[Bug tree-optimization/104922] New: bogus -Wformat-overflow=2 due to missing range for related variables

[Bug tree-optimization/104922] New: bogus -Wformat-overflow=2 due to missing range for related variables

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104922

            Bug ID: 104922
           Summary: bogus -Wformat-overflow=2 due to missing range for
                    related variables
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: diagnostic, lto
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
                CC: amacleod at redhat dot com, marxin at gcc dot gnu.org,
                    msebor at gcc dot gnu.org, unassigned at gcc dot gnu.org
        Depends on: 104746
  Target Milestone: ---

+++ This bug was initially created as a clone of Bug #104746 +++

As mentioned in bug 104746 comment 5, the following test case triggers
-Wformat-overflow (level 2) due to the constraint on i and j not being fully
exposed to the warning (each directive on its own can produce at most two
bytes/digits, but when one does produce two digits the other must produce
exactly one, so the output must fit in four bytes).  The same limitation
affects string directives with strings of bounded lengths.

As Andrew explains in bug 104746 comment 13, this can be improved in Ranger,
and should be made use of to avoid the warning.

char a[4];

void f (int i, int j)
{
  if (i < 0 || j < 0 || i + j > 19)
    return;

  __builtin_sprintf (a, "%u%u", i, j);
}

a.c: In function ‘f’:
a.c:8:26: warning: ‘%u’ directive writing between 1 and 10 bytes into a region
of size 4 [-Wformat-overflow=]
    8 |   __builtin_sprintf (a, "%u%u", i, j);
      |                          ^~
a.c:8:25: note: using the range [0, 4294967295] for directive argument
    8 |   __builtin_sprintf (a, "%u%u", i, j);
      |                         ^~~~~~
a.c:8:25: note: using the range [0, 4294967295] for directive argument
a.c:8:3: note: ‘__builtin_sprintf’ output between 3 and 21 bytes into a
destination of size 4
    8 |   __builtin_sprintf (a, "%u%u", i, j);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104746
[Bug 104746] False positive for -Wformat-overflow=2 since
r12-7033-g3c9f762ad02f398c

[Bug tree-optimization/104922] bogus -Wformat-overflow=2 due to missing range for related variables

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104922
Bug 104922 depends on bug 104746, which changed state.

Bug 104746 Summary: False positive for -Wformat-overflow=2 since r12-7033-g3c9f762ad02f398c
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104746

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|---                         |INVALID

[Bug tree-optimization/104922] bogus -Wformat-overflow=2 due to missing range for related variables

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104922

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|lto                         |missed-optimization
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-03-14

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed per bug 104746 comment 13.