[llvm] [VPlan] Rename isUniform(AfterVectorization) to isSingleScalar (NFC). (PR #140134)

[Mel Chen via llvm-commits]

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@@ -37,8 +37,9 @@ VPValue *getOrCreateVPValueForSCEVExpr(VPlan &Plan, const SCEV *Expr,
 /// SCEV expression could be constructed.
 const SCEV *getSCEVExprForVPValue(VPValue *V, ScalarEvolution &SE);
 
-/// Returns true if \p VPV is uniform after vectorization.
-inline bool isUniformAfterVectorization(const VPValue *VPV) {
+/// Returns true if \p VPV is a single scalar, either because it produces the
+/// same value for all lanes or only has its first lane used.
+inline bool isSingleScalar(const VPValue *VPV) {
   auto PreservesUniformity = [](unsigned Opcode) -> bool {
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Mel-Chen wrote:

BTW, does `PreservesUniformity` need to be renamed too?

https://github.com/llvm/llvm-project/pull/140134