[Clang] Add attributes alloc_size and alloc_align to mm_malloc

LLVM optimizes source codes with mm_malloc better, especially due to alignment info.

alloc align https://clang.llvm.org/docs/AttributeReference.html#alloc-align
alloc size https://clang.llvm.org/docs/AttributeReference.html#alloc-size

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D117091

clang/lib/Headers/mm_malloc.h

@@ -28,9 +28,9 @@ extern "C" int posix_memalign(void **__memptr, size_t __alignment, size_t __size
 
 #if !(defined(_WIN32) && defined(_mm_malloc))
 static __inline__ void *__attribute__((__always_inline__, __nodebug__,
-                                       __malloc__))
-_mm_malloc(size_t __size, size_t __align)
-{
+                                       __malloc__, __alloc_size__(1),
+                                       __alloc_align__(2)))
+_mm_malloc(size_t __size, size_t __align) {
   if (__align == 1) {
     return malloc(__size);
   }

clang/test/Headers/Inputs/include/malloc.h

@@ -0,0 +1,7 @@
+#if defined(__MINGW32__)
+void *__mingw_aligned_malloc(size_t, size_t);
+void __mingw_aligned_free(void *);
+#elif defined(_WIN32)
+void *_aligned_malloc(size_t, size_t);
+void _aligned_free(void *);
+#endif

clang/test/Headers/mm_malloc.c

@@ -0,0 +1,12 @@
+
+// RUN: %clang_cc1 -internal-isystem %S/Inputs/include %s -emit-llvm -O1 -triple x86_64-linux-gnu -o - | FileCheck %s
+#include <mm_malloc.h>
+
+_Bool align_test(void) {
+// CHECK-LABEL: @align_test(
+// CHECK:    ret i1 true
+     void *p = _mm_malloc(1024, 16);
+    _Bool ret = ((__UINTPTR_TYPE__)p % 16) == 0;
+    _mm_free(p);
+    return ret;
+}