[PATCH] SelectionDAG: fold (fp_to_u/sint (u/sint_to_fp val)) when possible

[Quentin Colombet]

On Feb 9, 2015, at 1:01 PM, Mehdi Amini <mehdi.amini at apple.com> wrote:

>> 
>> On Feb 9, 2015, at 11:48 AM, Fiona Glaser <fglaser at apple.com> wrote:
>> 
>> 
>>> On Feb 9, 2015, at 11:31 AM, Chandler Carruth <chandlerc at google.com> wrote:
>>> 
>>> 
>>> On Mon, Feb 9, 2015 at 11:30 AM, Fiona Glaser <fglaser at apple.com> wrote:
>>> I get the message ;-) Already redoing it in instcombine; turns out there’s actually already code for it, but it only triggers when TypeA == TypeB. Will have a patch in a few moments.
>>> 
>>> Oh, sorry, I just totally missed Duncan's email. Sorry for the noise!
>> 
>> No problem, thanks for the suggestion. I will eventually figure out the intuition for whether a fold belongs in Instcombine or DAG!
>> 
>> Here’s a new patch that works in instcombine instead.
> 
> 
> Are there some guidelines to find out what should be done only in InstCombine and not in the DAG?

InstCombine is a canonicalization, target independent pass.
DAG can still do some target independent things but it also uses target dependent information.

> 
> Target-specific expansion or combine can end-up with this situation when it was not catched by ints-combine.
> 
> So I believe we want it to be done *both* in inst-combine *and* in the DAG.

I agree. That is also what I meant in my initial message.

Cheers,
Q.

> 
> — 
> Mehdi
> 
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