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

[via llvm-commits]

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@@ -2650,7 +2650,7 @@ static void scalarizeInstruction(const Instruction *Instr,
 void VPReplicateRecipe::execute(VPTransformState &State) {
   Instruction *UI = getUnderlyingInstr();
   if (State.Lane) { // Generate a single instance.
-    assert((State.VF.isScalar() || !isUniform()) &&
+    assert((State.VF.isScalar() || !isSingleScalar()) &&
            "uniform recipe shouldn't be predicated");
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ayalz wrote:

```suggestion
           "single scalar recipe shouldn't be predicated");
```

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