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

[Matt Turner]

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.