From: Segher Boessenkool <segher@kernel•crashing.org>
To: Gabriel Paubert <paubert@iram•es>
Cc: olof@lixom•net, linuxppc-dev@ozlabs•org,
Paul Mackerras <paulus@samba•org>
Subject: Re: [PATCH] atomic_dec_if_positive sign extension fix
Date: Tue, 16 Jan 2007 09:36:41 +0100 [thread overview]
Message-ID: <318e675947afbb7406839eac28083d9e@kernel.crashing.org> (raw)
In-Reply-To: <20070116042829.GA24654@iram.es>
>> You can specify "cc" in the clobber list already, don't use
>> "xer" unless you're clobbering something else in the XER.
>>
>
> Hmm, I believed "cc" was an alias for cr0.
Yes it is and I'm just confused. Sorry about that.
My excuse is that "addic." would do that to anyone ;-)
> /* PSImode is used for the XER register. The XER register
> is not used for anything; perhaps it should be deleted,
> except that that would change register numbers. */
> PARTIAL_INT_MODE (SI);
>
> in gcc/config/rs6000-modes.def is actually a bit misleading since the
> XER is often clobbered by instructions. But the XER is actually never
> exposed to the instruction scheduler: all the patterns that set and use
> the carry are simple lists of machine instructions which will be put in
> the final object without modifications (only register number and
> possibly
> immediate value substitution).
Yes indeed. Replacing the XER in GCC with a "carry register"
has been on my todo list for years; it is one of the last
things that still require emitting more than one machine insn
at once.
Segher
next prev parent reply other threads:[~2007-01-16 8:36 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-01-14 22:55 [PATCH] atomic_dec_if_positive sign extension fix Robert Jennings
2007-01-14 23:09 ` Paul Mackerras
2007-01-14 23:20 ` Olof Johansson
2007-01-14 23:32 ` Segher Boessenkool
2007-01-14 23:43 ` Segher Boessenkool
2007-01-15 8:55 ` Gabriel Paubert
2007-01-15 16:01 ` Segher Boessenkool
2007-01-16 4:28 ` Gabriel Paubert
2007-01-16 8:36 ` Segher Boessenkool [this message]
2007-01-16 18:16 ` [PATCH][v2] " Robert Jennings
2007-01-16 20:08 ` Gabriel Paubert
2007-01-17 16:50 ` [PATCH][v3] " Robert Jennings
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