From: Lulu Cheng <chenglulu@loongson.cn>
To: Xi Ruoyao <xry111@xry111.site>, gcc-patches@gcc.gnu.org
Cc: Wang Xuerui <i@xen0n.name>, Chenghua Xu <xuchenghua@loongson.cn>
Subject: Re: [PATCH] LoongArch: fix signed overflow in loongarch_emit_int_compare
Date: Sun, 6 Nov 2022 09:46:16 +0800 [thread overview]
Message-ID: <9ed0e1ee-00da-a9e8-8c13-552b172fa08c@loongson.cn> (raw)
In-Reply-To: <20221104063942.1594844-1-xry111@xry111.site>
在 2022/11/4 下午2:39, Xi Ruoyao 写道:
> Signed overflow is an undefined behavior, so we need to prevent it from
> happening, instead of "checking" the result.
>
> gcc/ChangeLog:
>
> * config/loongarch/loongarch.cc (loongarch_emit_int_compare):
> Avoid signed overflow.
> ---
>
> Bootstrapped and regtested on loongarch64-linux-gnu. OK for trunk?
>
> gcc/config/loongarch/loongarch.cc | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
> index f54c233f90c..032fb1474c7 100644
> --- a/gcc/config/loongarch/loongarch.cc
> +++ b/gcc/config/loongarch/loongarch.cc
> @@ -4175,13 +4175,14 @@ loongarch_emit_int_compare (enum rtx_code *code, rtx *op0, rtx *op1)
> HOST_WIDE_INT new_rhs;
> bool increment = *code == mag_comparisons[i][0];
> bool decrement = *code == mag_comparisons[i][1];
> - if (!increment && !decrement)
> + if ((!increment && !decrement)
> + || (increment && rhs == HOST_WIDE_INT_MAX)
> + || (decrement && rhs == HOST_WIDE_INT_MIN))
> continue;
I think it should be here:
if (!increment && !decrement)
continue;
+ if ((increment && rhs == HOST_WIDE_INT_MAX)
+ || (decrement && rhs == HOST_WIDE_INT_MIN))
+ break;
+
It is not necessary to continue when *code matches one of
mag_comparisons[i].
>
> new_rhs = rhs + (increment ? 1 : -1);
> if (loongarch_integer_cost (new_rhs)
> - < loongarch_integer_cost (rhs)
> - && (rhs < 0) == (new_rhs < 0))
> + < loongarch_integer_cost (rhs))
> {
> *op1 = GEN_INT (new_rhs);
> *code = mag_comparisons[i][increment];
next prev parent reply other threads:[~2022-11-06 1:46 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-04 6:39 Xi Ruoyao
2022-11-06 1:46 ` Lulu Cheng [this message]
2022-11-06 8:00 ` Xi Ruoyao
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=9ed0e1ee-00da-a9e8-8c13-552b172fa08c@loongson.cn \
--to=chenglulu@loongson.cn \
--cc=gcc-patches@gcc.gnu.org \
--cc=i@xen0n.name \
--cc=xry111@xry111.site \
--cc=xuchenghua@loongson.cn \
/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 read-only IMAP folder(s) and NNTP newsgroup(s).