[libfirm] / ir / opt / return.c

/*
 * Copyright (C) 1995-2008 University of Karlsruhe.  All right reserved.
 *
 * This file is part of libFirm.
 *
 * This file may be distributed and/or modified under the terms of the
 * GNU General Public License version 2 as published by the Free Software
 * Foundation and appearing in the file LICENSE.GPL included in the
 * packaging of this file.
 *
 * Licensees holding valid libFirm Professional Edition licenses may use
 * this file in accordance with the libFirm Commercial License.
 * Agreement provided with the Software.
 *
 * This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
 * WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE.
 */

/**
 * @file
 * @brief   Normalize returns.
 * @author  Michael Beck
 * @version $Id$
 */
#include "config.h"

#include <stdbool.h>

#include "iroptimize.h"
#include "irgraph_t.h"
#include "ircons_t.h"
#include "irnode_t.h"
#include "irgmod.h"
#include "irpass.h"
#include "util.h"
#include "raw_bitset.h"

/*
 * Normalize the Returns of a graph by creating a new End block
 * with One Return(Phi).
 * This is the preferred input for the if-conversion.
 *
 * In pseudocode, it means:
 *
 * if (a)
 *   return b;
 * else
 *   return c;
 *
 * is transformed into
 *
 * if (a)
 *   res = b;
 * else
 *   res = c;
 * return res;
 */
void normalize_one_return(ir_graph *irg)
{
        ir_node   *endbl         = get_irg_end_block(irg);
        ir_entity *entity        = get_irg_entity(irg);
        ir_type   *type          = get_entity_type(entity);
        int        n_ret_vals    = get_method_n_ress(type) + 1;
        int        n_rets        = 0;
        bool       filter_dbgi   = false;
        dbg_info  *combined_dbgi = NULL;
        unsigned  *returns;
        int i, j, k, n, last_idx;
        ir_node **in, **retvals, **endbl_in;
        ir_node *block;

        /* look, if we have more than one return */
        n = get_Block_n_cfgpreds(endbl);
        if (n <= 0) {
                /* The end block has no predecessors, we have an endless
                   loop. In that case, no returns exists. */
                return;
        }

        rbitset_alloca(returns, n);

        for (i = 0; i < n; ++i) {
                ir_node *node = get_Block_cfgpred(endbl, i);

                if (is_Return(node)) {
                        dbg_info *dbgi = get_irn_dbg_info(node);

                        if (dbgi != NULL && dbgi != combined_dbgi) {
                                if (filter_dbgi) {
                                        combined_dbgi = NULL;
                                } else {
                                        combined_dbgi = dbgi;
                                        filter_dbgi   = true;
                                }
                        }

                        ++n_rets;
                        rbitset_set(returns, i);
                }
        }

        if (n_rets <= 1)
                return;

        in       = ALLOCAN(ir_node*, MAX(n_rets, n_ret_vals));
        retvals  = ALLOCAN(ir_node*, n_rets * n_ret_vals);
        endbl_in = ALLOCAN(ir_node*, n);

        last_idx = 0;
        for (j = i = 0; i < n; ++i) {
                ir_node *ret = get_Block_cfgpred(endbl, i);

                if (rbitset_is_set(returns, i)) {
                        ir_node *block = get_nodes_block(ret);

                        /* create a new Jmp for every Ret and place the in in */
                        in[j] = new_r_Jmp(block);

                        /* save the return values and shuffle them */
                        for (k = 0; k < n_ret_vals; ++k)
                                retvals[j + k*n_rets] = get_irn_n(ret, k);

                        ++j;
                } else {
                        endbl_in[last_idx++] = ret;
                }
        }

        /* ok, create a new block with all created in's */
        block = new_r_Block(irg, n_rets, in);

        /* now create the Phi nodes */
        for (j = i = 0; i < n_ret_vals; ++i, j += n_rets) {
                ir_mode *mode = get_irn_mode(retvals[j]);
                in[i] = new_r_Phi(block, n_rets, &retvals[j], mode);
        }

        endbl_in[last_idx++] = new_rd_Return(combined_dbgi, block, in[0], n_ret_vals-1, &in[1]);

        set_irn_in(endbl, last_idx, endbl_in);

        /* invalidate analysis information:
         * a new Block was added, so dominator, outs and loop are inconsistent,
         * trouts and callee-state should be still valid
         */
        clear_irg_state(irg, IR_GRAPH_STATE_CONSISTENT_DOMINANCE
                           | IR_GRAPH_STATE_VALID_EXTENDED_BLOCKS);
}

/* Create a graph pass. */
ir_graph_pass_t *normalize_one_return_pass(const char *name)
{
        return def_graph_pass(name ? name : "one_ret", normalize_one_return);
}

/**
 * Check, whether a Return can be moved on block upwards.
 *
 * In a block with a Return, all live nodes must be linked
 * with the Return, otherwise they are dead (because the Return leaves
 * the graph, so no more users of the other nodes can exists.
 *
 * We can move a Return, if its predecessors are Phi nodes or
 * comes from another block. In the later case, it is always possible
 * to move the Return one block up, because the predecessor block must
 * dominate the Return block (SSA) and then it dominates the predecessor
 * block of the Return block as well.
 *
 * All predecessors of the Return block must be Jmp's of course, or we
 * cannot move it up, so we add blocks if needed.
 */
static bool can_move_ret(ir_node *ret)
{
        ir_node *retbl = get_nodes_block(ret);
        int i, n = get_irn_arity(ret);

        for (i = 0; i < n; ++i) {
                ir_node *pred = get_irn_n(ret, i);

                if (! is_Phi(pred) && retbl == get_nodes_block(pred)) {
                        /* first condition failed, found a non-Phi predecessor
                         * then is in the Return block */
                        return false;
                }
        }

        /* check, that predecessors are Jmps */
        n = get_Block_n_cfgpreds(retbl);
        /* we cannot move above a labeled block, as this might kill the block */
        if (n <= 1 || has_Block_entity(retbl))
                return false;
        for (i = 0; i < n; ++i) {
                ir_node *pred = get_Block_cfgpred(retbl, i);

                pred = skip_Tuple(pred);
                if (! is_Jmp(pred) && !is_Bad(pred)) {
                        /* simply place a new block here */
                        ir_graph *irg  = get_irn_irg(retbl);
                        ir_node *block = new_r_Block(irg, 1, &pred);
                        ir_node *jmp   = new_r_Jmp(block);
                        set_Block_cfgpred(retbl, i, jmp);
                }
        }
        return true;
}

/*
 * Normalize the Returns of a graph by moving
 * the Returns upwards as much as possible.
 * This might be preferred for code generation.
 *
 * In pseudocode, it means:
 *
 * if (a)
 *   res = b;
 * else
 *   res = c;
 * return res;
 *
 * is transformed into
 *
 * if (a)
 *   return b;
 * else
 *   return c;
 */
void normalize_n_returns(ir_graph *irg)
{
        int i, j, n;
        ir_node  *list     = NULL;
        ir_node  *final    = NULL;
        unsigned  n_rets   = 0;
        unsigned  n_finals = 0;
        ir_node  *endbl    = get_irg_end_block(irg);
        int       n_ret_vals;
        ir_node **in;
        ir_node  *end;

        /*
         * First, link all returns:
         * These must be predecessors of the endblock.
         * Place Returns that can be moved on list, all others
         * on final.
         */
        n = get_Block_n_cfgpreds(endbl);
        for (i = 0; i < n; ++i) {
                ir_node *ret = get_Block_cfgpred(endbl, i);

                if (is_Bad(ret)) {
                        continue;
                } else if (is_Return(ret) && can_move_ret(ret)) {
                        /*
                         * Ok, all conditions met, we can move this Return, put it
                         * on our work list.
                         */
                        set_irn_link(ret, list);
                        list = ret;
                        ++n_rets;
                } else {
                        /* Put all nodes that are not changed on the final list. */
                        set_irn_link(ret, final);
                        final = ret;
                        ++n_finals;
                }
        }

        if (n_rets == 0)
                return;

        /*
         * Now move the Returns upwards. We move always one block up (and create n
         * new Returns), than we check if a newly created Return can be moved even
         * further. If yes, we simply add it to our work list, else to the final
         * list.
         */
        end        = get_irg_end(irg);
        n_ret_vals = get_irn_arity(list);
        in         = ALLOCAN(ir_node*, n_ret_vals);
        while (list != NULL) {
                ir_node  *ret   = list;
                ir_node  *block = get_nodes_block(ret);
                dbg_info *dbgi  = get_irn_dbg_info(ret);
                ir_node  *phiM;

                list = (ir_node*)get_irn_link(ret);
                --n_rets;

                n = get_Block_n_cfgpreds(block);
                for (i = 0; i < n; ++i) {
                        ir_node *jmp = get_Block_cfgpred(block, i);
                        ir_node *new_bl, *new_ret;

                        if (is_Bad(jmp))
                                continue;
                        assert(is_Jmp(jmp));

                        new_bl = get_nodes_block(jmp);

                        /* create the in-array for the new Return */
                        for (j = 0; j < n_ret_vals; ++j) {
                                ir_node *pred = get_irn_n(ret, j);

                                in[j] = (is_Phi(pred) && get_nodes_block(pred) == block) ? get_Phi_pred(pred, i) : pred;
                        }

                        new_ret = new_rd_Return(dbgi, new_bl, in[0], n_ret_vals-1, &in[1]);

                        if (! is_Bad(new_ret)) {
                                /*
                                 * The newly created node might be bad, if we
                                 * create it in a block with only Bad predecessors.
                                 * In that case ignore this block.
                                 *
                                 * We could even kill the jmp then ...
                                 */
                                if (can_move_ret(new_ret)) {
                                        set_irn_link(new_ret, list);
                                        list = new_ret;
                                        ++n_rets;
                                } else {
                                        set_irn_link(new_ret, final);
                                        final = new_ret;
                                        ++n_finals;
                                }
                        }

                        /* remove the Jmp, we have placed a Return here */
                        exchange(jmp, new_r_Bad(irg, mode_X));
                }

                /*
                 * if the memory of the old Return is a PhiM, remove it
                 * from the keep-alives, or it will keep the block which
                 * will crash the dominator algorithm.
                 */
                phiM = get_Return_mem(ret);
                if (is_Phi(phiM)) {
                        n = get_End_n_keepalives(end);
                        for (i = 0; i < n; ++i) {
                                if (get_End_keepalive(end, i) == phiM) {
                                        set_End_keepalive(end, i, new_r_Bad(irg, mode_M));
                                        break;
                                }
                        }
                }
        }

        /*
         * Last step: Create a new endblock, with all nodes on the final list as
         * predecessors.
         */
        in = ALLOCAN(ir_node*, n_finals);

        for (i = 0; final != NULL; ++i, final = (ir_node*)get_irn_link(final)) {
                in[i] = final;
        }

        exchange(endbl, new_r_Block(irg, n_finals, in));

        /* Invalidate analysis information:
         * Blocks become dead and new Returns were deleted, so dominator, outs and
         * loop are inconsistent, trouts and callee-state should be still valid */
        clear_irg_state(irg, IR_GRAPH_STATE_CONSISTENT_DOMINANCE
                           | IR_GRAPH_STATE_CONSISTENT_POSTDOMINANCE
                           | IR_GRAPH_STATE_ONE_RETURN
                           | IR_GRAPH_STATE_CONSISTENT_OUTS
                           | IR_GRAPH_STATE_NO_UNREACHABLE_CODE
                           | IR_GRAPH_STATE_NO_BADS
                           | IR_GRAPH_STATE_VALID_EXTENDED_BLOCKS);
}

/* Create a graph pass. */
ir_graph_pass_t *normalize_n_returns_pass(const char *name)
{
        return def_graph_pass(name ? name : "n_rets", normalize_n_returns);
}