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File _service:tar_scm:LoongArch-Avoid-non-returning-indirect-jumps-through.patch of Package gcc
From 7e759740048ee6f24c1055c32868fa21cabb4f75 Mon Sep 17 00:00:00 2001 From: Lulu Cheng <chenglulu@loongson.cn> Date: Wed, 7 Jun 2023 10:21:58 +0800 Subject: [PATCH 048/124] LoongArch: Avoid non-returning indirect jumps through $ra [PR110136] 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: PR target/110136 * 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> Signed-off-by: Peng Fan <fanpeng@loongson.cn> Signed-off-by: ticat_fp <fanpeng@loongson.cn> --- 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 b23248c33..c79951c1d 100644 --- a/gcc/config/loongarch/loongarch.md +++ b/gcc/config/loongarch/loongarch.md @@ -2895,6 +2895,10 @@ } [(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_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_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" -- 2.33.0
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