[Mesa-dev] [PATCH 09/10] i965/fs: Add a peephole pass to combine ADD with ADDC/SUBB.

[Ian Romanick]

On 09/24/2013 03:38 PM, Matt Turner wrote:
> On Tue, Sep 24, 2013 at 2:41 PM, Ian Romanick <idr at freedesktop.org> wrote:
>> For our own edification, we should add some feedback in the
>> INTEL_DEBUG=perf case.  If there is any case that an ADDC (or SUBB) from
>> the frontend doesn't get merged with an add, we should generate a perf
>> warning.  This probably indicates a failing of the optimization pass.
> 
> The peephole is called for every add emitted after we've seen an ADDC
> or SUBB, so it's not unexpected for the pass to not change anything.
> 
> Also, if only the carry is used dead code elimination at the IR level
> will remove the add, so no chance to peephole.

Hm... that makes sense.  I was thinking of something at the very end
that would notice that the ADDC and ADD hadn't been merged and complain.
 Maybe it would only complain if both the ADDC and ADD survived to the
end?  Dunno... it was just an idea.