[llvm] [LV] Move check if any vector insts will be generated to VPlan. (PR #96622)

[via llvm-commits]

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@@ -4795,9 +4783,92 @@ static void emitInvalidCostRemarks(SmallVector<InstructionVFPair> InvalidCosts,
   } while (!Tail.empty());
 }
 
+static bool willGenerateVectorInstructions(VPlan &Plan, ElementCount VF,
+                                           const TargetTransformInfo &TTI) {
+  assert(VF.isVector() && "Checking a scalar VF?");
+  VPTypeAnalysis TypeInfo(Plan.getCanonicalIV()->getScalarType(),
+                          Plan.getCanonicalIV()->getScalarType()->getContext());
+  for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
+           vp_depth_first_shallow(Plan.getVectorLoopRegion()->getEntry()))) {
+    for (VPRecipeBase &R : *VPBB) {
+      // Continue early if the recipe is considered to not produce a vector
+      // result. Note that this includes VPInstruction, where some opcodes may
+      // produce a vector to preserve existing behavior originally as
+      // VPInstructions model aspects not directly mapped to existing IR
+      // instructions.
+      switch (R.getVPDefID()) {
+      case VPDef::VPDerivedIVSC:
+      case VPDef::VPScalarIVStepsSC:
+      case VPDef::VPScalarCastSC:
+      case VPDef::VPReplicateSC:
+      case VPDef::VPInstructionSC:
+      case VPDef::VPCanonicalIVPHISC:
+      case VPDef::VPVectorPointerSC:
+      case VPDef::VPExpandSCEVSC:
+      case VPDef::VPEVLBasedIVPHISC:
+      case VPDef::VPPredInstPHISC:
+      case VPDef::VPBranchOnMaskSC:
+        continue;
+      case VPDef::VPReductionSC:
+      case VPDef::VPActiveLaneMaskPHISC:
+      case VPDef::VPWidenCallSC:
+      case VPDef::VPWidenCanonicalIVSC:
+      case VPDef::VPWidenCastSC:
+      case VPDef::VPWidenGEPSC:
+      case VPDef::VPWidenSC:
+      case VPDef::VPWidenSelectSC:
+      case VPDef::VPBlendSC:
+      case VPDef::VPFirstOrderRecurrencePHISC:
+      case VPDef::VPWidenPHISC:
+      case VPDef::VPWidenIntOrFpInductionSC:
+      case VPDef::VPWidenPointerInductionSC:
+      case VPDef::VPReductionPHISC:
+      case VPDef::VPInterleaveSC:
+      case VPDef::VPWidenLoadEVLSC:
+      case VPDef::VPWidenLoadSC:
+      case VPDef::VPWidenStoreEVLSC:
+      case VPDef::VPWidenStoreSC:
+        break;
+      default:
+        llvm_unreachable("unhandled recipe");
+      }
+
+      auto WillWiden = [&TypeInfo, &TTI, VF](VPValue *VPV) {
+        Type *ScalarTy = TypeInfo.inferScalarType(VPV);
+        Type *VectorTy = ToVectorTy(ScalarTy, VF);
+        unsigned NumLegalParts = TTI.getNumberOfParts(VectorTy);
+        if (!NumLegalParts)
+          return false;
+        if (VF.isScalable()) {
+          // <vscale x 1 x iN> is assumed to be profitable over iN because
+          // scalable registers are a distinct register class from scalar ones.
+          // If we ever find a target which wants to lower scalable vectors
+          // back to scalars, we'll need to update this code to explicitly
+          // ask TTI about the register class uses for each part.
+          return NumLegalParts <= VF.getKnownMinValue();
+        }
+        // Two or more parts that share a register - are vectorized.
+        return NumLegalParts < VF.getKnownMinValue();
+      };
+      SmallVector<VPValue *> VPValuesToCheck;
+      if (auto *WidenStore = dyn_cast<VPWidenStoreRecipe>(&R)) {
+        VPValuesToCheck.push_back(WidenStore->getOperand(1));
+      } else if (auto *IG = dyn_cast<VPInterleaveRecipe>(&R)) {
+        append_range(VPValuesToCheck, IG->getStoredValues());
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ayalz wrote:

This misses values defined by interleaved loads, for which getStoredValues() returns none. That is currently the only case having multiple def's, which are all of the same type - so suffice to check only one.

Another reminder to split VPInterleaveRecipe into interleaved loads and interleaved stores.

Another observation is that VPBranchOnMask should be a VPInstruction, producing no value - similar to BranchOnCond and BranchOnCount VPInstructions.

https://github.com/llvm/llvm-project/pull/96622