v8 atomicops: Drop SSE2 detection if __SSE2__ is defined.

src/base/atomicops_internals_x86_gcc.h

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file is an internal atomic implementation, use atomicops.h instead.
 
 #ifndef V8_BASE_ATOMICOPS_INTERNALS_X86_GCC_H_
 #define V8_BASE_ATOMICOPS_INTERNALS_X86_GCC_H_
 
 namespace v8 {
 namespace base {
 
 // This struct is not part of the public API of this module; clients may not
 // use it.
 // Features of this x86.  Values may not be correct before main() is run,
 // but are set conservatively.
 struct AtomicOps_x86CPUFeatureStruct {
   bool has_amd_lock_mb_bug;  // Processor has AMD memory-barrier bug; do lfence
                              // after acquire compare-and-swap.
+#if !defined(__SSE2__)
   bool has_sse2;             // Processor has SSE2.
+#endif
 };
 extern struct AtomicOps_x86CPUFeatureStruct AtomicOps_Internalx86CPUFeatures;
 
 #define ATOMICOPS_COMPILER_BARRIER() __asm__ __volatile__("" : : : "memory")
 
 // 32-bit low-level operations on any platform.
 
 inline Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
                                          Atomic32 old_value,
                                          Atomic32 new_value) {
@@ skipping 54 matching lines @@
 }
 
 inline void NoBarrier_Store(volatile Atomic8* ptr, Atomic8 value) {
   *ptr = value;
 }
 
 inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) {
   *ptr = value;
 }
 
-#if defined(__x86_64__)
+#if defined(__x86_64__) || defined(__SSE2__)
 
 // 64-bit implementations of memory barrier can be simpler, because it
 // "mfence" is guaranteed to exist.
 inline void MemoryBarrier() {
   __asm__ __volatile__("mfence" : : : "memory");
 }
 
 inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) {
   *ptr = value;
   MemoryBarrier();
@@ skipping 157 matching lines @@
   return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
 }
 
 #endif  // defined(__x86_64__)
 
 } }  // namespace v8::base
 
 #undef ATOMICOPS_COMPILER_BARRIER
 
 #endif  // V8_BASE_ATOMICOPS_INTERNALS_X86_GCC_H_