[VPlan] Exit earlier when trying to widen with scalar VFs.

[fhahn]

Summary

This simplifies the code a bit, suggested in D124718.

[fhahn]

Ping :)

[Ayal]

Thanks for following up!

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

8584

isOptimizableIVTruncate may hold for VF=1?

8599

(shouldWiden will bail out here for VF=1, if we didn’t bail out earlier)

[fhahn]

Move code to optimize truncates before scalar VF check. Test to check this added in 0c000d77ad09665a0debeb.

[fhahn]

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

8584

Good point, kept the code before checking for scalar VFs. I also added a test in 419e49621fb4.

8599

Yep, even though it doesn't explicitly check for scalar VFs.

[Ayal]

Thanks for following up!

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

8574

Unrelated nits while we're here: above could benefit slightly from condition reversal, below needs its indentation fixed.

8587–8598

Would be good to add a comment stating that all other "Widen" recipes from here on deal only with VF>1.

[fhahn]

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

8574

I'll fix the indent separately.

above could benefit slightly from condition reversal,

Do you mean handling the single line case first?

8587–8598

Good point, I added a comment in the committed version.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

 VPRecipeBase *VPRecipeBuilder::tryToWidenMemory(Instruction *I,
                                                 ArrayRef<VPValue *> Operands,
                                                 VFRange &Range,
                                                 VPlanPtr &Plan) {
   assert((isa<LoadInst>(I) || isa<StoreInst>(I)) &&
          "Must be called with either a load or store");
 
   auto willWiden = [&](ElementCount VF) -> bool {
-    if (VF.isScalar())
-      return false;
     LoopVectorizationCostModel::InstWidening Decision =
         CM.getWideningDecision(I, VF);
     assert(Decision != LoopVectorizationCostModel::CM_Unknown &&
            "CM decision should be taken at this point.");
     if (Decision == LoopVectorizationCostModel::CM_Interleave)
       return true;
     if (CM.isScalarAfterVectorization(I, VF) ||
         CM.isProfitableToScalarize(I, VF))
VPWidenCallRecipe *VPRecipeBuilder::tryToWidenCall(CallInst *CI,
   Intrinsic::ID ID = getVectorIntrinsicIDForCall(CI, TLI);
   if (ID && (ID == Intrinsic::assume || ID == Intrinsic::lifetime_end ||
              ID == Intrinsic::lifetime_start || ID == Intrinsic::sideeffect ||
              ID == Intrinsic::pseudoprobe ||
              ID == Intrinsic::experimental_noalias_scope_decl))
     return nullptr;
 
   auto willWiden = [&](ElementCount VF) -> bool {
-    if (VF.isScalar())
-       return false;
     Intrinsic::ID ID = getVectorIntrinsicIDForCall(CI, TLI);
     // The following case may be scalarized depending on the VF.
     // The flag shows whether we use Intrinsic or a usual Call for vectorized
     // version of the instruction.
     // Is it beneficial to perform intrinsic call compared to lib call?
     bool NeedToScalarize = false;
     InstructionCost CallCost = CM.getVectorCallCost(CI, VF, NeedToScalarize);
     InstructionCost IntrinsicCost = ID ? CM.getVectorIntrinsicCost(CI, VF) : 0;
VPRegionBlock *VPRecipeBuilder::createReplicateRegion(Instruction *Instr,
 
   return Region;
 }
 
 VPRecipeOrVPValueTy
 VPRecipeBuilder::tryToCreateWidenRecipe(Instruction *Instr,
                                         ArrayRef<VPValue *> Operands,
                                         VFRange &Range, VPlanPtr &Plan) {
-  // First, check for specific widening recipes that deal with calls, memory
-  // operations, inductions and Phi nodes.
-  if (auto *CI = dyn_cast<CallInst>(Instr))
-    return toVPRecipeResult(tryToWidenCall(CI, Operands, Range));
-
-  if (isa<LoadInst>(Instr) || isa<StoreInst>(Instr))
-    return toVPRecipeResult(tryToWidenMemory(Instr, Operands, Range, Plan));
-
+  // First, check for specific widening recipes that deal with inductions, Phi
+  // nodes, calls and memory operations.
   VPRecipeBase *Recipe;
   if (auto Phi = dyn_cast<PHINode>(Instr)) {
     if (Phi->getParent() != OrigLoop->getHeader())
       return tryToBlend(Phi, Operands, Plan);
     if ((Recipe = tryToOptimizeInductionPHI(Phi, Operands, *Plan, Range)))
       return toVPRecipeResult(Recipe);
 
     VPHeaderPHIRecipe *PhiRecipe = nullptr;
     assert((Legal->isReductionVariable(Phi) ||
             Legal->isFirstOrderRecurrence(Phi)) &&
            "can only widen reductions and first-order recurrences here");
     VPValue *StartV = Operands[0];
     if (Legal->isReductionVariable(Phi)) {
       const RecurrenceDescriptor &RdxDesc =
           Legal->getReductionVars().find(Phi)->second;
       assert(RdxDesc.getRecurrenceStartValue() ==
              Phi->getIncomingValueForBlock(OrigLoop->getLoopPreheader()));
       PhiRecipe = new VPReductionPHIRecipe(Phi, RdxDesc, *StartV,
                                            CM.isInLoopReduction(Phi),
                                            CM.useOrderedReductions(RdxDesc));
     } else {
       PhiRecipe = new VPFirstOrderRecurrencePHIRecipe(Phi, *StartV);
     }
 
       // Record the incoming value from the backedge, so we can add the incoming
       // value from the backedge after all recipes have been created.
       recordRecipeOf(cast<Instruction>(
           Phi->getIncomingValueForBlock(OrigLoop->getLoopLatch())));
       PhisToFix.push_back(PhiRecipe);
       return toVPRecipeResult(PhiRecipe);
   }
 
   if (isa<TruncInst>(Instr) &&
       (Recipe = tryToOptimizeInductionTruncate(cast<TruncInst>(Instr), Operands,
                                                Range, *Plan)))
     return toVPRecipeResult(Recipe);
 
+  // All widen recipes below deal only with VF > 1.
+  if (LoopVectorizationPlanner::getDecisionAndClampRange(
+          [&](ElementCount VF) { return VF.isScalar(); }, Range))
+    return nullptr;
+
+  if (auto *CI = dyn_cast<CallInst>(Instr))
+    return toVPRecipeResult(tryToWidenCall(CI, Operands, Range));
+
+  if (isa<LoadInst>(Instr) || isa<StoreInst>(Instr))
+    return toVPRecipeResult(tryToWidenMemory(Instr, Operands, Range, Plan));
+
   if (!shouldWiden(Instr, Range))
     return nullptr;
 
   if (auto GEP = dyn_cast<GetElementPtrInst>(Instr))
     return toVPRecipeResult(new VPWidenGEPRecipe(
         GEP, make_range(Operands.begin(), Operands.end()), OrigLoop));
 
   if (auto *SI = dyn_cast<SelectInst>(Instr)) {
     bool InvariantCond =