[LLVMdev] Turning on/off instruction extensions

[Hal Finkel]

On Thu, 2011-11-24 at 15:09 +0100, Pablo Barrio López-Cortijo wrote:
> Hi everybody,
> 
> I'm trying to run some examples with different backend options (turning
> on/off SSE, 3dnow, or MMX instructions). However, I don't see any
> difference in terms of execution time. Does anybody know which language
> constructs (in C/C++ preferably) should I try to make these instructions
> generated (and thus make a difference between a backend that enables
> them or not) ?
> 
> I tried generating vector instructions with loops but it's not
> happening. Perhaps Polly can generate vector instructions?

You can also try my basic-block autovectorization patch.

http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20111121/132206.html

After applying the patch (I recommend applying it to the current trunk),
then run clang with the flags:
-mllvm -vectorize -mllvm -unroll-allow-partial
(the -unroll-allow-partial is not necessary for the vectorization, but
tends to expose additional vectorization opportunities). The basic-block
vectorizer has a number of flags that can be used to customize its
behavior, so if it is not vectorizing something that you think it should
be (or is doing something performance detrimental), please let me know
and I'll be happy to help.

 -Hal

> 
> Thanks ahead,
> 
> Pablo
> DIE-UPM
> Madrid
> 
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory