[PATCH] D129207: [X86] isTargetShuffleEquivalent - attempt to match SM_SentinelZero shuffle mask elements using known bits

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:11818
       continue;
+    if (MaskIdx == SM_SentinelZero && 0 <= ExpectedIdx) {
+      // If we need this expected index to be a zero element, then update the
----------------
spatel wrote:
> What do you think about adding a clause above this and below the first clause like:
>     // If the mask is more defined than expected, the shuffles are not the same.
>     if (ExpectedIdx == SM_SentinelUndef)
>       return false;
> 
> I think that would then allow simplifying the later checks (converting to asserts).
We assert that ExpectedMask is isUndefOrZeroOrInRange above, although tbh I'm not certain how many callers ever have sentinal values in expected mask.


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  https://reviews.llvm.org/D129207/new/

https://reviews.llvm.org/D129207