Hi,
On 6/15/23 17:03, Xi Ruoyao wrote:
Xuerui: I guess this makes it sensible to show "ret" instead of "jirl
$zero, $ra, 0" in objdump -d output, but I don't know how to implement
it. Do you have some idea?
Thanks for the suggestion! Actually I have previously made this patch
series [1] which included just that. But the Loongson maintainers said
they're working on linker relaxation at that time so they would have to
postpone processing it, and I've never had a review since then; it's
expected to conflict with the relaxation patches so some rebasing would
be needed, but IIRC all review comments should be addressed. You can
take the series if you'd like to ;-)
[1]: https://sourceware.org/pipermail/binutils/2023-February/126088.html
On Thu, 2023-06-15 at 16:27 +0800, Lulu Cheng wrote:
Pushed to trunk and gcc-12 gcc-13.
r14-1866
r13-7448
r12-9698
在 2023/6/15 上午9:30, Lulu Cheng 写道:
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 <apin...@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"
