[Bug c/109507] Optimizer creates incorrect program

2023-04-14 Thread aran at 100acres dot us via Gcc-bugs 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109507

Aran Clauson  changed:

   What|Removed |Added

 Status|RESOLVED|CLOSED

--- Comment #4 from Aran Clauson  ---
Disregard.

[Bug c/109507] Optimizer creates incorrect program

2023-04-14 Thread redi at gcc dot gnu.org via Gcc-bugs 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109507

--- Comment #3 from Jonathan Wakely  ---
When you created this bug report there was a red banner at the top of the page
that begins by asking you to read https://gcc.gnu.org/bugs/ and that tells you
to try -fsanitize=undefined

[Bug c/109507] Optimizer creates incorrect program

2023-04-13 Thread pinskia at gcc dot gnu.org via Gcc-bugs 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109507

Andrew Pinski  changed:

   What|Removed |Added

 Resolution|--- |INVALID
 Status|UNCONFIRMED |RESOLVED

--- Comment #2 from Andrew Pinski  ---
-fsanitize=undefined, at runtime gives:

/app/example.cpp:4:7: runtime error: negation of -2147483648 cannot be
represented in type 'int'; cast to an unsigned type to negate this value to
itself

Note the message is slightly wrong but points you to the right reason.
There is an overflow. because ~0x8000 is 2147483648 and then you add 1 to
it giving you an overflow which is undefined. Note ~a+1 is the same as -a as
both cases will overflow at the same time with 0x8000 which is why GCC is
providing that error message rather then on dealing with +1 like clang does:

Note clang gives:
/app/example.cpp:4:15: runtime error: signed integer overflow: 2147483647 + 1
cannot be represented in type 'int'

[Bug c/109507] Optimizer creates incorrect program

2023-04-13 Thread sjames at gcc dot gnu.org via Gcc-bugs 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109507

Sam James  changed:

   What|Removed |Added

 CC||sjames at gcc dot gnu.org

--- Comment #1 from Sam James  ---
UBSAN with GCC:
```
$ /tmp/foo
/tmp/foo.c:4:7: runtime error: negation of -2147483648 cannot be represented in
type 'int'; cast to an unsigned type to negate this value to itself
0
```

UBSAN with Clang:
```
/tmp/foo.c:4:15: runtime error: signed integer overflow: 2147483647 + 1 cannot
be represented in type 'int'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /tmp/foo.c:4:15 in
0
```