[llvm] [ValueTracking][X86] Compute KnownBits for phadd/phsub (PR #92429)

[Simon Pilgrim via llvm-commits]

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@@ -541,6 +541,33 @@ void llvm::processShuffleMasks(
   }
 }
 
+void llvm::getHorizDemandedEltsForFirstOperand(unsigned VectorBitWidth,
+                                               const APInt &DemandedElts,
+                                               APInt &DemandedLHS,
+                                               APInt &DemandedRHS) {
+  int NumLanes = std::max<int>(1, VectorBitWidth / 128);
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RKSimon wrote:

Looks like we're still missing MMX test coverage - I have no preference to whether you add them to the valuetracking tests or drop the sub-128 handling.

https://github.com/llvm/llvm-project/pull/92429