From: Ian Lance Taylor <ian@airs.com>
To: Sanjiv Kumar Gupta <sanjiv.gupta@oracle.com>
Cc: Sanjiv Kumar Gupta <skgnu@yahoo.com>, gcc@gcc.gnu.org
Subject: Re: GCC 3.3.1 -O2 problem with sqrt.c
Date: Sat, 04 Jun 2005 02:58:00 -0000 [thread overview]
Message-ID: <m34qce6d5v.fsf@gossamer.airs.com> (raw)
In-Reply-To: <429B1B23.8070301@oracle.com>
Sanjiv Kumar Gupta <sanjiv.gupta@oracle.com> writes:
> >>I couldn't understand why the insns 620 and 621 are
> >>being generated here as DI moves.
> > I'm not sure specifically why it got a DI move here, but it doesn't
> > look wrong. It's treating the struct named parts as DImode.
> >
> >>This is creating problem since insn 621 gets splitted
> >>after reload into two SI moves,i.e. @(r21, -8) and
> >>@(r21, -4).
> >>This renders insns 619 as dead and hence insns 618 and
> >>insn 429 as dead, which are eliminated by flow2.
> > It does look rather suspicious, but it's hard to know whether it is
> > wrong without seeing the value in r1.
> >
> r1 looks unrelated to struct members, and is being used by the
> ifcvt pass to expand some comparison insns.
In your .23 file, this is insn 431:
(insn 431 430 432 39 0x1002f420 (set (subreg:SI (reg/v:DI 153) 0)
(reg/v:SI 77)) 6 {*movsi} (insn_list 429 (nil))
(expr_list:REG_DEAD (reg/v:SI 77)
(nil)))
So it is setting the first SI subreg of a DI value. reload decides to
do an output reload for register 153. Since register 153 is DImode,
it does a DImode reload.
It winds up copying the DImode value to r2, and then writing r2 to
memory. The double move is because there is a secondary reload
involved. That implies that SECONDARY_OUTPUT_RELOAD_CLASS is defined
and is returning something other than NO_REGS for this case.
I see that insn 429 is setting the high part of register 153. Insn
429 looks like this:
(insn 429 428 430 39 0x1002f420 (set (subreg:SI (reg/v:DI 153) 4)
(plus:SI (reg/v:SI 79)
(reg/v:SI 82))) 12 {addsi3} (insn_list 422 (nil))
(expr_list:REG_DEAD (reg/v:SI 82)
(expr_list:REG_DEAD (reg/v:SI 79)
(nil))))
But note that a set to a subreg is explicitly defined to set the other
parts of the register to garbage. Therefore the value set by insn 429
is destroyed by insn 431.
I would guess that you need a strict_low_part in insns 429 and 431.
See the RTL documentation.
Ian
next prev parent reply other threads:[~2005-06-04 2:58 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-05-27 13:42 Sanjiv Kumar Gupta
2005-05-27 17:49 ` Ian Lance Taylor
2005-05-30 15:28 ` Sanjiv Kumar Gupta
2005-05-31 12:13 ` Sanjiv Kumar Gupta
2005-05-30 15:28 ` Sanjiv Kumar Gupta
2005-06-02 13:19 ` Dave Korn
2005-06-04 2:58 ` Ian Lance Taylor [this message]
2005-06-17 12:55 ` Sanjiv Kumar Gupta
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