[Bug middle-end/109787] New: Warn about contract violations that can be detected at compile time

[Bug middle-end/109787] New: Warn about contract violations that can be detected at compile time

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109787

            Bug ID: 109787
           Summary: Warn about contract violations that can be detected at
                    compile time
           Product: gcc
           Version: 13.1.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
            Blocks: 87403
  Target Milestone: ---

struct array {
    int operator[](unsigned n) [[pre: n < 1]] { return 0; }
};
int main() {
    array a;
    return a[1];
}

When this C++ program is compiled with -fcontracts it will fail at runtime:

contract violation in function array<int, 1>::operator[] at contract.cc:7: n <
N
terminate called without an active exception
Aborted (core dumped)


The front-end inserts a call to this handler when the precondition check fails:

extern "C++" {
void handle_contract_violation (const std::experimental::contract_violation &);
}


It would be nice if the middle-end could notice that the contract handler is
reached on all paths, and so warn. If we can prove we're going to call the
contract violation handler, then we can prove the program is wrong, and we
should warn.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87403
[Bug 87403] [Meta-bug] Issues that suggest a new warning

[Bug middle-end/109787] Warn about contract violations that can be detected at compile time

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109787

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

[Bug middle-end/109787] Warn about contract violations that can be detected at compile time

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109787

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2023-05-09
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.