diff options
Diffstat (limited to 'lib/Transforms')
-rw-r--r-- | lib/Transforms/InstCombine/InstCombineCalls.cpp | 30 |
1 files changed, 29 insertions, 1 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineCalls.cpp b/lib/Transforms/InstCombine/InstCombineCalls.cpp index 0e464507a7..bfdc17eff7 100644 --- a/lib/Transforms/InstCombine/InstCombineCalls.cpp +++ b/lib/Transforms/InstCombine/InstCombineCalls.cpp @@ -475,7 +475,35 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) { } } break; - case Intrinsic::umul_with_overflow: + case Intrinsic::umul_with_overflow: { + Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1); + unsigned BitWidth = cast<IntegerType>(LHS->getType())->getBitWidth(); + APInt Mask = APInt::getAllOnesValue(BitWidth); + + APInt LHSKnownZero(BitWidth, 0); + APInt LHSKnownOne(BitWidth, 0); + ComputeMaskedBits(LHS, Mask, LHSKnownZero, LHSKnownOne); + APInt RHSKnownZero(BitWidth, 0); + APInt RHSKnownOne(BitWidth, 0); + ComputeMaskedBits(RHS, Mask, RHSKnownZero, RHSKnownOne); + + // Get the largest possible values for each operand, extended to be large + // enough so that every possible product of two BitWidth-sized ints fits. + APInt LHSMax = (~LHSKnownZero).zext(BitWidth*2); + APInt RHSMax = (~RHSKnownZero).zext(BitWidth*2); + + // If multiplying the maximum values does not overflow then we can turn + // this into a plain NUW mul. + if ((LHSMax * RHSMax).getActiveBits() <= BitWidth) { + Value *Mul = Builder->CreateNUWMul(LHS, RHS, "umul_with_overflow"); + Constant *V[] = { + UndefValue::get(LHS->getType()), + Builder->getFalse() + }; + Constant *Struct = ConstantStruct::get(II->getContext(), V, 2, false); + return InsertValueInst::Create(Struct, Mul, 0); + } + } // FALL THROUGH case Intrinsic::smul_with_overflow: // Canonicalize constants into the RHS. if (isa<Constant>(II->getArgOperand(0)) && |