diff --git a/clang/test/OpenMP/assumes_codegen.cpp b/clang/test/OpenMP/assumes_codegen.cpp
diff --git a/clang/test/OpenMP/assumes_include_nvptx.cpp b/clang/test/OpenMP/assumes_include_nvptx.cpp
diff --git a/clang/test/OpenMP/assumes_messages.c b/clang/test/OpenMP/assumes_messages.c
diff --git a/clang/test/OpenMP/assumes_print.cpp b/clang/test/OpenMP/assumes_print.cpp
diff --git a/clang/test/OpenMP/assumes_template_print.cpp b/clang/test/OpenMP/assumes_template_print.cpp
diff --git a/llvm/include/llvm/Frontend/OpenMP/OMP.td b/llvm/include/llvm/Frontend/OpenMP/OMP.td
@@ -1593,9 +1593,6 @@ def OMP_Scan : Directive<"scan"> {
     VersionedClause<OMPC_Exclusive, 50>
   ];
 }
-def OMP_Assumes : Directive<"assumes"> {}
-def OMP_BeginAssumes : Directive<"begin assumes"> {}
-def OMP_EndAssumes : Directive<"end assumes"> {}
 def OMP_BeginDeclareVariant : Directive<"begin declare variant"> {}
 def OMP_EndDeclareVariant : Directive<"end declare variant"> {}
 def OMP_ParallelWorkshare : Directive<"parallel workshare"> {

diff --git a/llvm/include/llvm/Frontend/OpenMP/OMPConstants.h b/llvm/include/llvm/Frontend/OpenMP/OMPConstants.h
@@ -16,7 +16,6 @@
 
 #include "llvm/ADT/BitmaskEnum.h"
 
-#include "llvm/ADT/StringRef.h"
 #include "llvm/Frontend/OpenMP/OMP.h.inc"
 
 namespace llvm {
@@ -80,33 +79,6 @@ enum class IdentFlag {
 #define OMP_IDENT_FLAG(Enum, ...) constexpr auto Enum = omp::IdentFlag::Enum;
 #include "llvm/Frontend/OpenMP/OMPKinds.def"
 
-/// Helper to describe assume clauses.
-struct AssumptionClauseMappingInfo {
-  /// The identifier describing the (beginning of the) clause.
-  llvm::StringLiteral Identifier;
-  /// Flag to determine if the identifier is a full name or the start of a name.
-  bool StartsWith;
-  /// Flag to determine if a directive lists follows.
-  bool HasDirectiveList;
-  /// Flag to determine if an expression follows.
-  bool HasExpression;
-};
-
-/// All known assume clauses.
-static constexpr AssumptionClauseMappingInfo AssumptionClauseMappings[] = {
-#define OMP_ASSUME_CLAUSE(Identifier, StartsWith, HasDirectiveList,            \
-                          HasExpression)                                       \
-  {Identifier, StartsWith, HasDirectiveList, HasExpression},
-#include "llvm/Frontend/OpenMP/OMPKinds.def"
-};
-
-inline std::string getAllAssumeClauseOptions() {
-  std::string S;
-  for (const AssumptionClauseMappingInfo &ACMI : AssumptionClauseMappings)
-    S += (S.empty() ? "'" : "', '") + ACMI.Identifier.str();
-  return S + "'";
-}
-
 } // end namespace omp
 
 } // end namespace llvm

diff --git a/llvm/include/llvm/Frontend/OpenMP/OMPKinds.def b/llvm/include/llvm/Frontend/OpenMP/OMPKinds.def
@@ -1224,27 +1224,3 @@ OMP_LAST_TRAIT_PROPERTY(
 #undef __OMP_REQUIRES_TRAIT
 #undef OMP_REQUIRES_TRAIT
 ///}
-
-
-/// Assumption clauses
-///
-///{
-
-#ifdef OMP_ASSUME_CLAUSE
-#define __OMP_ASSUME_CLAUSE(Identifier, StartsWith, HasDirectiveList, HasExpression) \
-OMP_ASSUME_CLAUSE(Identifier, StartsWith, HasDirectiveList, HasExpression)
-#else
-#define __OMP_ASSUME_CLAUSE(...)
-#endif
-
-__OMP_ASSUME_CLAUSE("ext_", true, false, false)
-__OMP_ASSUME_CLAUSE("absent", false, true, false)
-__OMP_ASSUME_CLAUSE("contains", false, true, false)
-__OMP_ASSUME_CLAUSE("holds", false, false, true)
-__OMP_ASSUME_CLAUSE("no_openmp", false, false, false)
-__OMP_ASSUME_CLAUSE("no_openmp_routines", false, false, false)
-__OMP_ASSUME_CLAUSE("no_parallelism", false, false, false)
-
-#undef __OMP_ASSUME_CLAUSE
-#undef OMP_ASSUME_CLAUSE
-///}
diff --git a/llvm/include/llvm/Support/AlignOf.h b/llvm/include/llvm/Support/AlignOf.h
@@ -20,9 +20,10 @@ namespace llvm {
 /// A suitably aligned and sized character array member which can hold elements
 /// of any type.
 ///
-/// These types may be arrays, structs, or any other types. This exposes a
-/// `buffer` member which can be used as suitable storage for a placement new of
-/// any of these types.
+/// This template is equivalent to std::aligned_union_t<1, ...>, but we cannot
+/// use it due to a bug in the MSVC x86 compiler:
+/// https://github.com/microsoft/STL/issues/1533
+/// Using `alignas` here works around the bug.
 template <typename T, typename... Ts> struct AlignedCharArrayUnion {
   using AlignedUnion = std::aligned_union_t<1, T, Ts...>;
   alignas(alignof(AlignedUnion)) char buffer[sizeof(AlignedUnion)];