[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
Tue Jan 15 17:48:58 PST 2019

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.

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