[Bug middle-end/104965] [11/12 Regression] Yet another -Warray-bounds false positive
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104965 Richard Biener changed: What|Removed |Added Target Milestone|11.3|11.4 --- Comment #5 from Richard Biener --- GCC 11.3 is being released, retargeting bugs to GCC 11.4.
[Bug middle-end/104965] [11/12 Regression] Yet another -Warray-bounds false positive
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104965 --- Comment #4 from Andrew Pinski --- I think the missed optimization is recorded as either PR 79349 or PR 103827.
[Bug middle-end/104965] [11/12 Regression] Yet another -Warray-bounds false positive
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104965
Martin Sebor changed:
What|Removed |Added
CC||msebor at gcc dot gnu.org
--- Comment #3 from Martin Sebor ---
It looks like an escape analysis limitation. With this simpler test case using
different types to rule out aliasing assumptions:
#include
int main()
{
std::basic_string s;
auto p = new int[s.size ()]{ };
char c = 0;
if (s.size())
c = *p;
delete[] p;
return c;
}
pr104965.C:9:9: warning: array subscript 0 is outside array bounds of ‘void
[0]’ [-Warray-bounds]
9 | c = *p;
| ^~
pr104965.C:6:34: note: object of size 0 allocated by ‘operator new []’
6 | auto p = new short[s.size ()]{ };
| ^
One of the stores to the local s escapes its address which is then assumed to
have been clobbered by operator new:
[local count: 1073741824]:
s ={v} {CLOBBER};
MEM[(struct _Alloc_hider *)] ={v} {CLOBBER};
MEM[(struct _Alloc_hider *)]._M_p = _M_local_buf;
s._M_string_length = 0;
MEM[(char_type &) + 16] = 0;
_5 = operator new [] (0);
[local count: 1073741824]:
_10 = s._M_string_length;
if (_10 != 0)
goto ; [50.00%]
else
goto ; [50.00%]
[local count: 536870913]:
_1 = MEM[(int *)_5];
c_6 = (char) _1;
[Bug middle-end/104965] [11/12 Regression] Yet another -Warray-bounds false positive
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104965 --- Comment #2 from Jonathan Wakely --- In this case s.size() reads a local variable that can't be altered by new.
[Bug middle-end/104965] [11/12 Regression] Yet another -Warray-bounds false positive
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104965 Richard Biener changed: What|Removed |Added Target Milestone|--- |11.3 --- Comment #1 from Richard Biener --- Likely a similar issue as PR104966, avoid relying on memory CSE across a call to 'new'.
