https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83382
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |msebor at gcc dot gnu.org
Ever confirmed|0 |1
Known to fail| |10.2.0, 11.0, 8.3.0, 9.3.0
Status|UNCONFIRMED |NEW
Last reconfirmed| |2021-04-06
--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
Reconfirmed with GCC 11. The warning sees the IL below and triggers for the
call to .UBSAN_NULL() after the CFG pass has removed the initialization of p.1.
A simple way to avoid it is to suppress warnings for calls to the sanitizer
internal functions.
Interestingly, this bug is only reproducible with C++, not when the same code
is compiled as C.
$ gcc -O0 -S -Wall -fsanitize=undefined -fdump-tree-cfg-details=/dev/stdout
-xc++ pr83382.c
pr83382.c: In function ‘void f()’:
pr83382.c:6:5: warning: value computed is not used [-Wunused-value]
6 | i >> ((!0 || c) && (0 ? j : *p));
| ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
;; Function f (_Z1fv, funcdef_no=0, decl_uid=2788, cgraph_uid=1,
symbol_order=5)
Scope blocks:
{ Scope block #0
}
Removing basic block 3
;; basic block 3, loop depth 0
;; pred:
p.1 = p; <<< initialization removed
.UBSAN_NULL (p.1, 2B, 4);
_1 = MEM[(const int &)p.1];
_2 = _1 != 0;
_3 = (int) _2;
_4 = (unsigned long) _3;
_5 = (unsigned long) i.0;
__builtin___ubsan_handle_shift_out_of_bounds (&*.Lubsan_data0, _5, _4);
;; succ: 4
;; 1 loops found
;;
;; Loop 0
;; header 0, latch 1
;; depth 0, outer -1
;; nodes: 0 1 2 3
;; 2 succs { 3 }
;; 3 succs { 1 }
void f ()
{
int * p.1; <<< not initialized
int i.0;
<bb 2> :
i.0 = i;
<bb 3> :
.UBSAN_NULL (p.1, 2B, 4); <<< -Wuninitialized
_6 = MEM[(const int &)p.1];
_7 = _6 != 0;
_8 = (int) _7;
return;
}
pr83382.c:6:25: warning: ‘p.1’ is used uninitialized [-Wuninitialized]
6 | i >> ((!0 || c) && (0 ? j : *p));
| ~~~^~~~~~~~~
pr83382.c:6:25: note: ‘p.1’ was declared here
6 | i >> ((!0 || c) && (0 ? j : *p));
| ~~~^~~~~~~~~
