[libc] [libclc] [flang] [lldb] [libcxx] [compiler-rt] [libcxxabi] [clang] [lld] [clang-tools-extra] [llvm] [VPlan] Add new VPScalarCastRecipe, use for IV & step trunc. (PR #78113)

[via llvm-commits]

================
@@ -491,17 +491,39 @@ void VPlanTransforms::removeDeadRecipes(VPlan &Plan) {
 
 static VPValue *createScalarIVSteps(VPlan &Plan, const InductionDescriptor &ID,
                                     ScalarEvolution &SE, Instruction *TruncI,
-                                    Type *IVTy, VPValue *StartV,
-                                    VPValue *Step) {
+                                    VPValue *StartV, VPValue *Step) {
   VPBasicBlock *HeaderVPBB = Plan.getVectorLoopRegion()->getEntryBasicBlock();
   auto IP = HeaderVPBB->getFirstNonPhi();
   VPCanonicalIVPHIRecipe *CanonicalIV = Plan.getCanonicalIV();
-  Type *TruncTy = TruncI ? TruncI->getType() : IVTy;
-  VPValue *BaseIV = CanonicalIV;
-  if (!CanonicalIV->isCanonical(ID.getKind(), StartV, Step, TruncTy)) {
-    BaseIV = new VPDerivedIVRecipe(ID, StartV, CanonicalIV, Step,
-                                   TruncI ? TruncI->getType() : nullptr);
-    HeaderVPBB->insert(BaseIV->getDefiningRecipe(), IP);
+  VPSingleDefRecipe *BaseIV = CanonicalIV;
+  if (!CanonicalIV->isCanonical(ID.getKind(), StartV, Step)) {
+    BaseIV = new VPDerivedIVRecipe(ID, StartV, CanonicalIV, Step);
+    HeaderVPBB->insert(BaseIV, IP);
+  }
+
+  // Truncate base induction if needed.
+  VPTypeAnalysis TypeInfo(SE.getContext());
+  Type *ResultTy = TypeInfo.inferScalarType(BaseIV);
+  if (TruncI) {
+    Type *TruncTy = TruncI->getType();
+    assert(ResultTy->getScalarSizeInBits() > TruncTy->getScalarSizeInBits() &&
+           "Not truncating.");
+    assert(ResultTy->isIntegerTy() && "Truncation requires an integer type");
+    BaseIV = new VPScalarCastRecipe(Instruction::Trunc, BaseIV, TruncTy);
+    HeaderVPBB->insert(BaseIV, IP);
+    ResultTy = TruncTy;
+  }
+
+  // Truncate step if needed.
+  Type *StepTy = TypeInfo.inferScalarType(Step);
+  if (ResultTy != StepTy) {
+    assert(StepTy->getScalarSizeInBits() > ResultTy->getScalarSizeInBits() &&
+           "Not truncating.");
+    assert(StepTy->isIntegerTy() && "Truncation requires an integer type");
+    Step = new VPScalarCastRecipe(Instruction::Trunc, Step, ResultTy);
+    auto *VecPreheader =
+        cast<VPBasicBlock>(Plan.getVectorLoopRegion()->getSinglePredecessor());
----------------
ayalz wrote:

```suggestion
    auto *VecPreheader =
        cast<VPBasicBlock>(HeaderVPBB->getSingleHierarchicalPredecessor());
```
?

https://github.com/llvm/llvm-project/pull/78113