RE: [patch] gcc/config/h8300/h8300.md

[Kazu Hirata <kazu at hxi dot com>]

Hi Jeff,

> Hmmm, I didn't think caller-save used push/pop insns to save/restore
> registers around calls.  I thought it used simple stores.
> 
> I'd be very surprised if this change was useful for caller-saves.  Can
> you show me precisely how we're getting "push" instructions instead of
> "mov" instructions.

/* h8300-hms-gcc -ms -O2 -fomit-frame-pointer */
typedef long elm;

elm ret1 ();
elm arg7 (elm a, elm b, elm c, elm d, elm e, elm f, elm g);

void
test2 ()
{
  elm a = ret1 ();
  elm b = ret1 ();
  elm c = ret1 ();
  elm d = ret1 ();
  elm e = ret1 ();
  elm f = ret1 ();
  elm g = ret1 ();

  arg7 (a, b, c, d, e, f, g);
}

The above code example compiles to the following. By the way, on H8 in
general, "push.l er0" is an alias for "mov.l er0,@-sp", where sp is an alias
for er7.

There is one drawback. If you change "typedef long elm" to "typedef int
elm", then the peephole optimization does not work because it requires a
sequence of SI pushes with no HI push mixed in. On H8/300H and H8/S,
movqi_push, movhi_push, and movsi_push all translate to push.l, but of
course, their rtx'es are all different. So, the optimization seems
impossible unless you write out all possible combinations of pushes. Is
there any clever way?

; -O2

        .h8300s
        .file   "gccbug2.c"
        .section .text
        .align 1
        .global _test2
_test2:
        sub     #12,sp
        stm.l er4-er6,@-sp
        jsr     @_ret1
        mov.l   er0,@(20,er7)
        jsr     @_ret1
        mov.l   er0,@(16,er7)
        jsr     @_ret1
        mov.l   er0,@(12,er7)
        jsr     @_ret1
        mov.l   er0,er6
        jsr     @_ret1
        mov.l   er0,er5
        jsr     @_ret1
        mov.l   er0,er4
        jsr     @_ret1
        mov.l   er0,@-er7
        stm.w   er4-er6,@-sp ; this used to be push.l er4, push.l er5,
push.l er6
        mov.l   @(28,er7),er2
        mov.l   @(32,er7),er1
        mov.l   @(36,er7),er0
        jsr     @_arg7
        add.l   #16,er7
        ldm.l @sp+,er4-er6
        add     #12,sp
        rts
        .end

Kazu Hirata