From: Richard Henderson <richard.henderson@linaro.org>
To: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>,
"qemu-devel@nongnu.org Developers" <qemu-devel@nongnu.org>
Subject: Re: Question about TCG liveness_pass_1
Date: Fri, 17 Mar 2023 07:02:01 -0700 [thread overview]
Message-ID: <a8d13f61-6354-454d-2983-eeb65cb6bc61@linaro.org> (raw)
In-Reply-To: <66de3418-1fbf-ead1-bf29-f9e06523cdf2@linux.alibaba.com>
On 3/16/23 19:57, LIU Zhiwei wrote:
> Hi Richard,
>
> When I read the tcg code, I find a corner case which may be a bug in liveness_pass_1.
>
> I see all TEMP_TBs or global temps are set to TS_DEAD | TS_MEM when enter liveness_pass_1.
> Think about the sequence.
>
>
> 1)Write_global_temp_0 // 0->TS_DEAD, but not recorded in arg_life
Here TS_MEM->TS_DEAD, so *is* recorded in arg_life.
> 2)INDEX_op_qemu_st //trigger an exception here.
Here TCG_OPF_SIDE_EFFECTS is set, so call la_global_sync, so 0->TS_MEM.
>
> 3)Ref_global_temp_0 // TS_DEAD->0
>
> 4)Write_global_temp_0 // TS_DEAD | TS_MEM -> TS_DEAD
>
> As 1) will not write to memory, its register will be reused by the 3). I think it may miss
> a write to global_temp_0 when enter an exception.
Was there a specific test case that you find is miscompiled?
r~
next prev parent reply other threads:[~2023-03-17 14:02 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-17 2:57 Question about TCG liveness_pass_1 LIU Zhiwei
2023-03-17 14:02 ` Richard Henderson [this message]
2023-03-18 10:10 ` LIU Zhiwei
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=a8d13f61-6354-454d-2983-eeb65cb6bc61@linaro.org \
--to=richard.henderson@linaro.org \
--cc=qemu-devel@nongnu.org \
--cc=zhiwei_liu@linux.alibaba.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).