[LLVMdev] How to get debug dump of candidate pairs selected in BBVectorizer?

[Hal Finkel]

----- Original Message -----
> From: "Karthik Bhat" <blitz.opensource at gmail.com>
> To: llvmdev at cs.uiuc.edu
> Sent: Thursday, April 24, 2014 6:23:15 AM
> Subject: [LLVMdev] How to get debug dump of candidate pairs selected in	BBVectorizer?
> 
> 
> 
> Hi All,
> I'm trying to understand BB Vectorizer and gone through
> http://llvm.org/devmtg/2012-04-12/Slides/Hal_Finkel.pdf
> 
> 
> Wanted to know how to use bb-vectorize-debug-candidate-selection and
> bb-vectorize-debug-pair-selection command arguments.
> 
> 
> I tried the command with debug build clang -
> clang -O2 test.c -mllvm -vectorize \
> -mllvm -debug-only=bb-vectorize \
> -mllvm -bb-vectorize-debug-pair-selection \
> -mllvm -bb-vectorize-debug-candidate-selection as mentioned in
> http://llvm.org/bugs/show_bug.cgi?id=11973 but it doesnt seem to
> dump the candidate pair info as shown in bug id.

A few things have changed since then. You'll need -vectorize-slp-aggressive instead of -vectorize.

>From clang, there are now direct flags:
-fvectorize == loop vectorizer
-fslp-vectorize == SLP vectorizer
-fslp-vectorizer-aggressive == BB vectorizer

Also, in case you don't know, most of the active upstream development has moved to the SLP vectorizer. The BB vectorizer still does a more expensive search, and I think it is mostly useful at this point for isolating useful cases that the SLP vectorizer misses.

 -Hal

> 
> Could someone help me out here with the command line argument to get
> candidate pair selected info.
> Thanks for the help! Regards Karthik Bhat
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-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory