[Bug analyzer/115564] New: -Wanalyzer-infinite-loop false negative when there are no source locations

[Bug analyzer/115564] New: -Wanalyzer-infinite-loop false negative when there are no source locations

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115564

            Bug ID: 115564
           Summary: -Wanalyzer-infinite-loop false negative when there are
                    no source locations
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: dmalcolm at gcc dot gnu.org
  Target Milestone: ---

Consider e.g.:

void test (unsigned b)
{
    for (unsigned i = b; i >= 0; --i) {
    }
}

-Wanalyzer-infinite-loop warns about this at -O1 and below:
  https://godbolt.org/z/axze96331

but at -O2 and above we don't warn. 
  https://godbolt.org/z/xjGMnP3P5

The warning is rejected at:

          if (inf_loop->m_loc == UNKNOWN_LOCATION)
            {
              if (get_logger ())
                get_logger ()->log
                  ("no location available for reporting infinite loop");
              continue;
            }

We have two basic blocks no statements, and location_t == UNKNOWN_LOCATION on
each of the edges connecting them.

Ideas for fixing:
* backtrack through the egraph to find the first useful location_t on a path to
the entry to the infinite loop
* ensure that location_t values are set on the CFG edges

[Bug analyzer/115564] -Wanalyzer-infinite-loop false negative when there are no source locations

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115564

David Malcolm <dmalcolm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2024-06-20
     Ever confirmed|0                           |1

--- Comment #1 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
Am testing a fix

[Bug analyzer/115564] -Wanalyzer-infinite-loop false negative when there are no source locations

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115564

David Malcolm <dmalcolm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |https://gcc.gnu.org/piperma
                   |                            |il/gcc-patches/2024-June/65
                   |                            |5424.html
             Status|ASSIGNED                    |WAITING
           Keywords|                            |patch

--- Comment #2 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
I've posted a patch for review here:
  https://gcc.gnu.org/pipermail/gcc-patches/2024-June/655424.html