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Re: [RFC] Contributing tree-ssa to mainline
- From: Jan Hubicka <hubicka at ucw dot cz>
- To: Richard Kenner <kenner at vlsi1 dot ultra dot nyu dot edu>
- Cc: rth at redhat dot com, gcc at gcc dot gnu dot org
- Date: Mon, 19 Jan 2004 13:00:15 +0100
- Subject: Re: [RFC] Contributing tree-ssa to mainline
- References: <10401191147.AA27388@vlsi1.ultra.nyu.edu>
> So we've missed the required factor of 2 on this test case by 0.8%.
> Since that seems likely to be in the relm of measurement error, I
> think that should qualify.
> I agree.
> With a bit more work unwravelling C++ front-end obfuscation, I would
> expect the 10-20% to be visible on just about any object abstraction
> test case. Particularly for any object that has more than one field,
> and thus can't benefit from rtl addressof. That seems like it should
> be a large enough class to qualify.
> However, it would be good to see cases of both of the above for C as well as
> C++: if the gain is just C++, one could argue that the most appropriate place
> for such code is in the C++ front end. (There are Ada-specific optimizations
> in the Ada front end, for example.)
While it is possible to find/construct C testcases with large
abstraction penalties, this is not as common as for C++ or other more
Even if tree-SSA didn't made important speedups for common C programs I
think this is not problem as long as it is not making C worse and do
make C++ and Java better. I don't think re-doing optimizations in each
frontend is good design decision.
In longer run, with the new loop optimizer or profile driven inlining,
we will see considerable benefits for C programs too, but I would
prefer this to not be blocker for tree-SSA acceptance.
The optimizations tree-SSA implement right now are just essentials to
get more work in this area done.
> The tree-ssa infrastructure is supposed to benefit *all* languages. If
> benefits can be shown in C, they will clearly apply to all languages. But
> that's not true for C++.