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Re: [tree-ssa] Out of SSA status and issues
- From: Diego Novillo <dnovillo at redhat dot com>
- To: Richard Kenner <kenner at vlsi1 dot ultra dot nyu dot edu>
- Cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
- Date: 13 May 2003 09:27:56 -0400
- Subject: Re: [tree-ssa] Out of SSA status and issues
- Organization: Red Hat Canada
- References: <10305131322.AA13680@vlsi1.ultra.nyu.edu>
On Tue, 2003-05-13 at 09:22, Richard Kenner wrote:
> I see nothing wrong in replacing 'i + 9' with '*p + 9'. It would
> probably not be efficient, but I can't see it being wrong.
>
> If an optimizer pessimizes the code, I'd consider that "wrong".
>
correctness != efficiency. But we agree, transformations that are known
to pessimize code will not be allowed.
> This isn't a machine-dependent issue: with CPU speeds the way they are,
> a memory reference is *always* many times more expensive than an addition.
>
Read the rest of my message. This is *exactly* why we don't do this
transformation.
Diego.