[llvm] [LV] Use original trip-count as the vector-trip-count if use predicated EVL instructions for tail-folding. (PR #132675)

[Florian Hahn via llvm-commits]

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@@ -2089,17 +2073,14 @@ void VPlanTransforms::convertToConcreteRecipes(VPlan &Plan) {
   for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
            vp_depth_first_deep(Plan.getEntry()))) {
     for (VPRecipeBase &R : make_early_inc_range(VPBB->phis())) {
-      if (!isa<VPCanonicalIVPHIRecipe, VPEVLBasedIVPHIRecipe>(&R))
-        continue;
-      auto *PhiR = cast<VPHeaderPHIRecipe>(&R);
-      StringRef Name =
-          isa<VPCanonicalIVPHIRecipe>(PhiR) ? "index" : "evl.based.iv";
-      auto *ScalarR = new VPInstruction(
-          Instruction::PHI, {PhiR->getStartValue(), PhiR->getBackedgeValue()},
-          PhiR->getDebugLoc(), Name);
-      ScalarR->insertBefore(PhiR);
-      PhiR->replaceAllUsesWith(ScalarR);
-      PhiR->eraseFromParent();
+      if (auto *PhiR = dyn_cast<VPCanonicalIVPHIRecipe>(&R)) {
+        auto *ScalarR = new VPInstruction(
+            Instruction::PHI, {PhiR->getStartValue(), PhiR->getBackedgeValue()},
+            PhiR->getDebugLoc(), "index");
+        ScalarR->insertBefore(PhiR);
+        PhiR->replaceAllUsesWith(ScalarR);
+        PhiR->eraseFromParent();
+      }
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fhahn wrote:

VPCanonicalIVPHIRecipe's step must be loop invariant, otherwise it isn't an induction.

If you want to do this transform, you must replace the canonical IV with a plain scalar phi recipe, like done in `convertToConcreteRecipes`

https://github.com/llvm/llvm-project/pull/132675