Re: Revisiting the use of cselib in alias.c for scheduling

[Maxim Kuvyrkov <maxim at codesourcery dot com>]

On 7/21/10 6:44 PM, Bernd Schmidt wrote:
> On 07/21/2010 03:06 PM, Steven Bosscher wrote:
> > 3. GCC now has better alias analysis than it used to, especially with
> > the alias-exporting stuff that exports the GIMPLE points-to analysis
> > results, but also just all the other little things that were
> > contributed over the last 10 years (little things like tree-ssa :)
> [...]
> > It looks like ~9% extra !true_dependence cases are found with cselib,
> > with is not insignificant:
...
> If that can't be improved, I think that rather than remove cselib from
> the scheduler, the question should be: if it's useful, why don't we use
> it for other schedulers rather than only sched-ebb?

Cselib can /always/ be used during second scheduling pass and on 
single-block regions during the first scheduling pass (after RA 
sched-rgn operates on single-block regions).

Modulo the bugs enabling cselib might surface, the only reason not to 
enable cselib for single-block regions in sched-rgn may be increased 
compile time.  That requires some benchmarking, but my gut feeling is 
that the benefits would outweigh the compile-time cost.

--
Maxim Kuvyrkov
CodeSourcery
maxim@codesourcery.com
(650) 331-3385 x724