Help with "unable to generate reloads for" atomic_exchangesi

[William Tambe]

On Tue, Sep 24, 2019 at 5:58 AM Richard Sandiford
<richard.sandiford@arm.com> wrote:
>
> William Tambe <tambewilliam@gmail.com> writes:
> > I have defined atomic_exchangesi as follow in the machine description:
> >
> > (define_insn "atomic_exchangesi"
> >  [(set (match_operand:SI 0 "register_operand" "=r,r")
> >        (match_operand:SI 1 "memory_operand" "+B,W"))
> >   (set (match_dup 1)
> >        (unspec:SI
> >         [(match_operand:SI 2 "register_operand" "0,0")
> >          (match_operand:SI 3 "const_int_operand")]
> >         0))]
>
> "+" operands have to be destinations, so I think you need to swap
> the match_operand:SI 1 and match_dup 1 around.  (It's OK to have
> a match_dup 1 source before a match_operand 1 destination.)

I changed things as follow, but got "operand 1 duplicated before defined" :

(define_insn "atomic_exchange<mode>"
 [(set (match_operand:SI 0 "register_operand" "=r,r")
       (match_dup 1))
  (set (match_operand:SI 1 "memory_operand" "+B,W")
       (unspec:SI
        [(match_operand:SI 2 "register_operand" "0,0")
         (match_operand:SI 3 "const_int_operand")]
        0))]
 ""
 "@
  ...
  ...")

I then tried changing the order of the parallel operations as follow
but still got the error "unable to generate reloads for" :

(define_insn "atomic_exchange<mode>"
 [(set (match_operand:LDSTMODE 1 "memory_operand" "+B,W")
       (unspec:LDSTMODE
        [(match_operand:LDSTMODE 2 "register_operand" "0,0")
         (match_operand:LDSTMODE 3 "const_int_operand")]
        0))
  (set (match_operand:LDSTMODE 0 "register_operand" "=r,r")
       (match_dup 1))]
 ""
 "@
  ...
  ...")

I am using GCC 9.2.0;

Any other suggestion I could try ?

>
> Richard
>
> >  ""
> >  "@
> >   ...
> >   ...")
> >
> >
> > However GCC throw the following error for atomic_exchangesi:
> > Any idea what could be the cause of such an error ?
> >
> > error: unable to generate reloads for:
> >   902 | }
> >       | ^
> > (insn 89 86 90 12 (parallel [
> >             (set (reg:SI 4 %4 [orig:36 _30 ] [36])
> >                 (mem/v:SI (plus:SI (reg/f:SI 0 %sp)
> >                         (const_int 36 [0x24])) [-1  S4 A32]))
> >             (set (mem/v:SI (plus:SI (reg/f:SI 0 %sp)
> >                         (const_int 36 [0x24])) [-1  S4 A32])
> >                 (unspec:SI [
> >                         (reg:SI 3 %3 [orig:34 _28 ] [34])
> >                         (const_int 32770 [0x8002])
> >                     ] 0))
> >         ]) "/linux/include/asm-generic/atomic.h":118:1 35 {atomic_exchangesi}
> >      (nil))
> > during RTL pass: reload