc
+
+// `__tls_get_addr` is somehow not invoked.
+// XFAIL: i386-linux
+
+// These don't intercept __tls_get_addr.
+// XFAIL: lsan,hwasan,ubsan
+
+#ifndef BUILD_SO
+#  include <assert.h>
+#  include <dlfcn.h>
+#  include <pthread.h>
+#  include <stdio.h>
+#  include <stdlib.h>
+
+// CHECK-COUNT-2: __sanitizer_get_dtls_size:
+size_t __sanitizer_get_dtls_size(const void *ptr) {
+  fprintf(stderr, "__sanitizer_get_dtls_size: %p\n", ptr);
+  return 0;
+}
+
+typedef long *(*get_t)();
+get_t GetTls;
+void *Thread(void *unused) { return GetTls(); }
+
+int main(int argc, char *argv[]) {
+  char path[4096];
+  snprintf(path, sizeof(path), "%s-so.so", argv[0]);
+  int i;
+
+  void *handle = dlopen(path, RTLD_LAZY);
+  if (!handle)
+    fprintf(stderr, "%s\n", dlerror());
+  assert(handle != 0);
+  GetTls = (get_t)dlsym(handle, "GetTls");
+  assert(dlerror() == 0);
+
+  pthread_t t;
+  pthread_create(&t, 0, Thread, 0);
+  pthread_join(t, 0);
+  pthread_create(&t, 0, Thread, 0);
+  pthread_join(t, 0);
+  return 0;
+}
+#else // BUILD_SO
+__thread long huge_thread_local_array[1 << 17];
+long *GetTls() { return &huge_thread_local_array[0]; }
+#endif
diff --git a/cross-project-tests/lit.cfg.py b/cross-project-tests/lit.cfg.py
@@ -81,13 +81,7 @@ def get_required_attr(config, attr_name):
 # use_clang() and use_lld() respectively, so set them to "", if needed.
 if not hasattr(config, "clang_src_dir"):
     config.clang_src_dir = ""
-# Facebook T92898286
-should_test_bolt = get_required_attr(config, "llvm_test_bolt")
-if should_test_bolt:
-    llvm_config.use_clang(required=("clang" in config.llvm_enabled_projects), additional_flags=["--post-link-optimize"])
-else:
-    llvm_config.use_clang(required=("clang" in config.llvm_enabled_projects))
-# End Facebook T92898286
+llvm_config.use_clang(required=("clang" in config.llvm_enabled_projects))
 
 if not hasattr(config, "lld_src_dir"):
     config.lld_src_dir = ""
@@ -300,9 +294,3 @@ def get_clang_default_dwarf_version_string(triple):
 # Allow 'REQUIRES: XXX-registered-target' in tests.
 for arch in config.targets_to_build:
     config.available_features.add(arch.lower() + "-registered-target")
-
-# Facebook T92898286
-# Ensure the user's PYTHONPATH is included.
-if "PYTHONPATH" in os.environ:
-    config.environment["PYTHONPATH"] = os.environ["PYTHONPATH"]
-# End Facebook T92898286
diff --git a/cross-project-tests/lit.site.cfg.py.in b/cross-project-tests/lit.site.cfg.py.in
@@ -21,10 +21,6 @@ config.mlir_src_root = "@MLIR_SOURCE_DIR@"
 
 config.llvm_use_sanitizer = "@LLVM_USE_SANITIZER@"
 
-# Facebook T92898286
-config.llvm_test_bolt = lit.util.pythonize_bool("@LLVM_TEST_BOLT@")
-# End Facebook T92898286
-
 import lit.llvm
 lit.llvm.initialize(lit_config, config)
 

diff --git a/flang/include/flang/Semantics/expression.h b/flang/include/flang/Semantics/expression.h
@@ -331,7 +331,7 @@ class ExpressionAnalyzer {
       const semantics::Scope &, bool C919bAlreadyEnforced = false);
   MaybeExpr CompleteSubscripts(ArrayRef &&);
   MaybeExpr ApplySubscripts(DataRef &&, std::vector<Subscript> &&);
-  void CheckConstantSubscripts(ArrayRef &);
+  void CheckSubscripts(ArrayRef &);
   bool CheckRanks(const DataRef &); // Return false if error exists.
   bool CheckPolymorphic(const DataRef &); // ditto
   bool CheckDataRef(const DataRef &); // ditto

diff --git a/flang/lib/Evaluate/intrinsics.cpp b/flang/lib/Evaluate/intrinsics.cpp
@@ -2264,7 +2264,7 @@ std::optional<SpecificCall> IntrinsicInterface::Match(
         messages.Say("'kind=' argument must be a constant scalar integer "
                      "whose value is a supported kind for the "
                      "intrinsic result type"_err_en_US);
-        return std::nullopt;
+        // use default kind below for error recovery
       } else if (kindDummyArg->flags.test(ArgFlag::defaultsToSameKind)) {
         CHECK(sameArg);
         resultType = *sameArg->GetType();
@@ -2274,6 +2274,8 @@ std::optional<SpecificCall> IntrinsicInterface::Match(
             DynamicType{TypeCategory::Integer, defaults.sizeIntegerKind()};
       } else {
         CHECK(kindDummyArg->flags.test(ArgFlag::defaultsToDefaultForResult));
+      }
+      if (!resultType) {
         int kind{defaults.GetDefaultKind(*category)};
         if (*category == TypeCategory::Character) { // ACHAR & CHAR
           resultType = DynamicType{kind, 1};

diff --git a/flang/lib/Semantics/check-call.cpp b/flang/lib/Semantics/check-call.cpp
@@ -1363,6 +1363,14 @@ static bool CheckElementalConformance(parser::ContextualMessages &messages,
     const auto &dummy{proc.dummyArguments.at(index++)};
     if (arg) {
       if (const auto *expr{arg->UnwrapExpr()}) {
+        if (const auto *wholeSymbol{evaluate::UnwrapWholeSymbolDataRef(arg)}) {
+          wholeSymbol = &ResolveAssociations(*wholeSymbol);
+          if (IsAssumedSizeArray(*wholeSymbol)) {
+            evaluate::SayWithDeclaration(messages, *wholeSymbol,
+                "Whole assumed-size array '%s' may not be used as an argument to an elemental procedure"_err_en_US,
+                wholeSymbol->name());
+          }
+        }
         if (auto argShape{evaluate::GetShape(context, *expr)}) {
           if (GetRank(*argShape) > 0) {
             std::string argName{"actual argument ("s + expr->AsFortran() +

diff --git a/flang/lib/Semantics/expression.cpp b/flang/lib/Semantics/expression.cpp
@@ -298,7 +298,7 @@ MaybeExpr ExpressionAnalyzer::CompleteSubscripts(ArrayRef &&ref) {
     // Subscripts of named constants are checked in folding.
     // Subscripts of DATA statement objects are checked in data statement
     // conversion to initializers.
-    CheckConstantSubscripts(ref);
+    CheckSubscripts(ref);
   }
   return Designate(DataRef{std::move(ref)});
 }
@@ -326,7 +326,7 @@ MaybeExpr ExpressionAnalyzer::ApplySubscripts(
       std::move(dataRef.u));
 }
 
-void ExpressionAnalyzer::CheckConstantSubscripts(ArrayRef &ref) {
+void ExpressionAnalyzer::CheckSubscripts(ArrayRef &ref) {
   // Fold subscript expressions and check for an empty triplet.
   const Symbol &arraySymbol{ref.base().GetLastSymbol()};
   Shape lb{GetLBOUNDs(foldingContext_, NamedEntity{arraySymbol})};
@@ -390,6 +390,13 @@ void ExpressionAnalyzer::CheckConstantSubscripts(ArrayRef &ref) {
   for (Subscript &ss : ref.subscript()) {
     auto dimLB{ToInt64(lb[dim])};
     auto dimUB{ToInt64(ub[dim])};
+    if (dimUB && dimLB && *dimUB < *dimLB) {
+      AttachDeclaration(
+          Say("Empty array dimension %d cannot be subscripted as an element or non-empty array section"_err_en_US,
+              dim + 1),
+          arraySymbol);
+      break;
+    }
     std::optional<ConstantSubscript> val[2];
     int vals{0};
     if (auto *triplet{std::get_if<Triplet>(&ss.u)}) {

diff --git a/flang/runtime/edit-input.cpp b/flang/runtime/edit-input.cpp
@@ -54,6 +54,10 @@ static RT_API_ATTRS bool CheckCompleteListDirectedField(
   }
 }
 
+static inline RT_API_ATTRS char32_t GetSeparatorChar(const DataEdit &edit) {
+  return edit.modes.editingFlags & decimalComma ? char32_t{';'} : char32_t{','};
+}
+
 template <int LOG2_BASE>
 static RT_API_ATTRS bool EditBOZInput(
     IoStatementState &io, const DataEdit &edit, void *n, std::size_t bytes) {
@@ -70,6 +74,7 @@ static RT_API_ATTRS bool EditBOZInput(
   // Count significant digits after any leading white space & zeroes
   int digits{0};
   int significantBits{0};
+  const char32_t comma{GetSeparatorChar(edit)};
   for (; next; next = io.NextInField(remaining, edit)) {
     char32_t ch{*next};
     if (ch == ' ' || ch == '\t') {
@@ -84,7 +89,7 @@ static RT_API_ATTRS bool EditBOZInput(
     } else if (LOG2_BASE >= 4 && ch >= '8' && ch <= '9') {
     } else if (LOG2_BASE >= 4 && ch >= 'A' && ch <= 'F') {
     } else if (LOG2_BASE >= 4 && ch >= 'a' && ch <= 'f') {
-    } else if (ch == ',') {
+    } else if (ch == comma) {
       break; // end non-list-directed field early
     } else {
       io.GetIoErrorHandler().SignalError(
@@ -209,6 +214,7 @@ RT_API_ATTRS bool EditIntegerInput(
   common::UnsignedInt128 value{0};
   bool any{!!sign};
   bool overflow{false};
+  const char32_t comma{GetSeparatorChar(edit)};
   for (; next; next = io.NextInField(remaining, edit)) {
     char32_t ch{*next};
     if (ch == ' ' || ch == '\t') {
@@ -221,9 +227,23 @@ RT_API_ATTRS bool EditIntegerInput(
     int digit{0};
     if (ch >= '0' && ch <= '9') {
       digit = ch - '0';
-    } else if (ch == ',') {
+    } else if (ch == comma) {
       break; // end non-list-directed field early
     } else {
+      if (edit.modes.inNamelist && ch == GetRadixPointChar(edit)) {
+        // Ignore any fractional part that might appear in NAMELIST integer
+        // input, like a few other Fortran compilers do.
+        // TODO: also process exponents?  Some compilers do, but they obviously
+        // can't just be ignored.
+        while ((next = io.NextInField(remaining, edit))) {
+          if (*next < '0' || *next > '9') {
+            break;
+          }
+        }
+        if (!next || *next == comma) {
+          break;
+        }
+      }
       io.GetIoErrorHandler().SignalError(
           "Bad character '%lc' in INTEGER input field", ch);
       return false;

diff --git a/flang/test/Semantics/elemental02.f90 b/flang/test/Semantics/elemental02.f90
@@ -0,0 +1,13 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1
+subroutine s(a)
+  real a(*)
+  interface
+    elemental function ef(efarg)
+      real, intent(in) :: efarg
+    end
+  end interface
+!ERROR: Whole assumed-size array 'a' may not be used as an argument to an elemental procedure
+  print *, sqrt(a)
+!ERROR: Whole assumed-size array 'a' may not be used as an argument to an elemental procedure
+  print *, ef(a)
+end
diff --git a/flang/test/Semantics/expr-errors06.f90 b/flang/test/Semantics/expr-errors06.f90
@@ -1,7 +1,7 @@
 ! RUN: %python %S/test_errors.py %s %flang_fc1 -Werror
 ! Check out-of-range subscripts
 subroutine subr(da)
-  real a(10), da(2,1)
+  real a(10), da(2,1), empty(1:0,1)
   integer, parameter :: n(2) = [1, 2]
   integer unknown
   !ERROR: DATA statement designator 'a(0_8)' is out of range
@@ -39,4 +39,10 @@ subroutine subr(da)
   print *, da(1,0)
   !WARNING: Subscript 2 is greater than upper bound 1 for dimension 2 of array
   print *, da(1,2)
+  print *, empty([(j,j=1,0)],1) ! ok
+  print *, empty(1:0,1) ! ok
+  print *, empty(:,1) ! ok
+  print *, empty(i:j,k) ! ok
+  !ERROR: Empty array dimension 1 cannot be subscripted as an element or non-empty array section
+  print *, empty(i,1)
 end
diff --git a/flang/test/Semantics/kinds06.f90 b/flang/test/Semantics/kinds06.f90
@@ -0,0 +1,4 @@
+!RUN: %python %S/test_errors.py %s %flang_fc1
+!ERROR: 'kind=' argument must be a constant scalar integer whose value is a supported kind for the intrinsic result type
+print *, real(1.,666)
+end
diff --git a/flang/unittests/Runtime/Namelist.cpp b/flang/unittests/Runtime/Namelist.cpp
@@ -305,4 +305,33 @@ TEST(NamelistTests, Comma) {
   EXPECT_EQ(got, expect);
 }
 
+// Tests REAL-looking input to integers
+TEST(NamelistTests, RealValueForInt) {
+  OwningPtr<Descriptor> scDesc{
+      MakeArray<TypeCategory::Integer, static_cast<int>(sizeof(int))>(
+          std::vector<int>{}, std::vector<int>{{}})};
+  const NamelistGroup::Item items[]{{"j", *scDesc}};
+  const NamelistGroup group{"nml", 1, items};
+  static char t1[]{"&nml j=123.456/"};
+  StaticDescriptor<1, true> statDesc;
+  Descriptor &internalDesc{statDesc.descriptor()};
+  internalDesc.Establish(TypeCode{CFI_type_char},
+      /*elementBytes=*/std::strlen(t1), t1, 0, nullptr, CFI_attribute_pointer);
+  auto inCookie{IONAME(BeginInternalArrayListInput)(
+      internalDesc, nullptr, 0, __FILE__, __LINE__)};
+  ASSERT_TRUE(IONAME(InputNamelist)(inCookie, group));
+  ASSERT_EQ(IONAME(EndIoStatement)(inCookie), IostatOk)
+      << "namelist real input for integer";
+  char out[16];
+  internalDesc.Establish(TypeCode{CFI_type_char}, /*elementBytes=*/sizeof out,
+      out, 0, nullptr, CFI_attribute_pointer);
+  auto outCookie{IONAME(BeginInternalArrayListOutput)(
+      internalDesc, nullptr, 0, __FILE__, __LINE__)};
+  ASSERT_TRUE(IONAME(OutputNamelist)(outCookie, group));
+  ASSERT_EQ(IONAME(EndIoStatement)(outCookie), IostatOk) << "namelist output";
+  std::string got{out, sizeof out};
+  static const std::string expect{" &NML J= 123/   "};
+  EXPECT_EQ(got, expect);
+}
+
 // TODO: Internal NAMELIST error tests
diff --git a/libcxx/.clang-format b/libcxx/.clang-format
@@ -43,7 +43,6 @@ AttributeMacros: [
                   '_LIBCPP_NO_SANITIZE',
                   '_LIBCPP_NO_UNIQUE_ADDRESS',
                   '_LIBCPP_NOALIAS',
-                  '_LIBCPP_NODISCARD',
                   '_LIBCPP_OVERRIDABLE_FUNC_VIS',
                   '_LIBCPP_STANDALONE_DEBUG',
                   '_LIBCPP_TEMPLATE_DATA_VIS',

diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
@@ -424,6 +424,7 @@ set(files
   __fwd/format.h
   __fwd/fstream.h
   __fwd/functional.h
+  __fwd/get.h
   __fwd/ios.h
   __fwd/istream.h
   __fwd/mdspan.h
@@ -440,6 +441,7 @@ set(files
   __fwd/string_view.h
   __fwd/subrange.h
   __fwd/tuple.h
+  __fwd/variant.h
   __fwd/vector.h
   __hash_table
   __ios/fpos.h

diff --git a/libcxx/include/__algorithm/adjacent_find.h b/libcxx/include/__algorithm/adjacent_find.h
@@ -26,7 +26,7 @@ _LIBCPP_PUSH_MACROS
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Iter, class _Sent, class _BinaryPredicate>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Iter
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Iter
 __adjacent_find(_Iter __first, _Sent __last, _BinaryPredicate&& __pred) {
   if (__first == __last)
     return __first;
@@ -40,13 +40,13 @@ __adjacent_find(_Iter __first, _Sent __last, _BinaryPredicate&& __pred) {
 }
 
 template <class _ForwardIterator, class _BinaryPredicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 adjacent_find(_ForwardIterator __first, _ForwardIterator __last, _BinaryPredicate __pred) {
   return std::__adjacent_find(std::move(__first), std::move(__last), __pred);
 }
 
 template <class _ForwardIterator>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 adjacent_find(_ForwardIterator __first, _ForwardIterator __last) {
   return std::adjacent_find(std::move(__first), std::move(__last), __equal_to());
 }

diff --git a/libcxx/include/__algorithm/all_of.h b/libcxx/include/__algorithm/all_of.h
@@ -19,7 +19,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _InputIterator, class _Predicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 all_of(_InputIterator __first, _InputIterator __last, _Predicate __pred) {
   for (; __first != __last; ++__first)
     if (!__pred(*__first))

diff --git a/libcxx/include/__algorithm/any_of.h b/libcxx/include/__algorithm/any_of.h
@@ -19,7 +19,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _InputIterator, class _Predicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 any_of(_InputIterator __first, _InputIterator __last, _Predicate __pred) {
   for (; __first != __last; ++__first)
     if (__pred(*__first))

diff --git a/libcxx/include/__algorithm/binary_search.h b/libcxx/include/__algorithm/binary_search.h
@@ -22,14 +22,14 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _ForwardIterator, class _Tp, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 binary_search(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value, _Compare __comp) {
   __first = std::lower_bound<_ForwardIterator, _Tp, __comp_ref_type<_Compare> >(__first, __last, __value, __comp);
   return __first != __last && !__comp(__value, *__first);
 }
 
 template <class _ForwardIterator, class _Tp>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 binary_search(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
   return std::binary_search(__first, __last, __value, __less<>());
 }

diff --git a/libcxx/include/__algorithm/count.h b/libcxx/include/__algorithm/count.h
@@ -79,7 +79,7 @@ __count(__bit_iterator<_Cp, _IsConst> __first, __bit_iterator<_Cp, _IsConst> __l
 }
 
 template <class _InputIterator, class _Tp>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __iter_diff_t<_InputIterator>
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __iter_diff_t<_InputIterator>
 count(_InputIterator __first, _InputIterator __last, const _Tp& __value) {
   __identity __proj;
   return std::__count<_ClassicAlgPolicy>(__first, __last, __value, __proj);

diff --git a/libcxx/include/__algorithm/count_if.h b/libcxx/include/__algorithm/count_if.h
@@ -20,7 +20,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _InputIterator, class _Predicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename iterator_traits<_InputIterator>::difference_type
 count_if(_InputIterator __first, _InputIterator __last, _Predicate __pred) {
   typename iterator_traits<_InputIterator>::difference_type __r(0);

diff --git a/libcxx/include/__algorithm/equal.h b/libcxx/include/__algorithm/equal.h
@@ -35,7 +35,7 @@ _LIBCPP_PUSH_MACROS
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _InputIterator1, class _InputIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __equal_iter_impl(
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __equal_iter_impl(
     _InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _BinaryPredicate& __pred) {
   for (; __first1 != __last1; ++__first1, (void)++__first2)
     if (!__pred(*__first1, *__first2))
@@ -49,28 +49,28 @@ template <class _Tp,
           __enable_if_t<__desugars_to_v<__equal_tag, _BinaryPredicate, _Tp, _Up> && !is_volatile<_Tp>::value &&
                             !is_volatile<_Up>::value && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
                         int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 __equal_iter_impl(_Tp* __first1, _Tp* __last1, _Up* __first2, _BinaryPredicate&) {
   return std::__constexpr_memcmp_equal(__first1, __first2, __element_count(__last1 - __first1));
 }
 
 template <class _InputIterator1, class _InputIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 equal(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _BinaryPredicate __pred) {
   return std::__equal_iter_impl(
       std::__unwrap_iter(__first1), std::__unwrap_iter(__last1), std::__unwrap_iter(__first2), __pred);
 }
 
 template <class _InputIterator1, class _InputIterator2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 equal(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2) {
   return std::equal(__first1, __last1, __first2, __equal_to());
 }
 
 #if _LIBCPP_STD_VER >= 14
 
 template <class _Iter1, class _Sent1, class _Iter2, class _Sent2, class _Pred, class _Proj1, class _Proj2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __equal_impl(
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __equal_impl(
     _Iter1 __first1, _Sent1 __last1, _Iter2 __first2, _Sent2 __last2, _Pred& __comp, _Proj1& __proj1, _Proj2& __proj2) {
   while (__first1 != __last1 && __first2 != __last2) {
     if (!std::__invoke(__comp, std::__invoke(__proj1, *__first1), std::__invoke(__proj2, *__first2)))
@@ -90,13 +90,13 @@ template <class _Tp,
                             __is_identity<_Proj2>::value && !is_volatile<_Tp>::value && !is_volatile<_Up>::value &&
                             __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
                         int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 __equal_impl(_Tp* __first1, _Tp* __last1, _Up* __first2, _Up*, _Pred&, _Proj1&, _Proj2&) {
   return std::__constexpr_memcmp_equal(__first1, __first2, __element_count(__last1 - __first1));
 }
 
 template <class _InputIterator1, class _InputIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 equal(_InputIterator1 __first1,
       _InputIterator1 __last1,
       _InputIterator2 __first2,
@@ -119,7 +119,7 @@ equal(_InputIterator1 __first1,
 }
 
 template <class _InputIterator1, class _InputIterator2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 equal(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2) {
   return std::equal(__first1, __last1, __first2, __last2, __equal_to());
 }

diff --git a/libcxx/include/__algorithm/equal_range.h b/libcxx/include/__algorithm/equal_range.h
@@ -60,7 +60,7 @@ __equal_range(_Iter __first, _Sent __last, const _Tp& __value, _Compare&& __comp
 }
 
 template <class _ForwardIterator, class _Tp, class _Compare>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_ForwardIterator, _ForwardIterator>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_ForwardIterator, _ForwardIterator>
 equal_range(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value, _Compare __comp) {
   static_assert(__is_callable<_Compare&, decltype(*__first), const _Tp&>::value, "The comparator has to be callable");
   static_assert(is_copy_constructible<_ForwardIterator>::value, "Iterator has to be copy constructible");
@@ -73,7 +73,7 @@ equal_range(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __valu
 }
 
 template <class _ForwardIterator, class _Tp>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_ForwardIterator, _ForwardIterator>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_ForwardIterator, _ForwardIterator>
 equal_range(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
   return std::equal_range(std::move(__first), std::move(__last), __value, __less<>());
 }

diff --git a/libcxx/include/__algorithm/find.h b/libcxx/include/__algorithm/find.h
@@ -167,7 +167,7 @@ struct __find_segment {
 
 // public API
 template <class _InputIterator, class _Tp>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
 find(_InputIterator __first, _InputIterator __last, const _Tp& __value) {
   __identity __proj;
   return std::__rewrap_iter(

diff --git a/libcxx/include/__algorithm/find_end.h b/libcxx/include/__algorithm/find_end.h
@@ -81,7 +81,7 @@ _LIBCPP_HIDE_FROM_ABI inline _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_Iter1, _Iter1>
 }
 
 template <class _ForwardIterator1, class _ForwardIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator1 __find_end_classic(
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator1 __find_end_classic(
     _ForwardIterator1 __first1,
     _ForwardIterator1 __last1,
     _ForwardIterator2 __first2,
@@ -102,7 +102,7 @@ _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Fo
 }
 
 template <class _ForwardIterator1, class _ForwardIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator1 find_end(
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator1 find_end(
     _ForwardIterator1 __first1,
     _ForwardIterator1 __last1,
     _ForwardIterator2 __first2,
@@ -112,7 +112,7 @@ _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Fo
 }
 
 template <class _ForwardIterator1, class _ForwardIterator2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator1
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator1
 find_end(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2, _ForwardIterator2 __last2) {
   return std::find_end(__first1, __last1, __first2, __last2, __equal_to());
 }

diff --git a/libcxx/include/__algorithm/find_first_of.h b/libcxx/include/__algorithm/find_first_of.h
@@ -35,7 +35,7 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator1 __find_fir
 }
 
 template <class _ForwardIterator1, class _ForwardIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator1 find_first_of(
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator1 find_first_of(
     _ForwardIterator1 __first1,
     _ForwardIterator1 __last1,
     _ForwardIterator2 __first2,
@@ -45,7 +45,7 @@ _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Fo
 }
 
 template <class _ForwardIterator1, class _ForwardIterator2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator1 find_first_of(
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator1 find_first_of(
     _ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2, _ForwardIterator2 __last2) {
   return std::__find_first_of_ce(__first1, __last1, __first2, __last2, __equal_to());
 }

diff --git a/libcxx/include/__algorithm/find_if.h b/libcxx/include/__algorithm/find_if.h
@@ -19,7 +19,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _InputIterator, class _Predicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
 find_if(_InputIterator __first, _InputIterator __last, _Predicate __pred) {
   for (; __first != __last; ++__first)
     if (__pred(*__first))

diff --git a/libcxx/include/__algorithm/find_if_not.h b/libcxx/include/__algorithm/find_if_not.h
@@ -19,7 +19,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _InputIterator, class _Predicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
 find_if_not(_InputIterator __first, _InputIterator __last, _Predicate __pred) {
   for (; __first != __last; ++__first)
     if (!__pred(*__first))

diff --git a/libcxx/include/__algorithm/includes.h b/libcxx/include/__algorithm/includes.h
@@ -47,7 +47,7 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __includes(
 }
 
 template <class _InputIterator1, class _InputIterator2, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 includes(_InputIterator1 __first1,
          _InputIterator1 __last1,
          _InputIterator2 __first2,
@@ -67,7 +67,7 @@ includes(_InputIterator1 __first1,
 }
 
 template <class _InputIterator1, class _InputIterator2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 includes(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2) {
   return std::includes(std::move(__first1), std::move(__last1), std::move(__first2), std::move(__last2), __less<>());
 }

diff --git a/libcxx/include/__algorithm/is_heap.h b/libcxx/include/__algorithm/is_heap.h
@@ -22,13 +22,13 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _RandomAccessIterator, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 is_heap(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compare __comp) {
   return std::__is_heap_until(__first, __last, static_cast<__comp_ref_type<_Compare> >(__comp)) == __last;
 }
 
 template <class _RandomAccessIterator>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 is_heap(_RandomAccessIterator __first, _RandomAccessIterator __last) {
   return std::is_heap(__first, __last, __less<>());
 }

diff --git a/libcxx/include/__algorithm/is_heap_until.h b/libcxx/include/__algorithm/is_heap_until.h
@@ -46,13 +46,13 @@ __is_heap_until(_RandomAccessIterator __first, _RandomAccessIterator __last, _Co
 }
 
 template <class _RandomAccessIterator, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _RandomAccessIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _RandomAccessIterator
 is_heap_until(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compare __comp) {
   return std::__is_heap_until(__first, __last, static_cast<__comp_ref_type<_Compare> >(__comp));
 }
 
 template <class _RandomAccessIterator>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _RandomAccessIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _RandomAccessIterator
 is_heap_until(_RandomAccessIterator __first, _RandomAccessIterator __last) {
   return std::__is_heap_until(__first, __last, __less<>());
 }

diff --git a/libcxx/include/__algorithm/is_partitioned.h b/libcxx/include/__algorithm/is_partitioned.h
@@ -18,7 +18,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _InputIterator, class _Predicate>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 is_partitioned(_InputIterator __first, _InputIterator __last, _Predicate __pred) {
   for (; __first != __last; ++__first)
     if (!__pred(*__first))

diff --git a/libcxx/include/__algorithm/is_permutation.h b/libcxx/include/__algorithm/is_permutation.h
@@ -113,7 +113,7 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __is_permutation_impl(
 
 // 2+1 iterators, predicate. Not used by range algorithms.
 template <class _AlgPolicy, class _ForwardIterator1, class _Sentinel1, class _ForwardIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __is_permutation(
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __is_permutation(
     _ForwardIterator1 __first1, _Sentinel1 __last1, _ForwardIterator2 __first2, _BinaryPredicate&& __pred) {
   // Shorten sequences as much as possible by lopping of any equal prefix.
   for (; __first1 != __last1; ++__first1, (void)++__first2) {
@@ -247,7 +247,7 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __is_permutation(
 
 // 2+1 iterators, predicate
 template <class _ForwardIterator1, class _ForwardIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool is_permutation(
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool is_permutation(
     _ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2, _BinaryPredicate __pred) {
   static_assert(__is_callable<_BinaryPredicate&, decltype(*__first1), decltype(*__first2)>::value,
                 "The comparator has to be callable");
@@ -257,7 +257,7 @@ _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool is_pe
 
 // 2+1 iterators
 template <class _ForwardIterator1, class _ForwardIterator2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2) {
   return std::is_permutation(__first1, __last1, __first2, __equal_to());
 }
@@ -266,7 +266,7 @@ is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIt
 
 // 2+2 iterators
 template <class _ForwardIterator1, class _ForwardIterator2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool is_permutation(
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool is_permutation(
     _ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2, _ForwardIterator2 __last2) {
   return std::__is_permutation<_ClassicAlgPolicy>(
       std::move(__first1),
@@ -280,7 +280,7 @@ _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 boo
 
 // 2+2 iterators, predicate
 template <class _ForwardIterator1, class _ForwardIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool is_permutation(
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool is_permutation(
     _ForwardIterator1 __first1,
     _ForwardIterator1 __last1,
     _ForwardIterator2 __first2,

diff --git a/libcxx/include/__algorithm/is_sorted.h b/libcxx/include/__algorithm/is_sorted.h
@@ -22,13 +22,13 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _ForwardIterator, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 is_sorted(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp) {
   return std::__is_sorted_until<__comp_ref_type<_Compare> >(__first, __last, __comp) == __last;
 }
 
 template <class _ForwardIterator>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 is_sorted(_ForwardIterator __first, _ForwardIterator __last) {
   return std::is_sorted(__first, __last, __less<>());
 }

diff --git a/libcxx/include/__algorithm/is_sorted_until.h b/libcxx/include/__algorithm/is_sorted_until.h
@@ -35,13 +35,13 @@ __is_sorted_until(_ForwardIterator __first, _ForwardIterator __last, _Compare __
 }
 
 template <class _ForwardIterator, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 is_sorted_until(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp) {
   return std::__is_sorted_until<__comp_ref_type<_Compare> >(__first, __last, __comp);
 }
 
 template <class _ForwardIterator>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 is_sorted_until(_ForwardIterator __first, _ForwardIterator __last) {
   return std::is_sorted_until(__first, __last, __less<>());
 }

diff --git a/libcxx/include/__algorithm/lexicographical_compare.h b/libcxx/include/__algorithm/lexicographical_compare.h
@@ -98,7 +98,7 @@ __lexicographical_compare(_Tp* __first1, _Tp* __last1, _Tp* __first2, _Tp* __las
 #endif // _LIBCPP_STD_VER >= 14
 
 template <class _InputIterator1, class _InputIterator2, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool lexicographical_compare(
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool lexicographical_compare(
     _InputIterator1 __first1,
     _InputIterator1 __last1,
     _InputIterator2 __first2,
@@ -116,7 +116,7 @@ _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 boo
 }
 
 template <class _InputIterator1, class _InputIterator2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool lexicographical_compare(
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool lexicographical_compare(
     _InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2) {
   return std::lexicographical_compare(__first1, __last1, __first2, __last2, __less<>());
 }

diff --git a/libcxx/include/__algorithm/lower_bound.h b/libcxx/include/__algorithm/lower_bound.h
@@ -28,7 +28,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _AlgPolicy, class _Iter, class _Type, class _Proj, class _Comp>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Iter __lower_bound_bisecting(
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Iter __lower_bound_bisecting(
     _Iter __first,
     const _Type& __value,
     typename iterator_traits<_Iter>::difference_type __len,
@@ -58,7 +58,7 @@ _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Iter __lo
 // whereas the one-sided version will yield O(n) operations on both counts, with a \Omega(log(n)) bound on the number of
 // comparisons.
 template <class _AlgPolicy, class _ForwardIterator, class _Sent, class _Type, class _Proj, class _Comp>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 __lower_bound_onesided(_ForwardIterator __first, _Sent __last, const _Type& __value, _Comp& __comp, _Proj& __proj) {
   // step = 0, ensuring we can always short-circuit when distance is 1 later on
   if (__first == __last || !std::__invoke(__comp, std::__invoke(__proj, *__first), __value))
@@ -84,22 +84,22 @@ __lower_bound_onesided(_ForwardIterator __first, _Sent __last, const _Type& __va
 }
 
 template <class _AlgPolicy, class _ForwardIterator, class _Sent, class _Type, class _Proj, class _Comp>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 __lower_bound(_ForwardIterator __first, _Sent __last, const _Type& __value, _Comp& __comp, _Proj& __proj) {
   const auto __dist = _IterOps<_AlgPolicy>::distance(__first, __last);
   return std::__lower_bound_bisecting<_AlgPolicy>(__first, __value, __dist, __comp, __proj);
 }
 
 template <class _ForwardIterator, class _Tp, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 lower_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value, _Compare __comp) {
   static_assert(__is_callable<_Compare&, decltype(*__first), const _Tp&>::value, "The comparator has to be callable");
   auto __proj = std::__identity();
   return std::__lower_bound<_ClassicAlgPolicy>(__first, __last, __value, __comp, __proj);
 }
 
 template <class _ForwardIterator, class _Tp>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 lower_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
   return std::lower_bound(__first, __last, __value, __less<>());
 }

diff --git a/libcxx/include/__algorithm/max.h b/libcxx/include/__algorithm/max.h
@@ -25,27 +25,27 @@ _LIBCPP_PUSH_MACROS
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Tp, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 const _Tp&
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 const _Tp&
 max(_LIBCPP_LIFETIMEBOUND const _Tp& __a, _LIBCPP_LIFETIMEBOUND const _Tp& __b, _Compare __comp) {
   return __comp(__a, __b) ? __b : __a;
 }
 
 template <class _Tp>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 const _Tp&
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 const _Tp&
 max(_LIBCPP_LIFETIMEBOUND const _Tp& __a, _LIBCPP_LIFETIMEBOUND const _Tp& __b) {
   return std::max(__a, __b, __less<>());
 }
 
 #ifndef _LIBCPP_CXX03_LANG
 
 template <class _Tp, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp
 max(initializer_list<_Tp> __t, _Compare __comp) {
   return *std::__max_element<__comp_ref_type<_Compare> >(__t.begin(), __t.end(), __comp);
 }
 
 template <class _Tp>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp max(initializer_list<_Tp> __t) {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp max(initializer_list<_Tp> __t) {
   return *std::max_element(__t.begin(), __t.end(), __less<>());
 }
 

diff --git a/libcxx/include/__algorithm/max_element.h b/libcxx/include/__algorithm/max_element.h
@@ -36,15 +36,15 @@ __max_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp
 }
 
 template <class _ForwardIterator, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator
 max_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp) {
   static_assert(
       __is_callable<_Compare&, decltype(*__first), decltype(*__first)>::value, "The comparator has to be callable");
   return std::__max_element<__comp_ref_type<_Compare> >(__first, __last, __comp);
 }
 
 template <class _ForwardIterator>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator
 max_element(_ForwardIterator __first, _ForwardIterator __last) {
   return std::max_element(__first, __last, __less<>());
 }

diff --git a/libcxx/include/__algorithm/min.h b/libcxx/include/__algorithm/min.h
@@ -25,27 +25,27 @@ _LIBCPP_PUSH_MACROS
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Tp, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 const _Tp&
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 const _Tp&
 min(_LIBCPP_LIFETIMEBOUND const _Tp& __a, _LIBCPP_LIFETIMEBOUND const _Tp& __b, _Compare __comp) {
   return __comp(__b, __a) ? __b : __a;
 }
 
 template <class _Tp>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 const _Tp&
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 const _Tp&
 min(_LIBCPP_LIFETIMEBOUND const _Tp& __a, _LIBCPP_LIFETIMEBOUND const _Tp& __b) {
   return std::min(__a, __b, __less<>());
 }
 
 #ifndef _LIBCPP_CXX03_LANG
 
 template <class _Tp, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp
 min(initializer_list<_Tp> __t, _Compare __comp) {
   return *std::__min_element<__comp_ref_type<_Compare> >(__t.begin(), __t.end(), __comp);
 }
 
 template <class _Tp>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp min(initializer_list<_Tp> __t) {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp min(initializer_list<_Tp> __t) {
   return *std::min_element(__t.begin(), __t.end(), __less<>());
 }
 

diff --git a/libcxx/include/__algorithm/min_element.h b/libcxx/include/__algorithm/min_element.h
@@ -48,7 +48,7 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Iter __min_element(_Iter __
 }
 
 template <class _ForwardIterator, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator
 min_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp) {
   static_assert(
       __has_forward_iterator_category<_ForwardIterator>::value, "std::min_element requires a ForwardIterator");
@@ -59,7 +59,7 @@ min_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp)
 }
 
 template <class _ForwardIterator>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator
 min_element(_ForwardIterator __first, _ForwardIterator __last) {
   return std::min_element(__first, __last, __less<>());
 }

diff --git a/libcxx/include/__algorithm/minmax.h b/libcxx/include/__algorithm/minmax.h
@@ -24,21 +24,21 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Tp, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<const _Tp&, const _Tp&>
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<const _Tp&, const _Tp&>
 minmax(_LIBCPP_LIFETIMEBOUND const _Tp& __a, _LIBCPP_LIFETIMEBOUND const _Tp& __b, _Compare __comp) {
   return __comp(__b, __a) ? pair<const _Tp&, const _Tp&>(__b, __a) : pair<const _Tp&, const _Tp&>(__a, __b);
 }
 
 template <class _Tp>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<const _Tp&, const _Tp&>
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<const _Tp&, const _Tp&>
 minmax(_LIBCPP_LIFETIMEBOUND const _Tp& __a, _LIBCPP_LIFETIMEBOUND const _Tp& __b) {
   return std::minmax(__a, __b, __less<>());
 }
 
 #ifndef _LIBCPP_CXX03_LANG
 
 template <class _Tp, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_Tp, _Tp>
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_Tp, _Tp>
 minmax(initializer_list<_Tp> __t, _Compare __comp) {
   static_assert(__is_callable<_Compare&, _Tp, _Tp>::value, "The comparator has to be callable");
   __identity __proj;
@@ -47,7 +47,7 @@ minmax(initializer_list<_Tp> __t, _Compare __comp) {
 }
 
 template <class _Tp>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_Tp, _Tp>
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_Tp, _Tp>
 minmax(initializer_list<_Tp> __t) {
   return std::minmax(__t, __less<>());
 }

diff --git a/libcxx/include/__algorithm/minmax_element.h b/libcxx/include/__algorithm/minmax_element.h
@@ -79,7 +79,7 @@ __minmax_element_impl(_Iter __first, _Sent __last, _Comp& __comp, _Proj& __proj)
 }
 
 template <class _ForwardIterator, class _Compare>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_ForwardIterator, _ForwardIterator>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_ForwardIterator, _ForwardIterator>
 minmax_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp) {
   static_assert(
       __has_forward_iterator_category<_ForwardIterator>::value, "std::minmax_element requires a ForwardIterator");
@@ -90,7 +90,7 @@ minmax_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __com
 }
 
 template <class _ForwardIterator>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_ForwardIterator, _ForwardIterator>
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_ForwardIterator, _ForwardIterator>
 minmax_element(_ForwardIterator __first, _ForwardIterator __last) {
   return std::minmax_element(__first, __last, __less<>());
 }

diff --git a/libcxx/include/__algorithm/mismatch.h b/libcxx/include/__algorithm/mismatch.h
@@ -37,7 +37,7 @@ _LIBCPP_PUSH_MACROS
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Iter1, class _Sent1, class _Iter2, class _Pred, class _Proj1, class _Proj2>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Iter1, _Iter2>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Iter1, _Iter2>
 __mismatch_loop(_Iter1 __first1, _Sent1 __last1, _Iter2 __first2, _Pred& __pred, _Proj1& __proj1, _Proj2& __proj2) {
   while (__first1 != __last1) {
     if (!std::__invoke(__pred, std::__invoke(__proj1, *__first1), std::__invoke(__proj2, *__first2)))
@@ -49,15 +49,15 @@ __mismatch_loop(_Iter1 __first1, _Sent1 __last1, _Iter2 __first2, _Pred& __pred,
 }
 
 template <class _Iter1, class _Sent1, class _Iter2, class _Pred, class _Proj1, class _Proj2>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Iter1, _Iter2>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Iter1, _Iter2>
 __mismatch(_Iter1 __first1, _Sent1 __last1, _Iter2 __first2, _Pred& __pred, _Proj1& __proj1, _Proj2& __proj2) {
   return std::__mismatch_loop(__first1, __last1, __first2, __pred, __proj1, __proj2);
 }
 
 #if _LIBCPP_VECTORIZE_ALGORITHMS
 
 template <class _Iter>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Iter, _Iter>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Iter, _Iter>
 __mismatch_vectorized(_Iter __first1, _Iter __last1, _Iter __first2) {
   using __value_type              = __iter_value_type<_Iter>;
   constexpr size_t __unroll_count = 4;
@@ -124,7 +124,7 @@ template <class _Tp,
           __enable_if_t<is_integral<_Tp>::value && __desugars_to_v<__equal_tag, _Pred, _Tp, _Tp> &&
                             __is_identity<_Proj1>::value && __is_identity<_Proj2>::value,
                         int> = 0>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Tp*, _Tp*>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Tp*, _Tp*>
 __mismatch(_Tp* __first1, _Tp* __last1, _Tp* __first2, _Pred&, _Proj1&, _Proj2&) {
   return std::__mismatch_vectorized(__first1, __last1, __first2);
 }
@@ -137,7 +137,7 @@ template <class _Tp,
                             __is_identity<_Proj1>::value && __is_identity<_Proj2>::value &&
                             __can_map_to_integer_v<_Tp> && __libcpp_is_trivially_equality_comparable<_Tp, _Tp>::value,
                         int> = 0>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Tp*, _Tp*>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Tp*, _Tp*>
 __mismatch(_Tp* __first1, _Tp* __last1, _Tp* __first2, _Pred& __pred, _Proj1& __proj1, _Proj2& __proj2) {
   if (__libcpp_is_constant_evaluated()) {
     return std::__mismatch_loop(__first1, __last1, __first2, __pred, __proj1, __proj2);
@@ -150,7 +150,7 @@ __mismatch(_Tp* __first1, _Tp* __last1, _Tp* __first2, _Pred& __pred, _Proj1& __
 #endif // _LIBCPP_VECTORIZE_ALGORITHMS
 
 template <class _InputIterator1, class _InputIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_InputIterator1, _InputIterator2>
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_InputIterator1, _InputIterator2>
 mismatch(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _BinaryPredicate __pred) {
   __identity __proj;
   auto __res = std::__mismatch(
@@ -159,14 +159,14 @@ mismatch(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __fi
 }
 
 template <class _InputIterator1, class _InputIterator2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_InputIterator1, _InputIterator2>
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_InputIterator1, _InputIterator2>
 mismatch(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2) {
   return std::mismatch(__first1, __last1, __first2, __equal_to());
 }
 
 #if _LIBCPP_STD_VER >= 14
 template <class _Iter1, class _Sent1, class _Iter2, class _Sent2, class _Pred, class _Proj1, class _Proj2>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Iter1, _Iter2> __mismatch(
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Iter1, _Iter2> __mismatch(
     _Iter1 __first1, _Sent1 __last1, _Iter2 __first2, _Sent2 __last2, _Pred& __pred, _Proj1& __proj1, _Proj2& __proj2) {
   while (__first1 != __last1 && __first2 != __last2) {
     if (!std::__invoke(__pred, std::__invoke(__proj1, *__first1), std::__invoke(__proj2, *__first2)))
@@ -178,14 +178,14 @@ _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Iter
 }
 
 template <class _Tp, class _Pred, class _Proj1, class _Proj2>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Tp*, _Tp*>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Tp*, _Tp*>
 __mismatch(_Tp* __first1, _Tp* __last1, _Tp* __first2, _Tp* __last2, _Pred& __pred, _Proj1& __proj1, _Proj2& __proj2) {
   auto __len = std::min(__last1 - __first1, __last2 - __first2);
   return std::__mismatch(__first1, __first1 + __len, __first2, __pred, __proj1, __proj2);
 }
 
 template <class _InputIterator1, class _InputIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_InputIterator1, _InputIterator2>
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_InputIterator1, _InputIterator2>
 mismatch(_InputIterator1 __first1,
          _InputIterator1 __last1,
          _InputIterator2 __first2,
@@ -204,7 +204,7 @@ mismatch(_InputIterator1 __first1,
 }
 
 template <class _InputIterator1, class _InputIterator2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_InputIterator1, _InputIterator2>
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_InputIterator1, _InputIterator2>
 mismatch(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2) {
   return std::mismatch(__first1, __last1, __first2, __last2, __equal_to());
 }

diff --git a/libcxx/include/__algorithm/none_of.h b/libcxx/include/__algorithm/none_of.h
@@ -19,7 +19,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _InputIterator, class _Predicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 none_of(_InputIterator __first, _InputIterator __last, _Predicate __pred) {
   for (; __first != __last; ++__first)
     if (__pred(*__first))

diff --git a/libcxx/include/__algorithm/pstl.h b/libcxx/include/__algorithm/pstl.h
@@ -352,7 +352,7 @@ template <class _ExecutionPolicy,
           class _Predicate,
           class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
           enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI bool
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool
 is_partitioned(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
   _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator, "is_partitioned requires ForwardIterators");
   using _Implementation = __pstl::__dispatch<__pstl::__is_partitioned, __pstl::__current_configuration, _RawPolicy>;

diff --git a/libcxx/include/__algorithm/remove.h b/libcxx/include/__algorithm/remove.h
@@ -24,7 +24,7 @@ _LIBCPP_PUSH_MACROS
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _ForwardIterator, class _Tp>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 remove(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
   __first = std::find(__first, __last, __value);
   if (__first != __last) {

diff --git a/libcxx/include/__algorithm/remove_if.h b/libcxx/include/__algorithm/remove_if.h
@@ -23,7 +23,7 @@ _LIBCPP_PUSH_MACROS
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _ForwardIterator, class _Predicate>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 remove_if(_ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
   __first = std::find_if<_ForwardIterator, _Predicate&>(__first, __last, __pred);
   if (__first != __last) {

diff --git a/libcxx/include/__algorithm/search.h b/libcxx/include/__algorithm/search.h
@@ -160,7 +160,7 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_Iter1, _Iter1> __searc
 }
 
 template <class _ForwardIterator1, class _ForwardIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator1
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator1
 search(_ForwardIterator1 __first1,
        _ForwardIterator1 __last1,
        _ForwardIterator2 __first2,
@@ -173,7 +173,7 @@ search(_ForwardIterator1 __first1,
 }
 
 template <class _ForwardIterator1, class _ForwardIterator2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator1
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator1
 search(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2, _ForwardIterator2 __last2) {
   return std::search(__first1, __last1, __first2, __last2, __equal_to());
 }

diff --git a/libcxx/include/__algorithm/search_n.h b/libcxx/include/__algorithm/search_n.h
@@ -136,7 +136,7 @@ __search_n_impl(_Iter1 __first, _Sent1 __last, _DiffT __count, const _Type& __va
 }
 
 template <class _ForwardIterator, class _Size, class _Tp, class _BinaryPredicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator search_n(
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator search_n(
     _ForwardIterator __first, _ForwardIterator __last, _Size __count, const _Tp& __value, _BinaryPredicate __pred) {
   static_assert(
       __is_callable<_BinaryPredicate&, decltype(*__first), const _Tp&>::value, "The comparator has to be callable");
@@ -145,7 +145,7 @@ _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Fo
 }
 
 template <class _ForwardIterator, class _Size, class _Tp>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 search_n(_ForwardIterator __first, _ForwardIterator __last, _Size __count, const _Tp& __value) {
   return std::search_n(__first, __last, std::__convert_to_integral(__count), __value, __equal_to());
 }

diff --git a/libcxx/include/__algorithm/set_intersection.h b/libcxx/include/__algorithm/set_intersection.h
@@ -84,7 +84,7 @@ template <class _AlgPolicy,
           class _InForwardIter2,
           class _Sent2,
           class _OutIter>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
 _LIBCPP_CONSTEXPR_SINCE_CXX20 __set_intersection_result<_InForwardIter1, _InForwardIter2, _OutIter>
 __set_intersection(
     _InForwardIter1 __first1,
@@ -129,7 +129,7 @@ template <class _AlgPolicy,
           class _InInputIter2,
           class _Sent2,
           class _OutIter>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
 _LIBCPP_CONSTEXPR_SINCE_CXX20 __set_intersection_result<_InInputIter1, _InInputIter2, _OutIter>
 __set_intersection(
     _InInputIter1 __first1,
@@ -160,7 +160,7 @@ __set_intersection(
 }
 
 template <class _AlgPolicy, class _Compare, class _InIter1, class _Sent1, class _InIter2, class _Sent2, class _OutIter>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
 _LIBCPP_CONSTEXPR_SINCE_CXX20 __set_intersection_result<_InIter1, _InIter2, _OutIter>
 __set_intersection(
     _InIter1 __first1, _Sent1 __last1, _InIter2 __first2, _Sent2 __last2, _OutIter __result, _Compare&& __comp) {

diff --git a/libcxx/include/__algorithm/simd_utils.h b/libcxx/include/__algorithm/simd_utils.h
@@ -110,19 +110,19 @@ using __simd_vector_underlying_type_t = decltype(std::__simd_vector_underlying_t
 
 // This isn't inlined without always_inline when loading chars.
 template <class _VecT, class _Iter>
-_LIBCPP_NODISCARD _LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _VecT __load_vector(_Iter __iter) noexcept {
+[[__nodiscard__]] _LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _VecT __load_vector(_Iter __iter) noexcept {
   return [=]<size_t... _Indices>(index_sequence<_Indices...>) _LIBCPP_ALWAYS_INLINE noexcept {
     return _VecT{__iter[_Indices]...};
   }(make_index_sequence<__simd_vector_size_v<_VecT>>{});
 }
 
 template <class _Tp, size_t _Np>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI bool __all_of(__simd_vector<_Tp, _Np> __vec) noexcept {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool __all_of(__simd_vector<_Tp, _Np> __vec) noexcept {
   return __builtin_reduce_and(__builtin_convertvector(__vec, __simd_vector<bool, _Np>));
 }
 
 template <class _Tp, size_t _Np>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI size_t __find_first_set(__simd_vector<_Tp, _Np> __vec) noexcept {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_t __find_first_set(__simd_vector<_Tp, _Np> __vec) noexcept {
   using __mask_vec = __simd_vector<bool, _Np>;
 
   // This has MSan disabled du to https://github.com/llvm/llvm-project/issues/85876
@@ -151,7 +151,7 @@ _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI size_t __find_first_set(__simd_vector<_T
 }
 
 template <class _Tp, size_t _Np>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI size_t __find_first_not_set(__simd_vector<_Tp, _Np> __vec) noexcept {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_t __find_first_not_set(__simd_vector<_Tp, _Np> __vec) noexcept {
   return std::__find_first_set(~__vec);
 }
 

diff --git a/libcxx/include/__algorithm/unique.h b/libcxx/include/__algorithm/unique.h
@@ -29,7 +29,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 // unique
 
 template <class _AlgPolicy, class _Iter, class _Sent, class _BinaryPredicate>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 std::pair<_Iter, _Iter>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 std::pair<_Iter, _Iter>
 __unique(_Iter __first, _Sent __last, _BinaryPredicate&& __pred) {
   __first = std::__adjacent_find(__first, __last, __pred);
   if (__first != __last) {
@@ -46,13 +46,13 @@ __unique(_Iter __first, _Sent __last, _BinaryPredicate&& __pred) {
 }
 
 template <class _ForwardIterator, class _BinaryPredicate>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 unique(_ForwardIterator __first, _ForwardIterator __last, _BinaryPredicate __pred) {
   return std::__unique<_ClassicAlgPolicy>(std::move(__first), std::move(__last), __pred).first;
 }
 
 template <class _ForwardIterator>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 unique(_ForwardIterator __first, _ForwardIterator __last) {
   return std::unique(__first, __last, __equal_to());
 }

diff --git a/libcxx/include/__algorithm/upper_bound.h b/libcxx/include/__algorithm/upper_bound.h
@@ -49,7 +49,7 @@ __upper_bound(_Iter __first, _Sent __last, const _Tp& __value, _Compare&& __comp
 }
 
 template <class _ForwardIterator, class _Tp, class _Compare>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 upper_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value, _Compare __comp) {
   static_assert(__is_callable<_Compare&, const _Tp&, decltype(*__first)>::value, "The comparator has to be callable");
   static_assert(is_copy_constructible<_ForwardIterator>::value, "Iterator has to be copy constructible");
@@ -58,7 +58,7 @@ upper_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __valu
 }
 
 template <class _ForwardIterator, class _Tp>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 upper_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
   return std::upper_bound(std::move(__first), std::move(__last), __value, __less<>());
 }

diff --git a/libcxx/include/__bit/bit_cast.h b/libcxx/include/__bit/bit_cast.h
@@ -22,7 +22,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 #ifndef _LIBCPP_CXX03_LANG
 
 template <class _ToType, class _FromType>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI constexpr _ToType __bit_cast(const _FromType& __from) noexcept {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI constexpr _ToType __bit_cast(const _FromType& __from) noexcept {
   return __builtin_bit_cast(_ToType, __from);
 }
 

diff --git a/libcxx/include/__bit/countl.h b/libcxx/include/__bit/countl.h
@@ -27,15 +27,15 @@ _LIBCPP_PUSH_MACROS
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned __x) _NOEXCEPT {
   return __builtin_clz(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned long __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned long __x) _NOEXCEPT {
   return __builtin_clzl(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned long long __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned long long __x) _NOEXCEPT {
   return __builtin_clzll(__x);
 }
 

diff --git a/libcxx/include/__bit/countr.h b/libcxx/include/__bit/countr.h
@@ -26,20 +26,20 @@ _LIBCPP_PUSH_MACROS
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_ctz(unsigned __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_ctz(unsigned __x) _NOEXCEPT {
   return __builtin_ctz(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_ctz(unsigned long __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_ctz(unsigned long __x) _NOEXCEPT {
   return __builtin_ctzl(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_ctz(unsigned long long __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_ctz(unsigned long long __x) _NOEXCEPT {
   return __builtin_ctzll(__x);
 }
 
 template <class _Tp>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int __countr_zero(_Tp __t) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int __countr_zero(_Tp __t) _NOEXCEPT {
 #if __has_builtin(__builtin_ctzg)
   return __builtin_ctzg(__t, numeric_limits<_Tp>::digits);
 #else  // __has_builtin(__builtin_ctzg)

diff --git a/libcxx/include/__chrono/leap_second.h b/libcxx/include/__chrono/leap_second.h
@@ -43,9 +43,9 @@ class leap_second {
   _LIBCPP_HIDE_FROM_ABI leap_second(const leap_second&)            = default;
   _LIBCPP_HIDE_FROM_ABI leap_second& operator=(const leap_second&) = default;
 
-  _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI constexpr sys_seconds date() const noexcept { return __date_; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr sys_seconds date() const noexcept { return __date_; }
 
-  _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI constexpr seconds value() const noexcept { return __value_; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr seconds value() const noexcept { return __value_; }
 
 private:
   sys_seconds __date_;

diff --git a/libcxx/include/__config b/libcxx/include/__config
@@ -1116,15 +1116,6 @@ typedef __char32_t char32_t;
 #    define _LIBCPP_USING_IF_EXISTS
 #  endif
 
-#  if __has_cpp_attribute(__nodiscard__)
-#    define _LIBCPP_NODISCARD [[__nodiscard__]]
-#  else
-// We can't use GCC's [[gnu::warn_unused_result]] and
-// __attribute__((warn_unused_result)), because GCC does not silence them via
-// (void) cast.
-#    define _LIBCPP_NODISCARD
-#  endif
-
 #  if __has_attribute(__no_destroy__)
 #    define _LIBCPP_NO_DESTROY __attribute__((__no_destroy__))
 #  else

diff --git a/libcxx/include/__filesystem/path.h b/libcxx/include/__filesystem/path.h
@@ -812,7 +812,7 @@ class _LIBCPP_EXPORTED_FROM_ABI path {
   _LIBCPP_HIDE_FROM_ABI path extension() const { return string_type(__extension()); }
 
   // query
-  _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI bool empty() const noexcept { return __pn_.empty(); }
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool empty() const noexcept { return __pn_.empty(); }
 
   _LIBCPP_HIDE_FROM_ABI bool has_root_name() const { return !__root_name().empty(); }
   _LIBCPP_HIDE_FROM_ABI bool has_root_directory() const { return !__root_directory().empty(); }

diff --git a/libcxx/include/__functional/identity.h b/libcxx/include/__functional/identity.h
@@ -26,7 +26,7 @@ struct __is_identity : false_type {};
 
 struct __identity {
   template <class _Tp>
-  _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Tp&& operator()(_Tp&& __t) const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Tp&& operator()(_Tp&& __t) const _NOEXCEPT {
     return std::forward<_Tp>(__t);
   }
 

diff --git a/libcxx/include/__fwd/get.h b/libcxx/include/__fwd/get.h
@@ -0,0 +1,24 @@
+//===---------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===---------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___FWD_GET_H
+#define _LIBCPP___FWD_GET_H
+
+#include <__config>
+#include <__fwd/array.h>
+#include <__fwd/complex.h>
+#include <__fwd/pair.h>
+#include <__fwd/subrange.h>
+#include <__fwd/tuple.h>
+#include <__fwd/variant.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#endif // _LIBCPP___FWD_GET_H
diff --git a/libcxx/include/__fwd/variant.h b/libcxx/include/__fwd/variant.h
@@ -0,0 +1,77 @@
+//===---------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===---------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___FWD_VARIANT_H
+#define _LIBCPP___FWD_VARIANT_H
+
+#include <__config>
+#include <__cstddef/size_t.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 17
+
+template <class... _Types>
+class _LIBCPP_TEMPLATE_VIS variant;
+
+template <class _Tp>
+struct _LIBCPP_TEMPLATE_VIS variant_size;
+
+template <class _Tp>
+inline constexpr size_t variant_size_v = variant_size<_Tp>::value;
+
+template <size_t _Ip, class _Tp>
+struct _LIBCPP_TEMPLATE_VIS variant_alternative;
+
+template <size_t _Ip, class _Tp>
+using variant_alternative_t = typename variant_alternative<_Ip, _Tp>::type;
+
+inline constexpr size_t variant_npos = static_cast<size_t>(-1);
+
+template <size_t _Ip, class... _Types>
+_LIBCPP_HIDE_FROM_ABI
+_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS constexpr variant_alternative_t<_Ip, variant<_Types...>>&
+get(variant<_Types...>&);
+
+template <size_t _Ip, class... _Types>
+_LIBCPP_HIDE_FROM_ABI
+_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS constexpr variant_alternative_t<_Ip, variant<_Types...>>&&
+get(variant<_Types...>&&);
+
+template <size_t _Ip, class... _Types>
+_LIBCPP_HIDE_FROM_ABI
+_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS constexpr const variant_alternative_t<_Ip, variant<_Types...>>&
+get(const variant<_Types...>&);
+
+template <size_t _Ip, class... _Types>
+_LIBCPP_HIDE_FROM_ABI
+_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS constexpr const variant_alternative_t<_Ip, variant<_Types...>>&&
+get(const variant<_Types...>&&);
+
+template <class _Tp, class... _Types>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS constexpr _Tp& get(variant<_Types...>&);
+
+template <class _Tp, class... _Types>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS constexpr _Tp&& get(variant<_Types...>&&);
+
+template <class _Tp, class... _Types>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS constexpr const _Tp& get(const variant<_Types...>&);
+
+template <class _Tp, class... _Types>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS constexpr const _Tp&&
+get(const variant<_Types...>&&);
+
+#endif // _LIBCPP_STD_VER >= 17
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_VARIANT_H
diff --git a/libcxx/include/__math/abs.h b/libcxx/include/__math/abs.h
@@ -23,19 +23,19 @@ namespace __math {
 
 // fabs
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI float fabs(float __x) _NOEXCEPT { return __builtin_fabsf(__x); }
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI float fabs(float __x) _NOEXCEPT { return __builtin_fabsf(__x); }
 
 template <class = int>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI double fabs(double __x) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI double fabs(double __x) _NOEXCEPT {
   return __builtin_fabs(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI long double fabs(long double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI long double fabs(long double __x) _NOEXCEPT {
   return __builtin_fabsl(__x);
 }
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI double fabs(_A1 __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI double fabs(_A1 __x) _NOEXCEPT {
   return __builtin_fabs((double)__x);
 }
 

diff --git a/libcxx/include/__math/copysign.h b/libcxx/include/__math/copysign.h
@@ -24,16 +24,16 @@ namespace __math {
 
 // copysign
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI float copysign(float __x, float __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI float copysign(float __x, float __y) _NOEXCEPT {
   return ::__builtin_copysignf(__x, __y);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI long double copysign(long double __x, long double __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI long double copysign(long double __x, long double __y) _NOEXCEPT {
   return ::__builtin_copysignl(__x, __y);
 }
 
 template <class _A1, class _A2, __enable_if_t<is_arithmetic<_A1>::value && is_arithmetic<_A2>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI typename __promote<_A1, _A2>::type copysign(_A1 __x, _A2 __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI typename __promote<_A1, _A2>::type copysign(_A1 __x, _A2 __y) _NOEXCEPT {
   return ::__builtin_copysign(__x, __y);
 }
 

diff --git a/libcxx/include/__math/min_max.h b/libcxx/include/__math/min_max.h
@@ -25,43 +25,43 @@ namespace __math {
 
 // fmax
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI float fmax(float __x, float __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI float fmax(float __x, float __y) _NOEXCEPT {
   return __builtin_fmaxf(__x, __y);
 }
 
 template <class = int>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI double fmax(double __x, double __y) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI double fmax(double __x, double __y) _NOEXCEPT {
   return __builtin_fmax(__x, __y);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI long double fmax(long double __x, long double __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI long double fmax(long double __x, long double __y) _NOEXCEPT {
   return __builtin_fmaxl(__x, __y);
 }
 
 template <class _A1, class _A2, __enable_if_t<is_arithmetic<_A1>::value && is_arithmetic<_A2>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI typename __promote<_A1, _A2>::type fmax(_A1 __x, _A2 __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI typename __promote<_A1, _A2>::type fmax(_A1 __x, _A2 __y) _NOEXCEPT {
   using __result_type = typename __promote<_A1, _A2>::type;
   static_assert(!(_IsSame<_A1, __result_type>::value && _IsSame<_A2, __result_type>::value), "");
   return __math::fmax((__result_type)__x, (__result_type)__y);
 }
 
 // fmin
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI float fmin(float __x, float __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI float fmin(float __x, float __y) _NOEXCEPT {
   return __builtin_fminf(__x, __y);
 }
 
 template <class = int>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI double fmin(double __x, double __y) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI double fmin(double __x, double __y) _NOEXCEPT {
   return __builtin_fmin(__x, __y);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI long double fmin(long double __x, long double __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI long double fmin(long double __x, long double __y) _NOEXCEPT {
   return __builtin_fminl(__x, __y);
 }
 
 template <class _A1, class _A2, __enable_if_t<is_arithmetic<_A1>::value && is_arithmetic<_A2>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI typename __promote<_A1, _A2>::type fmin(_A1 __x, _A2 __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI typename __promote<_A1, _A2>::type fmin(_A1 __x, _A2 __y) _NOEXCEPT {
   using __result_type = typename __promote<_A1, _A2>::type;
   static_assert(!(_IsSame<_A1, __result_type>::value && _IsSame<_A2, __result_type>::value), "");
   return __math::fmin((__result_type)__x, (__result_type)__y);

diff --git a/libcxx/include/__math/roots.h b/libcxx/include/__math/roots.h
@@ -39,19 +39,19 @@ inline _LIBCPP_HIDE_FROM_ABI double sqrt(_A1 __x) _NOEXCEPT {
 
 // cbrt
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI float cbrt(float __x) _NOEXCEPT { return __builtin_cbrtf(__x); }
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI float cbrt(float __x) _NOEXCEPT { return __builtin_cbrtf(__x); }
 
 template <class = int>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI double cbrt(double __x) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI double cbrt(double __x) _NOEXCEPT {
   return __builtin_cbrt(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI long double cbrt(long double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI long double cbrt(long double __x) _NOEXCEPT {
   return __builtin_cbrtl(__x);
 }
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI double cbrt(_A1 __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI double cbrt(_A1 __x) _NOEXCEPT {
   return __builtin_cbrt((double)__x);
 }
 

diff --git a/libcxx/include/__math/rounding_functions.h b/libcxx/include/__math/rounding_functions.h
@@ -26,37 +26,37 @@ namespace __math {
 
 // ceil
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI float ceil(float __x) _NOEXCEPT { return __builtin_ceilf(__x); }
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI float ceil(float __x) _NOEXCEPT { return __builtin_ceilf(__x); }
 
 template <class = int>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI double ceil(double __x) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI double ceil(double __x) _NOEXCEPT {
   return __builtin_ceil(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI long double ceil(long double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI long double ceil(long double __x) _NOEXCEPT {
   return __builtin_ceill(__x);
 }
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI double ceil(_A1 __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI double ceil(_A1 __x) _NOEXCEPT {
   return __builtin_ceil((double)__x);
 }
 
 // floor
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI float floor(float __x) _NOEXCEPT { return __builtin_floorf(__x); }
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI float floor(float __x) _NOEXCEPT { return __builtin_floorf(__x); }
 
 template <class = int>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI double floor(double __x) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI double floor(double __x) _NOEXCEPT {
   return __builtin_floor(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI long double floor(long double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI long double floor(long double __x) _NOEXCEPT {
   return __builtin_floorl(__x);
 }
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI double floor(_A1 __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI double floor(_A1 __x) _NOEXCEPT {
   return __builtin_floor((double)__x);
 }
 
@@ -126,21 +126,21 @@ inline _LIBCPP_HIDE_FROM_ABI long lround(_A1 __x) _NOEXCEPT {
 
 // nearbyint
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI float nearbyint(float __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI float nearbyint(float __x) _NOEXCEPT {
   return __builtin_nearbyintf(__x);
 }
 
 template <class = int>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI double nearbyint(double __x) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI double nearbyint(double __x) _NOEXCEPT {
   return __builtin_nearbyint(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI long double nearbyint(long double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI long double nearbyint(long double __x) _NOEXCEPT {
   return __builtin_nearbyintl(__x);
 }
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI double nearbyint(_A1 __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI double nearbyint(_A1 __x) _NOEXCEPT {
   return __builtin_nearbyint((double)__x);
 }
 
@@ -186,55 +186,55 @@ inline _LIBCPP_HIDE_FROM_ABI double nexttoward(_A1 __x, long double __y) _NOEXCE
 
 // rint
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI float rint(float __x) _NOEXCEPT { return __builtin_rintf(__x); }
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI float rint(float __x) _NOEXCEPT { return __builtin_rintf(__x); }
 
 template <class = int>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI double rint(double __x) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI double rint(double __x) _NOEXCEPT {
   return __builtin_rint(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI long double rint(long double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI long double rint(long double __x) _NOEXCEPT {
   return __builtin_rintl(__x);
 }
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI double rint(_A1 __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI double rint(_A1 __x) _NOEXCEPT {
   return __builtin_rint((double)__x);
 }
 
 // round
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI float round(float __x) _NOEXCEPT { return __builtin_round(__x); }
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI float round(float __x) _NOEXCEPT { return __builtin_round(__x); }
 
 template <class = int>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI double round(double __x) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI double round(double __x) _NOEXCEPT {
   return __builtin_round(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI long double round(long double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI long double round(long double __x) _NOEXCEPT {
   return __builtin_roundl(__x);
 }
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI double round(_A1 __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI double round(_A1 __x) _NOEXCEPT {
   return __builtin_round((double)__x);
 }
 
 // trunc
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI float trunc(float __x) _NOEXCEPT { return __builtin_trunc(__x); }
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI float trunc(float __x) _NOEXCEPT { return __builtin_trunc(__x); }
 
 template <class = int>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI double trunc(double __x) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI double trunc(double __x) _NOEXCEPT {
   return __builtin_trunc(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI long double trunc(long double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI long double trunc(long double __x) _NOEXCEPT {
   return __builtin_truncl(__x);
 }
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI double trunc(_A1 __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI double trunc(_A1 __x) _NOEXCEPT {
   return __builtin_trunc((double)__x);
 }
 

diff --git a/libcxx/include/__math/traits.h b/libcxx/include/__math/traits.h
@@ -12,7 +12,6 @@
 #include <__config>
 #include <__type_traits/enable_if.h>
 #include <__type_traits/is_arithmetic.h>
-#include <__type_traits/is_floating_point.h>
 #include <__type_traits/is_integral.h>
 #include <__type_traits/is_signed.h>
 #include <__type_traits/promote.h>
@@ -34,52 +33,65 @@ namespace __math {
 #  define _LIBCPP_SIGNBIT_CONSTEXPR
 #endif
 
-template <class _A1, __enable_if_t<is_floating_point<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_SIGNBIT_CONSTEXPR _LIBCPP_HIDE_FROM_ABI bool signbit(_A1 __x) _NOEXCEPT {
+// The universal C runtime (UCRT) in the WinSDK provides floating point overloads
+// for std::signbit(). By defining our overloads as templates, we can work around
+// this issue as templates are less preferred than non-template functions.
+template <class = void>
+[[__nodiscard__]] inline _LIBCPP_SIGNBIT_CONSTEXPR _LIBCPP_HIDE_FROM_ABI bool signbit(float __x) _NOEXCEPT {
+  return __builtin_signbit(__x);
+}
+
+template <class = void>
+[[__nodiscard__]] inline _LIBCPP_SIGNBIT_CONSTEXPR _LIBCPP_HIDE_FROM_ABI bool signbit(double __x) _NOEXCEPT {
+  return __builtin_signbit(__x);
+}
+
+template <class = void>
+[[__nodiscard__]] inline _LIBCPP_SIGNBIT_CONSTEXPR _LIBCPP_HIDE_FROM_ABI bool signbit(long double __x) _NOEXCEPT {
   return __builtin_signbit(__x);
 }
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value && is_signed<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_SIGNBIT_CONSTEXPR _LIBCPP_HIDE_FROM_ABI bool signbit(_A1 __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_SIGNBIT_CONSTEXPR _LIBCPP_HIDE_FROM_ABI bool signbit(_A1 __x) _NOEXCEPT {
   return __x < 0;
 }
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value && !is_signed<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_SIGNBIT_CONSTEXPR _LIBCPP_HIDE_FROM_ABI bool signbit(_A1) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_SIGNBIT_CONSTEXPR _LIBCPP_HIDE_FROM_ABI bool signbit(_A1) _NOEXCEPT {
   return false;
 }
 
 // isfinite
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(_A1) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(_A1) _NOEXCEPT {
   return true;
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(float __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(float __x) _NOEXCEPT {
   return __builtin_isfinite(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(double __x) _NOEXCEPT {
   return __builtin_isfinite(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(long double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(long double __x) _NOEXCEPT {
   return __builtin_isfinite(__x);
 }
 
 // isinf
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isinf(_A1) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isinf(_A1) _NOEXCEPT {
   return false;
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isinf(float __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isinf(float __x) _NOEXCEPT {
   return __builtin_isinf(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI
 #ifdef _LIBCPP_PREFERRED_OVERLOAD
 _LIBCPP_PREFERRED_OVERLOAD
 #endif
@@ -88,22 +100,22 @@ _LIBCPP_PREFERRED_OVERLOAD
   return __builtin_isinf(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isinf(long double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isinf(long double __x) _NOEXCEPT {
   return __builtin_isinf(__x);
 }
 
 // isnan
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(_A1) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(_A1) _NOEXCEPT {
   return false;
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(float __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(float __x) _NOEXCEPT {
   return __builtin_isnan(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI
 #ifdef _LIBCPP_PREFERRED_OVERLOAD
 _LIBCPP_PREFERRED_OVERLOAD
 #endif
@@ -112,73 +124,73 @@ _LIBCPP_PREFERRED_OVERLOAD
   return __builtin_isnan(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(long double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(long double __x) _NOEXCEPT {
   return __builtin_isnan(__x);
 }
 
 // isnormal
 
 template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(_A1 __x) _NOEXCEPT {
+[[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(_A1 __x) _NOEXCEPT {
   return __x != 0;
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(float __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(float __x) _NOEXCEPT {
   return __builtin_isnormal(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(double __x) _NOEXCEPT {
   return __builtin_isnormal(__x);
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(long double __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(long double __x) _NOEXCEPT {
   return __builtin_isnormal(__x);
 }
 
 // isgreater
 
 template <class _A1, class _A2, __enable_if_t<is_arithmetic<_A1>::value && is_arithmetic<_A2>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI bool isgreater(_A1 __x, _A2 __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI bool isgreater(_A1 __x, _A2 __y) _NOEXCEPT {
   using type = typename __promote<_A1, _A2>::type;
   return __builtin_isgreater((type)__x, (type)__y);
 }
 
 // isgreaterequal
 
 template <class _A1, class _A2, __enable_if_t<is_arithmetic<_A1>::value && is_arithmetic<_A2>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI bool isgreaterequal(_A1 __x, _A2 __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI bool isgreaterequal(_A1 __x, _A2 __y) _NOEXCEPT {
   using type = typename __promote<_A1, _A2>::type;
   return __builtin_isgreaterequal((type)__x, (type)__y);
 }
 
 // isless
 
 template <class _A1, class _A2, __enable_if_t<is_arithmetic<_A1>::value && is_arithmetic<_A2>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI bool isless(_A1 __x, _A2 __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI bool isless(_A1 __x, _A2 __y) _NOEXCEPT {
   using type = typename __promote<_A1, _A2>::type;
   return __builtin_isless((type)__x, (type)__y);
 }
 
 // islessequal
 
 template <class _A1, class _A2, __enable_if_t<is_arithmetic<_A1>::value && is_arithmetic<_A2>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI bool islessequal(_A1 __x, _A2 __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI bool islessequal(_A1 __x, _A2 __y) _NOEXCEPT {
   using type = typename __promote<_A1, _A2>::type;
   return __builtin_islessequal((type)__x, (type)__y);
 }
 
 // islessgreater
 
 template <class _A1, class _A2, __enable_if_t<is_arithmetic<_A1>::value && is_arithmetic<_A2>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI bool islessgreater(_A1 __x, _A2 __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI bool islessgreater(_A1 __x, _A2 __y) _NOEXCEPT {
   using type = typename __promote<_A1, _A2>::type;
   return __builtin_islessgreater((type)__x, (type)__y);
 }
 
 // isunordered
 
 template <class _A1, class _A2, __enable_if_t<is_arithmetic<_A1>::value && is_arithmetic<_A2>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI bool isunordered(_A1 __x, _A2 __y) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI bool isunordered(_A1 __x, _A2 __y) _NOEXCEPT {
   using type = typename __promote<_A1, _A2>::type;
   return __builtin_isunordered((type)__x, (type)__y);
 }

diff --git a/libcxx/include/__memory/allocate_at_least.h b/libcxx/include/__memory/allocate_at_least.h
@@ -35,7 +35,7 @@ struct __allocation_result {
 };
 
 template <class _Alloc>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
 _LIBCPP_CONSTEXPR __allocation_result<typename allocator_traits<_Alloc>::pointer>
 __allocate_at_least(_Alloc& __alloc, size_t __n) {
   return {__alloc.allocate(__n), __n};

diff --git a/libcxx/include/__memory/allocator.h b/libcxx/include/__memory/allocator.h
@@ -93,7 +93,7 @@ class _LIBCPP_TEMPLATE_VIS allocator : private __non_trivial_if<!is_void<_Tp>::v
   template <class _Up>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 allocator(const allocator<_Up>&) _NOEXCEPT {}
 
-  _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp* allocate(size_t __n) {
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp* allocate(size_t __n) {
     static_assert(sizeof(_Tp) >= 0, "cannot allocate memory for an incomplete type");
     if (__n > allocator_traits<allocator>::max_size(*this))
       __throw_bad_array_new_length();
@@ -138,7 +138,7 @@ class _LIBCPP_TEMPLATE_VIS allocator : private __non_trivial_if<!is_void<_Tp>::v
     return std::addressof(__x);
   }
 
-  _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX17 _Tp* allocate(size_t __n, const void*) {
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX17 _Tp* allocate(size_t __n, const void*) {
     return allocate(__n);
   }
 

diff --git a/libcxx/include/__memory/allocator_traits.h b/libcxx/include/__memory/allocator_traits.h
@@ -275,13 +275,13 @@ struct _LIBCPP_TEMPLATE_VIS allocator_traits {
   };
 #endif // _LIBCPP_CXX03_LANG
 
-  _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static pointer
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static pointer
   allocate(allocator_type& __a, size_type __n) {
     return __a.allocate(__n);
   }
 
   template <class _Ap = _Alloc, __enable_if_t<__has_allocate_hint<_Ap, size_type, const_void_pointer>::value, int> = 0>
-  _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static pointer
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static pointer
   allocate(allocator_type& __a, size_type __n, const_void_pointer __hint) {
     _LIBCPP_SUPPRESS_DEPRECATED_PUSH
     return __a.allocate(__n, __hint);
@@ -290,7 +290,7 @@ struct _LIBCPP_TEMPLATE_VIS allocator_traits {
   template <class _Ap                                                                           = _Alloc,
             class                                                                               = void,
             __enable_if_t<!__has_allocate_hint<_Ap, size_type, const_void_pointer>::value, int> = 0>
-  _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static pointer
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static pointer
   allocate(allocator_type& __a, size_type __n, const_void_pointer) {
     return __a.allocate(__n);
   }

diff --git a/libcxx/include/__memory/assume_aligned.h b/libcxx/include/__memory/assume_aligned.h
@@ -23,7 +23,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <size_t _Np, class _Tp>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __assume_aligned(_Tp* __ptr) {
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __assume_aligned(_Tp* __ptr) {
   static_assert(_Np != 0 && (_Np & (_Np - 1)) == 0, "std::assume_aligned<N>(p) requires N to be a power of two");
 
   if (__libcpp_is_constant_evaluated()) {

diff --git a/libcxx/include/__memory/temporary_buffer.h b/libcxx/include/__memory/temporary_buffer.h
@@ -22,7 +22,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Tp>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _LIBCPP_DEPRECATED_IN_CXX17 pair<_Tp*, ptrdiff_t>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _LIBCPP_DEPRECATED_IN_CXX17 pair<_Tp*, ptrdiff_t>
 get_temporary_buffer(ptrdiff_t __n) _NOEXCEPT {
   pair<_Tp*, ptrdiff_t> __r(0, 0);
   const ptrdiff_t __m =

diff --git a/libcxx/include/__mutex/lock_guard.h b/libcxx/include/__mutex/lock_guard.h
@@ -27,13 +27,13 @@ class _LIBCPP_TEMPLATE_VIS _LIBCPP_THREAD_SAFETY_ANNOTATION(scoped_lockable) loc
   mutex_type& __m_;
 
 public:
-  _LIBCPP_NODISCARD
+  [[__nodiscard__]]
   _LIBCPP_HIDE_FROM_ABI explicit lock_guard(mutex_type& __m) _LIBCPP_THREAD_SAFETY_ANNOTATION(acquire_capability(__m))
       : __m_(__m) {
     __m_.lock();
   }
 
-  _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI lock_guard(mutex_type& __m, adopt_lock_t)
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI lock_guard(mutex_type& __m, adopt_lock_t)
       _LIBCPP_THREAD_SAFETY_ANNOTATION(requires_capability(__m))
       : __m_(__m) {}
   _LIBCPP_HIDE_FROM_ABI ~lock_guard() _LIBCPP_THREAD_SAFETY_ANNOTATION(release_capability()) { __m_.unlock(); }