https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111334
--- Comment #11 from chenglulu <chenglulu at loongson dot cn> ---
(In reply to Xi Ruoyao from comment #10)
> (In reply to Xi Ruoyao from comment #9)
>
> > (define_insn "<optab>di3_fake"
> > [(set (match_operand:DI 0 "register_operand" "=r,&r,&r")
> > - (sign_extend:DI
> > - (any_div:SI (match_operand:DI 1 "register_operand" "r,r,0")
> > - (match_operand:DI 2 "register_operand" "r,r,r"))))]
> > - ""
> > + (if_then_else
> > + (and (eq (match_operand:DI 1 "register_operand" "r,r,0")
> > + (sign_extend:DI (subreg:SI (match_dup 1) 0)))
> > + (eq (match_operand:DI 2 "register_operand" "r,r,r")
> > + (sign_extend:DI (subreg:SI (match_dup 2) 0))))
> > + (sign_extend:DI
> > + (any_div:SI (subreg:SI (match_dup 1) 0)
> > + (subreg:SI (match_dup 2) 0)))
> > + (unspec:DI [(const_int 0)] UNSPEC_BAD_DIVW)))]
>
> With this the compiler will still believe all bad {div,mod}.w{,u}
I think this is already defined as UNSPEC. Isn’t the simpler the logic, the
better?
> instructions generate the exactly same unspecified value. But I don't think
> this is really relevant: if a program depends on the unspecified value (no
> matter one value or multiple values) it's already wrong.
>
> If we are really "paranoid" about this we can make 4 UNSPEC_BAD_* constants
> and use [(match_dup 1) (match_dup 2)] instead of [(const_int 0)].
>
> > + "TARGET_64BIT"
> > {
> > return loongarch_output_division ("<insn>.w<u>\t%0,%1,%2", operands);
> > }
