This is the mail archive of the mailing list for the GCC project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [patch i386]: Combine memory and indirect jump

On 06/13/14 10:59, Kai Tietz wrote:
2014-06-13 17:58 GMT+02:00 Jeff Law <>:
On 06/13/14 09:56, Richard Henderson wrote:

On 06/13/2014 08:36 AM, Jeff Law wrote:

So you may have answered this already, but why can't this be a combiner

Until pass_duplicate_computed_gotos, we (intentionally) have a single
branch in the entire function.  This vastly reduces the size of the CFG.

Ah, the factoring bits.  Should have known.

Peep2 is currently running before d_c_g, so currently Kai can't solve this
problem in peep2.

I don't think peep2 should run after sched2, but I'll bet we can reorder
a bit so that d_c_g runs before peep2.

Yea, seems worth a try.


Well, I tested to put the second sched2 pass before the sched2 pass.
That works in general.  There are just some opportunties which weren't
caught then.  I attached a sample, which demonstrates that pretty
well.  I noticed that I had to put that pass behind reload blocks was
necessary for better hit-rate of the peephole optimization.
So can you tell us why this sample code misses opportunities? Otherwise we have to dig into it ourselves to tease out that information.

I think we're zeroing in on a path to move d_c_g before peep2, but I'd like to have a clearer understanding of why we'd still be missing opportunities. If we can avoid running peep2 twice, that'd be good.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]