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Re: birthpoints in rtl.
- From: "Steven Bosscher" <stevenb dot gcc at gmail dot com>
- To: "Diego Novillo" <dnovillo at google dot com>
- Cc: "Kenneth Zadeck" <zadeck at naturalbridge dot com>, gcc <gcc at gcc dot gnu dot org>, "Bonzini, Paolo" <bonzini at gnu dot org>, "Park, Seongbae" <seongbae dot park at gmail dot com>, "Ian Lance Taylor" <iant at google dot com>, "Richard Sandiford" <rsandifo at nildram dot co dot uk>
- Date: Sat, 1 Mar 2008 01:04:16 +0100
- Subject: Re: birthpoints in rtl.
- References: <47C5EF2A.email@example.com> <47C6B132.firstname.lastname@example.org> <47C88C6B.email@example.com>
On Fri, Feb 29, 2008 at 11:51 PM, Diego Novillo <firstname.lastname@example.org> wrote:
> If we are not going to use a rewriting SSA form, I believe that the
> original problems we had with RTL-SSA can be avoided.
The nice thing about birth points would be that most RTL optimizers
can look through NOPs (amazingly ;-). That's a big plus IMHO.
I am not sure what would happen if GCC would start using FUD chains.
Is it like in SSA that every register is assigned only once? That
would break all RTL optimizers that look at lexical equivalence of
expressions, like e.g. all optimizations in gcse.c. When faced with a
PHI node, those optimizers would punt and lose.