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Re: Proposed major change to combine
- To: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
- Subject: Re: Proposed major change to combine
- From: Richard Earnshaw <rearnsha at arm dot com>
- Date: Thu, 08 Mar 2001 15:36:54 +0000
- cc: gcc at gcc dot gnu dot org, Richard dot Earnshaw at arm dot com
- Organization: ARM Ltd.
- Reply-To: Richard dot Earnshaw at arm dot com
> I'd like to propose getting rid of the mechanisms where it tries to
> substitute things inside RTL and instead always make new RTL. This costs
> most memory, but is less of an issue with GC.
>
> Aside from making the code cleaner, the major advantage of this is that then
> all the simplification code in combine.c can be moved into simplify-rtx.c and
> all the other passes will benefit from it.
>
> Any comments/objections?
I'm a bit concerned about the potential memory costs (my current finger in
the air estimates, from looking at "top", are that gcc-3.0 requires about
twice as much memory for compiling the same C source file as gcc-2.95
required). However, if we could avoid unsharing RTL in advance that might
alleviate some of the problems, and if we could run GC (if needed) after
each BB was processed then the costs might not be too bad.
R.