From: Lulu Cheng <chenglulu@loongson.cn>
To: gcc-patches@gcc.gnu.org
Cc: xry111@xry111.site, i@xen0n.name, xuchenghua@loongson.cn,
Lulu Cheng <chenglulu@loongson.cn>,
Andrew Pinski <apinski@marvell.com>
Subject: [PATCH v3] LoongArch: Avoid non-returning indirect jumps through $ra [PR110136]
Date: Thu, 15 Jun 2023 09:30:34 +0800 [thread overview]
Message-ID: <20230615013033.505823-1-chenglulu@loongson.cn> (raw)
Micro-architecture unconditionally treats a "jr $ra" as "return from subroutine",
hence doing "jr $ra" would interfere with both subroutine return prediction and
the more general indirect branch prediction.
Therefore, a problem like PR110136 can cause a significant increase in branch error
prediction rate and affect performance. The same problem exists with "indirect_jump".
gcc/ChangeLog:
* config/loongarch/loongarch.md: Modify the register constraints for template
"jumptable" and "indirect_jump" from "r" to "e".
Co-authored-by: Andrew Pinski <apinski@marvell.com>
---
v1 -> v2:
1. Modify the description.
2. Modify the register constraints of the template "indirect_jump".
v2 -> v3:
1. Modify the description.
---
gcc/config/loongarch/loongarch.md | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/gcc/config/loongarch/loongarch.md b/gcc/config/loongarch/loongarch.md
index 816a943d155..b37e070660f 100644
--- a/gcc/config/loongarch/loongarch.md
+++ b/gcc/config/loongarch/loongarch.md
@@ -2895,6 +2895,10 @@ (define_insn "*jump_pic"
}
[(set_attr "type" "branch")])
+;; Micro-architecture unconditionally treats a "jr $ra" as "return from subroutine",
+;; non-returning indirect jumps through $ra would interfere with both subroutine
+;; return prediction and the more general indirect branch prediction.
+
(define_expand "indirect_jump"
[(set (pc) (match_operand 0 "register_operand"))]
""
@@ -2905,7 +2909,7 @@ (define_expand "indirect_jump"
})
(define_insn "@indirect_jump<mode>"
- [(set (pc) (match_operand:P 0 "register_operand" "r"))]
+ [(set (pc) (match_operand:P 0 "register_operand" "e"))]
""
"jr\t%0"
[(set_attr "type" "jump")
@@ -2928,7 +2932,7 @@ (define_expand "tablejump"
(define_insn "@tablejump<mode>"
[(set (pc)
- (match_operand:P 0 "register_operand" "r"))
+ (match_operand:P 0 "register_operand" "e"))
(use (label_ref (match_operand 1 "" "")))]
""
"jr\t%0"
--
2.31.1
next reply other threads:[~2023-06-15 1:31 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-15 1:30 Lulu Cheng [this message]
2023-06-15 8:27 ` [pushed][PATCH " Lulu Cheng
2023-06-15 9:03 ` Xi Ruoyao
2023-06-18 13:03 ` WANG Xuerui
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=20230615013033.505823-1-chenglulu@loongson.cn \
--to=chenglulu@loongson.cn \
--cc=apinski@marvell.com \
--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).