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Add BUILTIN_EXPECT Support/Compiler macro.

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- Use for exceptional buffer conditions in raw_ostream:write to shave
   off a cycle or two.

 - Please rename if you have a better one.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@67103 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Daniel Dunbar 2009-03-17 21:15:18 +00:00
parent 3985728bde
commit b372c1114c
2 changed files with 8 additions and 1 deletions
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6
include/llvm/Support/Compiler.h
View File

@ -29,6 +29,12 @@
#define ATTRIBUTE_USED
#endif
#if (__GNUC__ >= 4)
#define BUILTIN_EXPECT(EXPR, VALUE) __builtin_expect((EXPR), (VALUE))
#else
#define BUILTIN_EXPECT(EXPR, VALUE) (EXPR)
#endif
// C++ doesn't support 'extern template' of template specializations. GCC does,
// but requires __extension__ before it. In the header, use this:
// EXTERN_TEMPLATE_INSTANTIATION(class foo<bar>);

3
lib/Support/raw_ostream.cpp
View File

@ -16,6 +16,7 @@
#include "llvm/System/Program.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Config/config.h"
#include "llvm/Support/Compiler.h"
#include <ostream>
#if defined(HAVE_UNISTD_H)
@ -142,7 +143,7 @@ raw_ostream &raw_ostream::write(unsigned char C) {
raw_ostream &raw_ostream::write(const char *Ptr, unsigned Size) {
// Group exceptional cases into a single branch.
if (OutBufCur+Size > OutBufEnd) {
if (BUILTIN_EXPECT(OutBufCur+Size > OutBufEnd, false)) {
if (Unbuffered) {
write_impl(Ptr, Size);
return *this;