memset (was: Redundant memset in AIO read_events)

[Etienne Lorrain]

 Note that using memset() is better reserved to initialise variable-size
 structures or buffers. Even if memset() is extremely optimised,
 it is still not as fast as not doing anything.

read_events(...) {
   struct io_event ent;
   memset(&ent, 0, sizeof(ent));
   while (...) {
      aio_read_evt(ctx, &ent);
   }
   ...
}

 Should be written (when "ent" has to be cleared):
read_events(...) {
   struct io_event ent = {};
   while (...) {
      aio_read_evt(ctx, &ent);
   }
   ...
}

  Just compare the code generated by (using GCC):
   struct io_event ent;
   memset(&ent, 0, sizeof(ent));
   ent.data = 0;
   if (ent.obj != 0) printf ("bad");

  And:
   struct io_event ent = {};
   ent.data = 0;
   if (ent.obj != 0) printf ("bad");

  and that is even without speaking of complete variable elimination
 when the structure is not used, unknown pointer alignement when
 memset function is not inlined, or aliasing optimisation.

  Etienne.

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