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Re: [PATCH] Disable CSE skip-blocks
- From: "Steven Bosscher" <stevenb dot gcc at gmail dot com>
- To: "Richard Kenner" <kenner at vlsi1 dot ultra dot nyu dot edu>
- Cc: gcc-patches at gcc dot gnu dot org, paolo dot bonzini at lu dot unisi dot ch
- Date: Sun, 29 Oct 2006 15:03:38 +0100
- Subject: Re: [PATCH] Disable CSE skip-blocks
- References: <firstname.lastname@example.org> <10610291400.AA21768@vlsi1.ultra.nyu.edu>
On 10/29/06, Richard Kenner <email@example.com> wrote:
> flag_cse_follow_jumps = 1;
> - flag_cse_skip_blocks = 1;
I would really like to be able to eliminate both of these.
With just cse-follow-jumps, CSE works on extended basic blocks, which
is really as simple as we should go I think. Doing CSE only locally
requires more work (like fwprop) to catch some simple things.
wrote both pieces of code and they were meant as temporary until we had
"proper" global optimization. Unfortunately, gcse wasn't good enough to
eliminate them. Your numbers suggest that we now MIGHT be able to,
I do *not* want to enter that discussion. Period. We have discussed
disabling CSE path following many times before, we know what we'd
miss, we've written passes to catch most of the things we'd miss, and
still the conclusion always was that it was not a good idea to disable
path following completely.
So again, that is *not* my intent. If someone wants to investigate
this, I can only encourage that, but I'm not going to do it.
All I want at this point, is to disable -fcse-skip-blocks, so that I
can work from there on the things that, I believe, do *really* matter,
- cfglayout mode in more passes
- improving the passes in gcse to subsume rtl jump threading
So I'd like to discuss the merits of disabling *just* -fcse-skip-blocks, please.