diff options
| -rw-r--r-- | lib/Analysis/ScalarEvolution.cpp | 19 |
1 files changed, 11 insertions, 8 deletions
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp index 0512429ad8..ca959ab437 100644 --- a/lib/Analysis/ScalarEvolution.cpp +++ b/lib/Analysis/ScalarEvolution.cpp @@ -6394,11 +6394,14 @@ ScalarEvolution::HowManyLessThans(const SCEV *LHS, const SCEV *RHS, // With unit stride, the iteration never steps past the limit value. } else if (isKnownPositive(Step)) { // Test whether a positive iteration can step past the limit value and - // past the maximum value for its type in a single step. The NSW/NUW flags - // can imply that stepping past RHS would immediately result in undefined - // behavior. No self-wrap is not useful here because the loop counter may - // signed or unsigned wrap but continue iterating and terminate with - // defined behavior without ever self-wrapping. + // past the maximum value for its type in a single step. Constant negative + // stride should be rare because LHS > RHS comparisons are canonicalized + // to -LHS < -RHS. + // + // NSW/NUW flags imply that stepping past RHS would immediately result in + // undefined behavior. No self-wrap is not useful here because the loop + // counter may signed or unsigned wrap but continue iterating and + // terminate with defined behavior without ever self-wrapping. const SCEV *One = getConstant(Step->getType(), 1); if (isSigned) { if (!AddRec->getNoWrapFlags(SCEV::FlagNSW)) { @@ -6413,10 +6416,10 @@ ScalarEvolution::HowManyLessThans(const SCEV *LHS, const SCEV *RHS, .ult(getUnsignedRange(RHS).getUnsignedMax())) return getCouldNotCompute(); } - } else - // TODO: Handle negative strides here and below. + } else { + // Cannot handle variable stride. return getCouldNotCompute(); - + } // We know the LHS is of the form {n,+,s} and the RHS is some loop-invariant // m. So, we count the number of iterations in which {n,+,s} < m is true. // Note that we cannot simply return max(m-n,0)/s because it's not safe to |