From: David Edelsohn <dje@watson.ibm.com>
To: Bernd Schmidt <bernds@redhat.co.uk>, Jan Hubicka <jh@suse.cz>,
Richard Henderson <rth@redhat.com>
Cc: gcc@gcc.gnu.org, degger@fhm.edu
Subject: cant_combine_insn_p hard_reg->reg moves
Date: Tue, 25 Dec 2001 23:13:00 -0000 [thread overview]
Message-ID: <200112260202.VAA29248@makai.watson.ibm.com> (raw)
In-Reply-To: Message from degger@fhm.edu of "Tue, 18 Dec 2001 12:49:49 +0100." <20011218125633.C322E6E18@Nicole.fhm.edu>
At Daniel's prompting, I finally tracked down the cause of the
code pessimization with respect to function arguments and return values.
Daniel tracked it down to somewhere in combine.
The problem is cant_combine_insn_p disallowing hard registers.
Arguments and return values are specified as hard regs. So this change
from December 2000 now often inserts a move between the hard reg allocated
to the pseudo of a computation and the hard regs of arguments and return
values. This is rather pessimistic for some architecture, especially for
ABIs with register-based calling conventions.
How can this improved? Could cant_combine_insn_p test for hard
regs with either REG_EQUIV involving computations of ARG_POINTER_REGNUM or
FUNCTION_VALUE_REGNO_P?
Thanks, David
next prev parent reply other threads:[~2001-12-26 2:06 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-12-17 10:30 rs6000: Trivial code generation stupidity degger
2001-12-17 10:31 ` David Edelsohn
2001-12-17 12:54 ` degger
2001-12-17 13:12 ` David Edelsohn
2001-12-17 13:21 ` David Edelsohn
2001-12-18 3:53 ` Analysis try (was: Re: rs6000: Trivial code generation stupidity) degger
2001-12-25 23:13 ` David Edelsohn [this message]
2001-12-26 1:18 ` cant_combine_insn_p hard_reg->reg moves Richard Henderson
2001-12-26 4:13 ` Jan Hubicka
2001-12-26 11:25 ` Richard Henderson
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