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From: "vmakarov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/61231] [4.9/4.10 Regression] bootstrap comparision failure on powerpc64le-linux-gnu
Date: Wed, 21 May 2014 15:14:00 -0000	[thread overview]
Message-ID: <bug-61231-4-7AveZLvxxL@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-61231-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61231

--- Comment #10 from Vladimir Makarov <vmakarov at gcc dot gnu.org> ---
(In reply to Alan Modra from comment #9)
> So, what's happening here on the testcase is that before r210519, from the
> ira dump for pseudo reg 171 we have
> 
> a15 (r171,l0) best GENERAL_REGS, allocno GENERAL_REGS
> 
> a15(r171,l0) costs: BASE_REGS:0,0 GENERAL_REGS:0,0
> NON_SPECIAL_REGS:3264,3264 LINK_REGS:1224,1224 CTR_REGS:1224,1224
> LINK_OR_CTR_REGS:1224,1224 SPECIAL_REGS:1224,1224 SPEC_OR_GEN_REGS:1224,1224
> NON_FLOAT_REGS:4896,4896 ALL_REGS:4896,4896 MEM:0,0
> 
> and after
> 
> a15 (r171,l0) best NO_REGS, allocno NO_REGS
> 
> a15(r171,l0) costs: BASE_REGS:0,0 GENERAL_REGS:0,0
> NON_SPECIAL_REGS:1224,1224 LINK_REGS:1224,1224 CTR_REGS:1224,1224
> LINK_OR_CTR_REGS:1224,1224 SPECIAL_REGS:1224,1224 SPEC_OR_GEN_REGS:1224,1224
> NON_FLOAT_REGS:2448,2448 ALL_REGS:2448,2448 MEM:-320,-320
> 
> (hmm, negative cost, is that really allowed??)
> 
>

Yes, it is allowed.  It might be a saving.  For example, if you have insn
loading pseudo from a equivalent memory.  Assigning the equivalent memory will
remove the insn.

There is also a discrepancy between LRA and reload in many cases (e.g. in
treatment constraints with only 'm').  The patch which triggered the bug was
for x86 using LRA.  PPC is using reload by default.  I guess switching to LRA
would remove some future troubles.


  parent reply	other threads:[~2014-05-21 15:14 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-05-19 12:36 [Bug target/61231] New: " doko at gcc dot gnu.org
2014-05-19 12:49 ` [Bug target/61231] " rguenth at gcc dot gnu.org
2014-05-19 16:27 ` doko at gcc dot gnu.org
2014-05-19 18:40 ` fche at redhat dot com
2014-05-20 10:32 ` doko at gcc dot gnu.org
2014-05-20 10:59 ` fche at redhat dot com
2014-05-20 15:17 ` doko at gcc dot gnu.org
2014-05-20 15:42 ` bergner at gcc dot gnu.org
2014-05-20 15:45 ` bergner at gcc dot gnu.org
2014-05-21  7:49 ` amodra at gmail dot com
2014-05-21 15:14 ` vmakarov at gcc dot gnu.org [this message]
2014-05-22 15:37 ` bergner at gcc dot gnu.org
2014-05-22 17:41 ` vmakarov at gcc dot gnu.org
2014-05-23  1:18 ` amodra at gcc dot gnu.org
2014-05-23  1:24 ` amodra at gcc dot gnu.org
2014-05-23  1:29 ` amodra at gcc dot gnu.org
2014-06-25 11:07 ` jakub at gcc dot gnu.org
2014-06-25 11:37 ` doko at gcc dot gnu.org

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