sim/cgen: mask uninitialized variable warning in cgen-run.c

I see an uninitialized variable warning (with gcc 9.3.1) from
cgen-run.c, like this:

  /tmp/build/sim/../../src/sim/cris/../common/cgen-run.c: In function ‘sim_resume’:
  /tmp/build/sim/../../src/sim/cris/../common/cgen-run.c:259:5: warning: ‘engine_fns$’ may be used uninitialized in this function [-Wmaybe-uninitialized]
    259 |    (* engine_fns[next_cpu_nr]) (cpu);
        |    ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  /tmp/build/sim/../../src/sim/cris/../common/cgen-run.c:232:14: note: ‘engine_fns$’ was declared here
    232 |   ENGINE_FN *engine_fns[MAX_NR_PROCESSORS];
        |              ^~~~~~~~~~

This is a false positive - we over allocate engine_fn, and then only
initialize the nr_cpus entries which we will later go on to use.

However, we can easily silence this warning by initializing the unused
entries in engine_fns to NULL, this might also help if anyone ever
looks at engine_fns in a debugger, it should now be obvious which
entries are in use, and which are not.

With this change the warning is gone.

There should be no change in behaviour with this commit.

1 files changed, 5 insertions, 0 deletions

diff --git a/sim/common/cgen-run.c b/sim/common/cgen-run.c
index 9a13b0c..a9a493c 100644
--- a/sim/common/cgen-run.c
+++ b/sim/common/cgen-run.c
@@ -242,6 +242,11 @@ engine_run_n (SIM_DESC sd, int next_cpu_nr, int nr_cpus, int max_insns, int fast
       prime_cpu (cpu, max_insns);
     }
 
+  /* Ensure the remaining engine_fns slots are initialized, this silences a
+     compiler warning when engine_fns is used below.  */
+  for (i = nr_cpus; i < MAX_NR_PROCESSORS; ++i)
+    engine_fns[i] = NULL;
+
   while (1)
     {
       SIM_ENGINE_PREFIX_HOOK (sd);