[Bug rtl-optimization/45472] [4.5/4.6 Regression] ICE: in move_op_ascend, at sel-sched.c:6124 with -fselective-scheduling2

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45472

--- Comment #8 from Paolo Bonzini <bonzini at gnu dot org> 2010-10-18 12:20:39 UTC ---
Would it make sense to make the statement volatile even if only some
subcomponents (or all subcomponents) are volatile?

I like (2); if I understand it correctly, in this case vv1 and vv2 would not be
volatile, but you'd still have

   vv1 ={v} vv2;

in the GIMPLE source.  It should be possible to use a bit on
{ARRAY,RECORD,UNION,QUAL_UNION}_TYPE to cache this, e.g.

#define TYPE_HAS_VOLATILE_PARTS(T) \
   (AGGREGATE_TYPE_P (T) \
    ? TYPE_UNSIGNED (T) \
    : TYPE_VOLATILE (T))

#define AGGREGATE_TYPE_CHECK(T) \
   TREE_CHECK4(T, ARRAY_TYPE, RECORD_TYPE, UNION_TYPE, QUAL_UNION_TYPE)

#define SET_TYPE_HAS_VOLATILE_PARTS(T, V) \
   (TYPE_UNSIGNED (AGGREGATE_TYPE_CHECK (T)) = (V))

Separately, expand would of course need to be taught about expanding accesses
to volatile subcomponents as mem/v.  If this approach was feasible, it would
have the advantage of splitting the task in two parts, one for GIMPLE
(including possibly the verifier) and one for expand.