[PATCH] D112725: [LoopVectorize] Extract the last lane from a uniform store

[Florian Hahn via Phabricator via llvm-commits]

fhahn requested changes to this revision.
fhahn added inline comments.
This revision now requires changes to proceed.


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Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:5480
+      // A uniform memory op is itself uniform.
+      if (Legal->isUniformMemOp(I))
         addToWorklistIfAllowed(&I);
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Unfortunately this is incorrect now. The worklist currently relies on instructions only demanding the first lane, and this is used to propagate this property later on, using: if all users of an operand demand the first lane only, the operand itself also only needs to compute the first lane. I added a clarifying comment in b4992dbb21ff9159285ae0aec73f3d760344b0e5

Adding stores violates that. You should probably be able to work around that by adding them to `Uniforms` without adding them to the worklist.  It might be worth calling out that entries in Uniforms may demand the first or last lane.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D112725/new/

https://reviews.llvm.org/D112725