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

[via llvm-commits]

================
@@ -491,17 +491,38 @@ 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);
----------------
ayalz wrote:

Ah, ResultTy should be reset to TruncTy here, so that Step will be truncated to the updated type of BaseIV, rather than its original type. (Or reset right after the asserts, so that both truncations use ResultTy.) Wonder about test coverage if all pass?

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