path: root/src/freedreno/ir3/ir3_sched.c

/*
 * Copyright (C) 2014 Rob Clark <robclark@freedesktop.org>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 * Authors:
 *    Rob Clark <robclark@freedesktop.org>
 */


#include "util/dag.h"
#include "util/u_math.h"

#include "ir3.h"
#include "ir3_compiler.h"

#ifdef DEBUG
#define SCHED_DEBUG (ir3_shader_debug & IR3_DBG_SCHEDMSGS)
#else
#define SCHED_DEBUG 0
#endif
#define d(fmt, ...) do { if (SCHED_DEBUG) { \
	printf("SCHED: "fmt"\n", ##__VA_ARGS__); \
} } while (0)

#define di(instr, fmt, ...) do { if (SCHED_DEBUG) { \
	printf("SCHED: "fmt": ", ##__VA_ARGS__); \
	ir3_print_instr(instr); \
} } while (0)

/*
 * Instruction Scheduling:
 *
 * A block-level pre-RA scheduler, which works by creating a DAG of
 * instruction dependencies, and heuristically picking a DAG head
 * (instruction with no unscheduled dependencies).
 *
 * Where possible, it tries to pick instructions that avoid nop delay
 * slots, but it will prefer to pick instructions that reduce (or do
 * not increase) the number of live values.
 *
 * If the only possible choices are instructions that increase the
 * number of live values, it will try to pick the one with the earliest
 * consumer (based on pre-sched program order).
 *
 * There are a few special cases that need to be handled, since sched
 * is currently independent of register allocation.  Usages of address
 * register (a0.x) or predicate register (p0.x) must be serialized.  Ie.
 * if you have two pairs of instructions that write the same special
 * register and then read it, then those pairs cannot be interleaved.
 * To solve this, when we are in such a scheduling "critical section",
 * and we encounter a conflicting write to a special register, we try
 * to schedule any remaining instructions that use that value first.
 *
 * TODO we can detect too-large live_values here.. would be a good place
 * to "spill" cheap things, like move from uniform/immed.  (Constructing
 * list of ssa def consumers before sched pass would make this easier.
 * Also, in general it is general it might be best not to re-use load_immed
 * across blocks.
 *
 * TODO we can use (abs)/(neg) src modifiers in a lot of cases to reduce
 * the # of immediates in play (or at least that would help with
 * dEQP-GLES31.functional.ubo.random.all_per_block_buffers.*).. probably
 * do this in a nir pass that inserts fneg/etc?  The cp pass should fold
 * these into src modifiers..
 */

struct ir3_sched_ctx {
	struct ir3_block *block;           /* the current block */
	struct dag *dag;

	struct list_head unscheduled_list; /* unscheduled instructions */
	struct ir3_instruction *scheduled; /* last scheduled instr */
	struct ir3_instruction *addr0;     /* current a0.x user, if any */
	struct ir3_instruction *addr1;     /* current a1.x user, if any */
	struct ir3_instruction *pred;      /* current p0.x user, if any */

	int remaining_kills;

	bool error;
};

struct ir3_sched_node {
	struct dag_node dag;     /* must be first for util_dynarray_foreach */
	struct ir3_instruction *instr;

	unsigned delay;
	unsigned max_delay;

	/* For instructions that are a meta:collect src, once we schedule
	 * the first src of the collect, the entire vecN is live (at least
	 * from the PoV of the first RA pass.. the 2nd scalar pass can fill
	 * in some of the gaps, but often not all).  So we want to help out
	 * RA, and realize that as soon as we schedule the first collect
	 * src, there is no penalty to schedule the remainder (ie. they
	 * don't make additional values live).  In fact we'd prefer to
	 * schedule the rest ASAP to minimize the live range of the vecN.
	 *
	 * For instructions that are the src of a collect, we track the
	 * corresponding collect, and mark them as partially live as soon
	 * as any one of the src's is scheduled.
	 */
	struct ir3_instruction *collect;
	bool partially_live;

	/* Is this instruction a direct or indirect dependency for a kill?
	 * If so, we should prioritize it when possible
	 */
	bool kill_path;
};

#define foreach_sched_node(__n, __list) \
	list_for_each_entry(struct ir3_sched_node, __n, __list, dag.link)

static void sched_node_init(struct ir3_sched_ctx *ctx, struct ir3_instruction *instr);
static void sched_node_add_dep(struct ir3_instruction *instr, struct ir3_instruction *src, int i);

static bool is_scheduled(struct ir3_instruction *instr)
{
	return !!(instr->flags & IR3_INSTR_MARK);
}

static void
schedule(struct ir3_sched_ctx *ctx, struct ir3_instruction *instr)
{
	debug_assert(ctx->block == instr->block);

	/* remove from depth list:
	 */
	list_delinit(&instr->node);

	if (writes_addr0(instr)) {
		debug_assert(ctx->addr0 == NULL);
		ctx->addr0 = instr;
	}

	if (writes_addr1(instr)) {
		debug_assert(ctx->addr1 == NULL);
		ctx->addr1 = instr;
	}

	if (writes_pred(instr)) {
		debug_assert(ctx->pred == NULL);
		ctx->pred = instr;
	}

	instr->flags |= IR3_INSTR_MARK;

	di(instr, "schedule");

	list_addtail(&instr->node, &instr->block->instr_list);
	ctx->scheduled = instr;

	if (is_kill(instr)){
		ctx->remaining_kills--;
	}

	struct ir3_sched_node *n = instr->data;

	/* If this instruction is a meta:collect src, mark the remaining
	 * collect srcs as partially live.
	 */
	if (n->collect) {
		struct ir3_instruction *src;
		foreach_ssa_src (src, n->collect) {
			if (src->block != instr->block)
				continue;
			struct ir3_sched_node *sn = src->data;
			sn->partially_live = true;
		}
	}

	dag_prune_head(ctx->dag, &n->dag);
}

struct ir3_sched_notes {
	/* there is at least one kill which could be scheduled, except
	 * for unscheduled bary.f's:
	 */
	bool blocked_kill;
	/* there is at least one instruction that could be scheduled,
	 * except for conflicting address/predicate register usage:
	 */
	bool addr0_conflict, addr1_conflict, pred_conflict;
};

/* could an instruction be scheduled if specified ssa src was scheduled? */
static bool
could_sched(struct ir3_instruction *instr, struct ir3_instruction *src)
{
	struct ir3_instruction *other_src;
	foreach_ssa_src (other_src, instr) {
		/* if dependency not scheduled, we aren't ready yet: */
		if ((src != other_src) && !is_scheduled(other_src)) {
			return false;
		}
	}
	return true;
}

/* Check if instruction is ok to schedule.  Make sure it is not blocked
 * by use of addr/predicate register, etc.
 */
static bool
check_instr(struct ir3_sched_ctx *ctx, struct ir3_sched_notes *notes,
		struct ir3_instruction *instr)
{
	debug_assert(!is_scheduled(instr));

	if (ctx->remaining_kills && (is_tex(instr) || is_mem(instr))) {
		/* avoid texture/memory access if we have unscheduled kills
		 * that could make the expensive operation unnecessary.  By
		 * definition, if there are remaining kills, and this instr
		 * is not a dependency of a kill, there are other instructions
		 * that we can choose from.
		 */
		struct ir3_sched_node *n = instr->data;
		if (!n->kill_path)
			return false;
	}

	/* For instructions that write address register we need to
	 * make sure there is at least one instruction that uses the
	 * addr value which is otherwise ready.
	 *
	 * NOTE if any instructions use pred register and have other
	 * src args, we would need to do the same for writes_pred()..
	 */
	if (writes_addr0(instr)) {
		struct ir3 *ir = instr->block->shader;
		bool ready = false;
		for (unsigned i = 0; (i < ir->a0_users_count) && !ready; i++) {
			struct ir3_instruction *indirect = ir->a0_users[i];
			if (!indirect)
				continue;
			if (indirect->address != instr)
				continue;
			ready = could_sched(indirect, instr);
		}

		/* nothing could be scheduled, so keep looking: */
		if (!ready)
			return false;
	}

	if (writes_addr1(instr)) {
		struct ir3 *ir = instr->block->shader;
		bool ready = false;
		for (unsigned i = 0; (i < ir->a1_users_count) && !ready; i++) {
			struct ir3_instruction *indirect = ir->a1_users[i];
			if (!indirect)
				continue;
			if (indirect->address != instr)
				continue;
			ready = could_sched(indirect, instr);
		}

		/* nothing could be scheduled, so keep looking: */
		if (!ready)
			return false;
	}

	/* if this is a write to address/predicate register, and that
	 * register is currently in use, we need to defer until it is
	 * free:
	 */
	if (writes_addr0(instr) && ctx->addr0) {
		debug_assert(ctx->addr0 != instr);
		notes->addr0_conflict = true;
		return false;
	}

	if (writes_addr1(instr) && ctx->addr1) {
		debug_assert(ctx->addr1 != instr);
		notes->addr1_conflict = true;
		return false;
	}

	if (writes_pred(instr) && ctx->pred) {
		debug_assert(ctx->pred != instr);
		notes->pred_conflict = true;
		return false;
	}

	/* if the instruction is a kill, we need to ensure *every*
	 * bary.f is scheduled.  The hw seems unhappy if the thread
	 * gets killed before the end-input (ei) flag is hit.
	 *
	 * We could do this by adding each bary.f instruction as
	 * virtual ssa src for the kill instruction.  But we have
	 * fixed length instr->regs[].
	 *
	 * TODO we could handle this by false-deps now, probably.
	 */
	if (is_kill(instr)) {
		struct ir3 *ir = instr->block->shader;

		for (unsigned i = 0; i < ir->baryfs_count; i++) {
			struct ir3_instruction *baryf = ir->baryfs[i];
			if (baryf->flags & IR3_INSTR_UNUSED)
				continue;
			if (!is_scheduled(baryf)) {
				notes->blocked_kill = true;
				return false;
			}
		}
	}

	return true;
}

/* Find the instr->ip of the closest use of an instruction, in
 * pre-sched order.  This isn't going to be the same as post-sched
 * order, but it is a reasonable approximation to limit scheduling
 * instructions *too* early.  This is mostly to prevent bad behavior
 * in cases where we have a large number of possible instructions
 * to choose, to avoid creating too much parallelism (ie. blowing
 * up register pressure)
 *
 * See dEQP-GLES31.functional.atomic_counter.layout.reverse_offset.inc_dec.8_counters_5_calls_1_thread
 */
static int
nearest_use(struct ir3_instruction *instr)
{
	unsigned nearest = ~0;
	foreach_ssa_use (use, instr)
		if (!is_scheduled(use))
			nearest = MIN2(nearest, use->ip);

	/* slight hack.. this heuristic tends to push bary.f's to later
	 * in the shader, closer to their uses.  But we actually would
	 * prefer to get these scheduled earlier, to unlock varying
	 * storage for more VS jobs:
	 */
	if (is_input(instr))
		nearest /= 2;

	return nearest;
}

static int
use_count(struct ir3_instruction *instr)
{
	unsigned cnt = 0;
	foreach_ssa_use (use, instr)
		if (!is_scheduled(use))
			cnt++;
	return cnt;
}

/* find net change to live values if instruction were scheduled: */
static int
live_effect(struct ir3_instruction *instr)
{
	struct ir3_sched_node *n = instr->data;
	struct ir3_instruction *src;
	int new_live = n->partially_live ? 0 : dest_regs(instr);
	int freed_live = 0;

	/* if we schedule something that causes a vecN to be live,
	 * then count all it's other components too:
	 */
	if (n->collect)
		new_live *= n->collect->regs_count - 1;

	foreach_ssa_src_n (src, n, instr) {
		if (__is_false_dep(instr, n))
			continue;

		if (instr->block != src->block)
			continue;

		if (use_count(src) == 1)
			freed_live += dest_regs(src);
	}

	return new_live - freed_live;
}

/**
 * Chooses an instruction to schedule using the Goodman/Hsu (1988) CSR (Code
 * Scheduling for Register pressure) heuristic.
 */
static struct ir3_sched_node *
choose_instr_csr(struct ir3_sched_ctx *ctx, struct ir3_sched_notes *notes)
{
	struct ir3_sched_node *chosen = NULL;

	/* Find a ready inst with regs freed and pick the one with max cost. */
	foreach_sched_node (n, &ctx->dag->heads) {
		unsigned d = ir3_delay_calc(ctx->block, n->instr, false, false);

		if (d > 0)
			continue;

		if (live_effect(n->instr) > -1)
			continue;

		if (!check_instr(ctx, notes, n->instr))
			continue;

		if (!chosen || chosen->max_delay < n->max_delay) {
			chosen = n;
		}
	}

	if (chosen) {
		di(chosen->instr, "csr: chose (freed+ready)");
		return chosen;
	}

	/* Find a leader with regs freed and pick the one with max cost. */
	foreach_sched_node (n, &ctx->dag->heads) {
		if (live_effect(n->instr) > -1)
			continue;

		if (!check_instr(ctx, notes, n->instr))
			continue;

		if (!chosen || chosen->max_delay < n->max_delay) {
			chosen = n;
		}
	}

	if (chosen) {
		di(chosen->instr, "csr: chose (freed)");
		return chosen;
	}

	/* Contra the paper, pick a leader with no effect on used regs.  This may
	 * open up new opportunities, as otherwise a single-operand instr consuming
	 * a value will tend to block finding freeing that value.  This had a
	 * massive effect on reducing spilling on V3D.
	 *
	 * XXX: Should this prioritize ready?
	 */
	foreach_sched_node (n, &ctx->dag->heads) {
		unsigned d = ir3_delay_calc(ctx->block, n->instr, false, false);

		if (d > 0)
			continue;

		if (live_effect(n->instr) > 0)
			continue;

		if (!check_instr(ctx, notes, n->instr))
			continue;

		if (!chosen || chosen->max_delay < n->max_delay)
			chosen = n;
	}

	if (chosen) {
		di(chosen->instr, "csr: chose (neutral+ready)");
		return chosen;
	}

	foreach_sched_node (n, &ctx->dag->heads) {
		if (live_effect(n->instr) > 0)
			continue;

		if (!check_instr(ctx, notes, n->instr))
			continue;

		if (!chosen || chosen->max_delay < n->max_delay)
			chosen = n;
	}

	if (chosen) {
		di(chosen->instr, "csr: chose (neutral)");
		return chosen;
	}

	/*
	 * From hear on out, we are picking something that increases
	 * register pressure.  So try to pick something which will
	 * be consumed soon:
	 */
	unsigned chosen_distance = 0;

	/* Pick the max delay of the remaining ready set. */
	foreach_sched_node (n, &ctx->dag->heads) {
		unsigned d = ir3_delay_calc(ctx->block, n->instr, false, false);

		if (d > 0)
			continue;

		if (!check_instr(ctx, notes, n->instr))
			continue;

		unsigned distance = nearest_use(n->instr);

		if (!chosen || distance < chosen_distance) {
			chosen = n;
			chosen_distance = distance;
		}
	}

	if (chosen) {
		di(chosen->instr, "csr: chose (distance+ready)");
		return chosen;
	}

	/* Pick the max delay of the remaining leaders. */
	foreach_sched_node (n, &ctx->dag->heads) {
		if (!check_instr(ctx, notes, n->instr))
			continue;

		unsigned distance = nearest_use(n->instr);

		if (!chosen || distance < chosen_distance) {
			chosen = n;
			chosen_distance = distance;
		}
	}

	if (chosen) {
		di(chosen->instr, "csr: chose (distance)");
		return chosen;
	}

	return NULL;
}

/* Handles instruction selections for instructions we want to prioritize
 * even if csp/csr would not pick them.
 */
static struct ir3_sched_node *
choose_instr_prio(struct ir3_sched_ctx *ctx, struct ir3_sched_notes *notes)
{
	struct ir3_sched_node *chosen = NULL;

	foreach_sched_node (n, &ctx->dag->heads) {
		if (!is_meta(n->instr))
			continue;

		if (!chosen || (chosen->max_delay < n->max_delay))
			chosen = n;
	}

	if (chosen) {
		di(chosen->instr, "prio: chose (meta)");
		return chosen;
	}

	return NULL;
}

static void
dump_state(struct ir3_sched_ctx *ctx)
{
	if (!SCHED_DEBUG)
		return;

	foreach_sched_node (n, &ctx->dag->heads) {
		di(n->instr, "maxdel=%3d le=%d del=%u ",
				n->max_delay, live_effect(n->instr),
				ir3_delay_calc(ctx->block, n->instr, false, false));

		util_dynarray_foreach(&n->dag.edges, struct dag_edge, edge) {
			struct ir3_sched_node *child = (struct ir3_sched_node *)edge->child;

			di(child->instr, " -> (%d parents) ", child->dag.parent_count);
		}
	}
}

/* find instruction to schedule: */
static struct ir3_instruction *
choose_instr(struct ir3_sched_ctx *ctx, struct ir3_sched_notes *notes)
{
	struct ir3_sched_node *chosen;

	dump_state(ctx);

	chosen = choose_instr_prio(ctx, notes);
	if (chosen)
		return chosen->instr;

	chosen = choose_instr_csr(ctx, notes);
	if (chosen)
		return chosen->instr;

	return NULL;
}

static struct ir3_instruction *
split_instr(struct ir3_sched_ctx *ctx, struct ir3_instruction *orig_instr)
{
	struct ir3_instruction *new_instr = ir3_instr_clone(orig_instr);
	di(new_instr, "split instruction");
	sched_node_init(ctx, new_instr);
	return new_instr;
}

/* "spill" the address registers by remapping any unscheduled
 * instructions which depend on the current address register
 * to a clone of the instruction which wrote the address reg.
 */
static struct ir3_instruction *
split_addr(struct ir3_sched_ctx *ctx, struct ir3_instruction **addr,
		   struct ir3_instruction **users, unsigned users_count)
{
	struct ir3_instruction *new_addr = NULL;
	unsigned i;

	debug_assert(*addr);

	for (i = 0; i < users_count; i++) {
		struct ir3_instruction *indirect = users[i];

		if (!indirect)
			continue;

		/* skip instructions already scheduled: */
		if (is_scheduled(indirect))
			continue;

		/* remap remaining instructions using current addr
		 * to new addr:
		 */
		if (indirect->address == *addr) {
			if (!new_addr) {
				new_addr = split_instr(ctx, *addr);
				/* original addr is scheduled, but new one isn't: */
				new_addr->flags &= ~IR3_INSTR_MARK;
			}
			indirect->address = new_addr;
			/* don't need to remove old dag edge since old addr is
			 * already scheduled:
			 */
			sched_node_add_dep(indirect, new_addr, 0);
			di(indirect, "new address");
		}
	}

	/* all remaining indirects remapped to new addr: */
	*addr = NULL;

	return new_addr;
}

/* "spill" the predicate register by remapping any unscheduled
 * instructions which depend on the current predicate register
 * to a clone of the instruction which wrote the address reg.
 */
static struct ir3_instruction *
split_pred(struct ir3_sched_ctx *ctx)
{
	struct ir3 *ir;
	struct ir3_instruction *new_pred = NULL;
	unsigned i;

	debug_assert(ctx->pred);

	ir = ctx->pred->block->shader;

	for (i = 0; i < ir->predicates_count; i++) {
		struct ir3_instruction *predicated = ir->predicates[i];

		/* skip instructions already scheduled: */
		if (is_scheduled(predicated))
			continue;

		/* remap remaining instructions using current pred
		 * to new pred:
		 *
		 * TODO is there ever a case when pred isn't first
		 * (and only) src?
		 */
		if (ssa(predicated->regs[1]) == ctx->pred) {
			if (!new_pred) {
				new_pred = split_instr(ctx, ctx->pred);
				/* original pred is scheduled, but new one isn't: */
				new_pred->flags &= ~IR3_INSTR_MARK;
			}
			predicated->regs[1]->instr = new_pred;
			/* don't need to remove old dag edge since old pred is
			 * already scheduled:
			 */
			sched_node_add_dep(predicated, new_pred, 0);
			di(predicated, "new predicate");
		}
	}

	/* all remaining predicated remapped to new pred: */
	ctx->pred = NULL;

	return new_pred;
}

static void
sched_node_init(struct ir3_sched_ctx *ctx, struct ir3_instruction *instr)
{
	struct ir3_sched_node *n = rzalloc(ctx->dag, struct ir3_sched_node);

	dag_init_node(ctx->dag, &n->dag);

	n->instr = instr;
	instr->data = n;
}

static void
sched_node_add_dep(struct ir3_instruction *instr, struct ir3_instruction *src, int i)
{
	/* don't consider dependencies in other blocks: */
	if (src->block != instr->block)
		return;

	/* we could have false-dep's that end up unused: */
	if (src->flags & IR3_INSTR_UNUSED) {
		debug_assert(__is_false_dep(instr, i));
		return;
	}

	struct ir3_sched_node *n = instr->data;
	struct ir3_sched_node *sn = src->data;

	/* If src is consumed by a collect, track that to realize that once
	 * any of the collect srcs are live, we should hurry up and schedule
	 * the rest.
	 */
	if (instr->opc == OPC_META_COLLECT)
		sn->collect = instr;

	dag_add_edge(&sn->dag, &n->dag, NULL);

	unsigned d = ir3_delayslots(src, instr, i, true);
	n->delay = MAX2(n->delay, d);
}

static void
mark_kill_path(struct ir3_instruction *instr)
{
	struct ir3_sched_node *n = instr->data;
	n->kill_path = true;
	struct ir3_instruction *src;
	foreach_ssa_src (src, instr) {
		if (src->block != instr->block)
			continue;
		mark_kill_path(src);
	}
}

static void
sched_node_add_deps(struct ir3_instruction *instr)
{
	struct ir3_instruction *src;

	/* Since foreach_ssa_src() already handles false-dep's we can construct
	 * the DAG easily in a single pass.
	 */
	foreach_ssa_src_n (src, i, instr) {
		sched_node_add_dep(instr, src, i);
	}

	/* NOTE that all inputs must be scheduled before a kill, so
	 * mark these to be prioritized as well:
	 */
	if (is_kill(instr) || is_input(instr)) {
		mark_kill_path(instr);
	}
}

static void
sched_dag_max_delay_cb(struct dag_node *node, void *state)
{
	struct ir3_sched_node *n = (struct ir3_sched_node *)node;
	uint32_t max_delay = 0;

	util_dynarray_foreach(&n->dag.edges, struct dag_edge, edge) {
		struct ir3_sched_node *child = (struct ir3_sched_node *)edge->child;
		max_delay = MAX2(child->max_delay, max_delay);
	}

	n->max_delay = MAX2(n->max_delay, max_delay + n->delay);
}

static void
sched_dag_init(struct ir3_sched_ctx *ctx)
{
	ctx->dag = dag_create(ctx);

	foreach_instr (instr, &ctx->unscheduled_list) {
		sched_node_init(ctx, instr);
		sched_node_add_deps(instr);
	}

	dag_traverse_bottom_up(ctx->dag, sched_dag_max_delay_cb, NULL);
}

static void
sched_dag_destroy(struct ir3_sched_ctx *ctx)
{
	ralloc_free(ctx->dag);
	ctx->dag = NULL;
}

static void
sched_block(struct ir3_sched_ctx *ctx, struct ir3_block *block)
{
	ctx->block = block;

	/* addr/pred writes are per-block: */
	ctx->addr0 = NULL;
	ctx->addr1 = NULL;
	ctx->pred = NULL;

	/* move all instructions to the unscheduled list, and
	 * empty the block's instruction list (to which we will
	 * be inserting).
	 */
	list_replace(&block->instr_list, &ctx->unscheduled_list);
	list_inithead(&block->instr_list);

	sched_dag_init(ctx);

	ctx->remaining_kills = 0;
	foreach_instr_safe (instr, &ctx->unscheduled_list) {
		if (is_kill(instr))
			ctx->remaining_kills++;
	}

	/* First schedule all meta:input instructions, followed by
	 * tex-prefetch.  We want all of the instructions that load
	 * values into registers before the shader starts to go
	 * before any other instructions.  But in particular we
	 * want inputs to come before prefetches.  This is because
	 * a FS's bary_ij input may not actually be live in the
	 * shader, but it should not be scheduled on top of any
	 * other input (but can be overwritten by a tex prefetch)
	 */
	foreach_instr_safe (instr, &ctx->unscheduled_list)
		if (instr->opc == OPC_META_INPUT)
			schedule(ctx, instr);

	foreach_instr_safe (instr, &ctx->unscheduled_list)
		if (instr->opc == OPC_META_TEX_PREFETCH)
			schedule(ctx, instr);

	while (!list_is_empty(&ctx->unscheduled_list)) {
		struct ir3_sched_notes notes = {0};
		struct ir3_instruction *instr;

		instr = choose_instr(ctx, &notes);
		if (instr) {
			unsigned delay = ir3_delay_calc(ctx->block, instr, false, false);
			d("delay=%u", delay);

			/* and if we run out of instructions that can be scheduled,
			 * then it is time for nop's:
			 */
			debug_assert(delay <= 6);
			while (delay > 0) {
				ir3_NOP(block);
				delay--;
			}

			schedule(ctx, instr);
		} else {
			struct ir3_instruction *new_instr = NULL;
			struct ir3 *ir = block->shader;

			/* nothing available to schedule.. if we are blocked on
			 * address/predicate register conflict, then break the
			 * deadlock by cloning the instruction that wrote that
			 * reg:
			 */
			if (notes.addr0_conflict) {
				new_instr = split_addr(ctx, &ctx->addr0,
									   ir->a0_users, ir->a0_users_count);
			} else if (notes.addr1_conflict) {
				new_instr = split_addr(ctx, &ctx->addr1,
									   ir->a1_users, ir->a1_users_count);
			} else if (notes.pred_conflict) {
				new_instr = split_pred(ctx);
			} else {
				d("unscheduled_list:");
				foreach_instr (instr, &ctx->unscheduled_list)
					di(instr, "unscheduled: ");
				debug_assert(0);
				ctx->error = true;
				return;
			}

			if (new_instr) {
				list_delinit(&new_instr->node);
				list_addtail(&new_instr->node, &ctx->unscheduled_list);
			}
		}
	}

	sched_dag_destroy(ctx);
}

int ir3_sched(struct ir3 *ir)
{
	struct ir3_sched_ctx *ctx = rzalloc(NULL, struct ir3_sched_ctx);

	foreach_block (block, &ir->block_list) {
		foreach_instr (instr, &block->instr_list) {
			instr->data = NULL;
		}
	}

	ir3_count_instructions(ir);
	ir3_clear_mark(ir);
	ir3_find_ssa_uses(ir, ctx, false);

	foreach_block (block, &ir->block_list) {
		sched_block(ctx, block);
	}

	int ret = ctx->error ? -1 : 0;

	ralloc_free(ctx);

	return ret;
}

static unsigned
get_array_id(struct ir3_instruction *instr)
{
	/* The expectation is that there is only a single array
	 * src or dst, ir3_cp should enforce this.
	 */

	for (unsigned i = 0; i < instr->regs_count; i++)
		if (instr->regs[i]->flags & IR3_REG_ARRAY)
			return instr->regs[i]->array.id;

	unreachable("this was unexpected");
}

/* does instruction 'prior' need to be scheduled before 'instr'? */
static bool
depends_on(struct ir3_instruction *instr, struct ir3_instruction *prior)
{
	/* TODO for dependencies that are related to a specific object, ie
	 * a specific SSBO/image/array, we could relax this constraint to
	 * make accesses to unrelated objects not depend on each other (at
	 * least as long as not declared coherent)
	 */
	if (((instr->barrier_class & IR3_BARRIER_EVERYTHING) && prior->barrier_class) ||
			((prior->barrier_class & IR3_BARRIER_EVERYTHING) && instr->barrier_class))
		return true;

	if (instr->barrier_class & prior->barrier_conflict) {
		if (!(instr->barrier_class & ~(IR3_BARRIER_ARRAY_R | IR3_BARRIER_ARRAY_W))) {
			/* if only array barrier, then we can further limit false-deps
			 * by considering the array-id, ie reads/writes to different
			 * arrays do not depend on each other (no aliasing)
			 */
			if (get_array_id(instr) != get_array_id(prior)) {
				return false;
			}
		}

		return true;
	}

	return false;
}

static void
add_barrier_deps(struct ir3_block *block, struct ir3_instruction *instr)
{
	struct list_head *prev = instr->node.prev;
	struct list_head *next = instr->node.next;

	/* add dependencies on previous instructions that must be scheduled
	 * prior to the current instruction
	 */
	while (prev != &block->instr_list) {
		struct ir3_instruction *pi =
			LIST_ENTRY(struct ir3_instruction, prev, node);

		prev = prev->prev;

		if (is_meta(pi))
			continue;

		if (instr->barrier_class == pi->barrier_class) {
			ir3_instr_add_dep(instr, pi);
			break;
		}

		if (depends_on(instr, pi))
			ir3_instr_add_dep(instr, pi);
	}

	/* add dependencies on this instruction to following instructions
	 * that must be scheduled after the current instruction:
	 */
	while (next != &block->instr_list) {
		struct ir3_instruction *ni =
			LIST_ENTRY(struct ir3_instruction, next, node);

		next = next->next;

		if (is_meta(ni))
			continue;

		if (instr->barrier_class == ni->barrier_class) {
			ir3_instr_add_dep(ni, instr);
			break;
		}

		if (depends_on(ni, instr))
			ir3_instr_add_dep(ni, instr);
	}
}

/* before scheduling a block, we need to add any necessary false-dependencies
 * to ensure that:
 *
 *  (1) barriers are scheduled in the right order wrt instructions related
 *      to the barrier
 *
 *  (2) reads that come before a write actually get scheduled before the
 *      write
 */
static void
calculate_deps(struct ir3_block *block)
{
	foreach_instr (instr, &block->instr_list) {
		if (instr->barrier_class) {
			add_barrier_deps(block, instr);
		}
	}
}

void
ir3_sched_add_deps(struct ir3 *ir)
{
	foreach_block (block, &ir->block_list) {
		calculate_deps(block);
	}
}