diff options
3 files changed, 23 insertions, 30 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h index 75fec3e79d3..452079354e4 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h +++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h @@ -212,19 +212,26 @@ IntrinsicIDToOverflowCheckFlavor(unsigned ID) { } } -/// Integer division/remainder require special handling to avoid undefined +/// Some binary operators require special handling to avoid poison and undefined /// behavior. If a constant vector has undef elements, replace those undefs with -/// '1' because that's always safe to execute. -static inline Constant *getSafeVectorConstantForIntDivRem(Constant *In) { - assert(In->getType()->isVectorTy() && "Not expecting scalars here"); - assert(In->getType()->getVectorElementType()->isIntegerTy() && - "Not expecting FP opcodes/operands/constants here"); - - unsigned NumElts = In->getType()->getVectorNumElements(); +/// identity constants because those are always safe to execute. If no identity +/// constant exists, replace undef with '1' or '1.0'. +static inline Constant *getSafeVectorConstantForBinop( + BinaryOperator::BinaryOps Opcode, Constant *In) { + Type *Ty = In->getType(); + assert(Ty->isVectorTy() && "Not expecting scalars here"); + + Type *EltTy = Ty->getVectorElementType(); + Constant *IdentityC = ConstantExpr::getBinOpIdentity(Opcode, EltTy, true); + if (!IdentityC) + IdentityC = EltTy->isIntegerTy() ? ConstantInt::get(EltTy, 1): + ConstantFP::get(EltTy, 1.0); + + unsigned NumElts = Ty->getVectorNumElements(); SmallVector<Constant *, 16> Out(NumElts); for (unsigned i = 0; i != NumElts; ++i) { Constant *C = In->getAggregateElement(i); - Out[i] = isa<UndefValue>(C) ? ConstantInt::get(C->getType(), 1) : C; + Out[i] = isa<UndefValue>(C) ? IdentityC : C; } return ConstantVector::get(Out); } diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp index 9b0746f2466..2239434256c 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp @@ -1288,33 +1288,18 @@ static Instruction *foldSelectShuffle(ShuffleVectorInst &Shuf, Mask->containsUndefElement() && (Instruction::isIntDivRem(BOpc) || Instruction::isShift(BOpc)); - Constant *NewC; + // Select the constant elements needed for the single binop. + Constant *NewC = ConstantExpr::getShuffleVector(C0, C1, Mask); Value *V; if (X == Y) { - NewC = ConstantExpr::getShuffleVector(C0, C1, Mask); - // The new binop constant must not have any potential for extra poison/UB. if (MightCreatePoisonOrUB) { // TODO: Use getBinOpAbsorber for LHS replacement constants? if (!ConstantsAreOp1) return nullptr; - Type *EltTy = Shuf.getType()->getVectorElementType(); - auto *IdC = ConstantExpr::getBinOpIdentity(BOpc, EltTy, true); - if (!IdC) - return nullptr; - - // Replace undef elements caused by the mask with identity constants. - NewC = ConstantExpr::getShuffleVector(C0, C1, Mask); - unsigned NumElts = Shuf.getType()->getVectorNumElements(); - SmallVector<Constant *, 16> VectorOfNewC(NumElts); - for (unsigned i = 0; i != NumElts; i++) { - if (isa<UndefValue>(Mask->getAggregateElement(i))) - VectorOfNewC[i] = IdC; - else - VectorOfNewC[i] = NewC->getAggregateElement(i); - } - NewC = ConstantVector::get(VectorOfNewC); + // Replace undef elements with identity constants. + NewC = getSafeVectorConstantForBinop(BOpc, NewC); } // Remove a binop and the shuffle by rearranging the constant: @@ -1340,7 +1325,6 @@ static Instruction *foldSelectShuffle(ShuffleVectorInst &Shuf, // Select the variable vectors first, then perform the binop: // shuffle (op X, C0), (op Y, C1), M --> op (shuffle X, Y, M), C' // shuffle (op C0, X), (op C1, Y), M --> op C', (shuffle X, Y, M) - NewC = ConstantExpr::getShuffleVector(C0, C1, Mask); V = Builder.CreateShuffleVector(X, Y, Mask); } diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp index 84535f971b5..c28c5138dab 100644 --- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp +++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp @@ -1423,8 +1423,10 @@ Instruction *InstCombiner::foldShuffledBinop(BinaryOperator &Inst) { // All other binop opcodes are always safe to speculate, and therefore, it // is fine to include undef elements for unused lanes (and using undefs // may help optimization). + // FIXME: This transform is also not poison-safe. Eg, shift-by-undef would + // create poison that may not exist in the original code. if (Inst.isIntDivRem()) - NewC = getSafeVectorConstantForIntDivRem(NewC); + NewC = getSafeVectorConstantForBinop(Inst.getOpcode(), NewC); // Op(shuffle(V1, Mask), C) -> shuffle(Op(V1, NewC), Mask) // Op(C, shuffle(V1, Mask)) -> shuffle(Op(NewC, V1), Mask) |
