From f2076c6a4c9c14538d71a3ef9c9e4fd40ee6ee00 Mon Sep 17 00:00:00 2001

From: Stephan Hartmann <stha09@googlemail.com>

Date: Sun, 31 May 2020 11:46:05 +0000

Subject: [PATCH] GCC: fix __has_builtin defines for non-clang compilers

Defining __has_builtin to 0 for non-clang compilers in base headers can

lead to wrong detection of features. For example in base/location.h

checking for __has_builtin macros succeeds for non-clang compilers,

because base/check_op.h defines __has_builtin to 0 and is included

before base/location.h. Instead of defining __has_builtin to 0 for

non-clang compilers, define an independent preprocessor symbol that

reflects support for requested feature. Undefine the symbol to avoid

collision.

While we're at it fix base/memory/aligned_memory.h too.

Bug: 819294

Change-Id: Iac40dc44e7356b600e7d06aa4ccd1294bb09ebce

---

diff --git a/base/check_op.h b/base/check_op.h

index 04b0c6f..28f4263a 100644

--- a/base/check_op.h

+++ b/base/check_op.h

@@ -48,8 +48,10 @@

                                  void (*stream_func)(std::ostream&,

                                                      const void*));

-#ifndef __has_builtin

-#define __has_builtin(x) 0  // Compatibility with non-clang compilers.

+#ifdef __has_builtin

+#define SUPPORTS_BUILTIN_ADDRESSOF (__has_builtin(__builtin_addressof))

+#else

+#define SUPPORTS_BUILTIN_ADDRESSOF 0

 #endif

 template <typename T>

@@ -65,7 +67,7 @@

   // operator& might be overloaded, so do the std::addressof dance.

   // __builtin_addressof is preferred since it also handles Obj-C ARC pointers.

   // Some casting is still needed, because T might be volatile.

-#if __has_builtin(__builtin_addressof)

+#if SUPPORTS_BUILTIN_ADDRESSOF

   const void* vp = const_cast<const void*>(

       reinterpret_cast<const volatile void*>(__builtin_addressof(v)));

 #else

@@ -75,6 +77,8 @@

   return StreamValToStr(vp, f);

 }

+#undef SUPPORTS_BUILTIN_ADDRESSOF

+

 // Overload for types that have no operator<< but do have .ToString() defined.

 template <typename T>

 inline typename std::enable_if<

diff --git a/base/memory/aligned_memory.h b/base/memory/aligned_memory.h

index d1cba0c..a0d9f13 100644

--- a/base/memory/aligned_memory.h

+++ b/base/memory/aligned_memory.h

@@ -57,13 +57,15 @@

   }

 };

-#ifndef __has_builtin

-#define __has_builtin(x) 0  // Compatibility with non-clang compilers.

+#ifdef __has_builtin

+#define SUPPORTS_BUILTIN_IS_ALIGNED (__has_builtin(__builtin_is_aligned))

+#else

+#define SUPPORTS_BUILTIN_IS_ALIGNED 0

 #endif

 inline bool IsAligned(uintptr_t val, size_t alignment) {

   // If the compiler supports builtin alignment checks prefer them.

-#if __has_builtin(__builtin_is_aligned)

+#if SUPPORTS_BUILTIN_IS_ALIGNED

   return __builtin_is_aligned(val, alignment);

 #else

   DCHECK(!((alignment - 1) & alignment))

@@ -72,6 +74,8 @@

 #endif

 }

+#undef SUPPORTS_BUILTIN_IS_ALIGNED

+

 inline bool IsAligned(void* val, size_t alignment) {

   return IsAligned(reinterpret_cast<uintptr_t>(val), alignment);

 }