[llvm] [VPlan] Use VPlan predecessors in VPWidenPHIRecipe (NFC). (PR #126388)

[via llvm-commits]

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@@ -3577,6 +3577,21 @@ void VPReductionPHIRecipe::print(raw_ostream &O, const Twine &Indent,
 }
 #endif
 
+VPBasicBlock *VPWidenPHIRecipe::getIncomingBlock(unsigned I) {
+  VPBasicBlock *Parent = getParent();
+  VPBlockBase *Pred = nullptr;
+  if (Parent->getNumPredecessors() == 0) {
+    auto *R = Parent->getParent();
+    assert(R && R->getEntry() == Parent);
+    assert(I < 2);
+    Pred = I == 0 ? R->getSinglePredecessor() : R;
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ayalz wrote:

If I == 1 then the enclosing region is returned, whose exiting block feeds the VPWidenPHIRecipe across the backedge? Worth a comment.

https://github.com/llvm/llvm-project/pull/126388