[InstCombine][NFC] Use ConstantExpr::getBinOpIdentity

[laytonio]

Summary

Delete duplicate implementation getSelectFoldableConstant and replace with ConstantExpr::getBinOpIdentity

[nikic]

LGTM

[laytonio]

Thanks for the review! Could you commit this for me? Layton Kifer <[e-mail]>

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

static unsigned getSelectFoldableOperands(BinaryOperator *I) {
   case Instruction::LShr:
   case Instruction::AShr:
     return 1;
   default:
     return 0;              // Cannot fold
   }
 }
 
-/// For the same transformation as the previous function, return the identity
-/// constant that goes into the select.
-static APInt getSelectFoldableConstant(BinaryOperator *I) {
-  switch (I->getOpcode()) {
-  default: llvm_unreachable("This cannot happen!");
-  case Instruction::Add:
-  case Instruction::Sub:
-  case Instruction::Or:
-  case Instruction::Xor:
-  case Instruction::Shl:
-  case Instruction::LShr:
-  case Instruction::AShr:
-    return APInt::getNullValue(I->getType()->getScalarSizeInBits());
-  case Instruction::And:
-    return APInt::getAllOnesValue(I->getType()->getScalarSizeInBits());
-  case Instruction::Mul:
-    return APInt(I->getType()->getScalarSizeInBits(), 1);
-  }
-}
-
 /// We have (select c, TI, FI), and we know that TI and FI have the same opcode.
 Instruction *InstCombinerImpl::foldSelectOpOp(SelectInst &SI, Instruction *TI,
                                               Instruction *FI) {
   // Don't break up min/max patterns. The hasOneUse checks below prevent that
   // for most cases, but vector min/max with bitcasts can be transformed. If the
   // one-use restrictions are eased for other patterns, we still don't want to
   // obfuscate min/max.
   if ((match(&SI, m_SMin(m_Value(), m_Value())) ||
if (TVI->hasOneUse() && !isa<Constant>(FalseVal)) {
         unsigned OpToFold = 0;
         if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
           OpToFold = 1;
         } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
           OpToFold = 2;
         }
 
         if (OpToFold) {
-          APInt CI = getSelectFoldableConstant(TVI);
+          Constant *C = ConstantExpr::getBinOpIdentity(TVI->getOpcode(),
+                                                       TVI->getType(), true);
           Value *OOp = TVI->getOperand(2-OpToFold);
           // Avoid creating select between 2 constants unless it's selecting
           // between 0, 1 and -1.
           const APInt *OOpC;
           bool OOpIsAPInt = match(OOp, m_APInt(OOpC));
-          if (!isa<Constant>(OOp) || (OOpIsAPInt && isSelect01(CI, *OOpC))) {
-            Value *C = ConstantInt::get(OOp->getType(), CI);
+          if (!isa<Constant>(OOp) ||
+              (OOpIsAPInt && isSelect01(C->getUniqueInteger(), *OOpC))) {
             Value *NewSel = Builder.CreateSelect(SI.getCondition(), OOp, C);
             NewSel->takeName(TVI);
             BinaryOperator *BO = BinaryOperator::Create(TVI->getOpcode(),
                                                         FalseVal, NewSel);
             BO->copyIRFlags(TVI);
             return BO;
           }
         }
       }
     }
   }
 
   if (auto *FVI = dyn_cast<BinaryOperator>(FalseVal)) {
     if (FVI->hasOneUse() && !isa<Constant>(TrueVal)) {
       if (unsigned SFO = getSelectFoldableOperands(FVI)) {
         unsigned OpToFold = 0;
         if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
           OpToFold = 1;
         } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
           OpToFold = 2;
         }
 
         if (OpToFold) {
-          APInt CI = getSelectFoldableConstant(FVI);
+          Constant *C = ConstantExpr::getBinOpIdentity(FVI->getOpcode(),
+                                                       FVI->getType(), true);
           Value *OOp = FVI->getOperand(2-OpToFold);
           // Avoid creating select between 2 constants unless it's selecting
           // between 0, 1 and -1.
           const APInt *OOpC;
           bool OOpIsAPInt = match(OOp, m_APInt(OOpC));
-          if (!isa<Constant>(OOp) || (OOpIsAPInt && isSelect01(CI, *OOpC))) {
-            Value *C = ConstantInt::get(OOp->getType(), CI);
+          if (!isa<Constant>(OOp) ||
+              (OOpIsAPInt && isSelect01(C->getUniqueInteger(), *OOpC))) {
             Value *NewSel = Builder.CreateSelect(SI.getCondition(), C, OOp);
             NewSel->takeName(FVI);
             BinaryOperator *BO = BinaryOperator::Create(FVI->getOpcode(),
                                                         TrueVal, NewSel);
             BO->copyIRFlags(FVI);
             return BO;
           }
         }