[llvm] [X86] SimplifyDemandedVectorEltsForTargetNode - reduce the size of VPERMV/VPERMV3 nodes if the upper elements are not demanded (PR #133923)

[Simon Pilgrim via llvm-commits]

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@@ -43814,6 +43815,66 @@ bool X86TargetLowering::SimplifyDemandedVectorEltsForTargetNode(
       }
       break;
     }
+    case X86ISD::VPERMV: {
+      SmallVector<int, 16> Mask;
+      SmallVector<SDValue, 2> Ops;
+      // TODO: Handle 128-bit PERMD/Q -> PSHUFD
+      if (Subtarget.hasVLX() &&
+          (VT.is512BitVector() || VT.getScalarSizeInBits() <= 16) &&
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RKSimon wrote:

OK - I'll try to add test coverage.

https://github.com/llvm/llvm-project/pull/133923