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

[Geoff Keating]

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 10:45:33 -0700

 > Date: Tue, 16 Jul 2002 09:20:27 +0930
 > From: Alan Modra <amodra@bigpond.net.au>
 
 > On Mon, Jul 15, 2002 at 12:43:02PM -0700, Geoff Keating wrote:
 > > > Date: Mon, 15 Jul 2002 18:56:03 +0930
 > > > From: Alan Modra <amodra@bigpond.net.au>
 > > 
 > > > This patch cures the testcase.  The !using_store_multiple code tests
 > > > whether regs are live before saving.  We need to do something similar
 > > > for using_store_multiple, in case all regs need not be saved.
 > > 
 > > Those registers are actually saved, whether they need to be or not,
 > > correct?
 > > 
 > > So the RTL generated is an accurate representation of the instruction,
 > > and the bug must be elsewhere.
 > 
 > 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.
 
 No, the code below causes unused registers to actually not be saved,
 which is correct (it does sometimes happen that all uses of a register
 are eliminated after reload).  This can be done when individual loads
 and stores are being used, you just don't emit that store.  It can't
 be done when store-multiple is being used.
 
 -- 
 - Geoffrey Keating <geoffk@geoffk.org> <geoffk@redhat.com>