[PATCH] D41578: [SCEV] Do not cache S -> V if S is not equivalent of V

[Evgeny Astigeevich via Phabricator via llvm-commits]

eastig added a comment.

Hi Sergey and Sanjoy,

To set flags ScalarEvolution::createSCEV calls:

  SCEV::NoWrapFlags ScalarEvolution::getNoWrapFlagsFromUB(const Value *V) {
    if (isa<ConstantExpr>(V)) return SCEV::FlagAnyWrap;
    const BinaryOperator *BinOp = cast<BinaryOperator>(V);
  
    // Return early if there are no flags to propagate to the SCEV.
    SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap;
    if (BinOp->hasNoUnsignedWrap())
      Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
    if (BinOp->hasNoSignedWrap())
      Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
    if (Flags == SCEV::FlagAnyWrap)
      return SCEV::FlagAnyWrap;
  
    return isSCEVExprNeverPoison(BinOp) ? Flags : SCEV::FlagAnyWrap;
  }

For "%mul86.i = mul nuw nsw i32 %p280, %p281" isSCEVExprNeverPoison return false which causes the SCEV '(%p280 * %p281)' to have SCEV::FlagAnyWrap instead of a combination of  SCEV::FlagNUW and Flags, SCEV::FlagNSW.

Am I correct SCEV::FlagAnyWrap means no poisoned values? If so, this looks strange. Shouldn't it be:

  return isSCEVExprNeverPoison(BinOp) ? SCEV::FlagAnyWrap : Flags;


Repository:
  rL LLVM

https://reviews.llvm.org/D41578