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

[via llvm-commits]

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@@ -207,24 +213,69 @@ 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>(UI) ||
-            (isa<VPIRInstruction>(UI) &&
-             isa<PHINode>(cast<VPIRInstruction>(UI)->getInstruction())))
+        const VPBlockBase *UserVPBB = UI->getParent();
+
+        // Verify incoming values of VPIRInstructions wrapping phis. V most
+        // dominate the end of the incoming block. The operand index of the
+        // incoming value matches the predecessor block index of the
+        // corresponding incoming block.
+        if (isVPIRInstructionPhi(*UI)) {
+          for (const auto &[Idx, Op] : enumerate(UI->operands())) {
+            if (V != Op)
+              continue;
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ayalz wrote:

This checks a phi-recipe as a user, coming from every definition reaching it (admittedly expecting only a couple more or less), searching backwards for its index. Would it be better to check phi-recipes upfront, scanning all their operands in order, say as part of `verifyPhiRecipes()`? That would also check live-in operands, although they surely dominate any incoming.

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