[llvm] [VPlan] Consistently use (Part, 0) for first lane scalar values (PR #80271)

[via llvm-commits]

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@@ -213,8 +213,13 @@ VPBasicBlock::iterator VPBasicBlock::getFirstNonPhi() {
 }
 
 Value *VPTransformState::get(VPValue *Def, const VPIteration &Instance) {
-  if (Def->isLiveIn())
-    return Def->getLiveInIRValue();
+  if (Def->isLiveIn()) {
+    if (Value *V = Def->getLiveInIRValue())
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ayalz wrote:

Ahh, thanks for reminding. This may deserve a better representation to avoid confusion.

An alternative way of handling non-IR-valued live-ins, is to complement them with one asap, i.e., have prepareToExecute() call setUnderlyingValue() on every such "symbolic invariant" variant of "live-in", instead of filling State. That way they will behave as any other live-in.

https://github.com/llvm/llvm-project/pull/80271