https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102303
Bug ID: 102303
Summary: optimizer elides -ftrapv overflow detection
Product: gcc
Version: 11.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: john at mcfarlane dot name
Target Milestone: ---
With flag, `-ftrapv`, the following program on CE with 'x86-64 gcc 11.2' has
exit status 139:
int main()
{
int n = 0x7fffffff;
return n+1;
}
This is expected behavior: run-time overflow trapping. But with flags, `-ftrapv
-O1`, it has exit status 0. I wouldn't expect optimization to change the
behavior of this program, which appears to be either UB or as-if `-fwrapv`.
https://godbolt.org/z/jvj9javcY
Behavior is inconsistent with Clang 12.0. Behavior is inconsistent with
`-fsanitize=signed-integer-overflow -fsanitize-undefined-trap-on-error`.
Inconsistency goes as far back as the 5.x series, where trapping of this
overflow first appears. Docs for -ftrapv
(https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html) don't mention
optimization.
