[llvm] [VPlan] Compute induction end values in VPlan. (PR #112145)

[via llvm-commits]

================
@@ -8955,24 +8854,83 @@ static void addCanonicalIVRecipes(VPlan &Plan, Type *IdxTy, bool HasNUW,
                        {CanonicalIVIncrement, &Plan.getVectorTripCount()}, DL);
 }
 
-/// Create resume phis in the scalar preheader for first-order recurrences and
-/// reductions and update the VPIRInstructions wrapping the original phis in the
-/// scalar header.
+/// Create and return a ResumePhi for \p PhiR, if it is wide induction recipe.
+/// If the induction recipe is not canonical, creates a VPDerivedIVRecipe to
+/// compute the end value of the induction.
+static VPValue *addResumePhiRecipeForInduction(VPHeaderPHIRecipe *PhiR,
+                                               VPBuilder &VectorPHBuilder,
+                                               VPBuilder &ScalarPHBuilder,
+                                               VPTypeAnalysis &TypeInfo,
+                                               VPValue *VectorTC) {
+  auto *WideIV = dyn_cast<VPWidenInductionRecipe>(PhiR);
+  if (!WideIV)
+    return nullptr;
+
+  auto *WideIntOrFp = dyn_cast<VPWidenIntOrFpInductionRecipe>(WideIV);
+  // Truncated wide inductions resume from the last lane of their vector value
+  // in the last vector iteration which is handled elsewhere.
+  if (WideIntOrFp && WideIntOrFp->getTruncInst())
+    return nullptr;
+
+  VPValue *Start = WideIV->getStartValue();
+  VPValue *Step = WideIV->getStepValue();
+  const InductionDescriptor &ID = WideIV->getInductionDescriptor();
+  VPValue *EndValue = VectorTC;
+  if (!WideIntOrFp || !WideIntOrFp->isCanonical()) {
+    EndValue = VectorPHBuilder.createDerivedIV(
+        ID.getKind(), dyn_cast_or_null<FPMathOperator>(ID.getInductionBinOp()),
+        Start, VectorTC, Step);
+  }
+
+  // EndValue is derived from the vector trip count (which has the same type as
+  // the widest induction) and thus may be wider than the induction here.
+  Type *ScalarTypeOfWideIV = TypeInfo.inferScalarType(WideIV);
+  if (ScalarTypeOfWideIV != TypeInfo.inferScalarType(EndValue)) {
+    EndValue = VectorPHBuilder.createScalarCast(Instruction::Trunc, EndValue,
+                                                ScalarTypeOfWideIV);
+  }
+
+  auto *ResumePhiRecipe =
+      ScalarPHBuilder.createNaryOp(VPInstruction::ResumePhi, {EndValue, Start},
+                                   WideIV->getDebugLoc(), "bc.resume.val");
+  return ResumePhiRecipe;
+}
+
+/// Create resume phis in the scalar preheader for first-order recurrences,
+/// reductions and inductions, and update the VPIRInstructions wrapping the
+/// original phis in the scalar header.
 static void addScalarResumePhis(VPRecipeBuilder &Builder, VPlan &Plan) {
+  VPTypeAnalysis TypeInfo(Plan.getCanonicalIV()->getScalarType());
   auto *ScalarPH = Plan.getScalarPreheader();
   auto *MiddleVPBB = cast<VPBasicBlock>(ScalarPH->getSinglePredecessor());
-  VPBuilder ScalarPHBuilder(ScalarPH);
+  VPBuilder VectorPHBuilder(
+      cast<VPBasicBlock>(Plan.getVectorLoopRegion()->getSinglePredecessor()));
   VPBuilder MiddleBuilder(MiddleVPBB, MiddleVPBB->getFirstNonPhi());
+  VPBuilder ScalarPHBuilder(ScalarPH);
   VPValue *OneVPV = Plan.getOrAddLiveIn(
       ConstantInt::get(Plan.getCanonicalIV()->getScalarType(), 1));
   for (VPRecipeBase &ScalarPhiR : *Plan.getScalarHeader()) {
     auto *ScalarPhiIRI = cast<VPIRInstruction>(&ScalarPhiR);
     auto *ScalarPhiI = dyn_cast<PHINode>(&ScalarPhiIRI->getInstruction());
     if (!ScalarPhiI)
       break;
+
     auto *VectorPhiR = cast<VPHeaderPHIRecipe>(Builder.getRecipe(ScalarPhiI));
-    if (!isa<VPFirstOrderRecurrencePHIRecipe, VPReductionPHIRecipe>(VectorPhiR))
+    if (isa<VPWidenInductionRecipe>(VectorPhiR)) {
+      if (VPValue *ResumePhi = addResumePhiRecipeForInduction(
+              VectorPhiR, VectorPHBuilder, ScalarPHBuilder, TypeInfo,
----------------
ayalz wrote:

```suggestion
    if (auto *WideIVR = dyn_cast<VPWidenInductionRecipe>(VectorPhiR)) {
      if (VPValue *ResumePhi = addResumePhiRecipeForInduction(
              WideIVR, VectorPHBuilder, ScalarPHBuilder, TypeInfo,
```
instead of the dyn_cast in addResumePhiRecipeForInduction().


https://github.com/llvm/llvm-project/pull/112145