[Bug target/38544] missed opportunity to use adc

["ubizjak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #1 from ubizjak at gmail dot com  2008-12-17 08:56 -------
There are various scary comments in ifcvt.c, noce_process_if_block() regarding
memory operands, like:

  /* Only operate on register destinations, and even then avoid extending
     the lifetime of hard registers on small register class machines.  */

and 

  /* Don't operate on sources that may trap or are volatile.  */

and

      /* Avoid store speculation: given "if (...) x = a" where x is a
         MEM, we only want to do the store if x is always set
         somewhere in the function.  This avoids cases like
           if (pthread_mutex_trylock(mutex))
             ++global_variable;
         where we only want global_variable to be changed if the mutex
         is held.  FIXME: This should ideally be expressed directly in
         RTL somehow.  */

I don't think it is always safe to simplify global memory operands.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38544