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Re: [tree-ssa] Lazy updating of stmt operands
- From: law at redhat dot com
- To: Diego Novillo <dnovillo at redhat dot com>
- Cc: Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
- Date: Thu, 11 Dec 2003 12:36:37 -0700
- Subject: Re: [tree-ssa] Lazy updating of stmt operands
- Reply-to: law at redhat dot com
In message <1070818186.7334.30.camel@frodo.toronto.redhat.com>, Diego Novillo w
rites:
>> > tree-dfa.c:compute_immediate_uses()
>>
>> Which needs to pass through every single statement in the program. Not
>> really terribly efficient.
>>
>*shrug*, it's used by SSA-CCP. Since def-use edges are only needed by
>some passes, I don't think it would be worth our while trying to
>maintain them in get_stmt_operands.
>
>But I'm ready to be convinced otherwise. Say, with an implementation
>comparing both approaches with timings over a reasonable code base (a
>typical GCC bootstrap or one of the compile-time related PRs).
IMHO, when we have the need, then we'll expand on the immediate uses
interface -- either by having a way to incrementally update it, or
rebuild it.
While it's nice to think about a world where you always have immediate uses,
you end up with FUD chains if you do that -- with ultimately a tangled nest
of pointers that is bloody impossible to work with in the real world.
jeff