From: coypu@sdf.org
To: Jeff Law <law@redhat.com>
Cc: gcc@gcc.gnu.org, port-vax@netbsd.org
Subject: Re: syncing the GCC vax port, atomic issue
Date: Sat, 21 Sep 2019 01:18:00 -0000 [thread overview]
Message-ID: <20190921011835.GA5931@SDF.ORG> (raw)
In-Reply-To: <20190920220756.GA10628@SDF.ORG>
On Fri, Sep 20, 2019 at 10:07:59PM +0000, coypu@sdf.org wrote:
> Introducing the reversed jbb* patterns doesn't seem to help with the
> original issue. It crashes building libatomic.
My loose understanding of what is going on:
- GCC emits this atomic in expand.
- When cleaning up, it looks for optimizations.
- It decides this is a branch to another branch situation, so maybe
can be improved.
- This fails to output an instruction for unrelated reasons.
- Hit an assert.
I don't think that we should be trying to combine regular branch +
atomic branch in very generic code.
My guess is that, if it didn't crash now, it might emit a different kind
of branch which loses the atomic qualities, and result in wrong code.
I tried to single-step GCC, and it might be trying entirely different
instruction patterns.
I'm not sure whether I should put a lot of trust in the line numbers
shown from .md files, but it's trying nonlocal_goto in vax.md.
In any case, nothing from builtins.md.
next prev parent reply other threads:[~2019-09-21 1:18 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-30 9:03 syncing the GCC vax port coypu
2019-03-31 17:26 ` Paul Koning
2019-03-31 17:41 ` coypu
2019-04-01 15:33 ` Jeff Law
2019-04-29 20:08 ` Jeff Law
2019-09-20 11:15 ` coypu
2019-09-20 21:04 ` syncing the GCC vax port, atomic issue coypu
2019-09-20 21:45 ` Jeff Law
2019-09-20 22:08 ` coypu
2019-09-21 1:18 ` coypu [this message]
2019-09-21 18:27 ` Paul Koning
2019-10-01 19:44 ` Jeff Law
2019-10-01 19:43 ` Jeff Law
2019-10-02 9:39 ` Richard Earnshaw (lists)
2019-10-02 17:17 ` Segher Boessenkool
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