[llvm-dev] [compiler-rt] Undefined negation in float emulation functions

[Steve Canon via llvm-dev]

On Oct 24, 2015, at 6:02 PM, Chris Lattner <clattner at apple.com> wrote:
> 
> 
>> On Oct 23, 2015, at 7:43 PM, Matthew Fernandez via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>> On 21/10/15 00:15, Stephen Canon wrote:
>>> Yup, this is UB.  If you want to propose a patch, I would do something like the following:
>>> 
>>>    rep_t sign = 0;
>>>    unsigned int aAbs = a;
>>>    if (a < 0) {
>>>        sign = signBit;
>>>        aAbs = -aAbs;
>>>    }
>>>    // Now use aAbs instead of a.
> 
> FWIW, another way to avoid the UB is to use an unsigned value.

I'm confused, that's exactly what this does.

- Steve