------- Comment #3 from reza dot yazdani at amd dot com 2010-03-04 18:37
-------
I reduced the test to:
--------------------------
extern void abort (void);
__attribute__ ((noinline)) int
foo (int *zzz, unsigned int kk)
{
int a, b, d;
a = b = 0;
for (d = 0; d < 1000; d++)
{
if (kk != 0)
b = *zzz;
}
return b;
}
int
main (void)
{
if (foo (0, 0) != 0)
abort();
return 0;
}
---------------------------
gcc tries to move an invariant unsigned test out of the loop. The following
three guarded loops are generated in the function "insert_guard(..)" in the
file "clast.c".
if (T_7 <= -1) {
for (scat_1=0;scat_1<=999;scat_1++) {
S3(scat_1) ;
S4(scat_1) ;
S5(scat_1) ;
}
}
if (T_7 >= 1) {
for (scat_1=0;scat_1<=999;scat_1++) {
S3(scat_1) ;
S4(scat_1) ;
S5(scat_1) ;
}
}
if (T_7 == 0) {
for (scat_1=0;scat_1<=999;scat_1++) {
S3(scat_1) ;
S5(scat_1) ;
}
}
S7() ;
$49 = void
kk is an "unsigned int" in the test program in the guard expression (kk != 0).
The T_7 represents kk in the above expressions. As kk is unsigned T_7 <= -1 is
always true and the dereference of the pointer (*zzz) is executed
unconditionally which causes the seg. fault. If the type of kk is changed to
signed, the correct code is generated.
I think, as unsigned expressions are bounded from one side, there must be a
constrain in insert_guard(..) that if the guard is unsigned, only the last two
cases should be generated.
--
reza dot yazdani at amd dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |reza dot yazdani at amd dot
| |com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43065
