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Re: [patch] Decompose gimplify_expr
- From: Steven Bosscher <stevenb at suse dot de>
- To: gcc-patches at gcc dot gnu dot org
- Cc: Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>, Daniel Berlin <dberlin at dberlin dot org>, Diego Novillo <dnovillo at redhat dot com>, Mark Mitchell <mark at codesourcery dot com>, Geoffrey Keating <geoffk at apple dot com>
- Date: Wed, 3 Aug 2005 11:26:18 +0200
- Subject: Re: [patch] Decompose gimplify_expr
- References: <20050722234109.GB23954@atrey.karlin.mff.cuni.cz> <1122829989.32467.10.camel@linux.site> <20050803091324.GA29641@atrey.karlin.mff.cuni.cz>
On Wednesday 03 August 2005 11:13, Zdenek Dvorak wrote:
> Hello,
>
> > > In any case, I don't intend to implement any complicated optimizations.
> > > I definitely will avoid any "special case handling";
> > > if the optimization is too complicated, it is hardly worth doing
> > > at the expansion time. I will be considering only simple optimizations
> > > like unreachable code removal and constant propagation that have
> > > a good chance to be very useful and save significant amount of memory
> > > and compile time (especially on code that uses macros a lot).\
> >
> > I will simply note that we have *already* run into issues because things
> > like "constant propagation" were added to cleanup_cfg. (It ends up
> > causing us to need to update ssa in some cases that it doesn't do, and
> > shouldn't have to, since it's a fricking cfg cleanup pass)
>
> constant propagation is not performed anywhere in cfg cleanup.
Constant propagation is performed in tree_merge_blocks when the PHI
argument is a constant. IIRC Richard Guenther had an example of this
actually happening in one of his test cases.
Gr.
Steven