On Wed, Jun 25, 2003 at 09:27:33AM +0100, Philip Blundell wrote:
> On Thu, 2003-06-19 at 16:26, Bill Allombert wrote:
> > Package: gcc-3.3
> > Version: 1:3.3-3
> > Severity: normal
> >
> > Dear GCC maintainers,
> >
> > gcc 3.3 (1:3.3ds9-3) miscompile pari (2.1.5) on arm with -O3, whereas
> > gcc 3.2 (3.2.3 20030331) worked fine.
> >
> > With -O2 gcc 3.3 works fine also
> >
> > The preprocessed miscompiled file is available at
> > http://people.debian.org/~ballombe/misc/init.i.gz
>
> Thanks for your report. Can you give any details of the miscompilation?
Well, it look like return statement are uncorrectly optimised with -O3:
The following file exhibit the problem:
----test.c--------
typedef long *GEN;
#define typ(x) ((((long)(x))&1)? 0: (((unsigned long) ((GEN) (x))[0]) >> 24))
GEN powrealraw(GEN x, long n);
GEN
powraw(GEN x, long n)
{
if (typ(x)==16)
return powrealraw(x,n);
else
return powrealraw(x,n);
}
------------------
Using a intermediary variable work around the problem:
GEN z=(typ(x)==16)? powrealraw(x,n): powrealraw(x,n);
return z;
Above is the diff of the asm file:
-O2 test2.S
-O3 test.S
--- test2.S 2003-06-25 20:05:52.000000000 +0000
+++ test.S 2003-06-25 20:05:41.000000000 +0000
@@ -12,8 +12,8 @@
mov r2, r0
mov ip, r1
bne .L2
- ldrb r3, [r0, #3] @ zero_extendqisi2
- cmp r3, #16
+ ldrb lr, [r0, #3] @ zero_extendqisi2
+ cmp lr, #16
beq .L4
.L2:
mov r0, r2
Here the supposed buggy test.S:
--test.S-------------------------
.file "test.c"
.text
.align 2
.global powraw
.type powraw, %function
powraw:
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
@ link register save eliminated.
tst r0, #1
@ lr needed for prologue
mov r2, r0
mov ip, r1
bne .L2
ldrb lr, [r0, #3] @ zero_extendqisi2
cmp lr, #16
beq .L4
.L2:
mov r0, r2
mov r1, ip
.L4:
b powrealraw
.size powraw, .-powraw
.ident "GCC: (GNU) 3.3 (Debian)"
------------------------------
A wild guess : '@ lr needed for prologue'
mean that lr must not be clobbered but
'ldrb lr, [r0, #3]' clobber it (??)
Cheers,
--
Bill. <[EMAIL PROTECTED]>
Imagine a large red swirl here.
