bespillutil.c 36.9 KB
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/*
 * This file is part of libFirm.
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 * Copyright (C) 2012 University of Karlsruhe.
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 */

/**
 * @file
 * @brief       implementation of the spill/reload placement abstraction layer
 * @author      Daniel Grund, Sebastian Hack, Matthias Braun
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 * @date        29.09.2005
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 */
#include <stdlib.h>
#include <stdbool.h>

#include "array.h"
#include "bearch.h"
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#include "bechordal_t.h"
#include "beirg.h"
#include "belive.h"
#include "bemodule.h"
#include "benode.h"
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#include "besched.h"
#include "bespill.h"
#include "bespillutil.h"
#include "bessaconstr.h"
#include "be_t.h"
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#include "beutil.h"
#include "debug.h"
#include "entity_t.h"
#include "execfreq.h"
#include "ident_t.h"
#include "irbackedge_t.h"
#include "ircons_t.h"
#include "iredges_t.h"
#include "irgmod.h"
#include "irgwalk.h"
#include "irnodehashmap.h"
#include "irnode_t.h"
#include "statev_t.h"
#include "type_t.h"
#include "util.h"
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DEBUG_ONLY(static firm_dbg_module_t *dbg;)
DEBUG_ONLY(static firm_dbg_module_t *dbg_constr;)
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#define REMAT_COST_INFINITE  1000

typedef struct reloader_t reloader_t;
struct reloader_t {
	reloader_t *next;
	ir_node    *reloader;
	int         remat_cost_delta; /** costs needed for rematerialization,
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	                                  compared to placing a reload */
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};

typedef struct spill_t spill_t;
struct spill_t {
	spill_t *next;
	ir_node *after;  /**< spill has to be placed after this node (or earlier) */
	ir_node *spill;
};

typedef struct spill_info_t spill_info_t;
struct spill_info_t {
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	ir_node      *to_spill;  /**< the value that should get spilled */
	reloader_t   *reloaders; /**< list of places where the value should get
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	                              reloaded */
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	spill_t      *spills;    /**< list of latest places where spill must be
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	                              placed */
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	spill_info_t *next;
	spill_info_t *next_mem_phi;
	double        spill_costs; /**< costs needed for spilling the value */
	bool          spilled_phi; /**< true when the whole Phi has been spilled and
	                                will be replaced with a PhiM. false if only
	                                the value of the Phi gets spilled */
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};

struct spill_env_t {
	ir_graph         *irg;
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	ir_nodehashmap_t  spillmap;
	spill_info_t     *spills;
	spill_info_t     *mem_phis;
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	struct obstack    obst;
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	int               spill_cost;  /**< the cost of a single spill node */
	int               reload_cost; /**< the cost of a reload node */
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	unsigned          spill_count;
	unsigned          reload_count;
	unsigned          remat_count;
	unsigned          spilled_phi_count;
};

/**
 * Returns spill info for a specific value (the value that is to be spilled)
 */
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static spill_info_t *get_spillinfo(spill_env_t *env, ir_node *value)
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{
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	spill_info_t *info = ir_nodehashmap_get(spill_info_t, &env->spillmap,
	                                        value);
	if (info == NULL) {
		info = OALLOCZ(&env->obst, spill_info_t);
		info->to_spill    = value;
		info->spill_costs = -1;
		ir_nodehashmap_insert(&env->spillmap, value, info);

		info->next = env->spills;
		env->spills = info;
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	}

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	return info;
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}

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spill_env_t *be_new_spill_env(ir_graph *irg)
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{
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	spill_env_t *env = XMALLOCZ(spill_env_t);
	env->irg         = irg;
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	env->spill_cost  = isa_if->spill_cost;
	env->reload_cost = isa_if->reload_cost;
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	ir_nodehashmap_init(&env->spillmap);
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	obstack_init(&env->obst);
	return env;
}

void be_delete_spill_env(spill_env_t *env)
{
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	ir_nodehashmap_destroy(&env->spillmap);
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	obstack_free(&env->obst, NULL);
	free(env);
}

void be_add_spill(spill_env_t *env, ir_node *to_spill, ir_node *after)
{
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	assert(!arch_irn_is(skip_Proj_const(to_spill), dont_spill));
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	DB((dbg, LEVEL_1, "Add spill of %+F after %+F\n", to_spill, after));

	/* Just for safety make sure that we do not insert the spill in front of a phi */
	assert(!is_Phi(sched_next(after)));

	/* spills that are dominated by others are not needed */
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	spill_info_t *spill_info = get_spillinfo(env, to_spill);
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	for (spill_t **anchor = &spill_info->spills; *anchor;) {
		spill_t *const s = *anchor;
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		/* no need to add this spill if it is dominated by another */
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		if (value_strictly_dominates(s->after, after)) {
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			DB((dbg, LEVEL_1, "...dominated by %+F, not added\n", s->after));
			return;
		}
		/* remove spills that we dominate */
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		if (value_strictly_dominates(after, s->after)) {
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			DB((dbg, LEVEL_1, "...remove old spill at %+F\n", s->after));
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			*anchor = s->next;
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		} else {
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			anchor = &s->next;
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		}
	}

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	spill_t *spill = OALLOC(&env->obst, spill_t);
	spill->after = after;
	spill->next  = spill_info->spills;
	spill->spill = NULL;
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	spill_info->spills = spill;
}

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void be_add_reload(spill_env_t *env, ir_node *to_spill, ir_node *before)
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{
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	assert(!arch_irn_is(skip_Proj_const(to_spill), dont_spill));
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	assert(!be_is_Keep(before));
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	spill_info_t *info = get_spillinfo(env, to_spill);
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	/* put reload into list */
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	reloader_t *rel       = OALLOC(&env->obst, reloader_t);
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	rel->next             = info->reloaders;
	rel->reloader         = before;
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	rel->remat_cost_delta = 0;
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	info->reloaders = rel;
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	DBG((dbg, LEVEL_1,
	     "creating spillinfo for %+F, will be reloaded before %+F\n",
	     to_spill, before));
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}

ir_node *be_get_end_of_block_insertion_point(const ir_node *block)
{
	ir_node *last = sched_last(block);

	/* we might have keeps behind the jump... */
	while (be_is_Keep(last)) {
		last = sched_prev(last);
		assert(!sched_is_end(last));
	}

	assert(is_cfop(last));

	/* add the reload before the (cond-)jump */
	return last;
}

/**
 * Returns the point at which you can insert a node that should be executed
 * before block @p block when coming from pred @p pos.
 */
static ir_node *get_block_insertion_point(ir_node *block, int pos)
{
	/* simply add the reload to the beginning of the block if we only have 1
	 * predecessor. We don't need to check for phis as there can't be any in a
	 * block with only 1 pred. */
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	if (get_Block_n_cfgpreds(block) == 1) {
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		assert(!is_Phi(sched_first(block)));
		return sched_first(block);
	}

	/* We have to reload the value in pred-block */
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	ir_node *predblock = get_Block_cfgpred_block(block, pos);
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	return be_get_end_of_block_insertion_point(predblock);
}

void be_add_reload_on_edge(spill_env_t *env, ir_node *to_spill, ir_node *block,
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                           int pos)
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{
	ir_node *before = get_block_insertion_point(block, pos);
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	be_add_reload(env, to_spill, before);
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}

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void be_spill_phi(spill_env_t *const env, ir_node *const phi)
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{
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	assert(is_Phi(phi));
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	spill_info_t *info = get_spillinfo(env, phi);
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	info->spilled_phi  = true;
	info->next_mem_phi = env->mem_phis;
	env->mem_phis      = info;
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	/* create spills for the phi arguments */
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	foreach_irn_in(phi, i, arg) {
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		ir_node *const insert = be_move_after_schedule_first(arg);
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		be_add_spill(env, arg, insert);
	}
}

static void determine_spill_costs(spill_env_t *env, spill_info_t *spillinfo);

/**
 * Creates a spill.
 *
 * @param senv      the spill environment
 * @param irn       the node that should be spilled
 * @param ctx_irn   an user of the spilled node
 * @return a be_Spill node
 */
static void spill_irn(spill_env_t *env, spill_info_t *spillinfo)
{
	/* determine_spill_costs must have been run before */
	assert(spillinfo->spill_costs >= 0);

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	ir_node *const to_spill = spillinfo->to_spill;
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	DBG((dbg, LEVEL_1, "spilling %+F ... \n", to_spill));
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	for (spill_t *spill = spillinfo->spills; spill != NULL;
	     spill = spill->next) {
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		ir_node *const after = be_move_after_schedule_first(spill->after);
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		spill->spill = isa_if->new_spill(to_spill, after);
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		DB((dbg, LEVEL_1, "\t%+F after %+F\n", spill->spill, after));
		env->spill_count++;
	}
	DBG((dbg, LEVEL_1, "\n"));
}

static void spill_node(spill_env_t *env, spill_info_t *spillinfo);

/**
 * If the first usage of a Phi result would be out of memory
 * there is no sense in allocating a register for it.
 * Thus we spill it and all its operands to the same spill slot.
 * Therefore the phi/dataB becomes a phi/Memory
 *
 * @param senv      the spill environment
 * @param phi       the Phi node that should be spilled
 * @param ctx_irn   an user of the spilled node
 */
static void spill_phi(spill_env_t *env, spill_info_t *spillinfo)
{
	assert(!get_opt_cse());
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	ir_node *phi = spillinfo->to_spill;
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	DBG((dbg, LEVEL_1, "spilling Phi %+F:\n", phi));

	/* build a new PhiM */
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	ir_node *const block = get_nodes_block(phi);
	ir_node *const phim  = be_new_Phi0(block, mode_M, arch_no_register_req);
	sched_add_after(block, phim);
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	/* override or replace spills list... */
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	spill_t *spill = OALLOC(&env->obst, spill_t);
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	spill->after = be_move_after_schedule_first(phi);
	spill->spill = phim;
	spill->next  = NULL;
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	spillinfo->spills = spill;
	env->spilled_phi_count++;

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	unsigned  const arity = get_Phi_n_preds(phi);
	ir_node **const ins   = ALLOCAN(ir_node*, arity);
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	foreach_irn_in(phi, i, arg) {
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		spill_info_t *arg_info = get_spillinfo(env, arg);

		determine_spill_costs(env, arg_info);
		spill_node(env, arg_info);

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		ins[i] = arg_info->spills->spill;
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	}
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	be_complete_Phi(phim, arity, ins);
	DBG((dbg, LEVEL_1, "... done spilling Phi %+F, created PhiM %+F\n", phi, phim));
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}

/**
 * Spill a node.
 *
 * @param senv      the spill environment
 * @param to_spill  the node that should be spilled
 */
static void spill_node(spill_env_t *env, spill_info_t *spillinfo)
{
	/* node is already spilled */
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	if (spillinfo->spills != NULL && spillinfo->spills->spill != NULL)
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		return;

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	if (spillinfo->spilled_phi) {
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		spill_phi(env, spillinfo);
	} else {
		spill_irn(env, spillinfo);
	}
}

/**
 * Tests whether value @p arg is available before node @p reloader
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 * @returns true if value is available
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 */
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static bool is_value_available(spill_env_t *env, const ir_node *arg)
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{
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	if (is_Unknown(arg) || is_NoMem(arg))
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		return true;
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	if (arch_irn_is(skip_Proj_const(arg), spill))
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		return true;
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	if (arg == get_irg_frame(env->irg))
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		return true;
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	if (get_irn_mode(arg) == mode_T)
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		return false;
	/* "Ignore registers" are always available */
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	if (arch_irn_is_ignore(arg))
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		return true;
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	return false;
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}

/**
 * Check if a node is rematerializable. This tests for the following conditions:
 *
 * - The node itself is rematerializable
 * - All arguments of the node are available or also rematerialisable
 * - The costs for the rematerialisation operation is less or equal a limit
 *
 * Returns the costs needed for rematerialisation or something
 * >= REMAT_COST_INFINITE if remat is not possible.
 */
static int check_remat_conditions_costs(spill_env_t *env,
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                                        const ir_node *spilled,
                                        const ir_node *reloader,
                                        int parentcosts)
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{
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	const ir_node *insn = skip_Proj_const(spilled);
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	assert(!arch_irn_is(insn, spill));
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	if (!arch_irn_is(insn, rematerializable))
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		return REMAT_COST_INFINITE;

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	int costs = arch_get_op_estimated_cost(insn);
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	if (parentcosts + costs >= env->reload_cost + env->spill_cost)
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		return REMAT_COST_INFINITE;
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	/* never rematerialize a node which modifies the flags.
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	 * (would be better to test whether the flags are actually live at point
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	 * reloader...)
	 */
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	if (arch_irn_is(insn, modify_flags))
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		return REMAT_COST_INFINITE;

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	int argremats = 0;
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	foreach_irn_in(insn, i, arg) {
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		if (is_value_available(env, arg))
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			continue;

		/* we have to rematerialize the argument as well */
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		++argremats;
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		if (argremats > 1) {
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			/* we only support rematerializing 1 argument at the moment,
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			 * as multiple arguments could increase register pressure */
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			return REMAT_COST_INFINITE;
		}

		costs += check_remat_conditions_costs(env, arg, reloader,
		                                      parentcosts + costs);
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		if (parentcosts + costs >= env->reload_cost + env->spill_cost)
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			return REMAT_COST_INFINITE;
	}

	return costs;
}

/**
 * Re-materialize a node.
 *
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 * @param env       the spill environment
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 * @param spilled   the node that was spilled
 * @param reloader  a irn that requires a reload
 */
static ir_node *do_remat(spill_env_t *env, ir_node *spilled, ir_node *reloader)
{
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	ir_node **ins = ALLOCAN(ir_node*, get_irn_arity(spilled));
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	foreach_irn_in(spilled, i, arg) {
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		if (is_value_available(env, arg)) {
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			ins[i] = arg;
		} else {
			ins[i] = do_remat(env, arg, reloader);
		}
	}

	/* create a copy of the node */
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	ir_node *const bl  = get_nodes_block(reloader);
	ir_node *const res = new_similar_node(spilled, bl, ins);
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	if (isa_if->mark_remat)
		isa_if->mark_remat(res);
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	DBG((dbg, LEVEL_1, "Insert remat %+F of %+F before reloader %+F\n", res,
	     spilled, reloader));
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	if (!is_Proj(res))
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		sched_add_before(reloader, res);

	return res;
}

double be_get_spill_costs(spill_env_t *env, ir_node *to_spill, ir_node *before)
{
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	(void)to_spill;
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	ir_node *block = get_nodes_block(before);
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	double   freq  = get_block_execfreq(block);
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	return env->spill_cost * freq;
}

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unsigned be_get_reload_costs_no_weight(spill_env_t *env,
                                       const ir_node *to_spill,
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                                       const ir_node *before)
{
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	if (be_do_remats) {
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		/* is the node rematerializable? */
		unsigned costs = check_remat_conditions_costs(env, to_spill, before, 0);
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		if (costs < (unsigned) env->reload_cost)
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			return costs;
	}

	return env->reload_cost;
}

double be_get_reload_costs(spill_env_t *env, ir_node *to_spill, ir_node *before)
{
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	ir_node *block = get_nodes_block(before);
	double   freq  = get_block_execfreq(block);
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	if (be_do_remats) {
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		/* is the node rematerializable? */
		int costs = check_remat_conditions_costs(env, to_spill, before, 0);
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		if (costs < env->reload_cost)
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			return costs * freq;
	}

	return env->reload_cost * freq;
}

double be_get_reload_costs_on_edge(spill_env_t *env, ir_node *to_spill,
                                   ir_node *block, int pos)
{
	ir_node *before = get_block_insertion_point(block, pos);
	return be_get_reload_costs(env, to_spill, before);
}

/**
 * analyzes how to best spill a node and determine costs for that
 */
static void determine_spill_costs(spill_env_t *env, spill_info_t *spillinfo)
{
	/* already calculated? */
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	if (spillinfo->spill_costs >= 0)
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		return;

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	ir_node       *to_spill = spillinfo->to_spill;
	const ir_node *insn     = skip_Proj_const(to_spill);
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	assert(!arch_irn_is(insn, dont_spill));
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	assert(!arch_irn_is(insn, reload));
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	ir_node *spill_block    = get_nodes_block(insn);
	double   spill_execfreq = get_block_execfreq(spill_block);
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	if (spillinfo->spilled_phi) {
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		/* TODO calculate correct costs...
		 * (though we can't remat this node anyway so no big problem) */
		spillinfo->spill_costs = env->spill_cost * spill_execfreq;
		return;
	}

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	/* calculate sum of execution frequencies of individual spills */
	assert(spillinfo->spills);
	double spills_execfreq = 0;
	for (spill_t *s = spillinfo->spills; s != NULL; s = s->next) {
		ir_node *spill_block = get_block(s->after);
		double   freq        = get_block_execfreq(spill_block);

		spills_execfreq += freq;
	}
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	DB((dbg, LEVEL_1, "%+F: latespillcosts %f after def: %f\n", to_spill,
			spills_execfreq * env->spill_cost,
			spill_execfreq * env->spill_cost));
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	/* multi-/latespill is advantageous -> return*/
	if (spills_execfreq < spill_execfreq) {
		DB((dbg, LEVEL_1, "use latespills for %+F\n", to_spill));
		spillinfo->spill_costs = spills_execfreq * env->spill_cost;
		return;
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	}

	/* override spillinfos or create a new one */
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	spill_t *spill = OALLOC(&env->obst, spill_t);
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	spill->after   = be_move_after_schedule_first(skip_Proj(to_spill));
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	spill->next    = NULL;
	spill->spill   = NULL;
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	spillinfo->spills      = spill;
	spillinfo->spill_costs = spill_execfreq * env->spill_cost;
	DB((dbg, LEVEL_1, "spill %+F after definition\n", to_spill));
}

void be_insert_spills_reloads(spill_env_t *env)
{
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	be_timer_push(T_RA_SPILL_APPLY);
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	/* create all phi-ms first, this is needed so, that phis, hanging on
	   spilled phis work correctly */
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	for (spill_info_t *info = env->mem_phis; info != NULL;
	     info = info->next_mem_phi) {
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		spill_node(env, info);
	}

	/* process each spilled node */
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	for (spill_info_t *si = env->spills; si != NULL; si = si->next) {
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		ir_node  *to_spill        = si->to_spill;
		ir_node **copies          = NEW_ARR_F(ir_node*, 0);
		double    all_remat_costs = 0; /** costs when we would remat all nodes */
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		bool      force_remat     = false;
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		DBG((dbg, LEVEL_1, "\nhandling all reloaders of %+F:\n", to_spill));

		determine_spill_costs(env, si);

		/* determine possibility of rematerialisations */
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		if (be_do_remats) {
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			/* calculate cost savings for each individual value when it would
			   be rematerialised instead of reloaded */
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			for (reloader_t *rld = si->reloaders; rld != NULL;
			     rld = rld->next) {
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				ir_node *reloader = rld->reloader;
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				if (rld->remat_cost_delta >= REMAT_COST_INFINITE) {
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					DBG((dbg, LEVEL_2, "\treload before %+F is forbidden\n",
					     reloader));
					all_remat_costs = REMAT_COST_INFINITE;
					continue;
				}

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				int remat_cost = check_remat_conditions_costs(env, to_spill,
				                                              reloader, 0);
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				if (remat_cost >= REMAT_COST_INFINITE) {
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					DBG((dbg, LEVEL_2, "\tremat before %+F not possible\n",
					     reloader));
					rld->remat_cost_delta = REMAT_COST_INFINITE;
					all_remat_costs       = REMAT_COST_INFINITE;
					continue;
				}

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				int remat_cost_delta  = remat_cost - env->reload_cost;
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				rld->remat_cost_delta = remat_cost_delta;
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				ir_node *block        = get_block(reloader);
				double   freq         = get_block_execfreq(block);
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				all_remat_costs      += remat_cost_delta * freq;
				DBG((dbg, LEVEL_2, "\tremat costs delta before %+F: "
				     "%d (rel %f)\n", reloader, remat_cost_delta,
				     remat_cost_delta * freq));
			}
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			if (all_remat_costs < REMAT_COST_INFINITE) {
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				/* we don't need the costs for the spill if we can remat
				   all reloaders */
				all_remat_costs -= si->spill_costs;
				DBG((dbg, LEVEL_2, "\tspill costs %d (rel %f)\n",
				     env->spill_cost, si->spill_costs));
			}

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			if (all_remat_costs < 0) {
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				force_remat = true;
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				DBG((dbg, LEVEL_1, "\nforcing remats of all reloaders (%f)\n",
				     all_remat_costs));
			}
		}

		/* go through all reloads for this spill */
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		for (reloader_t *rld = si->reloaders; rld != NULL; rld = rld->next) {
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			ir_node *copy; /* a reload is a "copy" of the original value */
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			if (be_do_remats && (force_remat || rld->remat_cost_delta < 0)) {
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				copy = do_remat(env, to_spill, rld->reloader);
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				++env->remat_count;
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			} else {
				/* make sure we have a spill */
				spill_node(env, si);

				/* create a reload, use the first spill for now SSA
				 * reconstruction for memory comes below */
				assert(si->spills != NULL);
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				copy = isa_if->new_reload(si->to_spill, si->spills->spill, rld->reloader);
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				env->reload_count++;
			}

			DBG((dbg, LEVEL_1, " %+F of %+F before %+F\n",
			     copy, to_spill, rld->reloader));
			ARR_APP1(ir_node*, copies, copy);
		}

		/* if we had any reloads or remats, then we need to reconstruct the
		 * SSA form for the spilled value */
		if (ARR_LEN(copies) > 0) {
			be_ssa_construction_env_t senv;
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			be_ssa_construction_init(&senv, env->irg);
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			be_ssa_construction_add_copy(&senv, to_spill);
			be_ssa_construction_add_copies(&senv, copies, ARR_LEN(copies));
			be_ssa_construction_fix_users(&senv, to_spill);
			be_ssa_construction_destroy(&senv);
		}
		/* need to reconstruct SSA form if we had multiple spills */
		if (si->spills != NULL && si->spills->next != NULL) {
			be_ssa_construction_env_t senv;
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			be_ssa_construction_init(&senv, env->irg);
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			unsigned spill_count = 0;
			for (spill_t *spill = si->spills ; spill != NULL;
			     spill = spill->next) {
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				/* maybe we rematerialized the value and need no spill */
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				if (spill->spill == NULL)
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					continue;
				be_ssa_construction_add_copy(&senv, spill->spill);
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				++spill_count;
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			}
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			if (spill_count > 1) {
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				/* all reloads are attached to the first spill, fix them now */
				be_ssa_construction_fix_users(&senv, si->spills->spill);
			}

			be_ssa_construction_destroy(&senv);
		}

		DEL_ARR_F(copies);
		si->reloaders = NULL;
	}

	stat_ev_dbl("spill_spills", env->spill_count);
	stat_ev_dbl("spill_reloads", env->reload_count);
	stat_ev_dbl("spill_remats", env->remat_count);
	stat_ev_dbl("spill_spilled_phis", env->spilled_phi_count);

	/* Matze: In theory be_ssa_construction should take care of the liveness...
	 * try to disable this again in the future */
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	be_invalidate_live_sets(env->irg);
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	be_remove_dead_nodes_from_schedule(env->irg);
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	be_timer_pop(T_RA_SPILL_APPLY);
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}

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static be_irg_t      *birg;
static be_lv_t       *lv;
static unsigned long  precol_copies;
static unsigned long  multi_precol_copies;
static unsigned long  constrained_livethrough_copies;

static void prepare_constr_insn(ir_node *const node)
{
	/* Insert a copy for constraint inputs attached to a value which can't
	 * fulfill the constraint
	 * (typical example: stack pointer as input to copyb)
	 * TODO: This really just checks precolored registers at the moment and
	 *       ignores the general case of not matching in/out constraints */
	foreach_irn_in(node, i, op) {
		const arch_register_req_t *const req
			= arch_get_irn_register_req_in(node, i);
		if (req->cls == NULL)
			continue;

		const arch_register_t *const reg = arch_get_irn_register(op);
		if (reg == NULL)
			continue;

		/* Precolored with an ignore register (which is not virtual). */
		if ((reg->type & arch_register_type_virtual) ||
		    rbitset_is_set(birg->allocatable_regs, reg->global_index))
			continue;

		if (!arch_register_req_is(req, limited))
			continue;
		if (rbitset_is_set(req->limited, reg->index))
			continue;

		ir_node *block = get_nodes_block(node);
		ir_node *copy  = be_new_Copy(block, op);
		sched_add_before(node, copy);
		set_irn_n(node, i, copy);
		++precol_copies;
		DBG((dbg_constr, LEVEL_3, "inserting ignore arg copy %+F for %+F pos %d\n",
		     copy, node, i));
	}

	/* insert copies for nodes that occur constrained more than once. */
	for (int i = 0, arity = get_irn_arity(node); i < arity; ++i) {
		const arch_register_req_t *const req
			= arch_get_irn_register_req_in(node, i);
		const arch_register_class_t *const cls = req->cls;
		if (cls == NULL)
			continue;
		if (!arch_register_req_is(req, limited))
			continue;

		ir_node *in = get_irn_n(node, i);
		const arch_register_req_t *const in_req
			= arch_get_irn_register_req(in);
		if (arch_register_req_is(in_req, ignore))
			continue;
		for (int i2 = i + 1; i2 < arity; ++i2) {
			const arch_register_req_t *const req2
				= arch_get_irn_register_req_in(node, i2);
			if (req2->cls != cls)
				continue;
			if (!arch_register_req_is(req2, limited))
				continue;

			ir_node *in2 = get_irn_n(node, i2);
			if (in2 != in)
				continue;

			/* if the constraint is the same, no copy is necessary
			 * TODO generalise to unequal but overlapping constraints */
			if (rbitsets_equal(req->limited, req2->limited, cls->n_regs))
				continue;

			ir_node *block = get_nodes_block(node);
			ir_node *copy  = be_new_Copy(block, in);
			sched_add_before(node, copy);
			set_irn_n(node, i2, copy);
			++multi_precol_copies;
			DBG((dbg_constr, LEVEL_3,
			     "inserting multiple constr copy %+F for %+F pos %d\n",
			     copy, node, i2));
		}
	}

	/* collect all registers occurring in out constraints. */
	unsigned *def_constr = NULL;
	be_foreach_value(node, value,
		const arch_register_req_t *const req = arch_get_irn_register_req(value);
		const arch_register_class_t *const cls = req->cls;
		if (cls == NULL)
			continue;
		if (!arch_register_req_is(req, limited))
			continue;
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		if (def_constr == NULL)
			def_constr = rbitset_alloca(isa_if->n_registers);
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		rbitset_foreach(req->limited, cls->n_regs, e) {
			const arch_register_t *reg = arch_register_for_index(cls, e);
			rbitset_set(def_constr, reg->global_index);
		}
	);
	/* no output constraints => we're good */
	if (def_constr == NULL)
		return;

	/* Insert copies for all constrained arguments living through the node and
	 * being constrained to a register which also occurs in out constraints. */
	for (int i = 0, arity = get_irn_arity(node); i < arity; ++i) {
		/* Check, if
		 * 1) the operand is constrained.
		 * 2) lives through the node.
		 * 3) is constrained to a register occurring in out constraints. */
		const arch_register_req_t *const req
			= arch_get_irn_register_req_in(node, i);
		const arch_register_class_t *const cls = req->cls;
		if (cls == NULL)
			continue;
		if (!arch_register_req_is(req, limited))
			continue;
		ir_node *in = get_irn_n(node, i);
		const arch_register_req_t *const in_req
			= arch_get_irn_register_req(in);
		if (arch_register_req_is(in_req, ignore))
			continue;
		/* Only create the copy if the operand is no copy.
		 * this is necessary since the assure constraints phase inserts
		 * Copies and Keeps for operands which must be different from the
		 * results. Additional copies here would destroy this. */
		if (be_is_Copy(in))
			continue;
		if (!be_value_live_after(in, node))
			continue;

		bool common_limits = false;
		rbitset_foreach(req->limited, cls->n_regs, e) {
			const arch_register_t *reg = arch_register_for_index(cls, e);
			if (rbitset_is_set(def_constr, reg->global_index)) {
				common_limits = true;
				break;
			}
		}
		if (!common_limits)
			continue;

		ir_node *block = get_nodes_block(node);
		ir_node *copy  = be_new_Copy(block, in);
		sched_add_before(node, copy);
		set_irn_n(node, i, copy);
		++constrained_livethrough_copies;
		DBG((dbg_constr, LEVEL_3, "inserting constr copy %+F for %+F pos %d\n",
		     copy, node, i));
		be_liveness_update(lv, in);
	}
}

static void add_missing_copies_in_block(ir_node *block, void *data)
{
	(void)data;
	sched_foreach(block, node) {
		prepare_constr_insn(node);
	}
}

static bool has_irn_users(const ir_node *irn)
{
	return get_irn_out_edge_first_kind(irn, EDGE_KIND_NORMAL) != 0;
}

static ir_node *find_copy(ir_node *irn, ir_node *op)
{
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	for (ir_node *cur_node = irn;;) {
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		cur_node = sched_prev(cur_node);
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		if (!be_is_Copy(cur_node))
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			return NULL;
		if (be_get_Copy_op(cur_node) == op && arch_irn_is(cur_node, dont_spill))
			return cur_node;
	}
}

/** Environment for constraints. */
typedef struct {
	ir_nodehashmap_t op_set;
	struct obstack   obst;
} constraint_env_t;

/** Associates an ir_node with its copy and CopyKeep. */
typedef struct {
	ir_nodeset_t copies; /**< all non-spillable copies of this irn */
} op_copy_assoc_t;

static void gen_assure_different_pattern(ir_node *irn, ir_node *other_different, constraint_env_t *env)
{
	arch_register_req_t const *const req = arch_get_irn_register_req(other_different);
	if (arch_register_req_is(req, ignore) ||
			!mode_is_data(get_irn_mode(other_different))) {
		DB((dbg_constr, LEVEL_1, "ignore constraint for %+F because other_irn is ignore or not a data node\n", irn));
		return;
	}

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	ir_nodehashmap_t *op_set = &env->op_set;
	ir_node          *block  = get_nodes_block(irn);
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	/* Make a not spillable copy of the different node   */
	/* this is needed because the different irn could be */
	/* in block far far away                             */
	/* The copy is optimized later if not needed         */

	/* check if already exists such a copy in the schedule immediately before */
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	ir_node *cpy = find_copy(skip_Proj(irn), other_different);
	if (cpy == NULL) {
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		cpy = be_new_Copy(block, other_different);
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		arch_add_irn_flags(cpy, arch_irn_flag_dont_spill);
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		DB((dbg_constr, LEVEL_1, "created non-spillable %+F for value %+F\n", cpy, other_different));
	} else {
		DB((dbg_constr, LEVEL_1, "using already existing %+F for value %+F\n", cpy, other_different));
	}

	/* Add the Keep resp. CopyKeep and reroute the users */
	/* of the other_different irn in case of CopyKeep.   */
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	ir_node *keep;
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	if (has_irn_users(other_different)) {
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		ir_node *const in[] = { irn };
		keep = be_new_CopyKeep(block, cpy, ARRAY_SIZE(in), in);
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	} else {
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		ir_node *in[] = { irn, cpy };
		keep = be_new_Keep(block, ARRAY_SIZE(in), in);
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	}

	DB((dbg_constr, LEVEL_1, "created %+F(%+F, %+F)\n\n", keep, irn, cpy));

	/* insert copy and keep into schedule */
	assert(sched_is_scheduled(irn) && "need schedule to assure constraints");
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	if (!sched_is_scheduled(cpy))
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		sched_add_before(skip_Proj(irn), cpy);
	sched_add_after(skip_Proj(irn), keep);

	/* insert the other different and its copies into the map */
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	op_copy_assoc_t *entry
		= ir_nodehashmap_get(op_copy_assoc_t, op_set, other_different);
	if (entry == NULL) {
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		entry = OALLOC(&env->obst, op_copy_assoc_t);
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		ir_nodeset_init(&entry->copies);

		ir_nodehashmap_insert(op_set, other_different, entry);
	}

	/* insert copy */
	ir_nodeset_insert(&entry->copies, cpy);

	/* insert keep in case of CopyKeep */
	if (be_is_CopyKeep(keep))
		ir_nodeset_insert(&entry->copies, keep);
}

/**
 * Checks if node has a must_be_different constraint in output and adds a Keep
 * then to assure the constraint.
 *
 * @param irn          the node to check
 * @param skipped_irn  if irn is a Proj node, its predecessor, else irn
 * @param env          the constraint environment
 */
static void assure_different_constraints(ir_node *irn, ir_node *skipped_irn, constraint_env_t *env)
{
	const arch_register_req_t *req = arch_get_irn_register_req(irn);

	if (arch_register_req_is(req, must_be_different)) {
		const unsigned other = req->other_different;

		if (arch_register_req_is(req, should_be_same)) {
			const unsigned same = req->other_same;

			if (is_po2(other) && is_po2(same)) {
				int idx_other = ntz(other);
				int idx_same  = ntz(same);

				/*
				 * We can safely ignore a should_be_same x must_be_different y
				 * IFF both inputs are equal!
				 */
				if (get_irn_n(skipped_irn, idx_other) == get_irn_n(skipped_irn, idx_same)) {
					return;
				}
			}
		}
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		for (unsigned i = 0; 1U << i <= other; ++i) {
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			if (other & (1U << i)) {
				ir_node *different_from = get_irn_n(skipped_irn, i);
				gen_assure_different_pattern(irn, different_from, env);
			}
		}
	}
}

/**
 * Calls the functions to assure register constraints.
 *
 * @param block    The block to be checked
 * @param walk_env The walker environment
 */
static void assure_constraints_walker(ir_node *block, void *walk_env)
{
	constraint_env_t *env = (constraint_env_t*)walk_env;

	sched_foreach_reverse(block, irn) {
		be_foreach_value(irn, value,
			if (mode_is_data(get_irn_mode(value)))
				assure_different_constraints(value, irn, env);
		);
	}
}

/**
 * Melt all copykeeps pointing to the same node
 * (or Projs of the same node), copying the same operand.
 */
static void melt_copykeeps(constraint_env_t *cenv)
{
	struct obstack obst;
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