valid_gimple_expression_p claims validity of invalid gimple

[Daniel Berlin]

On 7/14/07, Eric Botcazou <ebotcazou@adacore.com> wrote:
> > First is_gimple_min_invariant in try_to_simplify where it chooses
> > DECL_INITIAL should be valid_gimple_expression_p instead.
>
> That's a known problem, see tree-ssa-ccp.c:

I had forgotten about this because i hadn't done IPA in a while.  At
some point, we should just create special initializer functions and
gimplify these into them.
>
> /* The regular is_gimple_min_invariant does a shallow test of the object.
>    It assumes that full gimplification has happened, or will happen on the
>    object.  For a value coming from DECL_INITIAL, this is not true, so we
>    have to be more strict ourselves.  */
>
> static bool
> ccp_decl_initial_min_invariant (tree t)
> {
>   if (!is_gimple_min_invariant (t))
>     return false;
>   if (TREE_CODE (t) == ADDR_EXPR)
>     {
>       /* Inline and unroll is_gimple_addressable.  */
>       while (1)
>         {
>           t = TREE_OPERAND (t, 0);
>           if (is_gimple_id (t))
>             return true;
>           if (!handled_component_p (t))
>             return false;
>         }
>     }
>   return true;
> }
>
> static tree
> get_symbol_constant_value (tree sym)
> {
>   if (TREE_STATIC (sym)
>       && TREE_READONLY (sym)
>       && !MTAG_P (sym))
>     {
>       tree val = DECL_INITIAL (sym);
>       if (val
>           && ccp_decl_initial_min_invariant (val))
>         return val;
>     }
>
>   return NULL_TREE;
> }
>
> You could turn ccp_decl_initial_min_invariant into a global predicate and
> invoke it from tree-ssa-sccvn.c on the DECL_INITIAL.
>
> > However, even if i fix this, the testcase still fails because
> > valid_gimple_expression says something that is clearly invalid is
> > valid.
> >
> > (gdb) p valid_gimple_expression_p ($2)
> > $3 = 1 '\001'
> > (gdb) p debug_generic_stmt ($2)
> > &((struct RegisterLayout *) (char *) &SimulatedRegisters)->intmask;
> >
> > This is not valid gimple by a longshot :)
>
> Almost. :-)  The function was extracted unchanged from set_rhs but it looks
> like it needs to be beefed up a bit if it is to become of general use.
>
> > If you fix this part, i'll happily fix the bug report with the first part.
>
> The problem is again the ADDR_EXPR case, because it drags lvalues into the
> game.  This would be something like:

I'll try this and submit it as part of my patch if it works.

Thanks a ton!