middle-end: maintain LCSSA throughout loop peeling

This final patch updates peeling to maintain LCSSA all the way through.

It's significantly easier to maintain it during peeling while we still know
where all new edges connect rather than touching it up later as is currently
being done.

This allows us to remove many of the helper functions that touch up the loops
at various parts.  The only complication is for loop distribution where we
should be able to use the same,  however ldist depending on whether
redirect_lc_phi_defs is true or not will either try to maintain a limited LCSSA
form itself or removes are non-virtual phis.

The problem here is that if we maintain LCSSA then in some cases the blocks
connecting the two loops get PHIs to keep the loop IV up to date.

However there is no loop, the guard condition is rewritten as 0 != 0, to the
"loop" always exits.   However due to the PHI nodes the probabilities get
completely wrong.  It seems to think that the impossible exit is the likely
edge.  This causes incorrect warnings and the presence of the PHIs prevent the
blocks to be simplified.

While it may be possible to make ldist work with LCSSA form, doing so seems more
work than not.  For that reason the peeling code has an additional parameter
used by only ldist to not connect the two loops during peeling.

This preserves the current behaviour from ldist until I can dive into the
implementation more.  Hopefully that's ok for now.

gcc/ChangeLog:

	* tree-loop-distribution.cc (copy_loop_before): Request no LCSSA.
	* tree-vect-loop-manip.cc (adjust_phi_and_debug_stmts): Add additional
	asserts.
	(slpeel_tree_duplicate_loop_to_edge_cfg): Keep LCSSA during peeling.
	(find_guard_arg): Look value up through explicit edge and original defs.
	(vect_do_peeling): Use it.
	(slpeel_update_phi_nodes_for_guard2): Take explicit exit edge.
	(slpeel_update_phi_nodes_for_lcssa, slpeel_update_phi_nodes_for_loops):
	Remove.
	* tree-vect-loop.cc (vect_create_epilog_for_reduction): Initialize phi.
	* tree-vectorizer.h (slpeel_tree_duplicate_loop_to_edge_cfg): Add
	optional param to turn off LCSSA mode.

1 files changed, 1 insertions, 1 deletions

diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
index 605b6fd..a4043e4 100644
--- a/gcc/tree-vectorizer.h
+++ b/gcc/tree-vectorizer.h
@@ -2189,7 +2189,7 @@ extern bool slpeel_can_duplicate_loop_p (const class loop *, const_edge,
 					 const_edge);
 class loop *slpeel_tree_duplicate_loop_to_edge_cfg (class loop *, edge,
 						    class loop *, edge,
-						    edge, edge *);
+						    edge, edge *, bool = true);
 class loop *vect_loop_versioning (loop_vec_info, gimple *);
 extern class loop *vect_do_peeling (loop_vec_info, tree, tree,
 				    tree *, tree *, tree *, int, bool, bool,