Detect nuw and nsw in LLVM IR

Question

Please let me know how to detect the presence of instructions with nsw and nuw flags set on them in the LLVM IR.

Answer 1

OverflowingBinaryOperator has the hasNoUnsignedWrap and hasNoSignedWrap predicates for this purpose.

More specifically, given some instruction ii:

   if (OverflowingBinaryOperator *op = dyn_cast<OverflowingBinaryOperator>(ii)) {
       if (op->hasNoUnsignedWrap())
           errs() << "  has nuw\n";
       else if (op->hasNoSignedWrap())
           errs() << "  has nsw\n";
       }
   }