base atomicops: Drop SSE2 detection, we always require SSE2 starting in m35.

base/atomicops_internals_x86_gcc.h

 // Copyright (c) 2011 The Chromium 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 base/atomicops.h instead.
 
 #ifndef BASE_ATOMICOPS_INTERNALS_X86_GCC_H_
 #define BASE_ATOMICOPS_INTERNALS_X86_GCC_H_
 
 #include "base/base_export.h"
 
 // This struct is not part of the public API of this module; clients may not
 // use it.  (However, it's exported via BASE_EXPORT because clients implicitly
 // do use it at link time by inlining these functions.)
 // 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.
-  bool has_sse2;            // Processor has SSE2.
 };
 BASE_EXPORT extern struct AtomicOps_x86CPUFeatureStruct
     AtomicOps_Internalx86CPUFeatures;
 
 #define ATOMICOPS_COMPILER_BARRIER() __asm__ __volatile__("" : : : "memory")
 
 namespace base {
 namespace subtle {
 
 // 32-bit low-level operations on any platform.
@@ skipping 54 matching lines @@
 inline Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
                                        Atomic32 old_value,
                                        Atomic32 new_value) {
   return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
 }
 
 inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) {
   *ptr = value;
 }
 
-#if defined(__x86_64__)
-
-// 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();
 }
 
-#else
-
-inline void MemoryBarrier() {
-  if (AtomicOps_Internalx86CPUFeatures.has_sse2) {
-    __asm__ __volatile__("mfence" : : : "memory");
-  } else { // mfence is faster but not present on PIII
-    Atomic32 x = 0;
-    NoBarrier_AtomicExchange(&x, 0);  // acts as a barrier on PIII
-  }
-}
-
-inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) {
-  if (AtomicOps_Internalx86CPUFeatures.has_sse2) {
-    *ptr = value;
-    __asm__ __volatile__("mfence" : : : "memory");
-  } else {
-    NoBarrier_AtomicExchange(ptr, value);
-                          // acts as a barrier on PIII
-  }
-}
-#endif
-
 inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) {
   ATOMICOPS_COMPILER_BARRIER();
   *ptr = value; // An x86 store acts as a release barrier.
   // See comments in Atomic64 version of Release_Store(), below.
 }
 
 inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) {
   return *ptr;
 }
 
@@ skipping 120 matching lines @@
 }
 
 #endif  // defined(__x86_64__)
 
 } // namespace base::subtle
 } // namespace base
 
 #undef ATOMICOPS_COMPILER_BARRIER
 
 #endif  // BASE_ATOMICOPS_INTERNALS_X86_GCC_H_