Add a mechanism to override the detected cpu features.

BUG=
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/23523060

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16772 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/assembler-arm.h

@@ -89,6 +89,7 @@ class CpuFeatures : public AllStatic {
   static unsigned cache_line_size_;
 
   friend class ExternalReference;
+  friend class PlatformFeatureScope;
   DISALLOW_COPY_AND_ASSIGN(CpuFeatures);
 };
 

src/assembler.cc

@@ -206,6 +206,26 @@ CpuFeatureScope::~CpuFeatureScope() {
 #endif
 
 
+// -----------------------------------------------------------------------------
+// Implementation of PlatformFeatureScope
+
+PlatformFeatureScope::PlatformFeatureScope(CpuFeature f)
+    : old_supported_(CpuFeatures::supported_),
+      old_found_by_runtime_probing_only_(
+          CpuFeatures::found_by_runtime_probing_only_) {
+  uint64_t mask = static_cast<uint64_t>(1) << f;
+  CpuFeatures::supported_ |= mask;
+  CpuFeatures::found_by_runtime_probing_only_ &= ~mask;
+}
+
+
+PlatformFeatureScope::~PlatformFeatureScope() {
+  CpuFeatures::supported_ = old_supported_;
+  CpuFeatures::found_by_runtime_probing_only_ =
+      old_found_by_runtime_probing_only_;
+}
+
+
 // -----------------------------------------------------------------------------
 // Implementation of Label
 

src/assembler.h

@@ -134,6 +134,19 @@ class CpuFeatureScope BASE_EMBEDDED {
 };
 
 
+// Enable a unsupported feature within a scope for cross-compiling for a
+// different CPU.
+class PlatformFeatureScope BASE_EMBEDDED {
+ public:
+  explicit PlatformFeatureScope(CpuFeature f);
+  ~PlatformFeatureScope();
+
+ private:
+  uint64_t old_supported_;
+  uint64_t old_found_by_runtime_probing_only_;
+};
+
+
 // -----------------------------------------------------------------------------
 // Labels represent pc locations; they are typically jump or call targets.
 // After declaration, a label can be freely used to denote known or (yet)

src/ia32/assembler-ia32.h

@@ -561,6 +561,7 @@ class CpuFeatures : public AllStatic {
   static uint64_t found_by_runtime_probing_only_;
 
   friend class ExternalReference;
+  friend class PlatformFeatureScope;
   DISALLOW_COPY_AND_ASSIGN(CpuFeatures);
 };
 

src/mips/assembler-mips.h

@@ -426,6 +426,7 @@ class CpuFeatures : public AllStatic {
   static unsigned found_by_runtime_probing_only_;
 
   friend class ExternalReference;
+  friend class PlatformFeatureScope;
   DISALLOW_COPY_AND_ASSIGN(CpuFeatures);
 };
 

src/x64/assembler-x64.h

@@ -504,6 +504,7 @@ class CpuFeatures : public AllStatic {
   static uint64_t found_by_runtime_probing_only_;
 
   friend class ExternalReference;
+  friend class PlatformFeatureScope;
   DISALLOW_COPY_AND_ASSIGN(CpuFeatures);
 };