https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110228
--- Comment #32 from Sergei Trofimovich <slyfox at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #29)
> I can't reproduce the original failure on trunk or with GCC 13.1, but the
> testcase from comment#16 is now fixed. I also cannot reproduce the testcase
> from comment#21 before the fix.
>
> Can people double-check this is now fixed, maybe also on the branch when this
> fix is cherry-picked?
Test suite on llvm-16 still fails the same single 'LLVM ::
ExecutionEngine/JITLink/X86/MachO_weak_references.s' test for me.
gcc was built from 2c12ccf800fc7890925402d30a02f0fa9e2627cc.
The following test still fails for me:
$ cat bug.c
static unsigned a[4] = {1,1,1,1};
__attribute__((noipa))
static void bug(unsigned * p, unsigned *t, int n) {
unsigned LookupFlags;
for(int i = 0; i < n; i++) {
unsigned v = t[i];
if (v == 0) LookupFlags = 0;
else if (v == 1) LookupFlags = 1;
*p = LookupFlags;
}
}
int main() {
unsigned r = 42;
bug(&r, a, 4);
if (r != 1) __builtin_abort();
return 0;
}
$ gcc bug.c -o bug -O1 -Wall && ./bug
bug.c: In function 'bug':
bug.c:10:15: warning: 'LookupFlags' may be used uninitialized
[-Wmaybe-uninitialized]
10 | else if (v == 1) LookupFlags = 1;
| ^
bug.c:5:15: note: 'LookupFlags' was declared here
5 | unsigned LookupFlags;
| ^~~~~~~~~~~
Aborted (core dumped)
bug.c.255t.optimized still turns stores into '|=' against uninit value:
__attribute__((noipa, noinline, noclone, no_icf))
void bug (unsigned int * p, unsigned int * t, int n)
{
unsigned long ivtmp.8;
unsigned int v;
unsigned int LookupFlags;
_Bool _16;
unsigned int _17;
unsigned int _18;
void * _19;
unsigned long _20;
unsigned long _26;
unsigned long _28;
<bb 2> [local count: 118111600]:
if (n_10(D) > 0)
goto <bb 3>; [89.00%]
else
goto <bb 7>; [11.00%]
<bb 3> [local count: 105119324]:
ivtmp.8_21 = (unsigned long) t_11(D);
_20 = (unsigned long) n_10(D);
_26 = _20 * 4;
_28 = ivtmp.8_21 + _26;
<bb 4> [local count: 955630225]:
# LookupFlags_22 = PHI <LookupFlags_4(6), LookupFlags_8(D)(3)>
# ivtmp.8_6 = PHI <ivtmp.8_5(6), ivtmp.8_21(3)>
_19 = (void *) ivtmp.8_6;
v_12 = MEM[(unsigned int *)_19];
if (v_12 == 0)
goto <bb 6>; [50.00%]
else
goto <bb 5>; [50.00%]
<bb 5> [local count: 477815112]:
_16 = v_12 == 1;
_17 = (unsigned int) _16;
_18 = _17 | LookupFlags_22;
<bb 6> [local count: 955630225]:
# LookupFlags_4 = PHI <v_12(4), _18(5)>
*p_13(D) = LookupFlags_4;
ivtmp.8_5 = ivtmp.8_6 + 4;
if (ivtmp.8_5 != _28)
goto <bb 4>; [89.00%]
else
goto <bb 7>; [11.00%]
<bb 7> [local count: 118111600]:
return;
}
