diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Analysis/ValueTracking.cpp | 23 | ||||
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp | 2 |
2 files changed, 18 insertions, 7 deletions
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp index cb1e285e8f3..3a0efa76b2f 100644 --- a/llvm/lib/Analysis/ValueTracking.cpp +++ b/llvm/lib/Analysis/ValueTracking.cpp @@ -2686,10 +2686,11 @@ OverflowResult llvm::computeOverflowForUnsignedMul(Value *LHS, Value *RHS, // Ref: "Hacker's Delight" by Henry Warren unsigned BitWidth = LHS->getType()->getScalarSizeInBits(); APInt LHSKnownZero(BitWidth, 0); + APInt LHSKnownOne(BitWidth, 0); APInt RHSKnownZero(BitWidth, 0); - APInt TmpKnownOne(BitWidth, 0); - computeKnownBits(LHS, LHSKnownZero, TmpKnownOne, DL, /*Depth=*/0, AT, CxtI, DT); - computeKnownBits(RHS, RHSKnownZero, TmpKnownOne, DL, /*Depth=*/0, AT, CxtI, DT); + APInt RHSKnownOne(BitWidth, 0); + computeKnownBits(LHS, LHSKnownZero, LHSKnownOne, DL, /*Depth=*/0, AT, CxtI, DT); + computeKnownBits(RHS, RHSKnownZero, RHSKnownOne, DL, /*Depth=*/0, AT, CxtI, DT); // Note that underestimating the number of zero bits gives a more // conservative answer. unsigned ZeroBits = LHSKnownZero.countLeadingOnes() + @@ -2705,9 +2706,17 @@ OverflowResult llvm::computeOverflowForUnsignedMul(Value *LHS, Value *RHS, // We know the multiply operation doesn't overflow if the maximum values for // each operand will not overflow after we multiply them together. - bool Overflow; - LHSMax.umul_ov(RHSMax, Overflow); + bool MaxOverflow; + LHSMax.umul_ov(RHSMax, MaxOverflow); + if (!MaxOverflow) + return OverflowResult::NeverOverflows; + + // We know it always overflows if multiplying the smallest possible values for + // the operands also results in overflow. + bool MinOverflow; + LHSKnownOne.umul_ov(RHSKnownOne, MinOverflow); + if (MinOverflow) + return OverflowResult::AlwaysOverflows; - return Overflow ? OverflowResult::MayOverflow - : OverflowResult::NeverOverflows; + return OverflowResult::MayOverflow; } diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp index 34caf1a5ab9..20310b41689 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp @@ -443,6 +443,8 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) { OverflowResult OR = computeOverflowForUnsignedMul(LHS, RHS, II); if (OR == OverflowResult::NeverOverflows) { return CreateOverflowTuple(II, Builder->CreateNUWMul(LHS, RHS), false); + } else if (OR == OverflowResult::AlwaysOverflows) { + return CreateOverflowTuple(II, Builder->CreateMul(LHS, RHS), true); } } // FALL THROUGH case Intrinsic::smul_with_overflow: |
