[PATCH] D127950: [SimplifyCFG] Check isSafeToSpeculativelyExecute before computeSpeculationCost

[chenglin.bi via Phabricator via llvm-commits]

bcl5980 added a comment.

In D127950#3588529 <https://reviews.llvm.org/D127950#3588529>, @nikic wrote:

> I believe the real problem here is that canTrap() only checks for division by zero, but not division of SIGNED_MIN by -1, which also traps. This leads to an inconsistency between canTrap() and isSafeToSpeculativelyExecute().

Is this what you want to do ?

  --- a/llvm/lib/IR/Constants.cpp
  +++ b/llvm/lib/IR/Constants.cpp
  @@ -592,7 +592,10 @@ static bool canTrapImpl(const Constant *C,
     case Instruction::URem:
     case Instruction::SRem:
       // Div and rem can trap if the RHS is not known to be non-zero.
  -    if (!isa<ConstantInt>(CE->getOperand(1)) ||CE->getOperand(1)->isNullValue())
  +    if (!isa<ConstantInt>(CE->getOperand(1)) ||
  +        CE->getOperand(1)->isNullValue() ||
  +        (CE->getOperand(0)->isMinSignedValue() &&
  +         CE->getOperand(1)->isAllOnesValue()))
         return true;
       return false;
     }


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https://reviews.llvm.org/D127950