Re: other/7114: ICE building strcoll.op from glibc-2.2.5

[Geoff Keating <geoffk@geoffk.org>]

The following reply was made to PR other/7114; it has been noted by GNATS.

From: Geoff Keating <geoffk@geoffk.org>
To: amodra@bigpond.net.au
Cc: d.mueller@elsoft.ch, gcc-gnats@gcc.gnu.org, gcc-patches@gcc.gnu.org,
   dje@watson.ibm.com
Subject: Re: other/7114: ICE building strcoll.op from glibc-2.2.5
Date: Tue, 16 Jul 2002 10:48:14 -0700

 > Date: Tue, 16 Jul 2002 11:08:16 +0930
 > From: Alan Modra <amodra@bigpond.net.au>
 > Mail-Followup-To: Geoff Keating <geoffk@redhat.com>, d.mueller@elsoft.ch,
 > 	gcc-gnats@gcc.gnu.org, gcc-patches@gcc.gnu.org, dje@watson.ibm.com
 > Content-Disposition: inline
 > User-Agent: Mutt/1.3.25i
 > 
 > On Tue, Jul 16, 2002 at 09:20:27AM +0930, Alan Modra wrote:
 > > The testcase saves r30 and r31, but both are marked unused (don't
 > > appear in regs_ever_live).  Later rtl analysis decides that the
 > > save instruction can be eliminated, thus the ICE.  The real bug is
 > > that r30 is not marked used when current_function_needs_context.
 > > This is also the reason for PR5967.
 > > 
 > > The code that I copied from the !using_store_multiple case just
 > > papers over this bug.  So the above patch merely makes -mmultiple
 > > and -mno-multiple consistently wrong.
 > 
 > It gets worse.  rs6000/sysv4.h sets PROFILE_BEFORE_PROLOGUE.  That
 > means it is completely wrong for first_reg_to_save to decide r30
 > needs saving when profiling and current_function_needs_context.
 > It's too late to think about saving r30.  What really needs to
 > happen is one of
 > 
 > a) Don't use PROFILE_BEFORE_PROLOGUE.
 > or
 > b) Save the static chain reg on the stack somewhere before the mcount
 >    call.
 > or
 > c) Clobber r30 in a call to a nested function when profiling is
 >    enabled.
 > 
 > People would probably scream if we went with (a) as special purpose
 > implementations of mcount might make assumptions about the stack.
 > So, anyone want to speak up on the best way to solve this?
 
 The profiling function isn't allowed to clobber r30.  It never has
 been, so this should be no surprise.
 
 -- 
 - Geoffrey Keating <geoffk@geoffk.org> <geoffk@redhat.com>