Re: [tree-ssa] More overlapping live range infrastructure.

[Diego Novillo <dnovillo at redhat dot com>]

On Wed, May 07, 2003 at 03:21:02PM -0400, Andrew MacLeod wrote:

> 2003-05-02  Andrew MacLeod  <amacleod@redhat.com>
> 
> 	* tree-cfg.c (pdom_info): New file level static.
> 	(cleanup_tree_cfg): Free dominance info, if it was used.
> 	(bsi_replace): New. Replace a stmt with a new one.
> 	(linearize_cond_expr): Use post dominator info to determine is a 
> 	conditional can be safely removed.
> 	(find_insert_location): New. Determine where to insert a new stmt that 
> 	is placed on a split edge.
> 	(bsi_commit_first_edge_insert): Use find_insert_location to determine
> 	where to link a stmt when splitting an edge.
> 	(merge_tree_blocks): When deleting a basic block, remove it from the
> 	dominance structure if it exists.
> 	* tree-dfa.c (add_stmt_operand): Don't rename local statics. Treat 
> 	them just like globals.
> 	* tree-flow.h (struct var_ann_d): Add root_var_processed bit and 
> 	root_index fields.
> 	* tree-ssa-dce.c (process_worklist): Mark conditions feeding PHI's as
> 	necessary as well.
> 	(remove_dead_phis): Add missing debug information.
> 	* tree-ssa-live.c (var_union): Handle combining partitions when one
> 	has a root_variable as a representative.
> 	(compact_var_map): Add comments and use flags.
> 	(init_root_var): Use new root_var fields in struct var_ann_d.
> 	(dump_root_var): Send output to specified file, not stderr.
> 	(dump_var_map): Remove dump_flag parameter & some grotesque debug info.
> 	* tree-ssa-live.h (VAR_ANN_ROOT_INDEX): Define.
> 	(VARMAP_NORMAL, VARMAP_NO_SINGLE_DEFS): Define flags for compact_var_map.
> 	(var_to_partition_to_var): Return NULL if not in a partition.
> 	(find_root_var): Use VAR_ANN_ROOT_INDEX.
> 	* tree-ssa.c (insert_copy_on_edge): Add listing info.
> 	(coalesce_ssa_name): Coalesce live-on-entry variables to their root.
> 	Coalesce partitions across abnormal edges.
> 	(assign_vars): Remove redundant initialization code. Handle root_vars
> 	which have already been coalesced to a partition. 
> 	(rewrite_out_of_ssa): Add debug info & remove PHI nodes when processed.
> 	(rewrite_stmt): Don't redefine redundant expressions.
> 
OK.  Except the change to tree-ssa-dce.c:process_worklist.  I
think it's unnecessarily pessimistic.  When we talked about this
before, I suggested the following:

Given a live PHI node, look for all predecessor blocks for its
arguments.  If a predecessor block B has exactly one statement in
it, mark it live. 

Marking the predecessor statement live will in turn mark its
control dependent parent live which guarantees that the flowgraph
won't collapse for that PHI node.

Do you think that could work?  The change you made will make
blocks with more than one statement unnecessary live.

In find_insert_location, could you add a comment indicating
what the argument AFTER is used for?


Thanks.  Diego.