[Bug middle-end/79647] bogus warning when building openssl

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79647

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |msebor at gcc dot gnu.org
         Resolution|---                         |INVALID
           Assignee|unassigned at gcc dot gnu.org      |msebor at gcc dot 
gnu.org

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
I can reproduce the warning.  The VRP dump shows the following, indicating the
warning is correctly interpreting the range information passed to it.

    _2724: [18446744071562067968, +INF]
    _1184: [18446742819579101184, 18446744073709551032]
    ...
  speed_main (int argc, char * * argv)
    ...
   long unsigned int _2724;
   long unsigned int _1184;
    ...
    <bb 84> [0.06%]:
    if (async_jobs_550 != 0)
      goto <bb 567>; [25.00%]
    ...
    <bb 567> [0.02%]:
    loopargs_len.29_1198 = (unsigned int) async_jobs_550;
    _1196 = loopargs_len.29_1198 * 584;
    _2726 = (int) _1196;
    loopargs_1193 = app_malloc (_2726, "array of loopargs");
    _2724 = (long unsigned int) async_jobs_550;
    _1184 = _2724 * 584;
    memset (loopargs_1193, 0, _1184);

The call to memset above is introduced by jump threading from this one:

    memset(loopargs, 0, loopargs_len * sizeof(loopargs_t));

for negative values of async_jobs (its type is int and its value is returned
from atoi()).  I think the warning is justified (if not exactly clear(*)) and
indicative of a possible bug in the code.  To avoid the warning, prevent
negative async_jobs values from reaching the memset, e.g., like so:

@@ -19021,6 +19021,13 @@
         case OPT_ASYNCJOBS:

             async_jobs = atoi(opt_arg());
+           if (async_jobs < 0) {
+             BIO_printf(bio_err,
+                        "%s: async_jobs must be non-negative\n",
+                        prog);
+             goto opterr;
+           }
+
             if (!ASYNC_is_capable()) {
                 BIO_printf(bio_err,
                            "%s: async_jobs specified but async not
supported\n",

I'm resolving this report as invalid on that basis.

[*] The warning is unfortunately missing the inlining context which can make
some its instances hard to debug.  A patch with a fix for that was submitted
last month but deferred until GCC 8
(https://gcc.gnu.org/ml/gcc-patches/2017-01/msg01994.html).