Simplify handling of unreachable code

[libfirm] / ir / opt / code_placement.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    Code Placement.  Pins all floating nodes to a block where they
 *           will be executed only if needed.
 * @author   Christian Schaefer, Goetz Lindenmaier, Sebastian Felis,
 *           Michael Beck
 * @version  $Id$
 */
#include "config.h"

#include "iroptimize.h"
#include "adt/pdeq.h"
#include "irnode_t.h"
#include "irouts.h"
#include "irgopt.h"
#include "irpass.h"

static int is_Block_unreachable(ir_node *block)
{
        return get_Block_dom_depth(block) < 0;
}

/**
 * Find the earliest correct block for node n.  --- Place n into the
 * same Block as its dominance-deepest Input.
 *
 * We have to avoid calls to get_nodes_block() here
 * because the graph is floating.
 *
 * move_out_of_loops() expects that place_floats_early() have placed
 * all "living" nodes into a living block. That's why we must
 * move nodes in dead block with "live" successors into a valid
 * block.
 * We move them just into the same block as its successor (or
 * in case of a Phi into the effective use block). For Phi successors,
 * this may still be a dead block, but then there is no real use, as
 * the control flow will be dead later.
 *
 * @param n         the node to be placed
 * @param worklist  a worklist, predecessors of non-floating nodes are placed here
 */
static void place_floats_early(ir_node *n, waitq *worklist)
{
        int i, irn_arity;

        /* we must not run into an infinite loop */
        assert(!irn_visited(n));
        mark_irn_visited(n);

        /* Place floating nodes. */
        if (get_irn_pinned(n) == op_pin_state_floats) {
                ir_node *curr_block = get_nodes_block(n);
                int in_dead_block   = is_Block_unreachable(curr_block);
                int depth           = 0;
                ir_node *b          = NULL;   /* The block to place this node in */
                ir_graph *irg       = get_irn_irg(n);

                assert(!is_Block(n));

                if (is_irn_start_block_placed(n)) {
                        /* These nodes will not be placed by the loop below. */
                        b = get_irg_start_block(irg);
                        depth = 1;
                }

                /* find the block for this node. */
                irn_arity = get_irn_arity(n);
                for (i = 0; i < irn_arity; i++) {
                        ir_node *pred = get_irn_n(n, i);
                        ir_node *pred_block;

                        if (!irn_visited(pred)
                            && (get_irn_pinned(pred) == op_pin_state_floats)) {

                                /*
                                 * If the current node is NOT in a dead block, but one of its
                                 * predecessors is, we must move the predecessor to a live
                                 * block.
                                 * Such thing can happen, if global CSE chose a node from a
                                 * dead block. We move it simply to our block.
                                 * Note that neither Phi nor End nodes are floating, so we don't
                                 * need to handle them here.
                                 */
                                if (! in_dead_block) {
                                        if (get_irn_pinned(pred) == op_pin_state_floats &&
                                                is_Block_unreachable(get_nodes_block(pred)))
                                                set_nodes_block(pred, curr_block);
                                }
                                place_floats_early(pred, worklist);
                        }

                        /*
                         * A node in the Bad block must stay in the bad block,
                         * so don't compute a new block for it.
                         */
                        if (in_dead_block)
                                continue;

                        /* Because all loops contain at least one op_pin_state_pinned node,
                           now all our inputs are either op_pin_state_pinned or
                           place_early() has already been finished on them.
                           We do not have any unfinished inputs! */
                        pred_block = get_nodes_block(pred);
                        if (get_Block_dom_depth(pred_block) > depth) {
                                b = pred_block;
                                depth = get_Block_dom_depth(pred_block);
                        }
                        /* Avoid that the node is placed in the Start block if we are not
                           in the backend phase. */
                        if (depth == 1 &&
                                        get_Block_dom_depth(get_nodes_block(n)) > 1 &&
                                        get_irg_phase_state(irg) != phase_backend) {
                                b = get_Block_cfg_out(get_irg_start_block(irg), 0);
                                assert(b != get_irg_start_block(irg));
                                depth = 2;
                        }
                }
                if (b)
                        set_nodes_block(n, b);
        }

        /*
         * Add predecessors of non floating nodes and non-floating predecessors
         * of floating nodes to worklist and fix their blocks if the are in dead
         * block.
         */
        irn_arity = get_irn_arity(n);

        if (is_End(n)) {
                /*
                 * Simplest case: End node. Predecessors are keep-alives,
                 * no need to move out of dead block.
                 */
                for (i = -1; i < irn_arity; ++i) {
                        ir_node *pred = get_irn_n(n, i);
                        if (!irn_visited(pred))
                                waitq_put(worklist, pred);
                }
        } else if (is_Block(n)) {
                /*
                 * Blocks: Predecessors are control flow, no need to move
                 * them out of dead block.
                 */
                for (i = irn_arity - 1; i >= 0; --i) {
                        ir_node *pred = get_irn_n(n, i);
                        if (!irn_visited(pred))
                                waitq_put(worklist, pred);
                }
        } else if (is_Phi(n)) {
                ir_node *pred;
                ir_node *curr_block = get_nodes_block(n);
                int in_dead_block   = is_Block_unreachable(curr_block);

                /*
                 * Phi nodes: move nodes from dead blocks into the effective use
                 * of the Phi-input if the Phi is not in a bad block.
                 */
                pred = get_nodes_block(n);
                if (!irn_visited(pred))
                        waitq_put(worklist, pred);

                for (i = irn_arity - 1; i >= 0; --i) {
                        ir_node *pred = get_irn_n(n, i);

                        if (!irn_visited(pred)) {
                                if (! in_dead_block &&
                                        get_irn_pinned(pred) == op_pin_state_floats &&
                                        is_Block_unreachable(get_nodes_block(pred))) {
                                        set_nodes_block(pred, get_Block_cfgpred_block(curr_block, i));
                                }
                                waitq_put(worklist, pred);
                        }
                }
        } else {
                ir_node *pred;
                ir_node *curr_block = get_nodes_block(n);
                int in_dead_block   = is_Block_unreachable(curr_block);

                /*
                 * All other nodes: move nodes from dead blocks into the same block.
                 */
                pred = get_nodes_block(n);
                if (!irn_visited(pred))
                        waitq_put(worklist, pred);

                for (i = irn_arity - 1; i >= 0; --i) {
                        ir_node *pred = get_irn_n(n, i);

                        if (!irn_visited(pred)) {
                                if (! in_dead_block &&
                                        get_irn_pinned(pred) == op_pin_state_floats &&
                                        is_Block_unreachable(get_nodes_block(pred))) {
                                        set_nodes_block(pred, curr_block);
                                }
                                waitq_put(worklist, pred);
                        }
                }
        }
}

/**
 * Floating nodes form subgraphs that begin at nodes as Const, Load,
 * Start, Call and that end at op_pin_state_pinned nodes as Store, Call.
 * Place_early places all floating nodes reachable from its argument through
 * floating nodes and adds all beginnings at op_pin_state_pinned nodes to the
 * worklist.
 *
 * @param worklist   a worklist, used for the algorithm, empty on in/output
 */
static void place_early(ir_graph *irg, waitq *worklist)
{
        assert(worklist);
        inc_irg_visited(irg);

        /* this inits the worklist */
        place_floats_early(get_irg_end(irg), worklist);

        /* Work the content of the worklist. */
        while (!waitq_empty(worklist)) {
                ir_node *n = (ir_node*)waitq_get(worklist);
                if (!irn_visited(n))
                        place_floats_early(n, worklist);
        }
        set_irg_pinned(irg, op_pin_state_pinned);
}

/**
 * Compute the deepest common dominator tree ancestor of block and dca.
 *
 * @param dca    the deepest common dominator tree ancestor so far,
 *               might be NULL
 * @param block  a block
 *
 * @return  the deepest common dominator tree ancestor of block and dca
 */
static ir_node *calc_dom_dca(ir_node *dca, ir_node *block)
{
        assert(block != NULL);

        /* We found a first legal placement. */
        if (!dca)
                return block;

        /* Find a placement that is dominates both, dca and block. */
        while (get_Block_dom_depth(block) > get_Block_dom_depth(dca))
                block = get_Block_idom(block);

        while (get_Block_dom_depth(dca) > get_Block_dom_depth(block)) {
                dca = get_Block_idom(dca);
        }

        while (block != dca) {
                block = get_Block_idom(block); dca = get_Block_idom(dca);
        }
        return dca;
}

/**
 * Deepest common dominance ancestor of DCA and CONSUMER of PRODUCER.
 * I.e., DCA is the block where we might place PRODUCER.
 * A data flow edge points from producer to consumer.
 */
static ir_node *consumer_dom_dca(ir_node *dca, ir_node *consumer, ir_node *producer)
{
        /* Compute the last block into which we can place a node so that it is
           before consumer. */
        if (is_Phi(consumer)) {
                /* our consumer is a Phi-node, the effective use is in all those
                   blocks through which the Phi-node reaches producer */
                ir_node *phi_block = get_nodes_block(consumer);
                int      arity     = get_irn_arity(consumer);
                int      i;

                for (i = 0;  i < arity; i++) {
                        if (get_Phi_pred(consumer, i) == producer) {
                                ir_node *new_block = get_Block_cfgpred_block(phi_block, i);
                                if (is_Bad(new_block))
                                        continue;

                                if (!is_Block_unreachable(new_block))
                                        dca = calc_dom_dca(dca, new_block);
                        }
                }
        } else {
                dca = calc_dom_dca(dca, get_nodes_block(consumer));
        }
        return dca;
}

static inline int get_block_loop_depth(ir_node *block)
{
        return get_loop_depth(get_irn_loop(block));
}

/**
 * Move n to a block with less loop depth than its current block. The
 * new block must be dominated by early.
 *
 * @param n      the node that should be moved
 * @param early  the earliest block we can n move to
 */
static void move_out_of_loops(ir_node *n, ir_node *early)
{
        ir_node *best, *dca;
        assert(n && early);


        /* Find the region deepest in the dominator tree dominating
           dca with the least loop nesting depth, but still dominated
           by our early placement. */
        dca = get_nodes_block(n);

        best = dca;
        while (dca != early) {
                dca = get_Block_idom(dca);
                if (!dca || is_Bad(dca)) break; /* may be Bad if not reachable from Start */
                if (get_block_loop_depth(dca) < get_block_loop_depth(best)) {
                        best = dca;
                }
        }
        if (best != get_nodes_block(n))
                set_nodes_block(n, best);
}

/**
 * Calculate the deepest common ancestor in the dominator tree of all nodes'
 * blocks depending on node; our final placement has to dominate DCA.
 *
 * @param node  the definition node
 * @param dca   the deepest common ancestor block so far, initially
 *              NULL
 *
 * @return the deepest common dominator ancestor of all blocks of node's users
 */
static ir_node *get_deepest_common_dom_ancestor(ir_node *node, ir_node *dca)
{
        int i;

        for (i = get_irn_n_outs(node) - 1; i >= 0; --i) {
                ir_node *succ = get_irn_out(node, i);

                if (is_End(succ)) {
                        /*
                         * This consumer is the End node, a keep alive edge.
                         * This is not a real consumer, so we ignore it
                         */
                        continue;
                }

                if (is_Proj(succ)) {
                        /* Proj nodes are in the same block as node, so
                         * the users of Proj are our users. */
                        dca = get_deepest_common_dom_ancestor(succ, dca);
                } else {
                        /* ignore if succ is in dead code */
                        ir_node *succ_blk = get_nodes_block(succ);
                        if (is_Block_unreachable(succ_blk))
                                continue;
                        dca = consumer_dom_dca(dca, succ, node);
                }
        }
        return dca;
}

/**
 * Put all the Proj nodes of a node into a given block.
 *
 * @param node   the mode_T node
 * @param block  the block to put the Proj nodes to
 */
static void set_projs_block(ir_node *node, ir_node *block)
{
        int i;

        for (i = get_irn_n_outs(node) - 1; i >= 0; --i) {
                ir_node *succ = get_irn_out(node, i);

                assert(is_Proj(succ));

                if (get_irn_mode(succ) == mode_T) {
                        set_projs_block(succ, block);
                }
                set_nodes_block(succ, block);
        }
}

/**
 * Find the latest legal block for N and place N into the
 * `optimal' Block between the latest and earliest legal block.
 * The `optimal' block is the dominance-deepest block of those
 * with the least loop-nesting-depth.  This places N out of as many
 * loops as possible and then makes it as control dependent as
 * possible.
 *
 * @param n         the node to be placed
 * @param worklist  a worklist, all successors of non-floating nodes are
 *                  placed here
 */
static void place_floats_late(ir_node *n, pdeq *worklist)
{
        int i, n_outs;
        ir_node *early_blk;

        assert(!irn_visited(n)); /* no multiple placement */

        mark_irn_visited(n);

        /* no need to place block nodes, control nodes are already placed. */
        if (!is_Block(n) &&
            (!is_cfop(n)) &&
            (get_irn_mode(n) != mode_X)) {
            ir_op *op;
                /* Remember the early_blk placement of this block to move it
                   out of loop no further than the early_blk placement. */
                early_blk = get_nodes_block(n);

                /*
                 * BEWARE: Here we also get code, that is live, but
                 * was in a dead block.  If the node is life, but because
                 * of CSE in a dead block, we still might need it.
                 */

                /* Assure that our users are all placed, except the Phi-nodes.
                --- Each data flow cycle contains at least one Phi-node.  We
                    have to break the `user has to be placed before the
                    producer' dependence cycle and the Phi-nodes are the
                    place to do so, because we need to base our placement on the
                    final region of our users, which is OK with Phi-nodes, as they
                    are op_pin_state_pinned, and they never have to be placed after a
                    producer of one of their inputs in the same block anyway. */
                for (i = get_irn_n_outs(n) - 1; i >= 0; --i) {
                        ir_node *succ = get_irn_out(n, i);
                        if (!irn_visited(succ) && !is_Phi(succ))
                                place_floats_late(succ, worklist);
                }

                /* do only move things that where not dead */
                op = get_irn_op(n);

                /* We have to determine the final block of this node... except for
                   constants and Projs */
                if ((get_irn_pinned(n) == op_pin_state_floats) &&
                        (op != op_Const)    &&
                        (op != op_SymConst) &&
                        (op != op_Proj))
                {
                        /* deepest common ancestor in the dominator tree of all nodes'
                           blocks depending on us; our final placement has to dominate
                           DCA. */
                        ir_node *dca = get_deepest_common_dom_ancestor(n, NULL);
                        if (dca != NULL) {
                                set_nodes_block(n, dca);
                                move_out_of_loops(n, early_blk);
                                if (get_irn_mode(n) == mode_T) {
                                        set_projs_block(n, get_nodes_block(n));
                                }
                        }
                }
        }

        /* Add successors of all non-floating nodes on list. (Those of floating
           nodes are placed already and therefore are marked.)  */
        n_outs = get_irn_n_outs(n);
        for (i = 0; i < n_outs; i++) {
                ir_node *succ = get_irn_out(n, i);
                if (!irn_visited(succ)) {
                        pdeq_putr(worklist, succ);
                }
        }
}

/**
 * Place floating nodes on the given worklist as late as possible using
 * the dominance tree.
 *
 * @param worklist   the worklist containing the nodes to place
 */
static void place_late(ir_graph *irg, waitq *worklist)
{
        assert(worklist);
        inc_irg_visited(irg);

        /* This fills the worklist initially. */
        place_floats_late(get_irg_start_block(irg), worklist);

        /* And now empty the worklist again... */
        while (!waitq_empty(worklist)) {
                ir_node *n = (ir_node*)waitq_get(worklist);
                if (!irn_visited(n))
                        place_floats_late(n, worklist);
        }
}

/* Code Placement. */
void place_code(ir_graph *irg)
{
        waitq *worklist;

        remove_critical_cf_edges(irg);

        /* Handle graph state */
        assert(get_irg_phase_state(irg) != phase_building);
        assure_irg_outs(irg);
        assure_doms(irg);
        assure_cf_loop(irg);

        /* Place all floating nodes as early as possible. This guarantees
         a legal code placement. */
        worklist = new_waitq();
        place_early(irg, worklist);

        /* Note: place_early changes only blocks, no data edges. So, the
         * data out edges are still valid, no need to recalculate them here. */

        /* Now move the nodes down in the dominator tree. This reduces the
           unnecessary executions of the node. */
        place_late(irg, worklist);

        set_irg_outs_inconsistent(irg);
        set_irg_loopinfo_inconsistent(irg);
        del_waitq(worklist);
}

/**
 * Wrapper for place_code() inside the place_code pass.
 */
static void place_code_wrapper(ir_graph *irg)
{
        set_opt_global_cse(1);
        optimize_graph_df(irg);
        place_code(irg);
        set_opt_global_cse(0);
}

ir_graph_pass_t *place_code_pass(const char *name)
{
        return def_graph_pass(name ? name : "place", place_code_wrapper);
}