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"
