On Tue, 2004-06-15 at 10:02, Zdenek Dvorak wrote:
you may use rewrite_ssa_into_ssa for this, as well as incremental
updating and often in an easier way. So I don't really see what you
protest against (so far you have provided no reason except for your
personal dislike of the concept, sorry).
The approach you took is too heavy handed. It is duplicating fields
from var_ann_d, replicating most of the SSA renamer, treating SSA_NAMEs
as not really unique definitions and forcing another scan over the IL
when all the optimization is doing are just local changes.
Let me go through what I think is the problem that you are trying to
solve. We have some loop:
|
v
+->START
| |
| +--------> END
| |
| v
| BODY
| |
+----+
which we want to convert into
|
v
START
|
+--------> END
| ^
v |
+->BODY |
| | |
| v |
| START' -------+
| |
+----+
Is that correct?
I'm assuming that we will have built a loop-closed form by inserting
EXIT_COPY nodes at END (new tree nodes) before going into SSA. I could
give you a patch for this in LNO soonish.
For this particular problem, we could do the following algorithm:
1. Replicate all the PHI nodes in START in the first block of
BODY. Remove the SSA_NAMEs from all the operands and make new
SSA_NAMEs for the LHS of each node.
2. Delete the back edge BODY->START. That will convert the PHI
nodes into assignments.
3. Create START' and attach it as shown above.
4. Copy statements from START in START'. Create new SSA_NAMEs for
every assignment found.
5. Do a dominator walk of loop body beginning at START keeping
track of current definitions and repairing USE/V_USE operands
that don't match up.