63 lines
2.0 KiB
Diff
63 lines
2.0 KiB
Diff
From 7e759740048ee6f24c1055c32868fa21cabb4f75 Mon Sep 17 00:00:00 2001
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From: Lulu Cheng <chenglulu@loongson.cn>
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Date: Wed, 7 Jun 2023 10:21:58 +0800
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Subject: [PATCH 048/124] LoongArch: Avoid non-returning indirect jumps through
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$ra [PR110136]
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Micro-architecture unconditionally treats a "jr $ra" as "return from subroutine",
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hence doing "jr $ra" would interfere with both subroutine return prediction and
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the more general indirect branch prediction.
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Therefore, a problem like PR110136 can cause a significant increase in branch error
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prediction rate and affect performance. The same problem exists with "indirect_jump".
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gcc/ChangeLog:
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PR target/110136
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* config/loongarch/loongarch.md: Modify the register constraints for template
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"jumptable" and "indirect_jump" from "r" to "e".
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Co-authored-by: Andrew Pinski <apinski@marvell.com>
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Signed-off-by: Peng Fan <fanpeng@loongson.cn>
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Signed-off-by: ticat_fp <fanpeng@loongson.cn>
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---
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gcc/config/loongarch/loongarch.md | 8 ++++++--
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1 file changed, 6 insertions(+), 2 deletions(-)
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diff --git a/gcc/config/loongarch/loongarch.md b/gcc/config/loongarch/loongarch.md
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index b23248c33..c79951c1d 100644
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--- a/gcc/config/loongarch/loongarch.md
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+++ b/gcc/config/loongarch/loongarch.md
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@@ -2895,6 +2895,10 @@
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}
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[(set_attr "type" "branch")])
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+;; Micro-architecture unconditionally treats a "jr $ra" as "return from subroutine",
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+;; non-returning indirect jumps through $ra would interfere with both subroutine
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+;; return prediction and the more general indirect branch prediction.
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+
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(define_expand "indirect_jump"
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[(set (pc) (match_operand 0 "register_operand"))]
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""
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@@ -2905,7 +2909,7 @@
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})
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(define_insn "@indirect_jump<mode>"
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- [(set (pc) (match_operand:P 0 "register_operand" "r"))]
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+ [(set (pc) (match_operand:P 0 "register_operand" "e"))]
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""
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"jr\t%0"
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[(set_attr "type" "jump")
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@@ -2928,7 +2932,7 @@
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(define_insn "@tablejump<mode>"
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[(set (pc)
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- (match_operand:P 0 "register_operand" "r"))
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+ (match_operand:P 0 "register_operand" "e"))
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(use (label_ref (match_operand 1 "" "")))]
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""
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"jr\t%0"
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--
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2.33.0
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