[cfe-commits] r108375 - in /cfe/trunk: include/clang/Basic/FileManager.h include/clang/Rewrite/Rewriter.h lib/Basic/FileManager.cpp lib/Checker/LLVMConventionsChecker.cpp lib/Frontend/PCHReader.cpp lib/Rewrite/Rewriter.cpp

[Chris Lattner]

On Jul 15, 2010, at 9:27 AM, Fariborz Jahanian wrote:

> 
> On Jul 14, 2010, at 4:19 PM, Benjamin Kramer wrote:
> 
>> Author: d0k
>> Date: Wed Jul 14 18:19:41 2010
>> New Revision: 108375
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=108375&view=rev
>> Log:
>> Pass StringRefs by value.
> 
> I don't seem to see the rational for changing const llvm::StringRef &  
> to StringRefs by value.

It's a (very small) performance win.  StringRef is a pair (pointer +length).  Passing it by value (e.g. on x86-64) causes it to be passed in two registers.  Passing it by reference passes the address, requiring the callee to dereference it and pinning it to the stack in the caller.

-Chris