[Bug target/110136] After optimization, the $r1 register will be broken when jumping to the jump table, resulting in a significant increase in the false prediction rate of branch prediction.

[chenglulu at loongson dot cn via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110136

--- Comment #4 from chenglulu <chenglulu at loongson dot cn> ---
(In reply to Andrew Pinski from comment #2)
> (In reply to Andrew Pinski from comment #1)
> > >In the regrename passover optimization
> > 
> > I am trying to understand the issue.
> > 
> > 5912         ldx.d   $r20,$r16,$r19
> >  5913         add.d   $r1,$r16,$r20
> >  5914         jr      $r1
> > 
> > Is the issue is jr does not like r1 register or some other kind of
> > performance issue?
> 
> If it is just r1 that is the issue, you could change the pattern in
> loongarch.md to discourage r1 by changing the constraints there.
> Because right now it assumes all registers are similar in cost:
> 
> (define_insn "@indirect_jump<mode>"
>   [(set (pc) (match_operand:P 0 "register_operand" "r"))]
>   ""
>   "jr\t%0"
>   [(set_attr "type" "jump")
>    (set_attr "mode" "none")])

Thank you very much, I modified the template to have a try.