[llvm] [VPlan] Dissolve replicate regions with vector live-outs. (PR #189022)

[via llvm-commits]

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@@ -1386,6 +1394,8 @@ bool VPInstruction::usesFirstLaneOnly(const VPValue *Op) const {
     return false;
   case Instruction::ExtractElement:
     return Op == getOperand(1);
+  case Instruction::InsertElement:
+    return Op != getOperand(0);
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ayalz wrote:

Independent: this API was originally meant to indicate whether the VPInstruction is conceptually folding an extract-first-lane from a vector operand as part of its operation, and seems to be confused for "is the operand single scalar". Would be good to clean-up, possibly by introducing explicit extracts.

https://github.com/llvm/llvm-project/pull/189022