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Re: [PATCH 1/3] function: Do the CLEANUP_EXPENSIVE after shrink-wrapping, not before
- From: Segher Boessenkool <segher at kernel dot crashing dot org>
- To: Eric Botcazou <ebotcazou at adacore dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Tue, 17 May 2016 03:46:54 -0500
- Subject: Re: [PATCH 1/3] function: Do the CLEANUP_EXPENSIVE after shrink-wrapping, not before
- Authentication-results: sourceware.org; auth=none
- References: <213485283eede9da12b217737d95fc8f5c4be442 dot 1463428211 dot git dot segher at kernel dot crashing dot org> <1831730 dot xXXSthoG5j at polaris>
On Tue, May 17, 2016 at 10:05:57AM +0200, Eric Botcazou wrote:
> > We should do CLEANUP_EXPENSIVE after shrink-wrapping, because shrink-
> > wrapping creates constructs that CLEANUP_EXPENSIVE can optimise, and
> > nothing runs CLEANUP_EXPENSIVE later. We don't need cleanup_cfg before
> > shrink-wrapping, nothing in shrink-wrapping (or the other *logue insertion
> > code) cares at all.
>
> Are you sure of that? I agree that CLEANUP_EXPENSIVE might be overkill, but
> can't cleanup_cfg expose more opportunities to have multiple epilogues?
How would it? The shrink-wrapping algorithms do not much care how you
write your control flow. The only things I can think of are drastic
things like removing some dead code, or converting a switch to a direct
jump, but those had better be done for the immediately preceding passes
already (register allocation).
I can put back a cleanup_cfg (0) in front if that seems less tricky
(or just safer)?
Segher