[LLVMdev] The nsw story

[Chris Lattner]

On Dec 1, 2011, at 8:46 AM, Dan Gohman wrote:

> 
> On Nov 30, 2011, at 10:49 PM, Chris Lattner wrote:
> 
>> 
>> On Nov 29, 2011, at 3:21 PM, Dan Gohman wrote:
>> 
>>> 
>>> A natural reaction to this problem is to think that LLVM IR is so nice
>>> and pretty that naturally there must be a nice and pretty solution. Here
>>> are some alternatives that have been considered:
>>> 
>>> - Go back to using undef for overflow. There were no known real-world
>>> bugs with this. It's just inconsistent.
>> 
>> +1 for the simple and obvious answer.
> 
> To be clear, the main sign-extension elimination optimization is not valid under
> the simple and obvious answer.  Are you proposing to do it anyway?

Please define "valid".  We discussed this a very very long time ago, and I don't recall the details.

-Chris