[llvm] [VPlan] Verify dominance for incoming values of phi-like recipes. (PR #124838)

[via llvm-commits]

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@@ -220,12 +219,28 @@ bool VPlanVerifier::verifyVPBasicBlock(const VPBasicBlock *VPBB) {
 
       for (const VPUser *U : V->users()) {
         auto *UI = cast<VPRecipeBase>(U);
-        // TODO: check dominance of incoming values for phis properly.
-        if (!UI ||
-            isa<VPHeaderPHIRecipe, VPWidenPHIRecipe, VPPredInstPHIRecipe,
-                VPIRPhi>(UI) ||
-            (isa<VPInstruction>(UI) &&
-             cast<VPInstruction>(UI)->getOpcode() == Instruction::PHI))
+        if (auto *Phi = dyn_cast<VPPhiAccessors>(UI)) {
+          for (unsigned Idx = 0; Idx != Phi->getNumIncoming(); ++Idx) {
+            VPValue *IncVPV = Phi->getIncomingValue(Idx);
+            const VPBasicBlock *IncVPBB = Phi->getIncomingBlock(Idx);
+            if (IncVPV != V)
+              continue;
+            if (IncVPBB != VPBB && !VPDT.dominates(VPBB, IncVPBB)) {
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ayalz wrote:

Ah, right; a value can be defined in the header and feed a header phi (of the same header block) even when the loop has additional blocks. Can check that in this case it's the 2nd incoming of the phi, i.e., across the backedge.

https://github.com/llvm/llvm-project/pull/124838