[Bug analyzer/99771] Analyzer diagnostics should not say "<unknown>"

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99771

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by David Malcolm <dmalcolm@gcc.gnu.org>:

https://gcc.gnu.org/g:0af37ad4422052be4b7f779737e14c80e57d0ad9

commit r12-7525-g0af37ad4422052be4b7f779737e14c80e57d0ad9
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Mon Mar 7 14:19:30 2022 -0500

    analyzer: fix leak suppression at end of 'main' [PR101983]

    PR analyzer/101983 reports what I thought were false positives
    from -Wanalyzer-malloc-leak, but on closer inspection, the
    analyzer is correctly reporting heap-allocated buffers that are
    no longer reachable.

    However, these "leaks" occur at the end of "main".  The analyzer already
    has some logic to avoid reporting leaks at the end of main, where the
    leak is detected at the end of the EXIT basic block.  However, in this
case,
    the leak is detected at the clobber in BB 2 here:
      <bb 2> :
      func (&res);
      res ={v} {CLOBBER(eol)};
      _4 = 0;

      <bb 3> :
    <L0>:
      return _4;

    where we have a chain BB 2 -> BB 3 -> EXIT BB.

    This patch generalizes the "are we at the end of 'main'" detection to
    handle such cases, silencing -Wanalyzer-malloc-leak on them.

    There's a remaining issue where the analyzer unhelpfully describes one
    of the leaking values as '<unknown>', rather than 'res.a', but I'm
    leaving that for a followup (covered by PR analyzer/99771).

    gcc/analyzer/ChangeLog:
            PR analyzer/101983
            * engine.cc (returning_from_function_p): New.
            (impl_region_model_context::on_state_leak): Use it when rejecting
            leaks at the return from "main".

    gcc/testsuite/ChangeLog:
            PR analyzer/101983
            * gcc.dg/analyzer/pr101983-main.c: New test.
            * gcc.dg/analyzer/pr101983-not-main.c: New test.

    Signed-off-by: David Malcolm <dmalcolm@redhat.com>