[llvm] [VPlan] Add transform to replace VPWidenCanonicalIV with wide IV. (PR #194267)

[Ramkumar Ramachandra via llvm-commits]

================
@@ -691,6 +691,60 @@ static void removeRedundantCanonicalIVs(VPlan &Plan) {
   }
 }
 
+void VPlanTransforms::replaceWidenCanonicalIVWithWidenIV(
+    VPlan &Plan, ScalarEvolution &SE, const TargetTransformInfo &TTI,
+    TargetTransformInfo::TargetCostKind CostKind, ElementCount VF, unsigned UF,
+    const SmallPtrSetImpl<const Value *> &ValuesToIgnore) {
+  VPRegionBlock *LoopRegion = Plan.getVectorLoopRegion();
+  if (!LoopRegion || Plan.hasScalarVFOnly())
+    return;
+
+  VPValue *CanonicalIV = LoopRegion->getCanonicalIV();
+  auto *WideCanIV = vputils::findUserOf<VPWidenCanonicalIVRecipe>(CanonicalIV);
+  if (!WideCanIV)
+    return;
+
+  if (vputils::onlyFirstLaneUsed(WideCanIV) ||
+      vputils::onlyScalarValuesUsed(WideCanIV))
+    return;
+
+  // Introduce a new VPWidenIntOrFpInductionRecipe if profitable.
+  Type *CanIVTy = LoopRegion->getCanonicalIVType();
+  auto *VecTy = VectorType::get(CanIVTy, VF);
+  InstructionCost BroadcastCost = TTI.getShuffleCost(
+      TargetTransformInfo::SK_Broadcast, VecTy, VecTy, {}, CostKind);
+  InstructionCost PHICost = TTI.getCFInstrCost(Instruction::PHI, CostKind);
+  if (PHICost > BroadcastCost)
+    return;
+
+  // Bail out if the additional wide induction phi increase the expected spill
+  // cost.
+  VPRegisterUsage UnrolledBase =
+      calculateRegisterUsageForPlan(Plan, {VF}, TTI, ValuesToIgnore)[0];
+  for (auto &Pair : UnrolledBase.MaxLocalUsers)
+    Pair.second *= UF;
----------------
artagnon wrote:

```suggestion
  for (unsigned &NumUsers : make_second_range(UnrolledBase.MaxLocalUsers))
    NumUsers *= UF;
```

https://github.com/llvm/llvm-project/pull/194267