[llvm] [VPlan] Expand VPWidenIntOrFpInductionRecipe into separate recipes (PR #118638)

[Luke Lau via llvm-commits]

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@@ -2622,6 +2622,19 @@ static void replaceVPBBWithIRVPBB(VPBasicBlock *VPBB, BasicBlock *IRBB) {
   }
 
   VPBlockUtils::reassociateBlocks(VPBB, IRVPBB);
+
+  // Replace any references of VPBB in widened phi incoming blocks with IRBB.
+  for (auto *BB : IRVPBB->successors()) {
+    while (auto *Region = dyn_cast<VPRegionBlock>(BB))
+      BB = Region->getEntry();
+
+    for (auto &R : *cast<VPBasicBlock>(BB))
+      if (auto *WidenPhiR = dyn_cast<VPWidenPHIRecipe>(&R))
+        for (unsigned I = 0; I < WidenPhiR->getNumOperands(); I++)
+          if (WidenPhiR->getIncomingBlock(I) == VPBB)
+            WidenPhiR->setIncomingBlock(I, IRVPBB);
+  }
+
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lukel97 wrote:

After c7ebe4fd0afadcddd53ec89e6030f9a8f5370e1f we will crash in fixNonInductionPHIs if we use a VPWidenPHIRecipe with the vector preheader as an incoming block, because the phi will reference the old non-IRBB vector preheader.

The existing native vplan tests don't seem to hit this because they don't create any widened phis that have the vector preheader/scalar preheader/middle block as an incoming block.

https://github.com/llvm/llvm-project/pull/118638