[llvm-dev] Separate LoopVectorize LLVM pass (original) (raw)

Alex Susu via llvm-dev llvm-dev at lists.llvm.org
Mon Apr 17 03:01:44 PDT 2017

Hi. I managed to find the reason why my own LoopVectorize pass does not vectorize. Actually, the loop-simplify pass was getting executed, but because it did not run the passes loop-rotate and licm before it did not generate a proper loop preheader and the loops were not valid for vectorization.

 To make my own LoopVectorize pass vectorize I got inspired from the arguments

displayed on stdout of: opt -debug-pass=Arguments -O3 ... and looked at what other passes are being executed before and after -loop-vectorize .

 So I chose the following:
   opt -mem2reg -loop-rotate -licm -loop-unswitch -simplifycfg -domtree -basicaa -aa

-instcombine -loops -loop-simplify
-force-vector-width=128 -load MyLoopVectorize.so -my-loop-vectorize
-loop-simplify -scalar-evolution -aa -loop-accesses -loop-load-elim -basicaa -aa -instcombine -scalar-evolution -demanded-bits -slp-vectorizer

Best regards, Alex

On 4/14/2017 11:04 PM, Alex Susu wrote:

Hello. I am trying to create my own LoopVectorize.cpp pass as a separate pass from the LLVM trunk, as described in http://llvm.org/docs/CMake.html#embedding-llvm-in-your-project. Did anybody try something like this? I added close to the end of the .cpp file: /* this line seems to be required - it allows to run this pass as an embedded pass by giving opt -my-loop-vectorize */ static RegisterPass Z("my-loop-vectorize", "Write comments in source file.");

Note that I did NOT register my new pass in llvm/lib/Transforms/IPO/PassManagerBuilder.cpp - the original LoopVectorize module is registered there. However, when I give: opt -debug -load NewLoopVectorize.so -my-loop-vectorize test.c it does not vectorize a loop that was normally vectorized by the original LoopVectorize module in LLVM. My module gives: <> So I tried to explicitly run a few more passes before my new LoopVectorize to help it (I think the most important one is -loop-simplify, which canonicalizes the loop): opt -debug -loop-simplify -mem2reg -lcssa -load NewLoopVectorize.so -my-loop-vectorize test.c However, I do not see any line in the output of opt starting with "LoopSimplify" (when I have success, when I give opt -O3, I get "LoopSimplify: Creating pre-header for.body.preheader; LoopSimplify: Creating dedicated exit block for.end.loopexit" before LoopVectorize) and my LoopVectorize still does not vectorize the loop. Can anybody help me run explicitly the LoopSimplify pass (before my LoopVectorize pass)? Thank you. And wish you happy Easter holidays! Alex

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