[llvm-dev] Issues with using scalar evolution with newer versions of LLVM IR (original) (raw)

Sanjoy Das via llvm-dev llvm-dev at lists.llvm.org
Wed Jan 16 10:58:41 PST 2019

Can you please provide the files vecsum.c, vec4.ll and vec7.ll?

-- Sanjoy

On Tue, Jan 15, 2019 at 8:14 PM hameeza ahmed <hahmed2305 at gmail.com> wrote:

Thank You.. I used following command to generate .bc or .ll /Documents/clang+llvm-4.0.0-x8664-linux-gnu-ubuntu-16.04/bin/clang -O0 -emit-llvm -S -o vec4.ll vecsum.c /Documents/clang+llvm-7.0.0-x8664-linux-gnu-ubuntu-16.04/bin/clang -O0 -emit-llvm -S -o vec7.ll vecsum.c

On Wed, Jan 16, 2019 at 6:49 AM Sanjoy Das <sanjoy at playingwithpointers.com> wrote:

It is hard to tell what's going on from the information you have provided. How are you generating vec.bc? This could either be a regression in scalar evolution or a change in some optimization pass that is resulting in a different vec.bc. -- Sanjoy On Tue, Jan 15, 2019 at 1:42 PM hameeza ahmed via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > Hello, > > I am trying to use scalar evolution pass using following command; > > opt -analyze -mem2reg -indvars -loop-simplify -scalar-evolution < vec.bc_ _> when vec.bc is generated using newer version of LLVM i.e LLVM 6 and 7 i get following message in the end; > Determining loop execution counts for: @main > Loop %8: Unpredictable backedge-taken count. > Loop %8: Unpredictable max backedge-taken count. > Loop %8: Unpredictable predicated backedge-taken count. > which means it is unable to compute iteration count. > > However, when .bc file is generated using LLVM 4.0 i am getting following; > > Determining loop execution counts for: @main > Loop %4: backedge-taken count is 512 > Loop %4: max backedge-taken count is 512 > Loop %4: Predicated backedge-taken count is 512 > Predicates: > > Loop %4: Trip multiple is 513 > > means correct computation of loop count... > Why is that happening with newer version of LLVM? > > Please help. _> ________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

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