[LV] Use VPReplicateRecipe::isUniform instead isUniformAfterVec (NFCI).

[fhahn]

Summary

In scalarizeInstruction(), isUniformAfterVectorization is used to detect
cases where it is sufficient to always access the first lane. This
should map directly checking whether the operand is a uniform replicate
recipe.

As an alternative, VPTransformState::get could check for uniforms
directly, as in D91501.

[david-arm]

LGTM! I think this looks like a sensible change. I see we also call isUniformAfterVectorization in InnerLoopVectorizer::fixLCSSAPHIs, but in that case we are using a VPWidenPHIRecipe. :( Not sure if that matters and anyway it doesn't hold up this patch.

[fhahn]

Rebase on top of recent changes.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

void InnerLoopVectorizer::scalarizeInstruction(Instruction *Instr,
 
   State.Builder.SetInsertPoint(Builder.GetInsertBlock(),
                                Builder.GetInsertPoint());
   // Replace the operands of the cloned instructions with their scalar
   // equivalents in the new loop.
   for (auto &I : enumerate(RepRecipe->operands())) {
     auto InputInstance = Instance;
     VPValue *Operand = I.value();
-    if (State.Plan->isUniformAfterVectorization(Operand))
+    VPReplicateRecipe *OperandR = dyn_cast<VPReplicateRecipe>(Operand);
+    if (OperandR && OperandR->isUniform())
       InputInstance.Lane = VPLane::getFirstLane();
     Cloned->setOperand(I.index(), State.get(Operand, InputInstance));
   }
   addNewMetadata(Cloned, Instr);
 
   // Place the cloned scalar in the new loop.
   Builder.Insert(Cloned);