[PATCH] D78353: [LV] Don't emit the Vector IV if it is not used.

[Ayal Zaks via Phabricator via llvm-commits]

Ayal added inline comments.


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Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:1890
     Value *ScalarIV = CreateScalarIV(Step);
     CreateSplatIV(ScalarIV, Step);
     return;
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This doesn't really broadcast when VF<=1 so should be fine?


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Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:1920
   Value *ScalarIV = CreateScalarIV(Step);
   CreateSplatIV(ScalarIV, Step);
   buildScalarSteps(ScalarIV, Step, EntryVal, ID);
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Would it be possible to avoid generating the undesired broadcasting by wrapping this CreateSplatIV() under an "if (needsVectorInduction(EntryVal))" that checks if any user !shouldScalarizeInstruction(), analogous to needsScalarInduction(EntryVal) above?

Better avoid generating and carrying potential garbage to begin with if it's easy; or potentially augment cse() clean-up at the end.


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  https://reviews.llvm.org/D78353/new/

https://reviews.llvm.org/D78353