diff options
Diffstat (limited to 'llvm/lib/Analysis/ValueTracking.cpp')
| -rw-r--r-- | llvm/lib/Analysis/ValueTracking.cpp | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp index 0144ce4..ed196b1 100644 --- a/llvm/lib/Analysis/ValueTracking.cpp +++ b/llvm/lib/Analysis/ValueTracking.cpp @@ -4841,6 +4841,15 @@ OverflowResult llvm::computeOverflowForUnsignedSub(const Value *LHS, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { + // X - (X % ?) + // The remainder of a value can't have greater magnitude than itself, + // so the subtraction can't overflow. + // TODO: There are other patterns like this. + // See simplifyICmpWithBinOpOnLHS() for candidates. + if (match(RHS, m_URem(m_Specific(LHS), m_Value())) && + isGuaranteedNotToBeUndefOrPoison(LHS, AC, CxtI, DT)) + return OverflowResult::NeverOverflows; + // Checking for conditions implied by dominating conditions may be expensive. // Limit it to usub_with_overflow calls for now. if (match(CxtI, @@ -4864,6 +4873,13 @@ OverflowResult llvm::computeOverflowForSignedSub(const Value *LHS, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { + // X - (X % ?) + // The remainder of a value can't have greater magnitude than itself, + // so the subtraction can't overflow. + if (match(RHS, m_SRem(m_Specific(LHS), m_Value())) && + isGuaranteedNotToBeUndefOrPoison(LHS, AC, CxtI, DT)) + return OverflowResult::NeverOverflows; + // If LHS and RHS each have at least two sign bits, the subtraction // cannot overflow. if (ComputeNumSignBits(LHS, DL, 0, AC, CxtI, DT) > 1 && |