SSA usage question

[Richard Kenner]

> (1) Add two operands to the ARRAY_REF node.  One is a copy of TYPE_MIN_VALUE
> of the index and the second is a copy of TYPE_SIZE_UNIT of the element type.
> (2) Add an operand to COMPONENT_REF that's a copy of DECL_FIELD_POSITION of
> the second operand.
> 
> In both cases, any PLACEHOLDER_EXPRs will be expanded, the copy will be
> gimplified, and the operand will not be present if it would be a constant.

    How would this look in GIMPLE?

Exactly as I said: I'm describing the GIMPLE.

    What assignments and uses will this create?  

It will create no assignments and will create uses of those variables.

    Because of all the broken mail headers, I haven't been able to
    understand a single thing that was discussed in this thread.  Could
    you point me at the original problem description?

Well, there's no "original" description because discovering this has
been a iterative rocess.  See the C example I sent about an hour ago.
That's a trivial example of the sort of thing that doesn't currently
work.  But the tree allows a very general degree of variable positions
and sizes and Ada will use that complete generality.

We need to find a way to express that in GIMPLE without losing critical
reference information or generating copies of aggregates.