[PATCH] D123163: [TLI] `TargetLowering::SimplifyDemandedVectorElts()`: narrowing bitcast: fill known zero elts from known src bits

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


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Comment at: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:2771
+        for (unsigned SubElt = 0; SubElt != Scale; ++SubElt) {
+          if (!Known.Zero.extractBits(EltSizeInBits, SubElt * EltSizeInBits)
+                   .isAllOnes())
----------------
Known is only guaranteed to be correct for the requested SrcDemandedBits/SrcDemandedElts - is that going to work in a different way to the DemandedElts check below? Sorry I haven't investigated properly yet, but we might have to check that we were demanding those src bits?


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  https://reviews.llvm.org/D123163/new/

https://reviews.llvm.org/D123163