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Re: [tree-ssa] PATCH to improve optimization at ssa rewrite time
- From: Andrew MacLeod <amacleod at redhat dot com>
- To: Daniel Berlin <dberlin at dberlin dot org>
- Cc: Jason Merrill <jason at redhat dot com>,gcc-patches <gcc-patches at gcc dot gnu dot org>
- Date: 13 May 2003 17:04:41 -0400
- Subject: Re: [tree-ssa] PATCH to improve optimization at ssa rewrite time
- References: <3651DBBA-8584-11D7-9BD4-000A95A34564@dberlin.org>
On Tue, 2003-05-13 at 16:48, Daniel Berlin wrote:
> On Tuesday, May 13, 2003, at 04:33 PM, Andrew MacLeod wrote:
> > On Tue, 2003-05-13 at 15:50, Daniel Berlin wrote:
> > and then it seems pretty easy to do exactly the same thing with the
> > caclulation of b_7
> > its clear that on edge (1,3) b_7 can be calculated as 6 * 5, and on
> > edge (2,3) its 7 * 5...
> > So isn't it just as trivial for someone to insert temps on those
> > edges:
> Who is this someone?
> Are we going to do out-of-ssa const-prop too?
> Or do you think CCP should be doing it?
I think CCP ought to be able to handle that pretty easily. At least the
all constant side of it.
> Diego also suggested adding temps in this case, my response was, of
> Isn't it easier to make it not miss these optimizations in the first
> place by not const-prop'ing when we can't const-prop it everywhere
> (getting the trivial cases, but leaving the complex ones to passes that
> handle it right), than it is to add passes and code in them to fix it
right now, I dont know. I havent really had time to study it, and we
don't have enough working opimizations to do any real empirical studies
that are useful yet.
I definately tend to favour optimizations doing just their thing and
nothing else. They shouldn't be obfuscated by trying to do something
that just happens to be convienient. So I am a tad leery of these
into-ssa optimizations, but its pretty early too. :-)
We'll just have to measure and experiment. So does PRE do anything when
these are turned on?