https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104165
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
CC| |msebor at gcc dot gnu.org
Last reconfirmed| |2022-01-21
Blocks| |56456
Summary|[12 Regression] Incorrectly |[12 Regression]
|identifying array bounds |-Warray-bounds for
|with -O2 |unreachable code inlined
|-Werror=array-bounds |from std::sort()
Ever confirmed|0 |1
--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
The warning triggers for the out of bounds pointer addition in &f.148 + 64 for
an array of 16 chars:
int foo (int n)
{
unsigned char f.148[16];
...
<bb 8> [local count: 116203857]:
_25 = ASSERT_EXPR <_15, _15 != &f.148>;
_6 = (signed long) _14;
_19 = _6 /[ex] 4;
__n.3_20 = (long unsigned int) _19;
_21 = __builtin_clzl (__n.3_20);
_22 = 63 - _21;
_23 = (long int) _22;
_24 = _23 * 2;
std::__introsort_loop<int*, long int,
__gnu_cxx::__ops::_Iter_comp_iter<bar(int, int)::<lambda(int, int)> > >
(&f.148, _25, _24, __comp);
if (_14 > 64)
goto <bb 9>; [50.00%]
else
goto <bb 15>; [50.00%]
<bb 9> [local count: 58101929]:
std::__insertion_sort.constprop (&f.148, &MEM <int[0:D.48109]> [(void
*)&f.148 + 64B]); <<< -Warray-bounds
goto <bb 14>; [100.00%]
The basic block is removed later, in CCP3, as unreachable:
Removing basic block 8
;; basic block 8, loop depth 0
;; pred:
std::__insertion_sort.constprop (&f.148, &MEM <int[0:D.48109]> [(void *)&f.148
+ 64B]);
if (&MEM <int[0:D.48109]> [(void *)&f.148 + 64B] != _15)
goto <bb 9>; [89.00%]
else
goto <bb 13>; [11.00%]
;; succ: 9
;; 13
The warning runs too early to benefit from the subsequent simplification. This
is one instance of a false positive that something like __builtin_warning()
would cure.
GCC 11 emits (and eliminates) the same invalid expression but the warning is
suppressed because in GCC 11 -Warray-bounds wasn't issued code inlined from
system headers. That's a GCC 12 change.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56456
[Bug 56456] [meta-bug] bogus/missing -Warray-bounds
