Version 2.1.4
Fixed code cache lookup for keyed IC's (issue http://crbug.com/37853).
Performance improvements on all platforms.
git-svn-id: http://v8.googlecode.com/svn/trunk@4127 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
diff --git a/src/utils.h b/src/utils.h
index deab09f..3c8d873 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -29,6 +29,7 @@
#define V8_UTILS_H_
#include <stdlib.h>
+#include <string.h>
namespace v8 {
namespace internal {
@@ -396,7 +397,7 @@
if (this == &rhs) return *this;
Vector<T>::operator=(rhs);
memcpy(buffer_, rhs.buffer_, sizeof(T) * kSize);
- set_start(buffer_);
+ this->set_start(buffer_);
return *this;
}
@@ -599,6 +600,43 @@
// Calculate 10^exponent.
int TenToThe(int exponent);
+
+// The type-based aliasing rule allows the compiler to assume that pointers of
+// different types (for some definition of different) never alias each other.
+// Thus the following code does not work:
+//
+// float f = foo();
+// int fbits = *(int*)(&f);
+//
+// The compiler 'knows' that the int pointer can't refer to f since the types
+// don't match, so the compiler may cache f in a register, leaving random data
+// in fbits. Using C++ style casts makes no difference, however a pointer to
+// char data is assumed to alias any other pointer. This is the 'memcpy
+// exception'.
+//
+// Bit_cast uses the memcpy exception to move the bits from a variable of one
+// type of a variable of another type. Of course the end result is likely to
+// be implementation dependent. Most compilers (gcc-4.2 and MSVC 2005)
+// will completely optimize BitCast away.
+//
+// There is an additional use for BitCast.
+// Recent gccs will warn when they see casts that may result in breakage due to
+// the type-based aliasing rule. If you have checked that there is no breakage
+// you can use BitCast to cast one pointer type to another. This confuses gcc
+// enough that it can no longer see that you have cast one pointer type to
+// another thus avoiding the warning.
+template <class Dest, class Source>
+inline Dest BitCast(const Source& source) {
+ // Compile time assertion: sizeof(Dest) == sizeof(Source)
+ // A compile error here means your Dest and Source have different sizes.
+ typedef char VerifySizesAreEqual[sizeof(Dest) == sizeof(Source) ? 1 : -1];
+
+ Dest dest;
+ memcpy(&dest, &source, sizeof(dest));
+ return dest;
+}
+
+
} } // namespace v8::internal
#endif // V8_UTILS_H_