irextbb2.c 5.15 KB
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/*
 * Project:     libFIRM
 * File name:   ir/ana/irextbb2.c
 * Purpose:     Alternate extended basic block computation
 * Author:      Matthias Braun
 * Modified by:
 * Created:     5.2005
 * CVS-ID:      $Id$
 * Copyright:   (c) 2002-2005 Universitt Karlsruhe
 * Licence:     This file protected by GPL -  GNU GENERAL PUBLIC LICENSE.
 */

/**
 * @file irextbb.c
 *
 *  Alternative algorithm for computing extended basic blocks (using out edges
 *  and execution frequencies)
 *
 *  @author Matthias Braun
 */
#include "irextbb_t.h"
#include "irgwalk.h"
#include "irnode_t.h"
#include "irgraph_t.h"
#include "iredges_t.h"
#include "irouts.h"
#include "xmalloc.h"
#include "irprintf.h"
#include "execfreq.h"

typedef struct _env {
  	struct obstack *obst;   /**< the obstack where allocations took place */
	ir_extblk *head;        /**< head of the list of all extended blocks */
	exec_freq_t *execfreqs;
} env_t;

/**
 * allocate a new extended block header.
 */
static ir_extblk *allocate_extblk(ir_node *block, env_t *env)
{
	ir_extblk *extblk = obstack_alloc(env->obst, sizeof(*extblk));

	extblk->kind    = k_ir_extblk;
	extblk->visited = 1;
	extblk->blks    = (ir_node **)env->head;
	extblk->link    = block;
	env->head       = extblk;

	set_Block_extbb(block, extblk);
	set_irn_link(block, NULL);

	return extblk;
}

/**
 * add a block to an extended block
 */
static void addto_extblk(ir_extblk *extblk, ir_node *block)
{
	/* link all blocks belonging to this extended block */
	set_irn_link(block, extblk->link);

	extblk->link = block;
	extblk->visited++;

	set_Block_extbb(block, extblk);
}

/**
 * Returns the number of block successors.
 * we are interested only in 1, 2 and >2.
 */
static int get_block_n_succs(ir_node *block) {
	if (edges_activated(current_ir_graph)) {
		const ir_edge_t *edge;

		edge = get_block_succ_first(block);
		if (! edge)
			return 0;
		edge = get_block_succ_next(block, edge);
		if (! edge)
			return 1;
		edge = get_block_succ_next(block, edge);
		return edge ? 3 : 2;
	}

	return get_Block_n_cfg_outs(block);
}

static void pick_successor(ir_node *block, ir_extblk *extblk, env_t *env);

static void create_extblk(ir_node *block, env_t *env)
{
	if(irn_visited(block))
		return;

	ir_extblk *extblk = allocate_extblk(block, env);
	mark_irn_visited(block);

	pick_successor(block, extblk, env);
}

static void pick_successor(ir_node *block, ir_extblk *extblk, env_t *env)
{
	const ir_edge_t *edge;
	ir_node *best_succ = NULL;
	double best_execfreq = -1;

 	/* More than two successors means we have a jump table.
	 * we cannot include a jump target into the current extended
	 * basic block, so create a new one here.
	 */
	if(get_block_n_succs(block) > 2) {
		const ir_edge_t *edge;

		foreach_block_succ(block, edge) {
			ir_node *succ = get_edge_src_irn(edge);
			create_extblk(succ, env);
		}

		return;
	}

	foreach_block_succ(block, edge) {
		ir_node *succ = get_edge_src_irn(edge);
		double execfreq;

		if(get_Block_n_cfgpreds(succ) > 1) {
			create_extblk(succ, env);
			continue;
		}

		execfreq = get_block_execfreq(env->execfreqs, succ);

		// remember best sucessor and make non best successor with only 1
		// pred block to new extbb leaders
		if(execfreq > best_execfreq) {
			if(best_succ != NULL) {
				create_extblk(best_succ, env);
			}

			best_execfreq = execfreq;
			best_succ = succ;
		} else {
			create_extblk(succ, env);
		}
	}

	// add best successor and recursively try to pick more
	if(best_succ != NULL) {
		addto_extblk(extblk, best_succ);
		mark_irn_visited(best_succ);
		pick_successor(best_succ, extblk, env);
	}
}

/*
 * Compute the extended basic blocks for a graph
 */
void compute_extbb_execfreqs(ir_graph *irg, exec_freq_t *execfreqs) {
  	env_t env;
	ir_extblk *extbb, *next;
	ir_node *endblock;

	if (irg->extbb_obst) {
		obstack_free(irg->extbb_obst, NULL);
	} else {
		irg->extbb_obst = xmalloc(sizeof(*irg->extbb_obst));
	}
	obstack_init(irg->extbb_obst);

	env.obst = irg->extbb_obst;
	env.head = NULL;
	env.execfreqs = execfreqs;

	assure_irg_outs(irg);

	/* we must mark nodes, so increase the visited flag */
	inc_irg_visited(irg);
	create_extblk(get_irg_start_block(irg), &env);

	// the end block needs a extbb assigned (even for endless loops)
	endblock = get_irg_end_block(irg);
	if(!irn_visited(endblock)) {
		create_extblk(endblock, &env);
	}

	/*
	 * Ok, we have now the list of all extended blocks starting with env.head
	 * every extended block "knowns" the number of blocks in visited and
	 * the blocks are linked in link.
	 * Now we can create arrays that hold the blocks, some kind of "out" edges
	 * for the extended block
	 */
	for (extbb = env.head; extbb; extbb = next) {
		int i, len = (int)extbb->visited;
		ir_node *block;

		next = (ir_extblk *)extbb->blks;

		extbb->blks = NEW_ARR_D(ir_node *, env.obst, len);

		for (block = extbb->link, i = 0; i < len; ++i) {
			ir_node *nblock = get_irn_link(block);

			/* ensure that the leader is the first one */
			extbb->blks[len - 1 - i] = block;
			set_irn_link(block, NULL);
			block = nblock;
		}

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#if 0
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		for(i = 0; i < len; ++i) {
			if(i > 0)
				printf(", ");
			ir_printf("%+F", extbb->blks[i]);
		}
		printf("\n");
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#endif
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		extbb->link    = NULL;
		extbb->visited = 0;
	}

	irg->extblk_state = extblk_valid;
}