[LLVMdev] FYI: Phoronix GCC vs. LLVM-GCC benchmarks

David Greene dag at cray.com
Tue Sep 15 08:35:57 PDT 2009

On Tuesday 15 September 2009 08:16, Olivier Meurant wrote:

> llvm-gcc -v
> Using built-in specs.
> Target: i686-pc-linux-gnu

> gcc -v
> Using built-in specs.
> Target: i486-linux-gnu

Different targets.  It's no surprise 486 code would perform much worse than 
i686 code.  These compilers need to target the same architecture.  Ideally the 
Makefile would include appropriate -march/-mtune/whatever the gcc architecture 
switch of the day is.

All test reports should also include switches passed to the compiler for each 

Right now this isn't a fair test.  It's practically meaningless.

Remember, the goal here isn't to show how great LLVM is.  It's to get an 
honest assessment of where we are at.  Phoronix did us a big favor.  Getting
more details about his tests would help us even more.

For one thing, we (Cray) have a number of LLVM enhancements geared toward 
Opteron that make a big difference in performance.  I'm planning to contribute 
much of this to our open source community.  So there is definitely room for 
improvement to LLVM.  The biggest mistake we can make is to think we're the 


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