Revert of Remove old/unused atomicops code

base/atomicops_internals_x86_gcc.cc

+// Copyright (c) 2006-2008 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 module gets enough CPU information to optimize the
+// atomicops module on x86.
+
+#include <stdint.h>
+#include <string.h>
+
+#include "base/atomicops.h"
+
+// Inline cpuid instruction.  In PIC compilations, %ebx contains the address
+// of the global offset table.  To avoid breaking such executables, this code
+// must preserve that register's value across cpuid instructions.
+//
+// The include guards are the same as in atomicops.h.
+#if defined(__i386__)
+#define cpuid(a, b, c, d, inp) \
+  asm("mov %%ebx, %%edi\n"     \
+      "cpuid\n"                \
+      "xchg %%edi, %%ebx\n"    \
+      : "=a" (a), "=D" (b), "=c" (c), "=d" (d) : "a" (inp))
+#elif defined(__x86_64__)
+#define cpuid(a, b, c, d, inp) \
+  asm("mov %%rbx, %%rdi\n"     \
+      "cpuid\n"                \
+      "xchg %%rdi, %%rbx\n"    \
+      : "=a" (a), "=D" (b), "=c" (c), "=d" (d) : "a" (inp))
+#endif
+
+#if defined(cpuid)        // initialize the struct only on x86
+
+// Set the flags so that code will run correctly and conservatively, so even
+// if we haven't been initialized yet, we're probably single threaded, and our
+// default values should hopefully be pretty safe.
+struct AtomicOps_x86CPUFeatureStruct AtomicOps_Internalx86CPUFeatures = {
+  false, // bug can't exist before process spawns multiple threads
+  false, // Chrome requires SSE2, but for transition assume not and initialize
+         // this properly.
+  false, // cmpxchg16b isn't present on early AMD64 CPUs.
+};
+
+namespace {
+
+// Initialize the AtomicOps_Internalx86CPUFeatures struct.
+void AtomicOps_Internalx86CPUFeaturesInit() {
+  uint32_t eax;
+  uint32_t ebx;
+  uint32_t ecx;
+  uint32_t edx;
+
+  // Get vendor string (issue CPUID with eax = 0)
+  cpuid(eax, ebx, ecx, edx, 0);
+  char vendor[13];
+  memcpy(vendor, &ebx, 4);
+  memcpy(vendor + 4, &edx, 4);
+  memcpy(vendor + 8, &ecx, 4);
+  vendor[12] = 0;
+
+  // get feature flags in ecx/edx, and family/model in eax
+  cpuid(eax, ebx, ecx, edx, 1);
+
+  int family = (eax >> 8) & 0xf;        // family and model fields
+  int model = (eax >> 4) & 0xf;
+  if (family == 0xf) {                  // use extended family and model fields
+    family += (eax >> 20) & 0xff;
+    model += ((eax >> 16) & 0xf) << 4;
+  }
+
+  // Opteron Rev E has a bug in which on very rare occasions a locked
+  // instruction doesn't act as a read-acquire barrier if followed by a
+  // non-locked read-modify-write instruction.  Rev F has this bug in
+  // pre-release versions, but not in versions released to customers,
+  // so we test only for Rev E, which is family 15, model 32..63 inclusive.
+  if (strcmp(vendor, "AuthenticAMD") == 0 &&       // AMD
+      family == 15 &&
+      32 <= model && model <= 63) {
+    AtomicOps_Internalx86CPUFeatures.has_amd_lock_mb_bug = true;
+  } else {
+    AtomicOps_Internalx86CPUFeatures.has_amd_lock_mb_bug = false;
+  }
+
+  // edx bit 26 is SSE2 which we use to tell use whether we can use mfence
+  AtomicOps_Internalx86CPUFeatures.has_sse2 = ((edx >> 26) & 1);
+
+  // ecx bit 13 indicates whether the cmpxchg16b instruction is supported
+  AtomicOps_Internalx86CPUFeatures.has_cmpxchg16b = ((ecx >> 13) & 1);
+}
+
+class AtomicOpsx86Initializer {
+ public:
+  AtomicOpsx86Initializer() {
+    AtomicOps_Internalx86CPUFeaturesInit();
+  }
+};
+
+// A global to get use initialized on startup via static initialization :/
+AtomicOpsx86Initializer g_initer;
+
+}  // namespace
+
+#endif  // if x86