🚀 go-pugleaf

GCC 2.3.1 (m68k, Atari TT) generates wrong code for this file:

---------- test.c
typedef struct
{
  unsigned short b0, b1, b2, b3;
} four_quarters;

four_quarters x;
int a, b;

void f (four_quarters j)
{
  b = j.b2;
  a = j.b3;
}
----------

Compiled with: gcc -O -S test.c

---------- test.s
#NO_APP
gcc2_compiled.:
.text
	.even
.globl _f
_f:
	link a6,#0
	movel d2,sp@-
	movel a6@(8),d1
	movel a6@(12),d2
	movel d2,d0
	clrw d0
	swap d0
	movel d0,_b
	clrw _a
	movew d1,_a+2		| <--- should be d2
	movel a6@(-4),d2
	unlk a6
	rts
.comm _x,8
.comm _a,4
.comm _b,4
----------

I suppose that the bug is in combine.c (make_extraction), near line 4630:

----------
      else if (GET_CODE (inner) == REG)
	/* We can't call gen_lowpart_for_combine here since we always want
	   a SUBREG and it would sometimes return a new hard register.  */
	new = gen_rtx (SUBREG, tmode, inner,
		       (WORDS_BIG_ENDIAN
			&& GET_MODE_SIZE (is_mode) > UNITS_PER_WORD
			? ((GET_MODE_SIZE (is_mode) - GET_MODE_SIZE (tmode))
			   / UNITS_PER_WORD)
			: 0));
----------

If `is_mode' is changed to `inner_mode' (in both places), the bug disappears.
--
Andreas Schwab
schwab@ls5.informatik.uni-dortmund.de