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From: Alan Modra <amodra@gmail.com>
To: gcc-patches@gcc.gnu.org
Subject: Re: PR79286, ira combine_and_move_insns in loops
Date: Wed, 01 Feb 2017 21:37:00 -0000	[thread overview]
Message-ID: <20170201213722.GB3731@bubble.grove.modra.org> (raw)
In-Reply-To: <20170201134830.GA3731@bubble.grove.modra.org>

On Thu, Feb 02, 2017 at 12:18:31AM +1030, Alan Modra wrote:
> This patch cures PR79286 by restoring the REG_DEAD note test used
> prior to r235660, but modified to only exclude insns that may trap.
> I'd like to allow combine/move without a REG_DEAD note in loops
> because insns in loops often lack such notes, and I recall seeing
> quite a few cases at the time I wrote r235660 where loops benefited
> from allowing the combine/move to happen.

Ugh, the new testcase fails for x86 -m32 -Os, but not due to ira this
time but rather reload.  I haven't looked into what is going wrong in
reload yet, but the net result is the same:  The faulting mem read is
moved before the printf call.

There were no other testsuite regressions, apart from the random set
of fails I have been getting for a long time on x86_64 for
c-c++-common/ubsan/float-cast-overflow-10.c,
c-c++-common/ubsan/float-cast-overflow-2.c,
c-c++-common/ubsan/float-cast-overflow-8.c, and
c-c++-common/ubsan/overflow-mul-4.c.

What is the correct thing to do for a new testcase that fails like
this?  Add a dg-fail-if?  Assuming I or someone else can't fix the
reload fail.

The new testcase -Os failure occurs on gcc-4.x, gcc-5 and gcc-6, but
gcc-3.4 passes.

-- 
Alan Modra
Australia Development Lab, IBM

  reply	other threads:[~2017-02-01 21:37 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-02-01 13:48 Alan Modra
2017-02-01 21:37 ` Alan Modra [this message]
2017-02-02  9:31   ` Alan Modra
2017-02-03  8:55     ` Jeff Law
2017-02-11  0:52       ` Alan Modra
2017-02-16 23:08         ` Jeff Law
2017-02-04  0:08     ` Jeff Law
2017-02-18 14:28 Dominique d'Humières
2017-02-21 23:35 ` Alan Modra
2017-02-22 12:10   ` Dominique d'Humières
2017-02-22 16:32     ` Jeff Law
2017-02-22 16:57       ` Dominique d'Humières
2017-02-23  8:55         ` Jeff Law
2017-02-23 10:13           ` Alan Modra
2017-02-23 15:22             ` Jeff Law

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