[llvm] [VPlan] Make canonical IV part of the region (PR #156262)

[via llvm-commits]

================
@@ -3349,32 +3349,30 @@ void VPlanTransforms::canonicalizeEVLLoops(VPlan &Plan) {
   EVLPhi->replaceAllUsesWith(ScalarR);
   EVLPhi->eraseFromParent();
 
+  // The canonical IV phi is at the front of the header after dissolution.
   // Replace CanonicalIVInc with EVL-PHI increment.
-  auto *CanonicalIV = cast<VPPhi>(&*HeaderVPBB->begin());
-  VPValue *Backedge = CanonicalIV->getIncomingValue(1);
-  assert(match(Backedge, m_c_Add(m_Specific(CanonicalIV),
-                                 m_Specific(&Plan.getVFxUF()))) &&
-         "Unexpected canonical iv");
-  Backedge->replaceAllUsesWith(EVLIncrement);
-
-  // Remove unused phi and increment.
-  VPRecipeBase *CanonicalIVIncrement = Backedge->getDefiningRecipe();
-  CanonicalIVIncrement->eraseFromParent();
-  CanonicalIV->eraseFromParent();
+  auto *CanonicalIV = dyn_cast<VPPhi>(&HeaderVPBB->front());
+  if (!CanonicalIV)
+    return;
----------------
ayalz wrote:

Should we assert that at-least one such backedge value was found (and RAUW'd with EVLIncrement) as before?

https://github.com/llvm/llvm-project/pull/156262