Re: [tree-ssa] [RFC] loop versioning

[Devang Patel <dpatel at apple dot com>]

On Jan 5, 2004, at 10:35 PM, Richard Henderson wrote:

> Anyway, you should know that there are already routines to copy
> statements and blocks.  So all of this code looks redundant.

tree_duplicate_bb () is more suitable to copy loop header. For
other basic blocks inside loop, while duplicating a basic block
I may not have corresponding edge available. Because it is possible
that bb at other end of edge does not yet have corresponding
duplicate bb.  So what I do is, duplicate all basic blocks and
then make edge for second loop by following edges of original loop.
Plus there can be more than one incoming edges and tree_duplicate_bb()
does not handle it.

As I understand tree_duplicate_bb() performs this operation

before
     ---- edge e1 ----> [bb1]

after
     --- edge e1 --+    [bb1]
                 |
                 +---> [bb2]

What I need to do for loop versioning is:

before
    ---- edge e1 ---> [bb1] ---- edge e2 --->
after
    ---- edge e1 ---> [bb1] ---- edge e2 --->
    ---- edge e21 ---> [bb21] ---- edge e22 --->


And comment on top of tree_duplicate_bb () says that it does not
work over SSA. At the moment, I'm trying to make loop versioning
work over SSA.

If you think, I should update tree_duplicate_bb () and related APIs
to satisfy these requirements then I'll follow that path.

Thank you,
-
Devang