/* Generic dominator tree walker
- Copyright (C) 2003, 2004, 2005 Free Software Foundation, Inc.
+ Copyright (C) 2003, 2004, 2005, 2007, 2008 Free Software Foundation,
+ Inc.
Contributed by Diego Novillo <dnovillo@redhat.com>
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
-the Free Software Foundation; either version 2, or (at your option)
+the Free Software Foundation; either version 3, or (at your option)
any later version.
GCC is distributed in the hope that it will be useful,
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
-along with GCC; see the file COPYING. If not, write to
-the Free Software Foundation, 51 Franklin Street, Fifth Floor,
-Boston, MA 02110-1301, USA. */
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
-#include "tree.h"
#include "basic-block.h"
-#include "tree-flow.h"
#include "domwalk.h"
-#include "ggc.h"
+#include "sbitmap.h"
-/* This file implements a generic walker for dominator trees.
+/* This file implements a generic walker for dominator trees.
To understand the dominator walker one must first have a grasp of dominators,
immediate dominators and the dominator tree.
| +--9 11
| / |
+--- 10 ---> 12
-
-
+
+
We have a dominator tree which looks like
1
9
|
10
-
-
-
+
+
+
The dominator tree is the basis for a number of analysis, transformation
and optimization algorithms that operate on a semi-global basis.
-
+
The dominator walker is a generic routine which visits blocks in the CFG
via a depth first search of the dominator tree. In the example above
the dominator walker might visit blocks in the following order
1, 2, 3, 4, 5, 8, 9, 10, 6, 7, 11, 12.
-
+
The dominator walker has a number of callbacks to perform actions
during the walk of the dominator tree. There are two callbacks
which walk statements, one before visiting the dominator children,
- one after visiting the dominator children. There is a callback
+ one after visiting the dominator children. There is a callback
before and after each statement walk callback. In addition, the
dominator walker manages allocation/deallocation of data structures
which are local to each block visited.
-
+
The dominator walker is meant to provide a generic means to build a pass
which can analyze or transform/optimize a function based on walking
the dominator tree. One simply fills in the dominator walker data
structure with the appropriate callbacks and calls the walker.
-
+
We currently use the dominator walker to prune the set of variables
which might need PHI nodes (which can greatly improve compile-time
performance in some cases).
-
+
We also use the dominator walker to rewrite the function into SSA form
which reduces code duplication since the rewriting phase is inherently
a walk of the dominator tree.
- And (of course), we use the dominator walker to drive a our dominator
+ And (of course), we use the dominator walker to drive our dominator
optimizer, which is a semi-global optimizer.
TODO:
{
void *bd = NULL;
basic_block dest;
- block_stmt_iterator bsi;
- bool is_interesting;
+ basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks * 2);
+ int sp = 0;
+ sbitmap visited = sbitmap_alloc (last_basic_block + 1);
+ sbitmap_zero (visited);
+ SET_BIT (visited, ENTRY_BLOCK_PTR->index);
- /* If block BB is not interesting to the caller, then none of the
- callbacks that walk the statements in BB are going to be
- executed. */
- is_interesting = bb->index < 0
- || walk_data->interesting_blocks == NULL
- || TEST_BIT (walk_data->interesting_blocks, bb->index);
-
- /* Callback to initialize the local data structure. */
- if (walk_data->initialize_block_local_data)
+ while (true)
{
- bool recycled;
-
- /* First get some local data, reusing any local data pointer we may
- have saved. */
- if (VEC_length (void_p, walk_data->free_block_data) > 0)
+ /* Don't worry about unreachable blocks. */
+ if (EDGE_COUNT (bb->preds) > 0
+ || bb == ENTRY_BLOCK_PTR
+ || bb == EXIT_BLOCK_PTR)
{
- bd = VEC_pop (void_p, walk_data->free_block_data);
- recycled = 1;
+ /* Callback to initialize the local data structure. */
+ if (walk_data->initialize_block_local_data)
+ {
+ bool recycled;
+
+ /* First get some local data, reusing any local data
+ pointer we may have saved. */
+ if (VEC_length (void_p, walk_data->free_block_data) > 0)
+ {
+ bd = VEC_pop (void_p, walk_data->free_block_data);
+ recycled = 1;
+ }
+ else
+ {
+ bd = xcalloc (1, walk_data->block_local_data_size);
+ recycled = 0;
+ }
+
+ /* Push the local data into the local data stack. */
+ VEC_safe_push (void_p, heap, walk_data->block_data_stack, bd);
+
+ /* Call the initializer. */
+ walk_data->initialize_block_local_data (walk_data, bb,
+ recycled);
+
+ }
+
+ /* Callback for operations to execute before we have walked the
+ dominator children, but before we walk statements. */
+ if (walk_data->before_dom_children)
+ (*walk_data->before_dom_children) (walk_data, bb);
+
+ SET_BIT (visited, bb->index);
+
+ /* Mark the current BB to be popped out of the recursion stack
+ once children are processed. */
+ worklist[sp++] = bb;
+ worklist[sp++] = NULL;
+
+ for (dest = first_dom_son (walk_data->dom_direction, bb);
+ dest; dest = next_dom_son (walk_data->dom_direction, dest))
+ worklist[sp++] = dest;
}
- else
+ /* NULL is used to mark pop operations in the recursion stack. */
+ while (sp > 0 && !worklist[sp - 1])
{
- bd = xcalloc (1, walk_data->block_local_data_size);
- recycled = 0;
+ --sp;
+ bb = worklist[--sp];
+
+ /* Callback for operations to execute after we have walked the
+ dominator children, but before we walk statements. */
+ if (walk_data->after_dom_children)
+ (*walk_data->after_dom_children) (walk_data, bb);
+
+ if (walk_data->initialize_block_local_data)
+ {
+ /* And finally pop the record off the block local data stack. */
+ bd = VEC_pop (void_p, walk_data->block_data_stack);
+ /* And save the block data so that we can re-use it. */
+ VEC_safe_push (void_p, heap, walk_data->free_block_data, bd);
+ }
+ }
+ if (sp)
+ {
+ int spp;
+ spp = sp - 1;
+ if (walk_data->dom_direction == CDI_DOMINATORS)
+ /* Find the dominator son that has all its predecessors
+ visited and continue with that. */
+ while (1)
+ {
+ edge_iterator ei;
+ edge e;
+ bool found = true;
+ bb = worklist[spp];
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ {
+ if (!dominated_by_p (CDI_DOMINATORS, e->src, e->dest)
+ && !TEST_BIT (visited, e->src->index))
+ {
+ found = false;
+ break;
+ }
+ }
+ if (found)
+ break;
+ /* If we didn't find a dom child with all visited
+ predecessors just use the candidate we were checking.
+ This happens for candidates in irreducible loops. */
+ if (!worklist[spp - 1])
+ break;
+ --spp;
+ }
+ bb = worklist[spp];
+ worklist[spp] = worklist[--sp];
}
-
- /* Push the local data into the local data stack. */
- VEC_safe_push (void_p, heap, walk_data->block_data_stack, bd);
-
- /* Call the initializer. */
- walk_data->initialize_block_local_data (walk_data, bb, recycled);
-
- }
-
- /* Callback for operations to execute before we have walked the
- dominator children, but before we walk statements. */
- if (walk_data->before_dom_children_before_stmts)
- (*walk_data->before_dom_children_before_stmts) (walk_data, bb);
-
- /* Statement walk before walking dominator children. */
- if (is_interesting && walk_data->before_dom_children_walk_stmts)
- {
- if (walk_data->walk_stmts_backward)
- for (bsi = bsi_last (bb); !bsi_end_p (bsi); bsi_prev (&bsi))
- (*walk_data->before_dom_children_walk_stmts) (walk_data, bb, bsi);
- else
- for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
- (*walk_data->before_dom_children_walk_stmts) (walk_data, bb, bsi);
- }
-
- /* Callback for operations to execute before we have walked the
- dominator children, and after we walk statements. */
- if (walk_data->before_dom_children_after_stmts)
- (*walk_data->before_dom_children_after_stmts) (walk_data, bb);
-
- /* Recursively call ourselves on the dominator children of BB. */
- for (dest = first_dom_son (walk_data->dom_direction, bb);
- dest;
- dest = next_dom_son (walk_data->dom_direction, dest))
- {
- /* The destination block may have become unreachable, in
- which case there's no point in optimizing it. */
- if (EDGE_COUNT (dest->preds) > 0)
- walk_dominator_tree (walk_data, dest);
- }
-
- /* Callback for operations to execute after we have walked the
- dominator children, but before we walk statements. */
- if (walk_data->after_dom_children_before_stmts)
- (*walk_data->after_dom_children_before_stmts) (walk_data, bb);
-
- /* Statement walk after walking dominator children. */
- if (is_interesting && walk_data->after_dom_children_walk_stmts)
- {
- if (walk_data->walk_stmts_backward)
- for (bsi = bsi_last (bb); !bsi_end_p (bsi); bsi_prev (&bsi))
- (*walk_data->after_dom_children_walk_stmts) (walk_data, bb, bsi);
else
- for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
- (*walk_data->after_dom_children_walk_stmts) (walk_data, bb, bsi);
- }
-
- /* Callback for operations to execute after we have walked the
- dominator children and after we have walked statements. */
- if (walk_data->after_dom_children_after_stmts)
- (*walk_data->after_dom_children_after_stmts) (walk_data, bb);
-
- if (walk_data->initialize_block_local_data)
- {
- /* And save the block data so that we can re-use it. */
- VEC_safe_push (void_p, heap, walk_data->free_block_data, bd);
-
- /* And finally pop the record off the block local data stack. */
- VEC_pop (void_p, walk_data->block_data_stack);
+ break;
}
+ free (worklist);
+ sbitmap_free (visited);
}
void
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