LOOP_HEADER tree code?

[Devang Patel]

On 10/25/06, Zdenek Dvorak <rakdver@atrey.karlin.mff.cuni.cz> wrote:

> Many optimizers would need to be taught to know about TREE_USED (or any
> other bit you would use for that).  We do not have this type of
> restriction for any other ssa names, so this would be brand new
> functionality (on the other hand, most optimizers would not need to know
> anything special about LOOP_HEADER statements).
>
> This definitely is not a way I would take if I decide not to use
> LOOP_HEADER.  I would probably add some sort of "implicit" uses placed
> on some basic blocks (or in loops).  It would be a bit more difficult
> to teach the relevant optimizers to know about these uses, but at least
> I won't be introducing a new brand of ssa names that behave differently
> than all the other ssa names.

Yes, the idea is to record implict use somehow.

I did not realize that tree-ssa DCE does not use TREE_USED or
DECL_PRESERVE_P. I am not sure how function marked as
attribute((used)) will survive otherwise when IPO DCE is able to see
whole program.

-
Devang