[llvm] [X86] SimplifyDemandedVectorEltsForTargetNode - add general X86ISD::PSADBW handling (PR #208309)

[Simon Pilgrim via llvm-commits]

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@@ -12948,6 +12948,12 @@ static SDValue lowerShuffleAsZeroOrAnyExtend(
                                            InputV, Mask, Subtarget, DAG);
   };
 
+  // Match against a foldable v4i32 VZEXT_MOVL zero-extending instruction.
+  if (VT == MVT::v4i32 &&
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RKSimon wrote:

I can add v8i16 handling, but I'm not certain we'll be able to create a stable test case - that this case has only just appeared shows how tricky it is :/

https://github.com/llvm/llvm-project/pull/208309