[PATCH] D59422: [SelectionDAG] Use SimplifyDemandedBits on truncated SCALAR_TO_VECTORs

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added a reviewer: spatel.
RKSimon marked an inline comment as done.
RKSimon added a subscriber: spatel.
RKSimon added inline comments.


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Comment at: test/CodeGen/AArch64/arm64-build-vector.ll:28
 ; CHECK-NEXT:    mov w8, #44672
-; CHECK-NEXT:    fmov s1, w8
+; CHECK-NEXT:    dup.8h v1, w8
 ; CHECK-NEXT:    mul.8h v0, v0, v1
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efriedma wrote:
> This is in fact a regression, at least on some targets; on an A57, it has higher latency and uses an extra execution unit.
> 
> I'm guessing there's some issue with the priority between splat vs. zeroing in the case where the high elements are all undef?
Adding @spatel who I think hit some similar issue with splat vector vs scalarization combines recently


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https://reviews.llvm.org/D59422