From: Richard Sandiford <rdsandiford@googlemail.com>
To: Richard Earnshaw <rearnsha@arm.com>
Cc: Bernd Schmidt <bernds@codesourcery.com>,
GCC Patches <gcc-patches@gcc.gnu.org>,
"richard.sandiford\@linaro.org" <richard.sandiford@linaro.org>
Subject: Re: [PATCH 4/6] Shrink-wrapping
Date: Thu, 07 Jul 2011 20:19:00 -0000 [thread overview]
Message-ID: <87vcvdetw8.fsf@firetop.home> (raw)
In-Reply-To: <4E15D6CD.5020600@arm.com> (Richard Earnshaw's message of "Thu, 07 Jul 2011 16:54:53 +0100")
Richard Earnshaw <rearnsha@arm.com> writes:
> On 07/07/11 15:34, Richard Sandiford wrote:
>> It seems a shame to have both (return) and (simple_return). You said
>> that we need the distinction in order to cope with targets like ARM,
>> whose (return) instruction actually performs some of the epilogue too.
>> It feels like the load of the saved registers should really be expressed
>> in rtl, in parallel with the return. I realise that'd prevent
>> conditional returns though. Maybe there's no elegant way out...
>
> You'd still need to deal with distinct returns for shrink-wrapped code
> when the full (return) expands to
>
> ldm sp, {regs..., pc}
>
> The shrink wrapped version would always be
> bx lr
Sure, I understand that returns does more than return on ARM.
What I meant was: we'd normally want that other stuff to be
expressed in rtl alongside the (return) rtx. E.g. something like:
(parallel
[(return)
(set (reg r4) (mem (plus (reg sp) (const_int ...))))
(set (reg r5) (mem (plus (reg sp) (const_int ...))))
(set (reg sp) (plus (reg sp) (const_int ...)))])
And what I meant was: the reason we can't do that is that it would make
conditional execution harder. But the downside is that (return) and
(simple_return) will appear to do the same thing to register r4
(i.e. nothing). I.e. we are to some extent going to be lying to
the rtl optimisers.
Richard
next prev parent reply other threads:[~2011-07-07 20:08 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-23 14:44 Shrink-wrapping: Introduction Bernd Schmidt
2011-03-23 14:46 ` [PATCH 1/6] Disallow predicating the prologue Bernd Schmidt
2011-03-31 13:20 ` Jeff Law
2011-04-01 18:59 ` H.J. Lu
2011-04-01 21:08 ` Bernd Schmidt
2011-03-23 14:48 ` [PATCH 2/6] Unique return rtx Bernd Schmidt
2011-03-31 13:23 ` Jeff Law
2011-05-03 11:54 ` Bernd Schmidt
2011-03-23 14:51 ` [PATCH 3/6] Allow jumps in epilogues Bernd Schmidt
2011-03-23 16:46 ` Richard Henderson
2011-03-23 16:49 ` Bernd Schmidt
2011-03-23 17:19 ` Richard Henderson
2011-03-23 17:24 ` Bernd Schmidt
2011-03-23 17:27 ` Richard Henderson
2011-03-24 10:30 ` Bernd Schmidt
2011-03-25 17:51 ` Bernd Schmidt
2011-03-26 5:33 ` Richard Henderson
2011-03-31 20:09 ` Bernd Schmidt
2011-03-31 21:51 ` Richard Henderson
2011-03-31 22:36 ` Bernd Schmidt
2011-03-31 23:57 ` Richard Henderson
2011-04-05 21:59 ` Bernd Schmidt
2011-04-11 17:10 ` Richard Henderson
2011-04-13 14:16 ` Bernd Schmidt
2011-04-13 15:14 ` Bernd Schmidt
2011-04-13 15:16 ` Bernd Schmidt
2011-04-13 15:17 ` Bernd Schmidt
2011-04-13 15:28 ` Bernd Schmidt
2011-04-13 14:44 ` Richard Henderson
2011-04-13 14:54 ` Jakub Jelinek
2011-04-15 16:29 ` Bernd Schmidt
2011-03-23 14:56 ` [PATCH 5/6] Generate more shrink-wrapping opportunities Bernd Schmidt
2011-03-23 15:03 ` Jeff Law
2011-03-23 15:05 ` Bernd Schmidt
2011-03-23 15:18 ` Jeff Law
2011-03-31 13:26 ` Jeff Law
2011-03-31 13:34 ` Bernd Schmidt
2011-03-23 14:56 ` [PATCH 4/6] Shrink-wrapping Bernd Schmidt
2011-07-07 14:51 ` Richard Sandiford
2011-07-07 15:40 ` Bernd Schmidt
2011-07-07 17:00 ` Paul Koning
2011-07-07 17:02 ` Jeff Law
2011-07-07 17:05 ` Paul Koning
2011-07-07 17:08 ` Jeff Law
2011-07-07 17:30 ` Bernd Schmidt
2011-07-08 22:59 ` [pdp11] Emit prologue as rtl Richard Henderson
2011-07-09 13:46 ` Paul Koning
2011-07-09 16:53 ` Richard Henderson
2011-07-07 15:57 ` [PATCH 4/6] Shrink-wrapping Richard Earnshaw
2011-07-07 20:19 ` Richard Sandiford [this message]
2011-07-08 8:30 ` Richard Earnshaw
2011-07-08 13:57 ` Bernd Schmidt
2011-07-11 11:24 ` Richard Sandiford
2011-07-11 11:42 ` Bernd Schmidt
2011-07-21 3:57 ` Bernd Schmidt
2011-07-21 11:25 ` Richard Sandiford
2011-07-28 11:48 ` Bernd Schmidt
2011-07-28 12:45 ` Richard Sandiford
2011-07-28 23:30 ` Richard Earnshaw
2011-07-29 12:40 ` Bernd Schmidt
2011-08-03 10:42 ` Alan Modra
2011-08-03 11:19 ` Bernd Schmidt
2011-08-02 8:40 ` Bernd Schmidt
2011-08-03 15:39 ` Richard Sandiford
2011-08-24 19:23 ` Bernd Schmidt
2011-08-24 20:48 ` Richard Sandiford
2011-08-24 20:55 ` Bernd Schmidt
2011-08-26 14:49 ` Ramana Radhakrishnan
2011-08-26 14:58 ` Bernd Schmidt
2011-08-26 15:06 ` Ramana Radhakrishnan
2011-08-28 10:58 ` H.J. Lu
2011-07-07 21:41 ` Michael Hope
2011-03-23 14:57 ` [PATCH 6/6] A testcase Bernd Schmidt
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