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/* Layout of basic blocks.
Copyright (C) 2006-2008 Free Software Foundation, Inc.
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) any later
version.
GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the 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.
Authors:
Andrea Bona
Andrea Ornstein
Erven Rohou
Roberto Costa
Gabriele Svelto
Contact information at STMicroelectronics:
Andrea C. Ornstein <andrea.ornstein@st.com>
Erven Rohou <erven.rohou@st.com>
*/
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "timevar.h"
#include "tree.h"
#include "tree-flow.h"
#include "tree-pass.h"
static int marker = 0;
static inline void
visit_block (basic_block bb)
{
bb->aux = (void *) ▮
}
static inline bool
visited (basic_block bb)
{
return (bb->aux != NULL);
}
/* used to walk the blocks in original order, so that we can detect if the
layout changes */
static basic_block current_bb_at_pos = NULL;
/* Compute a simple layout for the CFG, placing a node after all its
predecessors have been placed. When a block has two successors, we place
the one with the highest probability first.
'bb_order' is an array of basic_blocks, allocated by the caller and large
enough to hold all the blocks. 'num_so_far' is the number of placed blocks.
*/
static void
compute_layout (basic_block bb, basic_block* bb_order, int* num_so_far,
bool* changed)
{
bool all_visited;
int num_edges, i;
int edge_pos = 0, edge_dir = 1;
visit_block (bb);
bb_order[*num_so_far] = bb;
/* check if we change the order */
if (current_bb_at_pos != bb)
*changed = true;
current_bb_at_pos = current_bb_at_pos->next_bb;
++*num_so_far;
num_edges = EDGE_COUNT (bb->succs);
/* Consider only the case of two edges: one edge is straightforward; more
than two is a switch, we leave it alone. */
if (num_edges == 2)
{
edge e1 = EDGE_SUCC (bb, 0);
edge e2 = EDGE_SUCC (bb, 1);
/* In case the second edge is heavier than the first one, we invert the
scanning order. */
if (e1->probability < e2->probability)
{
edge_pos = 1; /* start from second edge */
edge_dir = -1; /* and go backwards */
}
}
for(i = 0; i < num_edges; ++i)
{
edge pred_edge;
edge_iterator pred_it;
edge e = EDGE_SUCC (bb, edge_pos);
basic_block succ = e->dest;
edge_pos += edge_dir;
if ((succ == EXIT_BLOCK_PTR) || /* Skip EXIT block */
(e->flags & EDGE_DFS_BACK) || /* Skip back edges */
(visited (succ))) /* Already visited */
{
continue;
}
/* Check if successor has all its predecessors visited, not considering
backedges. */
all_visited = true;
for (pred_it = ei_start (succ->preds);
ei_cond (pred_it, &pred_edge);
ei_next (&pred_it))
{
if (pred_edge->flags & EDGE_DFS_BACK)
continue;
if ((visited (pred_edge->src)) == 0)
{
all_visited = false;
break;
}
}
if (all_visited)
compute_layout (succ, bb_order, num_so_far, changed);
}
}
static unsigned int
bblayout (void)
{
bool layout_changed = false;
int bb_num = 0;
int i;
basic_block* bb_order = NULL;
mark_dfs_back_edges ();
bb_order = (basic_block *) alloca (n_basic_blocks * sizeof (basic_block));
current_bb_at_pos = ENTRY_BLOCK_PTR;
compute_layout (ENTRY_BLOCK_PTR, bb_order, &bb_num, &layout_changed);
bb_order[bb_num++] = EXIT_BLOCK_PTR;
gcc_assert (bb_num == n_basic_blocks);
if (layout_changed)
{
bb_order[0]->prev_bb = NULL;
bb_order[0]->next_bb = bb_order[1];
for(i=1; i < bb_num-1; ++i)
{
bb_order[i]->prev_bb = bb_order[i-1];
bb_order[i]->next_bb = bb_order[i+1];
}
bb_order[bb_num-1]->prev_bb = bb_order[bb_num-2];
bb_order[bb_num-1]->next_bb = NULL;
}
clear_aux_for_blocks ();
return 0;
}
static bool
bblayout_gate (void)
{
return current_function_decl != NULL;
}
/* Define the parameters of the bb layout pass. */
struct tree_opt_pass pass_bb_layout =
{
"bblayout", /* name */
bblayout_gate, /* gate */
bblayout, /* execute */
NULL, /* sub */
NULL, /* next */
0, /* static_pass_number */
TV_REST_OF_COMPILATION, /* tv_id */
PROP_cfg, /* properties_required */
0, /* properties_provided */
/* ??? If TER is enabled, we also kill gimple. */
0, /* properties_destroyed */
0,
TODO_dump_func, /* todo_flags_finish */
0 /* letter */
};
/*
* Local variables:
* eval: (c-set-style "gnu")
* End:
*/
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