opt_ldst.c 62.8 KB
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/*
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 * Copyright (C) 1995-2011 University of Karlsruhe.  All right reserved.
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 *
 * 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   Dataflow driven Load/Store optimizations, uses some ideas from
 *          VanDrunen's LEPRE
 * @author  Michael Beck
 * @version $Id$
 */
#include "config.h"

#include "irnode_t.h"
#include "irflag_t.h"
#include "array_t.h"
#include "ircons.h"
#include "irdom.h"
#include "irgmod.h"
#include "irgwalk.h"
#include "irouts.h"
#include "irgraph.h"
#include "irgopt.h"
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#include "iropt.h"
#include "iroptimize.h"
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#include "irnodemap.h"
#include "raw_bitset.h"
#include "debug.h"
#include "error.h"
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#include "irpass.h"
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/* maximum number of output Proj's */
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#define MAX_PROJ ((long)pn_Load_max > (long)pn_Store_max ? (long)pn_Load_max : (long)pn_Store_max)
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/**
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 * Mapping an address to an dense ID.
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 */
typedef struct address_entry_t {
	unsigned id;          /**< The ID */
} address_entry;

/**
 * Memop-flags.
 */
enum memop_flags {
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	FLAG_KILL_ALL    = 1, /**< KILL all addresses */
	FLAG_KILLED_NODE = 2, /**< this node was killed */
	FLAG_EXCEPTION   = 4, /**< this node has exception flow */
	FLAG_IGNORE      = 8, /**< ignore this node (volatile or other) */
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};

/**
 * A value: This represents a value stored at a given address in
 * memory. Do not confuse with values from value numbering.
 */
typedef struct value_t value_t;
struct value_t {
	ir_node  *address;    /**< the address of this value */
	ir_node  *value;      /**< the value itself */
	ir_mode  *mode;       /**< the mode of the value */
	unsigned id;          /**< address id */
};

/**
 * A memop describes an memory-related operation.
 * These are Loads/Store and all other ops that might modify
 * memory (Calls, CopyB) or causing exceptions.
 */
typedef struct memop_t memop_t;
struct memop_t {
	value_t  value;      /**< the value of this memop: only defined for Load/Store */
	ir_node  *node;      /**< the memory op itself */
	ir_node  *mem;       /**< the memory FROM this node */
	ir_node  *replace;   /**< the replacement node if this memop is replaced */
	memop_t  *next;      /**< links to the next memory op in the block in forward order. */
	memop_t  *prev;      /**< links to the previous memory op in the block in forward order. */
	unsigned flags;      /**< memop flags */
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	ir_node  *projs[MAX_PROJ]; /**< Projs of this memory op */
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};

/**
 * Additional data for every basic block.
 */
typedef struct block_t block_t;
struct block_t {
	memop_t  *memop_forward;     /**< topologically sorted list of memory ops in this block */
	memop_t  *memop_backward;    /**< last memop in the list */
	unsigned *avail_out;         /**< out-set of available addresses */
	memop_t  **id_2_memop_avail; /**< maps avail address ids to memops */
	unsigned *anticL_in;         /**< in-set of anticipated Load addresses */
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	memop_t  **id_2_memop_antic; /**< maps anticipated address ids to memops */
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	ir_node  *block;             /**< the associated block */
	block_t  *forward_next;      /**< next block entry for forward iteration */
	block_t  *backward_next;     /**< next block entry for backward iteration */
	memop_t  *avail;             /**< used locally for the avail map */
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	memop_t  **trans_results;    /**< used to cached translated nodes due antic calculation. */
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};

/**
 * Metadata for this pass.
 */
typedef struct ldst_env_t {
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	struct obstack  obst;              /**< obstack for temporary data */
	ir_nodemap_t    adr_map;           /**< Map addresses to */
	block_t         *forward;          /**< Inverse post-order list of all blocks Start->End */
	block_t         *backward;         /**< Inverse post-order list of all blocks End->Start */
	ir_node         *start_bl;         /**< start block of the current graph */
	ir_node         *end_bl;           /**< end block of the current graph */
	unsigned        *curr_set;         /**< current set of addresses */
	memop_t         **curr_id_2_memop; /**< current map of address ids to memops */
	unsigned        curr_adr_id;       /**< number for address mapping */
	unsigned        n_mem_ops;         /**< number of memory operations (Loads/Stores) */
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	size_t          rbs_size;          /**< size of all bitsets in bytes */
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	int             max_cfg_preds;     /**< maximum number of block cfg predecessors */
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	int             changed;           /**< Flags for changed graph state */
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#ifdef DEBUG_libfirm
	ir_node         **id_2_address;    /**< maps an id to the used address */
#endif
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} ldst_env;

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/* the one and only environment */
static ldst_env env;

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#ifdef DEBUG_libfirm

static firm_dbg_module_t *dbg;

/**
 * Dumps the block list.
 *
 * @param ldst environment
 */
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static void dump_block_list(ldst_env *env)
{
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	block_t *entry;
	memop_t *op;
	int     i;

	for (entry = env->forward; entry != NULL; entry = entry->forward_next) {
		DB((dbg, LEVEL_2, "%+F {", entry->block));

		i = 0;
		for (op = entry->memop_forward; op != NULL; op = op->next) {
			if (i == 0) {
				DB((dbg, LEVEL_2, "\n\t"));
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			}
			DB((dbg, LEVEL_2, "%+F", op->node));
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			if ((op->flags & FLAG_KILL_ALL) == FLAG_KILL_ALL)
				DB((dbg, LEVEL_2, "X"));
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			else if (op->flags & FLAG_KILL_ALL)
				DB((dbg, LEVEL_2, "K"));
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			DB((dbg, LEVEL_2, ", "));

			i = (i + 1) & 3;
		}
		DB((dbg, LEVEL_2, "\n}\n\n"));
	}
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}  /* dump_block_list */
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/**
 * Dumps the current set.
 *
 * @param bl   current block
 * @param s    name of the set
 */
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static void dump_curr(block_t *bl, const char *s)
{
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	size_t end = env.rbs_size - 1;
	size_t pos;
	int    i;
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	DB((dbg, LEVEL_2, "%s[%+F] = {", s, bl->block));
	i = 0;
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	for (pos = rbitset_next(env.curr_set, 0, 1); pos < end; pos = rbitset_next(env.curr_set, pos + 1, 1)) {
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		memop_t *op = env.curr_id_2_memop[pos];
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		if (i == 0) {
			DB((dbg, LEVEL_2, "\n\t"));
		}
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		DB((dbg, LEVEL_2, "<%+F, %+F>, ", op->value.address, op->value.value));
		i = (i + 1) & 3;
	}
	DB((dbg, LEVEL_2, "\n}\n"));
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}  /* dump_curr */
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#else
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static void dump_block_list(ldst_env *env)
{
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	(void) env;
}
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static void dump_curr(block_t *bl, const char *s)
{
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	(void) bl;
	(void) s;
}
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#endif /* DEBUG_libfirm */

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/** Get the block entry for a block node */
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static block_t *get_block_entry(const ir_node *block)
{
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	assert(is_Block(block));

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	return (block_t*)get_irn_link(block);
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}  /* get_block_entry */
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/** Get the memop entry for a memory operation node */
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static memop_t *get_irn_memop(const ir_node *irn)
{
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	assert(! is_Block(irn));
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	return (memop_t*)get_irn_link(irn);
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}  /* get_irn_memop */
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/**
 * Walk over the memory edges from definition to users.
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 * This ensures, that even operation without memory output are found.
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 *
 * @param irn   start node
 * @param pre   pre walker function
 * @param post  post walker function
 * @param ctx   context parameter for the walker functions
 */
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static void walk_memory(ir_node *irn, irg_walk_func *pre, irg_walk_func *post, void *ctx)
{
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	int     i;
	ir_mode *mode;

	mark_irn_visited(irn);

	if (pre)
		pre(irn, ctx);

	mode = get_irn_mode(irn);
	if (mode == mode_M) {
		/* every successor uses memory */
		for (i = get_irn_n_outs(irn) - 1; i >= 0; --i) {
			ir_node *succ = get_irn_out(irn, i);

			if (! irn_visited(succ))
				walk_memory(succ, pre, post, ctx);
		}
	} else if (mode == mode_T) {
		/* only some Proj's uses memory */
		for (i = get_irn_n_outs(irn) - 1; i >= 0; --i) {
			ir_node *proj = get_irn_out(irn, i);

			if (get_irn_mode(proj) == mode_M && ! irn_visited(proj))
				walk_memory(proj, pre, post, ctx);
		}
	}
	if (post)
		post(irn, ctx);
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}  /* walk_memory */
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/**
 * Walks over all memory nodes of a graph.
 *
 * @param irg   a graph
 * @param pre   pre walker function
 * @param post  post walker function
 * @param ctx   context parameter for the walker functions
 */
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static void walk_memory_irg(ir_graph *irg, irg_walk_func pre, irg_walk_func post, void *ctx)
{
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	inc_irg_visited(irg);

	ir_reserve_resources(irg, IR_RESOURCE_IRN_VISITED);

	/*
	 * there are two possible sources for memory: initial_mem and nomem
	 * we ignore nomem as this should NOT change the memory
	 */
	walk_memory(get_irg_initial_mem(irg), pre, post, ctx);

	ir_free_resources(irg, IR_RESOURCE_IRN_VISITED);
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}  /* walk_memory_irg */
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/**
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 * Register an address and allocate a (sparse, 0..n) ID for it.
 *
 * @param adr  the IR-node representing the address
 *
 * @return the allocated id
 */
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static unsigned register_address(ir_node *adr)
{
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	address_entry *entry;

	/* skip Confirms and Casts */
restart:
	if (is_Confirm(adr)) {
		adr = get_Confirm_value(adr);
		goto restart;
	}
	if (is_Cast(adr)) {
		adr = get_Cast_op(adr);
		goto restart;
	}

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	entry = (address_entry*)ir_nodemap_get(&env.adr_map, adr);
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	if (entry == NULL) {
		/* new address */
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		entry = OALLOC(&env.obst, address_entry);
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		entry->id = env.curr_adr_id++;
		ir_nodemap_insert(&env.adr_map, adr, entry);

		DB((dbg, LEVEL_3, "ADDRESS %+F has ID %u\n", adr, entry->id));
#ifdef DEBUG_libfirm
		ARR_APP1(ir_node *, env.id_2_address, adr);
#endif
	}
	return entry->id;
}  /* register_address */


/**
 * translate an address through a Phi node into a given predecessor
 * block.
 *
 * @param address  the address
 * @param block    the block
 * @param pos      the position of the predecessor in block
 */
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static ir_node *phi_translate(ir_node *address, const ir_node *block, int pos)
{
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	if (is_Phi(address) && get_nodes_block(address) == block)
		address = get_Phi_pred(address, pos);
	return address;
}  /* phi_translate */

/**
 * Walker: allocate an block entry for every block
 * and register all potential addresses.
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 */
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static void prepare_blocks(ir_node *irn, void *ctx)
{
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	(void)ctx;
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	if (is_Block(irn)) {
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		block_t *entry = OALLOC(&env.obst, block_t);
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		int     n;

		entry->memop_forward    = NULL;
		entry->memop_backward   = NULL;
		entry->avail_out        = NULL;
		entry->id_2_memop_avail = NULL;
		entry->anticL_in        = NULL;
		entry->id_2_memop_antic = NULL;
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		entry->block            = irn;
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		entry->forward_next     = NULL;
		entry->backward_next    = NULL;
		entry->avail            = NULL;
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		entry->trans_results    = NULL;
		set_irn_link(irn, entry);
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		set_Block_phis(irn, NULL);
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		/* use block marks to track unreachable blocks */
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		set_Block_mark(irn, 0);
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		n = get_Block_n_cfgpreds(irn);
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		if (n > env.max_cfg_preds)
			env.max_cfg_preds = n;
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	} else {
		ir_mode *mode = get_irn_mode(irn);

		if (mode_is_reference(mode)) {
			/*
			 * Register ALL possible addresses: this is overkill yet but
			 * simpler then doing it for all possible translated addresses
			 * (which would be sufficient in the moment.
			 */
			(void)register_address(irn);
		}
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	}
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}  /* prepare_blocks */
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/**
 * Post-Walker, link in all Phi's
 */
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static void link_phis(ir_node *irn, void *ctx)
{
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	(void)ctx;
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	if (is_Phi(irn)) {
		ir_node *block = get_nodes_block(irn);
		add_Block_phi(block, irn);
	}
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}  /* link_phis */
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/**
 * Block walker: creates the inverse post-order list for the CFG.
 */
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static void inverse_post_order(ir_node *block, void *ctx)
{
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	block_t *entry = get_block_entry(block);

	(void)ctx;
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	/* mark this block IS reachable from start */
	set_Block_mark(block, 1);

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	/* create the list in inverse order */
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	entry->forward_next = env.forward;
	env.forward         = entry;

	/* remember the first visited (last in list) entry, needed for later */
	if (env.backward == NULL)
		env.backward = entry;
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}  /* inverse_post_order */
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/**
 * Block walker: create backward links for the memops of a block.
 */
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static void collect_backward(ir_node *block, void *ctx)
{
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	block_t *entry = get_block_entry(block);
	memop_t *last, *op;

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	(void)ctx;
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	/*
	 * Do NOT link in the end block yet. We want it to be
	 * the first in the list. This is NOT guaranteed by the walker
	 * if we have endless loops.
	 */
	if (block != env.end_bl) {
		entry->backward_next = env.backward;

		/* create the list in inverse order */
		env.backward = entry;
	}
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	/* create backward links for all memory ops */
	last = NULL;
	for (op = entry->memop_forward; op != NULL; op = op->next) {
		op->prev = last;
		last     = op;
	}
	entry->memop_backward = last;
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}  /* collect_backward */
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/**
 * Allocate a memop.
 *
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 * @param irn  the IR-node representing the memop or NULL
 *             if this is a translated (virtual) memop
 *
 * @return the allocated memop
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 */
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static memop_t *alloc_memop(ir_node *irn)
{
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	memop_t *m = OALLOC(&env.obst, memop_t);
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	m->value.address = NULL;
	m->value.value   = NULL;
	m->value.mode    = NULL;

	m->node          = irn;
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	m->mem           = NULL;
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	m->replace       = NULL;
	m->next          = NULL;
	m->flags         = 0;

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	memset(m->projs, 0, sizeof(m->projs));

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	if (irn != NULL)
		set_irn_link(irn, m);
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	return m;
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}  /* alloc_memop */
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/**
 * Create a memop for a Phi-replacement.
 *
 * @param op   the memop to clone
 * @param phi  the Phi-node representing the new value
 */
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static memop_t *clone_memop_phi(memop_t *op, ir_node *phi)
{
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	memop_t *m = OALLOC(&env.obst, memop_t);
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	m->value         = op->value;
	m->value.value   = phi;

	m->node          = phi;
	m->replace       = NULL;
	m->next          = NULL;
	m->flags         = 0;

	set_irn_link(phi, m);
	return m;
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}  /* clone_memop_phi */
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/**
 * Return the memory properties of a call node.
 *
 * @param call  the call node
 *
 * return a bitset of mtp_property_const and mtp_property_pure
 */
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static unsigned get_Call_memory_properties(ir_node *call)
{
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	ir_type *call_tp = get_Call_type(call);
	unsigned prop = get_method_additional_properties(call_tp);

	/* check first the call type */
	if ((prop & (mtp_property_const|mtp_property_pure)) == 0) {
		/* try the called entity */
		ir_node *ptr = get_Call_ptr(call);

		if (is_Global(ptr)) {
			ir_entity *ent = get_Global_entity(ptr);

			prop = get_entity_additional_properties(ent);
		}
	}
	return prop & (mtp_property_const|mtp_property_pure);
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}  /* get_Call_memory_properties */
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/**
 * Returns an entity if the address ptr points to a constant one.
 *
 * @param ptr  the address
 *
 * @return an entity or NULL
 */
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static ir_entity *find_constant_entity(ir_node *ptr)
{
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	for (;;) {
		if (is_SymConst(ptr) && get_SymConst_kind(ptr) == symconst_addr_ent) {
			return get_SymConst_entity(ptr);
		} else if (is_Sel(ptr)) {
			ir_entity *ent = get_Sel_entity(ptr);
			ir_type   *tp  = get_entity_owner(ent);

			/* Do not fiddle with polymorphism. */
			if (is_Class_type(get_entity_owner(ent)) &&
				((get_entity_n_overwrites(ent)    != 0) ||
				(get_entity_n_overwrittenby(ent) != 0)   ) )
				return NULL;

			if (is_Array_type(tp)) {
				/* check bounds */
				int i, n;

				for (i = 0, n = get_Sel_n_indexs(ptr); i < n; ++i) {
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					ir_node   *bound;
					ir_tarval *tlower, *tupper;
					ir_node   *index = get_Sel_index(ptr, i);
					ir_tarval *tv     = computed_value(index);
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					/* check if the index is constant */
					if (tv == tarval_bad)
						return NULL;

					bound  = get_array_lower_bound(tp, i);
					tlower = computed_value(bound);
					bound  = get_array_upper_bound(tp, i);
					tupper = computed_value(bound);

					if (tlower == tarval_bad || tupper == tarval_bad)
						return NULL;

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					if (tarval_cmp(tv, tlower) == ir_relation_less)
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						return NULL;
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					if (tarval_cmp(tupper, tv) == ir_relation_less)
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						return NULL;

					/* ok, bounds check finished */
				}
			}

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			if (get_entity_linkage(ent) == IR_LINKAGE_CONSTANT)
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				return ent;

			/* try next */
			ptr = get_Sel_ptr(ptr);
		} else if (is_Add(ptr)) {
			ir_node *l = get_Add_left(ptr);
			ir_node *r = get_Add_right(ptr);

			if (get_irn_mode(l) == get_irn_mode(ptr) && is_Const(r))
				ptr = l;
			else if (get_irn_mode(r) == get_irn_mode(ptr) && is_Const(l))
				ptr = r;
			else
				return NULL;

			/* for now, we support only one addition, reassoc should fold all others */
			if (! is_SymConst(ptr) && !is_Sel(ptr))
				return NULL;
		} else if (is_Sub(ptr)) {
			ir_node *l = get_Sub_left(ptr);
			ir_node *r = get_Sub_right(ptr);

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			if (get_irn_mode(l) == get_irn_mode(ptr) && is_Const(r))
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				ptr = l;
			else
				return NULL;
			/* for now, we support only one subtraction, reassoc should fold all others */
			if (! is_SymConst(ptr) && !is_Sel(ptr))
				return NULL;
		} else
			return NULL;
	}
}  /* find_constant_entity */

/**
 * Return the Selection index of a Sel node from dimension n
 */
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static long get_Sel_array_index_long(ir_node *n, int dim)
{
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	ir_node *index = get_Sel_index(n, dim);
	assert(is_Const(index));
	return get_tarval_long(get_Const_tarval(index));
}  /* get_Sel_array_index_long */

/**
 * Returns the accessed component graph path for an
 * node computing an address.
 *
 * @param ptr    the node computing the address
 * @param depth  current depth in steps upward from the root
 *               of the address
 */
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static compound_graph_path *rec_get_accessed_path(ir_node *ptr, size_t depth)
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{
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	compound_graph_path *res = NULL;
	ir_entity           *root, *field, *ent;
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	size_t              path_len, pos, idx;
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	ir_tarval           *tv;
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	ir_type             *tp;

	if (is_SymConst(ptr)) {
		/* a SymConst. If the depth is 0, this is an access to a global
		 * entity and we don't need a component path, else we know
		 * at least its length.
		 */
		assert(get_SymConst_kind(ptr) == symconst_addr_ent);
		root = get_SymConst_entity(ptr);
		res = (depth == 0) ? NULL : new_compound_graph_path(get_entity_type(root), depth);
	} else if (is_Sel(ptr)) {
		/* it's a Sel, go up until we find the root */
		res = rec_get_accessed_path(get_Sel_ptr(ptr), depth+1);
		if (res == NULL)
			return NULL;

		/* fill up the step in the path at the current position */
		field    = get_Sel_entity(ptr);
		path_len = get_compound_graph_path_length(res);
		pos      = path_len - depth - 1;
		set_compound_graph_path_node(res, pos, field);

		if (is_Array_type(get_entity_owner(field))) {
			assert(get_Sel_n_indexs(ptr) == 1 && "multi dim arrays not implemented");
			set_compound_graph_path_array_index(res, pos, get_Sel_array_index_long(ptr, 0));
		}
	} else if (is_Add(ptr)) {
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		ir_mode   *mode;
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		ir_tarval *tmp;
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		{
			ir_node *l = get_Add_left(ptr);
			ir_node *r = get_Add_right(ptr);
			if (is_Const(r) && get_irn_mode(l) == get_irn_mode(ptr)) {
				ptr = l;
				tv  = get_Const_tarval(r);
			} else {
				ptr = r;
				tv  = get_Const_tarval(l);
			}
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		}
ptr_arith:
		mode = get_tarval_mode(tv);
		tmp  = tv;

		/* ptr must be a Sel or a SymConst, this was checked in find_constant_entity() */
		if (is_Sel(ptr)) {
			field = get_Sel_entity(ptr);
		} else {
			field = get_SymConst_entity(ptr);
		}
		idx = 0;
		for (ent = field;;) {
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			unsigned  size;
			ir_tarval *sz, *tv_index, *tlower, *tupper;
			ir_node   *bound;
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			tp = get_entity_type(ent);
			if (! is_Array_type(tp))
				break;
			ent = get_array_element_entity(tp);
			size = get_type_size_bytes(get_entity_type(ent));
			sz   = new_tarval_from_long(size, mode);

			tv_index = tarval_div(tmp, sz);
			tmp      = tarval_mod(tmp, sz);

			if (tv_index == tarval_bad || tmp == tarval_bad)
				return NULL;

			assert(get_array_n_dimensions(tp) == 1 && "multiarrays not implemented");
			bound  = get_array_lower_bound(tp, 0);
			tlower = computed_value(bound);
			bound  = get_array_upper_bound(tp, 0);
			tupper = computed_value(bound);

			if (tlower == tarval_bad || tupper == tarval_bad)
				return NULL;

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			if (tarval_cmp(tv_index, tlower) == ir_relation_less)
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				return NULL;
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			if (tarval_cmp(tupper, tv_index) == ir_relation_less)
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				return NULL;

			/* ok, bounds check finished */
			++idx;
		}
		if (! tarval_is_null(tmp)) {
			/* access to some struct/union member */
			return NULL;
		}

		/* should be at least ONE array */
		if (idx == 0)
			return NULL;

		res = rec_get_accessed_path(ptr, depth + idx);
		if (res == NULL)
			return NULL;

		path_len = get_compound_graph_path_length(res);
		pos      = path_len - depth - idx;

		for (ent = field;;) {
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			unsigned   size;
			ir_tarval *sz, *tv_index;
			long       index;
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			tp = get_entity_type(ent);
			if (! is_Array_type(tp))
				break;
			ent = get_array_element_entity(tp);
			set_compound_graph_path_node(res, pos, ent);

			size = get_type_size_bytes(get_entity_type(ent));
			sz   = new_tarval_from_long(size, mode);

			tv_index = tarval_div(tv, sz);
			tv       = tarval_mod(tv, sz);

			/* worked above, should work again */
			assert(tv_index != tarval_bad && tv != tarval_bad);

			/* bounds already checked above */
			index = get_tarval_long(tv_index);
			set_compound_graph_path_array_index(res, pos, index);
			++pos;
		}
	} else if (is_Sub(ptr)) {
		ir_node *l = get_Sub_left(ptr);
		ir_node *r = get_Sub_right(ptr);

		ptr = l;
		tv  = get_Const_tarval(r);
		tv  = tarval_neg(tv);
		goto ptr_arith;
	}
	return res;
}  /* rec_get_accessed_path */

/**
 * Returns an access path or NULL.  The access path is only
 * valid, if the graph is in phase_high and _no_ address computation is used.
 */
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static compound_graph_path *get_accessed_path(ir_node *ptr)
{
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	compound_graph_path *gr = rec_get_accessed_path(ptr, 0);
	return gr;
}  /* get_accessed_path */

typedef struct path_entry {
	ir_entity         *ent;
	struct path_entry *next;
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	size_t            index;
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} path_entry;

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static ir_node *rec_find_compound_ent_value(ir_node *ptr, path_entry *next)
{
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	path_entry       entry, *p;
	ir_entity        *ent, *field;
	ir_initializer_t *initializer;
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	ir_tarval        *tv;
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	ir_type          *tp;
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	size_t           n;
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	entry.next = next;
	if (is_SymConst(ptr)) {
		/* found the root */
		ent         = get_SymConst_entity(ptr);
		initializer = get_entity_initializer(ent);
		for (p = next; p != NULL;) {
			if (initializer->kind != IR_INITIALIZER_COMPOUND)
				return NULL;
			n  = get_initializer_compound_n_entries(initializer);
			tp = get_entity_type(ent);

			if (is_Array_type(tp)) {
				ent = get_array_element_entity(tp);
				if (ent != p->ent) {
					/* a missing [0] */
					if (0 >= n)
						return NULL;
					initializer = get_initializer_compound_value(initializer, 0);
					continue;
				}
			}
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			if (p->index >= n)
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				return NULL;
			initializer = get_initializer_compound_value(initializer, p->index);

			ent = p->ent;
			p   = p->next;
		}
		tp = get_entity_type(ent);
		while (is_Array_type(tp)) {
			ent = get_array_element_entity(tp);
			tp = get_entity_type(ent);
			/* a missing [0] */
			n  = get_initializer_compound_n_entries(initializer);
			if (0 >= n)
				return NULL;
			initializer = get_initializer_compound_value(initializer, 0);
		}

		switch (initializer->kind) {
		case IR_INITIALIZER_CONST:
			return get_initializer_const_value(initializer);
		case IR_INITIALIZER_TARVAL:
		case IR_INITIALIZER_NULL:
		default:
			return NULL;
		}
	} else if (is_Sel(ptr)) {
		entry.ent = field = get_Sel_entity(ptr);
		tp = get_entity_owner(field);
		if (is_Array_type(tp)) {
			assert(get_Sel_n_indexs(ptr) == 1 && "multi dim arrays not implemented");
			entry.index = get_Sel_array_index_long(ptr, 0) - get_array_lower_bound_int(tp, 0);
		} else {
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			size_t i, n_members = get_compound_n_members(tp);
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			for (i = 0; i < n_members; ++i) {
				if (get_compound_member(tp, i) == field)
					break;
			}
			if (i >= n_members) {
				/* not found: should NOT happen */
				return NULL;
			}
			entry.index = i;
		}
		return rec_find_compound_ent_value(get_Sel_ptr(ptr), &entry);
	}  else if (is_Add(ptr)) {
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		ir_mode *mode;
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		unsigned pos;

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		{
			ir_node *l = get_Add_left(ptr);
			ir_node *r = get_Add_right(ptr);
			if (is_Const(r)) {
				ptr = l;
				tv  = get_Const_tarval(r);
			} else {
				ptr = r;
				tv  = get_Const_tarval(l);
			}
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		}
ptr_arith:
		mode = get_tarval_mode(tv);

		/* ptr must be a Sel or a SymConst, this was checked in find_constant_entity() */
		if (is_Sel(ptr)) {
			field = get_Sel_entity(ptr);
		} else {
			field = get_SymConst_entity(ptr);
		}

		/* count needed entries */
		pos = 0;
		for (ent = field;;) {
			tp = get_entity_type(ent);
			if (! is_Array_type(tp))
				break;
			ent = get_array_element_entity(tp);
			++pos;
		}
		/* should be at least ONE entry */
		if (pos == 0)
			return NULL;

		/* allocate the right number of entries */
		NEW_ARR_A(path_entry, p, pos);

		/* fill them up */
		pos = 0;
		for (ent = field;;) {
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			unsigned  size;
			ir_tarval *sz, *tv_index, *tlower, *tupper;
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			size_t    index;
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			ir_node   *bound;
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			tp = get_entity_type(ent);
			if (! is_Array_type(tp))
				break;
			ent = get_array_element_entity(tp);
			p[pos].ent  = ent;
			p[pos].next = &p[pos + 1];

			size = get_type_size_bytes(get_entity_type(ent));
			sz   = new_tarval_from_long(size, mode);

			tv_index = tarval_div(tv, sz);
			tv       = tarval_mod(tv, sz);

			if (tv_index == tarval_bad || tv == tarval_bad)
				return NULL;

			assert(get_array_n_dimensions(tp) == 1 && "multiarrays not implemented");
			bound  = get_array_lower_bound(tp, 0);
			tlower = computed_value(bound);
			bound  = get_array_upper_bound(tp, 0);
			tupper = computed_value(bound);

			if (tlower == tarval_bad || tupper == tarval_bad)
				return NULL;

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			if (tarval_cmp(tv_index, tlower) == ir_relation_less)
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				return NULL;
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			if (tarval_cmp(tupper, tv_index) == ir_relation_less)
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				return NULL;

			/* ok, bounds check finished */
			index = get_tarval_long(tv_index);
			p[pos].index = index;
			++pos;
		}
		if (! tarval_is_null(tv)) {
			/* hmm, wrong access */
			return NULL;
		}
		p[pos - 1].next = next;
		return rec_find_compound_ent_value(ptr, p);
	} else if (is_Sub(ptr)) {
		ir_node *l = get_Sub_left(ptr);
		ir_node *r = get_Sub_right(ptr);

		ptr = l;
		tv  = get_Const_tarval(r);
		tv  = tarval_neg(tv);
		goto ptr_arith;
	}
	return NULL;
}  /* rec_find_compound_ent_value */

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static ir_node *find_compound_ent_value(ir_node *ptr)
{
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	return rec_find_compound_ent_value(ptr, NULL);
}  /* find_compound_ent_value */

/**
 * Mark a Load memop to be replace by a definition
 *
 * @param op  the Load memop
 */
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static void mark_replace_load(memop_t *op, ir_node *def)
{
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	op->replace = def;
	op->flags |= FLAG_KILLED_NODE;
	env.changed = 1;
}  /* mark_replace_load */

/**
 * Mark a Store memop to be removed.