[Bug sanitizer/107912] New: UBsan at -O0 missed a signed integer overflow

[Bug sanitizer/107912] New: UBsan at -O0 missed a signed integer overflow

[shaohua.li at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107912

            Bug ID: 107912
           Summary: UBsan at -O0 missed a signed integer overflow
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shaohua.li at inf dot ethz.ch
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org, marxin at gcc dot gnu.org
  Target Milestone: ---

`gcc-trunk -O0 -fsanitize=undefined -fno-sanitize-recover=all` misses the
signed integer overflow, while `gcc-trunk -Ox -fsanitize=address
-fno-sanitize-recover=all` (x=1, 2, 3, or s) can detect it.

Compiler explorer: https://godbolt.org/z/n8qs3z6v4

% cat a.c
unsigned short a;
int b;
int main() {
  int c = b = -2147483648;
  a = (c && 0 == c) - b;
  __builtin_printf("%d\n", a);
}
%
% gcc-tk -O0 -fsanitize=undefined -fno-sanitize-recover=all a.c &&./a.out
0
% gcc-tk -O1 -fsanitize=undefined -fno-sanitize-recover=all -w a.c &&./a.out
a.c:5:21: runtime error: negation of -2147483648 cannot be represented in type
'int'; cast to an unsigned type to negate this value to itself
% gcc-tk -O3 -fsanitize=undefined -fno-sanitize-recover=all -w a.c &&./a.out
a.c:5:21: runtime error: negation of -2147483648 cannot be represented in type
'int'; cast to an unsigned type to negate this value to itself
%

[Bug sanitizer/107912] shorterning causes a missing signed integer overflow

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107912

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
           Keywords|diagnostic                  |
   Last reconfirmed|                            |2022-11-29
            Summary|UBsan at -O0 missed a       |shorterning causes a
                   |signed integer overflow     |missing signed integer
                   |                            |overflow

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Another example where optimization level does not matter:
```
unsigned short a;
int b;
int main() {
  int c = b = -2147483648;
  unsigned short t = 0;
  a = t - b;
  __builtin_printf("%d\n", a);
}
```
I thought we had there was a bug report about this but I can't find it right
now.

Anyways confirmed. The only reason why the original example works at -O1 and
above is because (c && c == 0) is figured out to be false (0) and then 0-b is
translated into -b and the shorterning does not happen.