wilson@vangogh.Berkeley.EDU (James E. Wilson) (01/28/89)
[gcc v1.32]
The use of "-O -ffloat-store" on a Sun3 can cause comparisons against zero
to fail. The program included below demonstrates this bug.
The problem is that output_move_double() requires at least two
instructions, and hence the condition codes will not be valid afterwards.
Gcc believes that the cc are valid, though, and proceeds to delete the
following floating point test instruction, as it considers it unneccesary.
I solved the problem by always invalidating the condition codes when
output_move_double() is called. I have included a context diff below.
This seems to work, although I am not sure if this is the best solution.
Also, a similar fix may be necessary for the other architectures supported
by gcc, someone should check.
*** orig.output-m68k.c Fri Jan 27 15:39:40 1989
--- output-m68k.c Fri Jan 27 19:00:44 1989
***************
*** 90,95 ****
--- 90,99 ----
rtx latehalf[2];
rtx addreg0 = 0, addreg1 = 0;
+ /* invalidate the condition codes, since it will take at least two
+ instructions to move the double value */
+ CC_STATUS_INIT;
+
/* First classify both operands. */
if (REG_P (operands[0]))
Script started on Fri Jan 27 19:37:05 1989
proxima<1>
proxima<1>cat tmp.c
/*
* With both -O and -ffloat-store, gcc v1.32 on a Sun3 will print "1 == 0???".
*/
main(void) {
double x = (double)1.0;
if (x == (double)0)
(void)printf("%.0f == 0???\n",x);
else
(void)printf("OK\n",x);
(void)exit(0);
}
proxima<2>
proxima<2>./gcc -O -S -ffloat-store tmp.c
0.3u 1.2s 0:06 23% 80+40k 16+11io 73pf+0w
proxima<3>
proxima<3>cat tmp.s
#NO_APP
gcc_compiled.:
.text
LC0:
.ascii "%.0f == 0???\12\0"
LC1:
.ascii "OK\12\0"
.even
.globl _main
_main:
link a6,#-8
movel #1072693248,a6@(-8)
clrl a6@(-4)
jne L2
movel a6@(-4),sp@-
movel a6@(-8),sp@-
pea LC0
jra L4
L2:
movel a6@(-4),sp@-
movel a6@(-8),sp@-
pea LC1
L4:
jbsr _printf
addw #12,sp
clrl sp@-
jbsr _exit
unlk a6
rts
proxima<4>
proxima<4>./gcc tmp.s
0.6u 1.9s 0:06 41% 16+24k 52+8io 0pf+0w
proxima<5>a.out
1 == 0???
proxima<6>
proxima<6>exit
proxima<7>
script done on Fri Jan 27 19:37:51 1989
Jim Wilson | For rain it hath a friendly sound
Internet: wilson@ernie.Berkeley.EDU | To one who's six feet under ground;
Usenet: ...!ucbvax!ucbernie!wilson | And scarce the friendly voice or face,
| A grave is such a quiet place.