[cfe-dev] request for comments on patch: detecting integer undefined behaviors

[John Regehr]

Awesome, thanks Chris.  More patches to follow.

John



On Sat, 11 Sep 2010, Chris Lattner wrote:

>
> On Sep 10, 2010, at 11:16 AM, John Regehr wrote:
>
>> Attached is a very small Clang patch that augments -ftrapv to check for divide by zero, mod by zero, and INT_MIN % -1.  The behavior on failure is inherited from trapv.
>
> Thanks!  I applied a slightly tweaked version of this in r113705.
>
> The tweaks were to rename the function to EmitUndefinedBehaviorIntegerDivAndRemCheck, to make it clear that it only applied to integer div/rem.
>
> I also changed this:
>
> +    llvm::Value *Cond2 = Builder.CreateAnd(
> +                                    Builder.CreateICmpEQ(Ops.LHS, IntMin),
> +                                    Builder.CreateICmpEQ(Ops.RHS, NegOne), "and");
>
> Because the order of evaluation of the calls isn't defined, so different compilers could emit the icmp's in different orders.
>
> Finally, I changed isFloatingType() to isRealFloatingType(), because the code wasn't safe on _Complex floats.
>
> Thanks again John,
>
> -Chris