[SLPVectorizer] Add initial alternate opcode support for cast instructions. (REAPPLIED-2)

We currently only support binary instructions in the alternate opcode shuffles.

This patch is an initial attempt at adding cast instructions as well, this raises several issues that we probably want to address as we continue to generalize the alternate mechanism:

1 - Duplication of cost determination - we should probably add scalar/vector costs helper functions and get BoUpSLP::getEntryCost to use them instead of determining costs directly.
2 - Support alternate instructions with the same opcode (e.g. casts with different src types) - alternate vectorization of calls with different IntrinsicIDs will require this.
3 - Allow alternates to be a different instruction type - mixing binary/cast/call etc.
4 - Allow passthrough of unsupported alternate instructions - related to PR30787/D28907 'copyable' elements.

Reapplied with fix to only accept 2 different casts if they come from the same source type (PR38154).

Differential Revision: https://reviews.llvm.org/D49135

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@336989 91177308-0d34-0410-b5e6-96231b3b80d8

Author: RKSimon

lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -353,23 +353,39 @@ static InstructionsState getSameOpcode(ArrayRef<Value *> VL,
   if (llvm::any_of(VL, [](Value *V) { return !isa<Instruction>(V); }))
     return InstructionsState(VL[BaseIndex], nullptr, nullptr);
 
+  bool IsCastOp = isa<CastInst>(VL[BaseIndex]);
   bool IsBinOp = isa<BinaryOperator>(VL[BaseIndex]);
   unsigned Opcode = cast<Instruction>(VL[BaseIndex])->getOpcode();
   unsigned AltOpcode = Opcode;
   unsigned AltIndex = BaseIndex;
 
   // Check for one alternate opcode from another BinaryOperator.
-  // TODO - can we support other operators (casts etc.)?
+  // TODO - generalize to support all operators (types, calls etc.).
   for (int Cnt = 0, E = VL.size(); Cnt < E; Cnt++) {
     unsigned InstOpcode = cast<Instruction>(VL[Cnt])->getOpcode();
-    if (InstOpcode != Opcode && InstOpcode != AltOpcode) {
-      if (Opcode == AltOpcode && IsBinOp && isa<BinaryOperator>(VL[Cnt])) {
+    if (IsBinOp && isa<BinaryOperator>(VL[Cnt])) {
+      if (InstOpcode == Opcode || InstOpcode == AltOpcode)
+        continue;
+      if (Opcode == AltOpcode) {
         AltOpcode = InstOpcode;
         AltIndex = Cnt;
         continue;
       }
-      return InstructionsState(VL[BaseIndex], nullptr, nullptr);
-    }
+    } else if (IsCastOp && isa<CastInst>(VL[Cnt])) {
+      Type *Ty0 = cast<Instruction>(VL[BaseIndex])->getOperand(0)->getType();
+      Type *Ty1 = cast<Instruction>(VL[Cnt])->getOperand(0)->getType();
+      if (Ty0 == Ty1) {
+        if (InstOpcode == Opcode || InstOpcode == AltOpcode)
+          continue;
+        if (Opcode == AltOpcode) {
+          AltOpcode = InstOpcode;
+          AltIndex = Cnt;
+          continue;
+        }
+      }
+    } else if (InstOpcode == Opcode || InstOpcode == AltOpcode)
+      continue;
+    return InstructionsState(VL[BaseIndex], nullptr, nullptr);
   }
 
   return InstructionsState(VL[BaseIndex], cast<Instruction>(VL[BaseIndex]),
@@ -2363,32 +2379,45 @@ int BoUpSLP::getEntryCost(TreeEntry *E) {
       return ReuseShuffleCost + VecCallCost - ScalarCallCost;
     }
     case Instruction::ShuffleVector: {
-      assert(S.isAltShuffle() && Instruction::isBinaryOp(S.getOpcode()) &&
-             Instruction::isBinaryOp(S.getAltOpcode()) &&
+      assert(S.isAltShuffle() &&
+             ((Instruction::isBinaryOp(S.getOpcode()) &&
+               Instruction::isBinaryOp(S.getAltOpcode())) ||
+              (Instruction::isCast(S.getOpcode()) &&
+               Instruction::isCast(S.getAltOpcode()))) &&
              "Invalid Shuffle Vector Operand");
       int ScalarCost = 0;
       if (NeedToShuffleReuses) {
         for (unsigned Idx : E->ReuseShuffleIndices) {
           Instruction *I = cast<Instruction>(VL[Idx]);
-          ReuseShuffleCost -=
-              TTI->getArithmeticInstrCost(I->getOpcode(), ScalarTy);
+          ReuseShuffleCost -= TTI->getInstructionCost(
+              I, TargetTransformInfo::TCK_RecipThroughput);
         }
         for (Value *V : VL) {
           Instruction *I = cast<Instruction>(V);
-          ReuseShuffleCost +=
-              TTI->getArithmeticInstrCost(I->getOpcode(), ScalarTy);
+          ReuseShuffleCost += TTI->getInstructionCost(
+              I, TargetTransformInfo::TCK_RecipThroughput);
         }
       }
       int VecCost = 0;
       for (Value *i : VL) {
         Instruction *I = cast<Instruction>(i);
         assert(S.isOpcodeOrAlt(I) && "Unexpected main/alternate opcode");
-        ScalarCost += TTI->getArithmeticInstrCost(I->getOpcode(), ScalarTy);
+        ScalarCost += TTI->getInstructionCost(
+            I, TargetTransformInfo::TCK_RecipThroughput);
       }
       // VecCost is equal to sum of the cost of creating 2 vectors
       // and the cost of creating shuffle.
-      VecCost = TTI->getArithmeticInstrCost(S.getOpcode(), VecTy);
-      VecCost += TTI->getArithmeticInstrCost(S.getAltOpcode(), VecTy);
+      if (Instruction::isBinaryOp(S.getOpcode())) {
+        VecCost = TTI->getArithmeticInstrCost(S.getOpcode(), VecTy);
+        VecCost += TTI->getArithmeticInstrCost(S.getAltOpcode(), VecTy);
+      } else {
+        Type *Src0SclTy = S.MainOp->getOperand(0)->getType();
+        Type *Src1SclTy = S.AltOp->getOperand(0)->getType();
+        VectorType *Src0Ty = VectorType::get(Src0SclTy, VL.size());
+        VectorType *Src1Ty = VectorType::get(Src1SclTy, VL.size());
+        VecCost = TTI->getCastInstrCost(S.getOpcode(), VecTy, Src0Ty);
+        VecCost += TTI->getCastInstrCost(S.getAltOpcode(), VecTy, Src1Ty);
+      }
       VecCost += TTI->getShuffleCost(TargetTransformInfo::SK_Select, VecTy, 0);
       return ReuseShuffleCost + VecCost - ScalarCost;
     }
@@ -3470,30 +3499,47 @@ Value *BoUpSLP::vectorizeTree(TreeEntry *E) {
     }
     case Instruction::ShuffleVector: {
       ValueList LHSVL, RHSVL;
-      assert(S.isAltShuffle() && Instruction::isBinaryOp(S.getOpcode()) &&
-             Instruction::isBinaryOp(S.getAltOpcode()) &&
+      assert(S.isAltShuffle() &&
+             ((Instruction::isBinaryOp(S.getOpcode()) &&
+               Instruction::isBinaryOp(S.getAltOpcode())) ||
+              (Instruction::isCast(S.getOpcode()) &&
+               Instruction::isCast(S.getAltOpcode()))) &&
              "Invalid Shuffle Vector Operand");
-      reorderAltShuffleOperands(S, E->Scalars, LHSVL, RHSVL);
-      setInsertPointAfterBundle(E->Scalars, S);
 
-      Value *LHS = vectorizeTree(LHSVL);
-      Value *RHS = vectorizeTree(RHSVL);
+      Value *LHS, *RHS;
+      if (Instruction::isBinaryOp(S.getOpcode())) {
+        reorderAltShuffleOperands(S, E->Scalars, LHSVL, RHSVL);
+        setInsertPointAfterBundle(E->Scalars, S);
+        LHS = vectorizeTree(LHSVL);
+        RHS = vectorizeTree(RHSVL);
+      } else {
+        ValueList INVL;
+        for (Value *V : E->Scalars)
+          INVL.push_back(cast<Instruction>(V)->getOperand(0));
+        setInsertPointAfterBundle(E->Scalars, S);
+        LHS = vectorizeTree(INVL);
+      }
 
       if (E->VectorizedValue) {
         LLVM_DEBUG(dbgs() << "SLP: Diamond merged for " << *VL0 << ".\n");
         return E->VectorizedValue;
       }
 
-      // Create a vector of LHS op1 RHS
-      Value *V0 = Builder.CreateBinOp(
+      Value *V0, *V1;
+      if (Instruction::isBinaryOp(S.getOpcode())) {
+        V0 = Builder.CreateBinOp(
           static_cast<Instruction::BinaryOps>(S.getOpcode()), LHS, RHS);
-
-      // Create a vector of LHS op2 RHS
-      Value *V1 = Builder.CreateBinOp(
+        V1 = Builder.CreateBinOp(
           static_cast<Instruction::BinaryOps>(S.getAltOpcode()), LHS, RHS);
+      } else {
+        V0 = Builder.CreateCast(
+            static_cast<Instruction::CastOps>(S.getOpcode()), LHS, VecTy);
+        V1 = Builder.CreateCast(
+            static_cast<Instruction::CastOps>(S.getAltOpcode()), LHS, VecTy);
+      }
 
       // Create shuffle to take alternate operations from the vector.
-      // Also, gather up odd and even scalar ops to propagate IR flags to
+      // Also, gather up main and alt scalar ops to propagate IR flags to
       // each vector operation.
       ValueList OpScalars, AltScalars;
       unsigned e = E->Scalars.size();