[llvm-commits] [llvm] r76215 - /llvm/trunk/include/llvm/Value.h

[Nick Lewycky]

Dan Gohman wrote:
> On Jul 18, 2009, at 1:06 PM, Duncan Sands wrote:
> 
> 
>> Hi Dan,
>>
>>
>>> This optional data is information like "signed overflow is  
>>> undefined".
>>>
>> why is this set up as optional data?  Shouldn't it be a full blown  
>> flag
>> on the operation, analogous to a parameter attribute?
> 
> The design idea here is that these are flags which are not necessary for
> correctness. A "signed add" is not a different operation from an "add";
> it's just an "add" with some value-range information that the optimizer
> may find useful.

I humbly object to the term "signed" here. There's no such thing as a 
signed add but there is such thing as an add that won't overflow. Since 
it won't overflow we aren't required to preserve the behaviour if it 
did. It's a 'nooverflow' add you might call it, as opposed to a wrapping 
add (what we have now), trapping add or saturating add.

Perhaps just 'nooverflow', 'wrap', 'trap' and 'saturate' as keywords? 
I'd like something shorter than nooverflow ('nowrap'?) if possible.

Nick