[tuples] gimple_assign_subcode for GIMPLE_SINGLE_RHS

[Zdenek Dvorak]

Hi,

> On Sun, Mar 9, 2008 at 2:17 PM, Diego Novillo <dnovillo@google.com> wrote:
> > On Sun, Mar 9, 2008 at 08:15, Richard Guenther
> >  <richard.guenther@gmail.com> wrote:
> >
> >  >  What is GIMPLE_SINGLE_RHS after all?
> >
> >  Represents a "copy" operation, an operand with no operator (e.g., a = 3, b = c)
> >
> >  '3' and 'c' are "single" operands.  There is no operator involved in
> >  the assignment.
> 
> So as opposed to a unary operation which would look exactly the same apart
> from having a subcode?  So what does gimple_assign_subcode () return
> for the GIMPLE_SINGLE_RHS case?  Some random garbage?

just now, it will return the TREE_CODE of the rhs of the assignment
(e.g. VAR_DECL and INTEGER_CST in the cases mentioned above).
The problem we discuss in this thread is that actually the code
is the TREE_CODE of rhs in the moment that the statement was built;
so after ssa form creation, the gimple_assign_subcode of b_1 = c_2
will still be VAR_DECL; and after constant propagation of c_2 = 4,
the gimple_assign_subcode of b_1 = 4 will still be VAR_DECL.
While this is essentially harmless (only the fact that the code
is in GIMPLE_SINGLE_RHS class is important for the semantics),
it seems likely to cause some confusion,

Zdenek