diff options
Diffstat (limited to 'llvm/lib/Transforms/InstCombine/InstructionCombining.cpp')
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstructionCombining.cpp | 25 |
1 files changed, 18 insertions, 7 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp index d29cf935751..5d5a9b2a272 100644 --- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp +++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp @@ -1451,29 +1451,40 @@ Instruction *InstCombiner::foldShuffledBinop(BinaryOperator &Inst) { /// sure the narrow op does not overflow. Instruction *InstCombiner::narrowMathIfNoOverflow(BinaryOperator &BO) { // We need at least one extended operand. - Value *LHS = BO.getOperand(0), *RHS = BO.getOperand(1); + Value *Op0 = BO.getOperand(0), *Op1 = BO.getOperand(1); + + // If this is a sub, we swap the operands since we always want an extension + // on the RHS. The LHS can be an extension or a constant. + if (BO.getOpcode() == Instruction::Sub) + std::swap(Op0, Op1); + Value *X; - bool IsSext = match(LHS, m_SExt(m_Value(X))); - if (!IsSext && !match(LHS, m_ZExt(m_Value(X)))) + bool IsSext = match(Op0, m_SExt(m_Value(X))); + if (!IsSext && !match(Op0, m_ZExt(m_Value(X)))) return nullptr; // If both operands are the same extension from the same source type and we // can eliminate at least one (hasOneUse), this might work. CastInst::CastOps CastOpc = IsSext ? Instruction::SExt : Instruction::ZExt; Value *Y; - if (!(match(RHS, m_ZExtOrSExt(m_Value(Y))) && X->getType() == Y->getType() && - cast<Operator>(RHS)->getOpcode() == CastOpc && - (LHS->hasOneUse() || RHS->hasOneUse()))) { + if (!(match(Op1, m_ZExtOrSExt(m_Value(Y))) && X->getType() == Y->getType() && + cast<Operator>(Op1)->getOpcode() == CastOpc && + (Op0->hasOneUse() || Op1->hasOneUse()))) { // If that did not match, see if we have a suitable constant operand. // Truncating and extending must produce the same constant. Constant *WideC; - if (!LHS->hasOneUse() || !match(RHS, m_Constant(WideC))) + if (!Op0->hasOneUse() || !match(Op1, m_Constant(WideC))) return nullptr; Constant *NarrowC = ConstantExpr::getTrunc(WideC, X->getType()); if (ConstantExpr::getCast(CastOpc, NarrowC, BO.getType()) != WideC) return nullptr; Y = NarrowC; } + + // Swap back now that we found our operands. + if (BO.getOpcode() == Instruction::Sub) + std::swap(X, Y); + // Both operands have narrow versions. Last step: the math must not overflow // in the narrow width. if (!willNotOverflow(BO.getOpcode(), X, Y, BO, IsSext)) |
