On 10/25/06, Zdenek Dvorak <[EMAIL PROTECTED]> 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
