[PATCH] D41948: [SLP] Fix vectorization for tree with trunc to minimum required bit width.

[Matthew Simpson via Phabricator via llvm-commits]

mssimpso added a comment.

Thanks for cleaning this up.



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Comment at: lib/Transforms/Vectorize/SLPVectorizer.cpp:2061-2064
+      int VecCost = 0;
+      // Check if the values are candidates to demote.
+      if (!MinBWs.count(VL0) || VecTy != SrcVecTy)
+        VecCost = TTI->getCastInstrCost(VL0->getOpcode(), VecTy, SrcVecTy, VL0);
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Makes sense.


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Comment at: lib/Transforms/Vectorize/SLPVectorizer.cpp:4023-4025
+    // Do not include top zext/sext/trunc operations to those to be demoted, it
+    // produces noise cast<vect>, trunc <vect>, exctract <vect>, cast <extract>
+    // sequence.
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What do you mean by "top" here?  Do you just mean that the initial Root should not be a cast? If so, would it be easier to check that here, rather than passing the flag in collectValuesToDemote?


https://reviews.llvm.org/D41948