🚀 go-pugleaf

	gcc for Motorola 68000 produces byzantine (but not strictly speaking
wrong) code for assignments to the fields of a structure whose total length
is <= 8 bytes.

	Using the suppiled m68k.md, and a home-made tm.h file which defines
MOTOROLA and SGS, then includes tm-m68k.h and fixes up some assembler stuff.
The host machine is a vms vax, so an un-modified xm-vms (aka config-vms)
was used. This was run on both Micro-vax II and III, although I doubt the
host machine has much to do with it. TARGET_DEFAULT was #defined 0, so
this was to produce code for a naked 68000.

Both 1.22 and 1.34 exhibit this behavior, as shown below. Increasing the
size of the structure above 8 bytes results in sane code. By this I mean
the "normal" use of move.b instructions rather than shifting and logical
ops between real regs and stack slots. FYI, note that while 1.34 was just
a touch "smarter" about the byte assignment to "row", it seems to have
become less intelligent about register life. Note the reload of the constant
16, and the fact that it used one more register, although it had a dead one
(d1 or d2, depending on viewpoint) available.

	I seldom use short structures, but thought you might be interested.

					Mike

| Mike Albaugh (albaugh@dms.UUCP || {...decwrl!turtlevax!}weitek!dms!albaugh)
| Atari Games Corp (Arcade Games, no relation to the makers of the ST)
| 675 Sycamore Dr. Milpitas, CA 95035		voice: (408)434-1709
| The opinions expressed are my own (Boy, are they ever)

The file (pre-processed):
----------------------------
# 1 "stru_tst.c"
typedef struct mt2
	{
	unsigned char	xxx;
	unsigned char	yyy;
	unsigned char	*text;
	char		chain;
	}  MT2;

extern char col,row;
extern void write_m();

static pmess(x,y,string)
char x,y,*string;
{
MT2 tbuff;
tbuff.xxx = x;
row = tbuff.yyy = y;
for (col = 0 ; string[col] ; col++);
col += x;
tbuff.text = string;
tbuff.chain = 0;
write_m(&tbuff,0);
}
--------------------
output from cc1 stru_tst.cpp -opt -o stru_tst.s_22
--------------------
 pmess

time in parse: 0.240000
time in integration: 0.000000
time in jump: 0.010000
time in cse: 0.080000
time in loop: 0.000000
time in flow: 0.060000
time in combine: 0.020000
time in local-alloc: 0.040000
time in global-alloc: 0.040000
time in final: 0.070000
time in varconst: 0.000000
time in symout: 0.000000
time in dump: 0.000000
--------------------------
file stru_tst.s_22
--------------------------
	SECTION 9
	DS.W 0
pmess:
	link a6,#-8
	movem.l d3/d2,-(sp)
	move.b 11(a6),d2
	move.l 16(a6),a0
	clr.l d0
	move.b d2,d0
	moveq.l #24,d3
	lsl.l d3,d0
	move.l #16777215,d1
	and.l -8(a6),d1
	move.l d1,-8(a6)
	or.l d0,d1
	move.l d1,-8(a6)
	clr.l d0
	move.b 15(a6),d0
	moveq.l #16,d3
	lsl.l d3,d0
	and.l #-16711681,d1
	move.l d1,-8(a6)
	or.l d0,d1
	move.l d1,-8(a6)
	lsr.l d3,d1
	and.b #255,d1
	move.b d1,row
	clr.b col
	bra L2
L4:
	addq.b #1,col
L2:
	move.b col,d0
	ext.w d0
	tst.b 0(a0,d0.w)
	bne L4
	add.b d2,col
	move.l a0,-8(a6)
	and.w #255,-2(a6)
	clr.l -(sp)
	pea -8(a6)
	jsr write_m
	movem.l -16(a6),d2/d3
	unlk a6
	rts
---------------------------------
using 1.34 as cc1, output from cc1 stru_tst.cpp -opt -o stru_tst.s_34
--------------------------------
 pmess

stru_tst.c:20: warning: assignment between incompatible pointer types

time in parse: 0.290000
time in integration: 0.000000
time in jump: 0.000000
time in cse: 0.090000
time in loop: 0.020000
time in flow: 0.020000
time in combine: 0.040000
time in local-alloc: 0.050000
time in global-alloc: 0.080000
time in final: 0.100000
time in varconst: 0.000000
time in symout: 0.000000
time in dump: 0.000000
----------------------------
the file stru_tst.s_34
----------------------------
gcc_compiled.:
	SECTION 9
	DS.W 0
pmess:
	link a6,#-8
	movem.l d4/d3/d2,-(sp)
	move.b 11(a6),d3
	move.b 15(a6),d1
	move.l 16(a6),a0
	clr.l d2
	move.b d3,d2
	moveq.l #24,d4
	lsl.l d4,d2
	move.l -8(a6),d0
	and.l #16777215,d0
	move.l d0,-8(a6)
	or.l d2,d0
	move.l d0,-8(a6)
	clr.l d2
	move.b d1,d2
	moveq.l #16,d4
	lsl.l d4,d2
	and.l #-16711681,d0
	move.l d0,-8(a6)
	or.l d2,d0
	move.l d0,-8(a6)
	moveq.l #16,d4
	lsr.l d4,d0
	move.b d0,row
	clr.b col
	bra L2
L4:
	addq.b #1,col
L2:
	move.b col,d0
	ext.w d0
	tst.b 0(a0,d0.w)
	bne L4
	add.b d3,col
	move.l a0,-8(a6)
	and.w #255,-2(a6)
	clr.l -(sp)
	pea -8(a6)
	jsr write_m
	movem.l -20(a6),d2/d3/d4
	unlk a6
	rts