[C++17] Support __GCC_[CON|DE]STRUCTIVE_SIZE

clang/docs/LanguageExtensions.rst

@@ -5571,3 +5571,17 @@ but the expression has no runtime effects.
 Type- and value-dependent expressions are not supported yet.
 
 This facility is designed to aid with testing name lookup machinery.
+
+Predefined Macros
+=================
+
+`__GCC_DESTRUCTIVE_SIZE` and `__GCC_CONSTRUCTIVE_SIZE`
+------------------------------------------------------
+Specify the mimum offset between two objects to avoid false sharing and the
+maximum size of contiguous memory to promote true sharing, respectively. These
+macros are predefined in all C and C++ language modes.
+
+**Note: the values the macros expand to are not stable between releases of Clang
+and do not need to match the values produced by GCC, so these macros should not
+be used from header files because they may not be stable across multiple TUs
+(the values may vary based on compiler version as well as CPU tuning).**

clang/docs/ReleaseNotes.rst

@@ -89,6 +89,18 @@ sections with improvements to Clang's support for those languages.
 C++ Language Changes
 --------------------
 
+C++17 Feature Support
+^^^^^^^^^^^^^^^^^^^^^
+- Clang now exposes ``__GCC_DESTRUCTIVE_SIZE`` and ``__GCC_CONSTRUCTIVE_SIZE``
+  predefined macros to support standard library implementations of
+  ``std::hardware_destructive_interference_size`` and
+  ``std::hardware_constructive_interference_size``, respectively. These macros
+  are predefined in all C and C++ language modes. The values the macros
+  expand to are not stable between releases of Clang and do not need to match
+  the values produced by GCC, so these macros should not be used from header
+  files because they may not be stable across multiple TUs (the values may vary
+  based on compiler version as well as CPU tuning). #GH60174
+
 C++20 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^
 

clang/include/clang/Basic/TargetInfo.h

@@ -1792,6 +1792,11 @@ class TargetInfo : public TransferrableTargetInfo,
   /// Whether to support HIP image/texture API's.
   virtual bool hasHIPImageSupport() const { return true; }
 
+  /// The minimum offset between two objects to avoid false sharing.
+  virtual unsigned hardwareDestructiveInterferenceSize() const { return 64; }
+  // The maximum size of contiguous memory to promote true sharing.
+  virtual unsigned hardwareConstructiveInterferenceSize() const { return 64; }
+
 protected:
   /// Copy type and layout related info.
   void copyAuxTarget(const TargetInfo *Aux);

clang/lib/Basic/Targets/ARM.h

@@ -225,6 +225,10 @@ class LLVM_LIBRARY_VISIBILITY ARMTargetInfo : public TargetInfo {
   bool hasBitIntType() const override { return true; }
 
   const char *getBFloat16Mangling() const override { return "u6__bf16"; };
+
+  virtual unsigned hardwareDestructiveInterferenceSize() const override {
+    return getTriple().isArch64Bit() ? 256 : 64;
+  }
 };
 
 class LLVM_LIBRARY_VISIBILITY ARMleTargetInfo : public ARMTargetInfo {

clang/lib/Basic/Targets/AVR.h

@@ -175,6 +175,13 @@ class LLVM_LIBRARY_VISIBILITY AVRTargetInfo : public TargetInfo {
   std::optional<std::string> handleAsmEscapedChar(char EscChar) const override;
   StringRef getABI() const override { return ABI; }
 
+  virtual unsigned hardwareDestructiveInterferenceSize() const override {
+    return 32;
+  }
+  virtual unsigned hardwareConstructiveInterferenceSize() const override {
+    return 32;
+  }
+
 protected:
   std::string CPU;
   StringRef ABI;

clang/lib/Basic/Targets/BPF.h

@@ -113,6 +113,13 @@ class LLVM_LIBRARY_VISIBILITY BPFTargetInfo : public TargetInfo {
     StringRef CPUName(Name);
     return isValidCPUName(CPUName);
   }
+
+  virtual unsigned hardwareDestructiveInterferenceSize() const override {
+    return 32;
+  }
+  virtual unsigned hardwareConstructiveInterferenceSize() const override {
+    return 32;
+  }
 };
 } // namespace targets
 } // namespace clang

clang/lib/Basic/Targets/M68k.h

@@ -56,6 +56,13 @@ class LLVM_LIBRARY_VISIBILITY M68kTargetInfo : public TargetInfo {
   BuiltinVaListKind getBuiltinVaListKind() const override;
   bool setCPU(const std::string &Name) override;
   CallingConvCheckResult checkCallingConvention(CallingConv CC) const override;
+
+  virtual unsigned hardwareDestructiveInterferenceSize() const override {
+    return 32;
+  }
+  virtual unsigned hardwareConstructiveInterferenceSize() const override {
+    return 32;
+  }
 };
 
 } // namespace targets

clang/lib/Basic/Targets/Mips.h

@@ -431,6 +431,13 @@ class LLVM_LIBRARY_VISIBILITY MipsTargetInfo : public TargetInfo {
 
   bool validateTarget(DiagnosticsEngine &Diags) const override;
   bool hasBitIntType() const override { return true; }
+
+  virtual unsigned hardwareDestructiveInterferenceSize() const override {
+    return 32;
+  }
+  virtual unsigned hardwareConstructiveInterferenceSize() const override {
+    return 32;
+  }
 };
 } // namespace targets
 } // namespace clang

clang/lib/Basic/Targets/PPC.h

@@ -422,6 +422,13 @@ class LLVM_LIBRARY_VISIBILITY PPC32TargetInfo : public PPCTargetInfo {
     // This is the ELF definition
     return TargetInfo::PowerABIBuiltinVaList;
   }
+
+  virtual unsigned hardwareDestructiveInterferenceSize() const override {
+    return 32;
+  }
+  virtual unsigned hardwareConstructiveInterferenceSize() const override {
+    return 32;
+  }
 };
 
 // Note: ABI differences may eventually require us to have a separate
@@ -502,6 +509,13 @@ class LLVM_LIBRARY_VISIBILITY PPC64TargetInfo : public PPCTargetInfo {
       return CCCR_Warning;
     }
   }
+
+  virtual unsigned hardwareDestructiveInterferenceSize() const override {
+    return 128;
+  }
+  virtual unsigned hardwareConstructiveInterferenceSize() const override {
+    return 128;
+  }
 };
 
 class LLVM_LIBRARY_VISIBILITY AIXPPC32TargetInfo :

clang/lib/Basic/Targets/RISCV.h

@@ -122,6 +122,13 @@ class RISCVTargetInfo : public TargetInfo {
   void fillValidTuneCPUList(SmallVectorImpl<StringRef> &Values) const override;
   bool supportsTargetAttributeTune() const override { return true; }
   ParsedTargetAttr parseTargetAttr(StringRef Str) const override;
+
+  virtual unsigned hardwareDestructiveInterferenceSize() const override {
+    return 32;
+  }
+  virtual unsigned hardwareConstructiveInterferenceSize() const override {
+    return 32;
+  }
 };
 class LLVM_LIBRARY_VISIBILITY RISCV32TargetInfo : public RISCVTargetInfo {
 public:

clang/lib/Basic/Targets/Sparc.h

@@ -140,6 +140,13 @@ class LLVM_LIBRARY_VISIBILITY SparcTargetInfo : public TargetInfo {
     CPU = getCPUKind(Name);
     return CPU != CK_GENERIC;
   }
+
+  virtual unsigned hardwareDestructiveInterferenceSize() const override {
+    return 32;
+  }
+  virtual unsigned hardwareConstructiveInterferenceSize() const override {
+    return 32;
+  }
 };
 
 // SPARC v8 is the 32-bit mode selected by Triple::sparc.

clang/lib/Basic/Targets/SystemZ.h

@@ -220,6 +220,13 @@ class LLVM_LIBRARY_VISIBILITY SystemZTargetInfo : public TargetInfo {
   int getEHDataRegisterNumber(unsigned RegNo) const override {
     return RegNo < 4 ? 6 + RegNo : -1;
   }
+
+  virtual unsigned hardwareDestructiveInterferenceSize() const override {
+    return 256;
+  }
+  virtual unsigned hardwareConstructiveInterferenceSize() const override {
+    return 256;
+  }
 };
 } // namespace targets
 } // namespace clang

clang/lib/Frontend/InitPreprocessor.cpp

@@ -1309,6 +1309,13 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
     Builder.defineMacro("__GCC_ATOMIC_TEST_AND_SET_TRUEVAL", "1");
   }
 
+  // GCC defines these macros in both C and C++ modes despite them being needed
+  // mostly for STL implementations in C++.
+  Builder.defineMacro("__GCC_DESTRUCTIVE_SIZE",
+                      Twine(TI.hardwareDestructiveInterferenceSize()));
+  Builder.defineMacro("__GCC_CONSTRUCTIVE_SIZE",
+                      Twine(TI.hardwareConstructiveInterferenceSize()));
+
   auto addLockFreeMacros = [&](const llvm::Twine &Prefix) {
     // Used by libc++ and libstdc++ to implement ATOMIC_<foo>_LOCK_FREE.
 #define DEFINE_LOCK_FREE_MACRO(TYPE, Type)                                     \

clang/test/Preprocessor/init-aarch64.c

@@ -119,6 +119,8 @@
 // AARCH64-NEXT: #define __FP_FAST_FMA 1
 // AARCH64-NEXT: #define __FP_FAST_FMAF 1
 // AARCH64-NEXT: #define __GCC_ASM_FLAG_OUTPUTS__ 1
+// AARCH64-NEXT: #define __GCC_CONSTRUCTIVE_SIZE {{.+}}
+// AARCH64-NEXT: #define __GCC_DESTRUCTIVE_SIZE {{.+}}
 // AARCH64-NEXT: #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_1 1
 // AARCH64-NEXT: #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 1
 // AARCH64-NEXT: #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2 1
@@ -220,11 +222,11 @@
 // AARCH64-NEXT: #define __LONG_MAX__ 9223372036854775807L
 // AARCH64-NEXT: #define __LONG_WIDTH__ 64
 // AARCH64-NEXT: #define __LP64__ 1
-// AARCH64-NEXT: #define __MEMORY_SCOPE_DEVICE 1 
-// AARCH64-NEXT: #define __MEMORY_SCOPE_SINGLE 4 
-// AARCH64-NEXT: #define __MEMORY_SCOPE_SYSTEM 0 
-// AARCH64-NEXT: #define __MEMORY_SCOPE_WRKGRP 2 
-// AARCH64-NEXT: #define __MEMORY_SCOPE_WVFRNT 3 
+// AARCH64-NEXT: #define __MEMORY_SCOPE_DEVICE 1
+// AARCH64-NEXT: #define __MEMORY_SCOPE_SINGLE 4
+// AARCH64-NEXT: #define __MEMORY_SCOPE_SYSTEM 0
+// AARCH64-NEXT: #define __MEMORY_SCOPE_WRKGRP 2
+// AARCH64-NEXT: #define __MEMORY_SCOPE_WVFRNT 3
 // AARCH64-NEXT: #define __NO_INLINE__ 1
 // AARCH64-NEXT: #define __NO_MATH_ERRNO__ 1
 // AARCH64-NEXT: #define __OBJC_BOOL_IS_BOOL 0

clang/test/Preprocessor/init.c

@@ -1,3 +1,10 @@
+// RUN: %clang_cc1 -E -dM < /dev/null | FileCheck -match-full-lines -check-prefix INTERFERENCE %s
+//
+// We purposefully do not test the values produced, only that the macros are
+// predefined to some value.
+// INTERFERENCE:#define __GCC_CONSTRUCTIVE_SIZE {{.+}}
+// INTERFERENCE:#define __GCC_DESTRUCTIVE_SIZE {{.+}}
+
 // RUN: %clang_cc1 -E -dM -x assembler-with-cpp < /dev/null | FileCheck -match-full-lines -check-prefix ASM %s
 //
 // ASM:#define __ASSEMBLER__ 1
@@ -1697,6 +1704,8 @@
 // WEBASSEMBLY-NEXT:#define __GCC_ATOMIC_SHORT_LOCK_FREE 2
 // WEBASSEMBLY-NEXT:#define __GCC_ATOMIC_TEST_AND_SET_TRUEVAL 1
 // WEBASSEMBLY-NEXT:#define __GCC_ATOMIC_WCHAR_T_LOCK_FREE 2
+// WEBASSEMBLY-NEXT:#define __GCC_CONSTRUCTIVE_SIZE {{.+}}
+// WEBASSEMBLY-NEXT:#define __GCC_DESTRUCTIVE_SIZE {{.+}}
 // WEBASSEMBLY-NEXT:#define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_1 1
 // WEBASSEMBLY-NEXT:#define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2 1
 // WEBASSEMBLY-NEXT:#define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 1
@@ -1806,11 +1815,11 @@
 // WEBASSEMBLY64-NEXT:#define __LONG_MAX__ 9223372036854775807L
 // WEBASSEMBLY64-NEXT:#define __LONG_WIDTH__ 64
 // WEBASSEMBLY64-NEXT:#define __LP64__ 1
-// WEBASSEMBLY-NEXT:#define __MEMORY_SCOPE_DEVICE 1 
-// WEBASSEMBLY-NEXT:#define __MEMORY_SCOPE_SINGLE 4 
-// WEBASSEMBLY-NEXT:#define __MEMORY_SCOPE_SYSTEM 0 
-// WEBASSEMBLY-NEXT:#define __MEMORY_SCOPE_WRKGRP 2 
-// WEBASSEMBLY-NEXT:#define __MEMORY_SCOPE_WVFRNT 3 
+// WEBASSEMBLY-NEXT:#define __MEMORY_SCOPE_DEVICE 1
+// WEBASSEMBLY-NEXT:#define __MEMORY_SCOPE_SINGLE 4
+// WEBASSEMBLY-NEXT:#define __MEMORY_SCOPE_SYSTEM 0
+// WEBASSEMBLY-NEXT:#define __MEMORY_SCOPE_WRKGRP 2
+// WEBASSEMBLY-NEXT:#define __MEMORY_SCOPE_WVFRNT 3
 // WEBASSEMBLY-NEXT:#define __NO_INLINE__ 1
 // WEBASSEMBLY-NEXT:#define __NO_MATH_ERRNO__ 1
 // WEBASSEMBLY-NEXT:#define __OBJC_BOOL_IS_BOOL 0
@@ -2126,11 +2135,11 @@
 // AVR:#define __LDBL_MIN__ 1.17549435e-38L
 // AVR:#define __LONG_LONG_MAX__ 9223372036854775807LL
 // AVR:#define __LONG_MAX__ 2147483647L
-// AVR:#define __MEMORY_SCOPE_DEVICE 1 
-// AVR:#define __MEMORY_SCOPE_SINGLE 4 
-// AVR:#define __MEMORY_SCOPE_SYSTEM 0 
-// AVR:#define __MEMORY_SCOPE_WRKGRP 2 
-// AVR:#define __MEMORY_SCOPE_WVFRNT 3 
+// AVR:#define __MEMORY_SCOPE_DEVICE 1
+// AVR:#define __MEMORY_SCOPE_SINGLE 4
+// AVR:#define __MEMORY_SCOPE_SYSTEM 0
+// AVR:#define __MEMORY_SCOPE_WRKGRP 2
+// AVR:#define __MEMORY_SCOPE_WVFRNT 3
 // AVR:#define __NO_INLINE__ 1
 // AVR:#define __ORDER_BIG_ENDIAN__ 4321
 // AVR:#define __ORDER_LITTLE_ENDIAN__ 1234
@@ -2422,11 +2431,11 @@
 // RISCV32: #define __LITTLE_ENDIAN__ 1
 // RISCV32: #define __LONG_LONG_MAX__ 9223372036854775807LL
 // RISCV32: #define __LONG_MAX__ 2147483647L
-// RISCV32: #define __MEMORY_SCOPE_DEVICE 1 
-// RISCV32: #define __MEMORY_SCOPE_SINGLE 4 
-// RISCV32: #define __MEMORY_SCOPE_SYSTEM 0 
-// RISCV32: #define __MEMORY_SCOPE_WRKGRP 2 
-// RISCV32: #define __MEMORY_SCOPE_WVFRNT 3 
+// RISCV32: #define __MEMORY_SCOPE_DEVICE 1
+// RISCV32: #define __MEMORY_SCOPE_SINGLE 4
+// RISCV32: #define __MEMORY_SCOPE_SYSTEM 0
+// RISCV32: #define __MEMORY_SCOPE_WRKGRP 2
+// RISCV32: #define __MEMORY_SCOPE_WVFRNT 3
 // RISCV32: #define __NO_INLINE__ 1
 // RISCV32: #define __POINTER_WIDTH__ 32
 // RISCV32: #define __PRAGMA_REDEFINE_EXTNAME 1
@@ -2634,11 +2643,11 @@
 // RISCV64: #define __LONG_LONG_MAX__ 9223372036854775807LL
 // RISCV64: #define __LONG_MAX__ 9223372036854775807L
 // RISCV64: #define __LP64__ 1
-// RISCV64: #define __MEMORY_SCOPE_DEVICE 1 
-// RISCV64: #define __MEMORY_SCOPE_SINGLE 4 
-// RISCV64: #define __MEMORY_SCOPE_SYSTEM 0 
-// RISCV64: #define __MEMORY_SCOPE_WRKGRP 2 
-// RISCV64: #define __MEMORY_SCOPE_WVFRNT 3 
+// RISCV64: #define __MEMORY_SCOPE_DEVICE 1
+// RISCV64: #define __MEMORY_SCOPE_SINGLE 4
+// RISCV64: #define __MEMORY_SCOPE_SYSTEM 0
+// RISCV64: #define __MEMORY_SCOPE_WRKGRP 2
+// RISCV64: #define __MEMORY_SCOPE_WVFRNT 3
 // RISCV64: #define __NO_INLINE__ 1
 // RISCV64: #define __POINTER_WIDTH__ 64
 // RISCV64: #define __PRAGMA_REDEFINE_EXTNAME 1

clang/test/Preprocessor/predefined-win-macros.c

@@ -3,7 +3,7 @@
 // RUN: %clang_cc1 %s -x c++ -E -dM -triple x86_64-pc-win32 -fms-extensions -fms-compatibility \
 // RUN:     -fms-compatibility-version=19.00 -std=c++14 -o - | FileCheck -match-full-lines %s --check-prefix=CHECK-MS64
 // RUN: %clang_cc1 %s -x c++ -E -dM -triple x86_64-pc-win32 -fms-extensions -fms-compatibility \
-// RUN:     -fms-compatibility-version=19.00 -std=c++14 -o - | grep GCC | count 5
+// RUN:     -fms-compatibility-version=19.00 -std=c++14 -o - | grep GCC | count 7
 // CHECK-MS64: #define _INTEGRAL_MAX_BITS 64
 // CHECK-MS64: #define _ISO_VOLATILE 1
 // CHECK-MS64: #define _MSC_EXTENSIONS 1
@@ -26,7 +26,7 @@
 // RUN: %clang_cc1 %s -x c++ -E -dM -triple i686-pc-win32 -fms-extensions -fms-compatibility \
 // RUN:     -fms-compatibility-version=19.00 -std=c++17 -o - | FileCheck -match-full-lines %s --check-prefix=CHECK-MS
 // RUN: %clang_cc1 %s -x c++ -E -dM -triple i686-pc-win32 -fms-extensions -fms-compatibility \
-// RUN:     -fms-compatibility-version=19.00 -std=c++17 -o - | grep GCC | count 5
+// RUN:     -fms-compatibility-version=19.00 -std=c++17 -o - | grep GCC | count 7
 // CHECK-MS: #define _INTEGRAL_MAX_BITS 64
 // CHECK-MS: #define _ISO_VOLATILE 1
 // CHECK-MS: #define _MSC_EXTENSIONS 1
@@ -39,6 +39,8 @@
 // CHECK-MS-NOT: GNU
 // CHECK-MS-NOT: GXX
 // CHECK-MS: #define __GCC_ASM_FLAG_OUTPUTS__ 1
+// CHECK-MS: #define __GCC_CONSTRUCTIVE_SIZE {{.+}}
+// CHECK-MS: #define __GCC_DESTRUCTIVE_SIZE {{.+}}
 // CHECK-MS: #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_1 1
 // CHECK-MS: #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2 1
 // CHECK-MS: #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 1

libcxx/test/std/language.support/support.dynamic/hardware_inference_size.compile.pass.cpp

@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14
-// XFAIL: (clang || apple-clang) && stdlib=libc++
+// XFAIL: (clang-17 || clang-18 || apple-clang-15) && stdlib=libc++
 
 #include <new>