From: Paul Brook <paul@codesourcery.com>
To: kenner@vlsi1.ultra.nyu.edu (Richard Kenner), matz@suse.de
Cc: gcc@gcc.gnu.org
Subject: Re: What to remove after tree-ssa is merged?
Date: Wed, 04 Feb 2004 18:39:00 -0000 [thread overview]
Message-ID: <200402041839.49784.paul@codesourcery.com> (raw)
In-Reply-To: <10402041757.AA02044@vlsi1.ultra.nyu.edu>
On Wednesday 04 February 2004 5:57 pm, Richard Kenner wrote:
> Sure, all expressions involving any P_E recursively would have to be
> expanded in the frontend, including such expressions (probably by
> using temporaries in order not to have to lower the whole tree). If
> that's feasible I don't know.
>
> You won't need temporaries within statements and it can't be done at all
> for the expressions within types.
It seems to me that the basic problem is thet there are expressions implicit
in the typing system, and two solutions to this:
(a) Lower these in the frontend/gimplifier and make all the implicit
expressions explicit. This is what is done for C99 VLAs.
(b) Teach the optimizers about these implicit expressions.
Neither of these seems particularly easy to my unexperienced eye.
On mainline we effectively have a bit of both. ie. constant folding does (b)
and then it gets expanded to RTL, which does (a).
There doesn't seem to be any consensus on which of these is easiest/best for
tree-ssa.
Is there any point continuing this thread given we don't have an
implementation of either, and no frontend(s) to test them with.
Paul
N.B. By "implicit expression" I mean an expression which depends on a variable
not mentioned directly.
e.g. in previously mentioned examples a COMPONENT_REF where the actual offset
depends on the size of an array which depends on the value of a variable.
next prev parent reply other threads:[~2004-02-04 18:39 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-02-04 17:54 Richard Kenner
2004-02-04 18:39 ` Paul Brook [this message]
-- strict thread matches above, loose matches on Subject: below --
2004-02-04 21:55 Richard Kenner
2004-02-04 21:25 Richard Kenner
2004-02-04 21:51 ` Paul Brook
2004-02-04 21:09 Richard Kenner
2004-02-05 5:32 ` Richard Henderson
2004-02-05 5:50 ` Geert Bosch
2004-02-04 20:55 Richard Kenner
2004-02-04 21:21 ` Paul Brook
2004-02-04 18:43 Richard Kenner
2004-02-04 19:49 ` Paul Brook
2004-02-04 20:15 ` Richard Henderson
2004-02-04 16:14 Richard Kenner
2004-02-04 16:39 ` Michael Matz
2004-02-04 15:49 Richard Kenner
2004-02-04 16:10 ` Michael Matz
2004-02-04 17:25 ` Robert Dewar
2004-02-04 15:21 Richard Kenner
2004-02-04 15:19 Richard Kenner
2004-02-04 15:31 ` Michael Matz
2004-02-04 15:16 S. Bosscher
2004-02-04 14:48 Richard Kenner
2004-02-04 14:36 Richard Kenner
2004-02-04 14:44 ` Andrew Pinski
2004-02-04 15:15 ` Michael Matz
2004-02-04 13:52 Richard Kenner
2004-02-04 13:29 S. Bosscher
2004-02-04 13:49 ` Paul Brook
2004-02-04 14:04 ` Michael Matz
2004-02-04 14:19 ` Robert Dewar
2004-02-04 14:31 ` Andrew Pinski
2004-02-04 14:53 ` Robert Dewar
2004-02-04 12:30 Richard Kenner
2004-02-03 16:20 "Documentation by paper" Richard Kenner
2004-02-03 16:54 ` Jan Hubicka
2004-02-03 16:58 ` What to remove after tree-ssa is merged? Paolo Bonzini
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