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/* Optimization of return nodes by merging them into one basic block.
Copyright (C) 2004 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, 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "errors.h"
#include "ggc.h"
#include "tree.h"
#include "flags.h"
#include "rtl.h"
#include "tm_p.h"
#include "basic-block.h"
#include "timevar.h"
#include "diagnostic.h"
#include "tree-flow.h"
#include "tree-pass.h"
#include "tree-dump.h"
static void tree_ssa_return (void);
/* Build a temporary. Make sure and register it to be renamed. */
static tree
make_temp (tree type)
{
tree t = create_tmp_var (type, NULL);
add_referenced_tmp_var (t);
bitmap_set_bit (vars_to_rename, var_ann (t)->uid);
return t;
}
static void
tree_ssa_return (void)
{
basic_block bb;
/* Search every basic block for return nodes we may be able to optimize. */
FOR_EACH_BB (bb)
{
tree returnstmt = last_stmt (bb);
edge pred = bb->pred;
basic_block bb_other = NULL;
tree returnstmt_other;
basic_block new_bb = NULL;
tree new_var = NULL;
block_stmt_iterator bsi, bsi_other, new_bsi;
tree ret_decl;
tree type;
/* If we have no predecessor, we can not do this for
the only basic block. */
if (!pred)
continue;
/* Cannot do this if there is no statements. */
if (!returnstmt)
continue;
if (TREE_CODE (returnstmt) == RETURN_EXPR)
;
else
continue;
/* Only do this optimization for basic blocks which
have only one predecessor. */
if (!pred || pred->pred_next)
continue;
/* Only do this for predecessor which are only conditional ones. */
if (pred->flags & (EDGE_TRUE_VALUE | EDGE_FALSE_VALUE))
;
else
continue;
/* Cannot do this optimization if predecessor is abnormal. */
if (pred->flags & EDGE_ABNORMAL)
continue;
/* No reason to do this if we are not returning a value. */
if (TREE_OPERAND (returnstmt, 0) == NULL)
continue;
/* Make sure that the predecessor's successor is not an abnormal. */
if (pred->src->succ->flags & EDGE_ABNORMAL)
continue;
/* Find the other basic block which is connected to the predecessor. */
if (pred->src->succ->dest == bb)
bb_other = pred->src->succ->succ_next->dest;
else
bb_other = pred->src->succ->dest;
/* If we do not have a basic block for the other edge, just continue. */
if (!bb_other)
continue;
/* Only do the optimization if are bb_other is only linked from one BB. */
if (bb_other->pred->src != pred->src)
continue;
else if (bb_other->pred->pred_next)
continue;
returnstmt_other = last_stmt (bb_other);
/* Cannot do the optimization if the other basic block does not
end with a return. */
if (!returnstmt_other || TREE_CODE (returnstmt_other) != RETURN_EXPR)
continue;
/* No reason to do this if we are not returning a value. */
if (TREE_OPERAND (returnstmt_other, 0) == NULL)
continue;
/* If we do not have a modify expression on both returns, there is no point
in doing this optimization. */
if (TREE_CODE (TREE_OPERAND (returnstmt, 0)) != MODIFY_EXPR)
continue;
if (TREE_CODE (TREE_OPERAND (returnstmt_other, 0)) != MODIFY_EXPR)
continue;
/* Create the new basic block. */
new_bb = create_empty_bb (bb_other);
/* Redirect the two basic blocks (the ones with the returns)
to the new basic block. */
redirect_edge_and_branch (bb->succ, new_bb);
redirect_edge_and_branch (bb_other->succ, new_bb);
bsi = bsi_last (bb);
bsi_other = bsi_last (bb_other);
ret_decl = TREE_OPERAND (TREE_OPERAND (returnstmt, 0), 0);
type = TREE_TYPE (ret_decl);
/* Add the new variable to hold the return values. */
new_var = make_temp (type);
if (TREE_CODE (ret_decl) == SSA_NAME)
ret_decl = SSA_NAME_VAR (ret_decl);
/* Assign the new temp variable to hold the return value of
the first side of the branch. */
bsi_insert_after (&bsi, build (MODIFY_EXPR, type, new_var,
TREE_OPERAND (TREE_OPERAND (returnstmt, 0), 1)),
BSI_NEW_STMT);
/* Do the other side. */
bsi_insert_after (&bsi_other, build (MODIFY_EXPR, type, new_var,
TREE_OPERAND (TREE_OPERAND (returnstmt_other,
0), 1)),
BSI_NEW_STMT);
/* Build the new basic block which continues the return. */
new_bsi = bsi_last (new_bb);
bsi_insert_after (&new_bsi, build1 (RETURN_EXPR, void_type_node,
build (MODIFY_EXPR, type, ret_decl,
new_var)), TSI_NEW_STMT);
/* Make sure that the return value gets renamed if needed */
bitmap_set_bit (vars_to_rename, var_ann (ret_decl)->uid);
/* The new basic block exits. */
make_edge (new_bb, EXIT_BLOCK_PTR, 0);
/* update the DOM info if we have to. */
if (dom_computed[CDI_DOMINATORS] >= DOM_CONS_OK)
set_immediate_dominator (CDI_DOMINATORS, new_bb, pred->src);
}
cleanup_tree_cfg ();
}
/* Always do these optimizations if we have SSA
trees to work on. */
static bool
gate_return (void)
{
return 1;
}
struct tree_opt_pass pass_return =
{
"return", /* name */
gate_return, /* gate */
tree_ssa_return, /* execute */
NULL, /* sub */
NULL, /* next */
0, /* static_pass_number */
TV_TREE_RETURN, /* tv_id */
PROP_cfg | PROP_ssa, /* properties_required */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
TODO_dump_func | TODO_ggc_collect /* todo_flags_finish */
| TODO_verify_ssa | TODO_rename_vars
| TODO_verify_flow
};
|
