[ADT] Move allocate_buffer to MemAlloc.h and out of line

There's an ABI breakage here if LLVM is compiled in C++14 without
aligned allocation and a user tries to use the result with aligned
allocation. If DenseMap or unique_function is used across that ABI
boundary it will break (PR45413). Moving it out of line is a bit of
a band-aid and LLVM doesn't really give ABI guarantees at this level,
but given the number of complaints I've received over this it still
seems worth fixing.

include/llvm/ADT/DenseMap.h

@@ -18,6 +18,7 @@
 #include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/MathExtras.h"
+#include "llvm/Support/MemAlloc.h"
 #include "llvm/Support/ReverseIteration.h"
 #include "llvm/Support/type_traits.h"
 #include <algorithm>

include/llvm/ADT/FunctionExtras.h

@@ -34,6 +34,7 @@
 
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/PointerUnion.h"
+#include "llvm/Support/MemAlloc.h"
 #include "llvm/Support/type_traits.h"
 #include <memory>
 

include/llvm/Support/Compiler.h

@@ -551,48 +551,4 @@ void AnnotateIgnoreWritesEnd(const char *file, int line);
 #define LLVM_ENABLE_EXCEPTIONS 1
 #endif
 
-#ifdef __cplusplus
-namespace llvm {
-
-/// Allocate a buffer of memory with the given size and alignment.
-///
-/// When the compiler supports aligned operator new, this will use it to to
-/// handle even over-aligned allocations.
-///
-/// However, this doesn't make any attempt to leverage the fancier techniques
-/// like posix_memalign due to portability. It is mostly intended to allow
-/// compatibility with platforms that, after aligned allocation was added, use
-/// reduced default alignment.
-inline void *allocate_buffer(size_t Size, size_t Alignment) {
-  return ::operator new(Size
-#ifdef __cpp_aligned_new
-                        ,
-                        std::align_val_t(Alignment)
-#endif
-  );
-}
-
-/// Deallocate a buffer of memory with the given size and alignment.
-///
-/// If supported, this will used the sized delete operator. Also if supported,
-/// this will pass the alignment to the delete operator.
-///
-/// The pointer must have been allocated with the corresponding new operator,
-/// most likely using the above helper.
-inline void deallocate_buffer(void *Ptr, size_t Size, size_t Alignment) {
-  ::operator delete(Ptr
-#ifdef __cpp_sized_deallocation
-                    ,
-                    Size
-#endif
-#ifdef __cpp_aligned_new
-                    ,
-                    std::align_val_t(Alignment)
-#endif
-  );
-}
-
-} // End namespace llvm
-
-#endif // __cplusplus
 #endif

include/llvm/Support/MemAlloc.h

@@ -62,5 +62,26 @@ LLVM_ATTRIBUTE_RETURNS_NONNULL inline void *safe_realloc(void *Ptr, size_t Sz) {
   return Result;
 }
 
-}
+/// Allocate a buffer of memory with the given size and alignment.
+///
+/// When the compiler supports aligned operator new, this will use it to to
+/// handle even over-aligned allocations.
+///
+/// However, this doesn't make any attempt to leverage the fancier techniques
+/// like posix_memalign due to portability. It is mostly intended to allow
+/// compatibility with platforms that, after aligned allocation was added, use
+/// reduced default alignment.
+LLVM_ATTRIBUTE_RETURNS_NONNULL LLVM_ATTRIBUTE_RETURNS_NOALIAS void *
+allocate_buffer(size_t Size, size_t Alignment);
+
+/// Deallocate a buffer of memory with the given size and alignment.
+///
+/// If supported, this will used the sized delete operator. Also if supported,
+/// this will pass the alignment to the delete operator.
+///
+/// The pointer must have been allocated with the corresponding new operator,
+/// most likely using the above helper.
+void deallocate_buffer(void *Ptr, size_t Size, size_t Alignment);
+
+} // namespace llvm
 #endif

lib/Support/CMakeLists.txt

@@ -115,6 +115,7 @@ add_llvm_component_library(LLVMSupport
   LowLevelType.cpp
   ManagedStatic.cpp
   MathExtras.cpp
+  MemAlloc.cpp
   MemoryBuffer.cpp
   MD5.cpp
   NativeFormatting.cpp

lib/Support/MemAlloc.cpp

@@ -0,0 +1,33 @@
+//===- MemAlloc.cpp - Memory allocation functions -------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/MemAlloc.h"
+
+// These are out of line to have __cpp_aligned_new not affect ABI.
+
+void *llvm::allocate_buffer(size_t Size, size_t Alignment) {
+  return ::operator new(Size
+#ifdef __cpp_aligned_new
+                        ,
+                        std::align_val_t(Alignment)
+#endif
+  );
+}
+
+void llvm::deallocate_buffer(void *Ptr, size_t Size, size_t Alignment) {
+  ::operator delete(Ptr
+#ifdef __cpp_sized_deallocation
+                    ,
+                    Size
+#endif
+#ifdef __cpp_aligned_new
+                    ,
+                    std::align_val_t(Alignment)
+#endif
+  );
+}