[PATCH] Speedup DOM and into-SSA

[Andrew Pinski <pinskia at physics dot uc dot edu>]

While looking why the testcase in PR 13776 was slow, I noticed that
at the top of the profile ggc_alloc was there.  This usually means we 
are
allocating too much in the GC space and I looked to figure out where
most of them were coming from.  They were coming from varrays
block_defs_stack in tree-into-ssa.c.  I decided to change it to VEC
which is allocated in the heap as we know the life time of the
stack.  I noticed a 10 seconds speedup by doing this.

Before the patch:
 tree SSA rewrite      :  11.87 ( 8%) usr   0.49 ( 2%) sys  14.41 ( 7%) 
wall
 dominator optimization:   9.09 ( 6%) usr   0.80 ( 3%) sys  12.35 ( 6%) 
wall

After:
 tree SSA rewrite      :   6.54 ( 5%) usr   0.41 ( 2%) sys   8.13 ( 4%) 
wall
 dominator optimization:   7.98 ( 6%) usr   0.80 ( 3%) sys   9.39 ( 5%) 
wall

Both good improvements for an easy change.

OK? Bootstrapped and tested on powerpc-darwin with no regressions

Thanks,
Andrew Pinski

ChangeLog:
	* tree-flow.h (tree2): Typedef because there is already a VEC(tree).
	Define a VEC(tree2) for head.
	(register_new_def): Change second argument to be a VEC(tree2).
	* tree-ssa-dom.c (block_defs_stack): Change to be a VEC(tree2).
	(tree_ssa_dominator_optimize): Initialize block_defs_stack with
	the VEC(tree2) function.  Also free it before returning.
	(dom_opt_initialize_block): Use VEC_safe_push instead of 
VARRAY_PUSH_TREE
	for block_defs_stack.
	(restore_currdefs_to_original_value): Use VEC_length instead of
	VARRAY_ACTIVE_SIZE. VEC_pop instead of VARRAY_TOP_TREE/VARRAY_POP.
	(dom_opt_finalize_block): Use VEC_safe_push instead of VARRAY_PUSH_TREE
	for block_defs_stack.
	* tree-into-ssa.c (block_defs_stack): Change to be a VEC(tree2).
	(rewrite_initialize_block): Use VEC_safe_push instead of 
VARRAY_PUSH_TREE
	for block_defs_stack.
	(ssa_register_new_def): Likewise.
	(ssa_rewrite_initialize_block): Likewise.
	(rewrite_finalize_block): Use VEC_length instead of
	VARRAY_ACTIVE_SIZE. VEC_pop instead of VARRAY_TOP_TREE/VARRAY_POP.
	(ssa_rewrite_finalize_block): Likewise.
	(register_new_def): Change second argument to be a VEC(tree2).
	Use VEC_safe_push instead of VARRAY_PUSH_TREE.
	(rewrite_blocks): Initialize block_defs_stack with
	the VEC(tree2) function.  Also free it before returning.
	(rewrite_ssa_into_ssa): Likewise.

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