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Re: [patch] for PR 18040
- From: Jason Merrill <jason at redhat dot com>
- To: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
- Cc: zack at codesourcery dot com, gcc-patches at gcc dot gnu dot org
- Date: Tue, 19 Oct 2004 18:56:47 -0400
- Subject: Re: [patch] for PR 18040
- References: <10410192251.AA14654@vlsi1.ultra.nyu.edu>
On Tue, 19 Oct 04 18:51:10 EDT, kenner@vlsi1.ultra.nyu.edu (Richard Kenner) wrote:
> In fact, some people have argued that
> we should be breaking up _all_ chains of dereference operations so
> that the optimizers can see better.
>
> The problem, however, is that the SSA-based optimizations operate mostly
> on *scalars*, so making more aggregate temporaries, which is what
> happens when you break up those chains, creates things that are hard to
> remove under the present optimization environment.
>
> Moreover, some of those temporaries will be of variable-size, which
> we don't currently support.
I don't think anybody is suggesting that we break up reference chains in a
way that would introduce aggregate temporaries. Only things that can be
expressed like
t = &a.b;
a.b.c => t->c
"t" here is a scalar temporary, so the optimizers should be able to do
useful things with it.
Jason