freedreno/ir3: convert block->predecessors to set

[mesa.git] / 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/u_math.h"

#include "ir3.h"

/*
 * Instruction Scheduling:
 *
 * A recursive depth based scheduling algo.  Recursively find an eligible
 * instruction to schedule from the deepest instruction (recursing through
 * it's unscheduled src instructions).  Normally this would result in a
 * lot of re-traversal of the same instructions, so we cache results in
 * instr->data (and clear cached results that would be no longer valid
 * after scheduling an instruction).
 *
 * 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.
 */

struct ir3_sched_ctx {
        struct ir3_block *block;           /* the current block */
        struct list_head depth_list;       /* depth sorted unscheduled instrs */
        struct ir3_instruction *scheduled; /* last scheduled instr XXX remove*/
        struct ir3_instruction *addr;      /* current a0.x user, if any */
        struct ir3_instruction *pred;      /* current p0.x user, if any */
        int live_values;                   /* estimate of current live values */
        bool error;
};

static bool is_sfu_or_mem(struct ir3_instruction *instr)
{
        return is_sfu(instr) || is_mem(instr);
}

static void
unuse_each_src(struct ir3_sched_ctx *ctx, struct ir3_instruction *instr)
{
        struct ir3_instruction *src;

        foreach_ssa_src_n(src, n, instr) {
                if (__is_false_dep(instr, n))
                        continue;
                if (instr->block != src->block)
                        continue;
                if ((src->opc == OPC_META_FI) || (src->opc == OPC_META_FO)) {
                        unuse_each_src(ctx, src);
                } else {
                        debug_assert(src->use_count > 0);

                        if (--src->use_count == 0) {
                                ctx->live_values -= dest_regs(src);
                                debug_assert(ctx->live_values >= 0);
                        }
                }
        }
}

static void use_instr(struct ir3_instruction *instr);

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

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

static void
use_instr(struct ir3_instruction *instr)
{
        if ((instr->opc == OPC_META_FI) || (instr->opc == OPC_META_FO)) {
                use_each_src(instr);
        } else {
                instr->use_count++;
        }
}

static void
update_live_values(struct ir3_sched_ctx *ctx, struct ir3_instruction *instr)
{
        if ((instr->opc == OPC_META_FI) || (instr->opc == OPC_META_FO))
                return;

        ctx->live_values += dest_regs(instr);
        unuse_each_src(ctx, instr);
}

static void
update_use_count(struct ir3 *ir)
{
        list_for_each_entry (struct ir3_block, block, &ir->block_list, node) {
                list_for_each_entry (struct ir3_instruction, instr, &block->instr_list, node) {
                        instr->use_count = 0;
                }
        }

        list_for_each_entry (struct ir3_block, block, &ir->block_list, node) {
                list_for_each_entry (struct ir3_instruction, instr, &block->instr_list, node) {
                        if ((instr->opc == OPC_META_FI) || (instr->opc == OPC_META_FO))
                                continue;

                        use_each_src(instr);
                }
        }

        /* Shader outputs are also used:
         */
        for (unsigned i = 0; i <  ir->noutputs; i++) {
                struct ir3_instruction  *out = ir->outputs[i];

                if (!out)
                        continue;

                use_instr(out);
        }
}

#define NULL_INSTR ((void *)~0)

static void
clear_cache(struct ir3_sched_ctx *ctx, struct ir3_instruction *instr)
{
        list_for_each_entry (struct ir3_instruction, instr2, &ctx->depth_list, node) {
                if ((instr2->data == instr) || (instr2->data == NULL_INSTR) || !instr)
                        instr2->data = NULL;
        }
}

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

        /* maybe there is a better way to handle this than just stuffing
         * a nop.. ideally we'd know about this constraint in the
         * scheduling and depth calculation..
         */
        if (ctx->scheduled && is_sfu_or_mem(ctx->scheduled) && is_sfu_or_mem(instr))
                ir3_NOP(ctx->block);

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

        if (writes_addr(instr)) {
                debug_assert(ctx->addr == NULL);
                ctx->addr = instr;
        }

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

        instr->flags |= IR3_INSTR_MARK;

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

        update_live_values(ctx, instr);

        if (writes_addr(instr) || writes_pred(instr) || is_input(instr)) {
                clear_cache(ctx, NULL);
        } else {
                /* invalidate only the necessary entries.. */
                clear_cache(ctx, instr);
        }
}

static struct ir3_instruction *
deepest(struct ir3_instruction **srcs, unsigned nsrcs)
{
        struct ir3_instruction *d = NULL;
        unsigned i = 0, id = 0;

        while ((i < nsrcs) && !(d = srcs[id = i]))
                i++;

        if (!d)
                return NULL;

        for (; i < nsrcs; i++)
                if (srcs[i] && (srcs[i]->depth > d->depth))
                        d = srcs[id = i];

        srcs[id] = NULL;

        return d;
}

/**
 * @block: the block to search in, starting from end; in first pass,
 *    this will be the block the instruction would be inserted into
 *    (but has not yet, ie. it only contains already scheduled
 *    instructions).  For intra-block scheduling (second pass), this
 *    would be one of the predecessor blocks.
 * @instr: the instruction to search for
 * @maxd:  max distance, bail after searching this # of instruction
 *    slots, since it means the instruction we are looking for is
 *    far enough away
 * @pred:  if true, recursively search into predecessor blocks to
 *    find the worst case (shortest) distance (only possible after
 *    individual blocks are all scheduled
 */
static unsigned
distance(struct ir3_block *block, struct ir3_instruction *instr,
                unsigned maxd, bool pred)
{
        unsigned d = 0;

        list_for_each_entry_rev (struct ir3_instruction, n, &block->instr_list, node) {
                if ((n == instr) || (d >= maxd))
                        return d;
                /* NOTE: don't count branch/jump since we don't know yet if they will
                 * be eliminated later in resolve_jumps().. really should do that
                 * earlier so we don't have this constraint.
                 */
                if (is_alu(n) || (is_flow(n) && (n->opc != OPC_JUMP) && (n->opc != OPC_BR)))
                        d++;
        }

        /* if coming from a predecessor block, assume it is assigned far
         * enough away.. we'll fix up later.
         */
        if (!pred)
                return maxd;

        if (pred && (block->data != block)) {
                /* Search into predecessor blocks, finding the one with the
                 * shortest distance, since that will be the worst case
                 */
                unsigned min = maxd - d;

                /* (ab)use block->data to prevent recursion: */
                block->data = block;

                set_foreach(block->predecessors, entry) {
                        struct ir3_block *pred = (struct ir3_block *)entry->key;
                        unsigned n;

                        n = distance(pred, instr, min, pred);

                        min = MIN2(min, n);
                }

                block->data = NULL;
                d += min;
        }

        return d;
}

/* calculate delay for specified src: */
static unsigned
delay_calc_srcn(struct ir3_block *block,
                struct ir3_instruction *assigner,
                struct ir3_instruction *consumer,
                unsigned srcn, bool soft, bool pred)
{
        unsigned delay = 0;

        if (is_meta(assigner)) {
                struct ir3_instruction *src;
                foreach_ssa_src(src, assigner) {
                        unsigned d;
                        d = delay_calc_srcn(block, src, consumer, srcn, soft, pred);
                        delay = MAX2(delay, d);
                }
        } else {
                if (soft) {
                        if (is_sfu(assigner)) {
                                delay = 4;
                        } else {
                                delay = ir3_delayslots(assigner, consumer, srcn);
                        }
                } else {
                        delay = ir3_delayslots(assigner, consumer, srcn);
                }
                delay -= distance(block, assigner, delay, pred);
        }

        return delay;
}

/* calculate delay for instruction (maximum of delay for all srcs): */
static unsigned
delay_calc(struct ir3_block *block, struct ir3_instruction *instr,
                bool soft, bool pred)
{
        unsigned delay = 0;
        struct ir3_instruction *src;

        foreach_ssa_src_n(src, i, instr) {
                unsigned d;
                d = delay_calc_srcn(block, src, instr, i, soft, pred);
                delay = MAX2(delay, d);
        }

        return delay;
}

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 addr_conflict, pred_conflict;
};

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

/* 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)
{
        /* 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.
         *
         * TODO if any instructions use pred register and have other
         * src args, we would need to do the same for writes_pred()..
         */
        if (writes_addr(instr)) {
                struct ir3 *ir = instr->block->shader;
                bool ready = false;
                for (unsigned i = 0; (i < ir->indirects_count) && !ready; i++) {
                        struct ir3_instruction *indirect = ir->indirects[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_addr(instr) && ctx->addr) {
                debug_assert(ctx->addr != instr);
                notes->addr_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 this wouldn't be quite right if we had multiple
         * basic blocks, if any block was conditional.  We'd need
         * to schedule the bary.f's outside of any block which
         * was conditional that contained a kill.. I think..
         */
        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 best instruction to schedule from specified instruction or
 * recursively it's ssa sources.
 */
static struct ir3_instruction *
find_instr_recursive(struct ir3_sched_ctx *ctx, struct ir3_sched_notes *notes,
                struct ir3_instruction *instr)
{
        struct ir3_instruction *srcs[__ssa_src_cnt(instr)];
        struct ir3_instruction *src;
        unsigned nsrcs = 0;

        if (is_scheduled(instr))
                return NULL;

        /* use instr->data to cache the results of recursing up the
         * instr src's.  Otherwise the recursive algo can scale quite
         * badly w/ shader size.  But this takes some care to clear
         * the cache appropriately when instructions are scheduled.
         */
        if (instr->data) {
                if (instr->data == NULL_INSTR)
                        return NULL;
                return instr->data;
        }

        /* find unscheduled srcs: */
        foreach_ssa_src(src, instr) {
                if (!is_scheduled(src) && (src->block == instr->block)) {
                        debug_assert(nsrcs < ARRAY_SIZE(srcs));
                        srcs[nsrcs++] = src;
                }
        }

        /* if all our src's are already scheduled: */
        if (nsrcs == 0) {
                if (check_instr(ctx, notes, instr)) {
                        instr->data = instr;
                        return instr;
                }
                return NULL;
        }

        while ((src = deepest(srcs, nsrcs))) {
                struct ir3_instruction *candidate;

                candidate = find_instr_recursive(ctx, notes, src);
                if (!candidate)
                        continue;

                if (check_instr(ctx, notes, candidate)) {
                        instr->data = candidate;
                        return candidate;
                }
        }

        instr->data = NULL_INSTR;
        return NULL;
}

/* find net change to live values if instruction were scheduled: */
static int
live_effect(struct ir3_instruction *instr)
{
        struct ir3_instruction *src;
        int new_live = dest_regs(instr);
        int old_live = 0;

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

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

                /* for fanout/split, just pass things along to the real src: */
                if (src->opc == OPC_META_FO)
                        src = ssa(src->regs[1]);

                /* for fanin/collect, if this is the last use of *each* src,
                 * then it will decrease the live values, since RA treats
                 * them as a whole:
                 */
                if (src->opc == OPC_META_FI) {
                        struct ir3_instruction *src2;
                        bool last_use = true;

                        foreach_ssa_src(src2, src) {
                                if (src2->use_count > 1) {
                                        last_use = false;
                                        break;
                                }
                        }

                        if (last_use)
                                old_live += dest_regs(src);

                } else {
                        debug_assert(src->use_count > 0);

                        if (src->use_count == 1) {
                                old_live += dest_regs(src);
                        }
                }
        }

        return new_live - old_live;
}

/* find instruction to schedule: */
static struct ir3_instruction *
find_eligible_instr(struct ir3_sched_ctx *ctx, struct ir3_sched_notes *notes,
                bool soft)
{
        struct ir3_instruction *best_instr = NULL;
        int best_rank = INT_MAX;      /* lower is better */
        unsigned deepest = 0;

        /* TODO we'd really rather use the list/array of block outputs.  But we
         * don't have such a thing.  Recursing *every* instruction in the list
         * will result in a lot of repeated traversal, since instructions will
         * get traversed both when they appear as ssa src to a later instruction
         * as well as where they appear in the depth_list.
         */
        list_for_each_entry_rev (struct ir3_instruction, instr, &ctx->depth_list, node) {
                struct ir3_instruction *candidate;

                candidate = find_instr_recursive(ctx, notes, instr);
                if (!candidate)
                        continue;

                if (is_meta(candidate))
                        return candidate;

                deepest = MAX2(deepest, candidate->depth);
        }

        /* traverse the list a second time.. but since we cache the result of
         * find_instr_recursive() it isn't as bad as it looks.
         */
        list_for_each_entry_rev (struct ir3_instruction, instr, &ctx->depth_list, node) {
                struct ir3_instruction *candidate;

                candidate = find_instr_recursive(ctx, notes, instr);
                if (!candidate)
                        continue;

                /* determine net change to # of live values: */
                int le = live_effect(candidate);

                /* if there is a net increase in # of live values, then apply some
                 * threshold to avoid instructions getting scheduled *too* early
                 * and increasing register pressure.
                 */
                if (le >= 1) {
                        unsigned threshold;

                        if (ctx->live_values > 4*4) {
                                threshold = 4;
                        } else {
                                threshold = 6;
                        }

                        /* Filter out any "shallow" instructions which would otherwise
                         * tend to get scheduled too early to fill delay slots even
                         * when they are not needed for a while.  There will probably
                         * be later delay slots that they could just as easily fill.
                         *
                         * A classic case where this comes up is frag shaders that
                         * write a constant value (like 1.0f) to one of the channels
                         * of the output color(s).  Since the mov from immed has no
                         * dependencies, it would otherwise get scheduled early to
                         * fill delay slots, occupying a register until the end of
                         * the program.
                         */
                        if ((deepest - candidate->depth) > threshold)
                                continue;
                }

                int rank = delay_calc(ctx->block, candidate, soft, false);

                /* if too many live values, prioritize instructions that reduce the
                 * number of live values:
                 */
                if (ctx->live_values > 16*4) {
                        rank = le;
                } else if (ctx->live_values > 4*4) {
                        rank += le;
                }

                if (rank < best_rank) {
                        best_instr = candidate;
                        best_rank = rank;
                }
        }

        return best_instr;
}

/* "spill" the address register 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 *ir;
        struct ir3_instruction *new_addr = NULL;
        unsigned i;

        debug_assert(ctx->addr);

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

        for (i = 0; i < ir->indirects_count; i++) {
                struct ir3_instruction *indirect = ir->indirects[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 == ctx->addr) {
                        if (!new_addr) {
                                new_addr = ir3_instr_clone(ctx->addr);
                                /* original addr is scheduled, but new one isn't: */
                                new_addr->flags &= ~IR3_INSTR_MARK;
                        }
                        ir3_instr_set_address(indirect, new_addr);
                }
        }

        /* all remaining indirects remapped to new addr: */
        ctx->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 = ir3_instr_clone(ctx->pred);
                                /* original pred is scheduled, but new one isn't: */
                                new_pred->flags &= ~IR3_INSTR_MARK;
                        }
                        predicated->regs[1]->instr = new_pred;
                }
        }

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

        return new_pred;
}

static void
sched_block(struct ir3_sched_ctx *ctx, struct ir3_block *block)
{
        struct list_head unscheduled_list;

        ctx->block = block;

        /* addr/pred writes are per-block: */
        ctx->addr = 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, &unscheduled_list);
        list_inithead(&block->instr_list);
        list_inithead(&ctx->depth_list);

        /* first a pre-pass to schedule all meta:input instructions
         * (which need to appear first so that RA knows the register is
         * occupied), and move remaining to depth sorted list:
         */
        list_for_each_entry_safe (struct ir3_instruction, instr, &unscheduled_list, node) {
                if (instr->opc == OPC_META_INPUT) {
                        schedule(ctx, instr);
                } else {
                        ir3_insert_by_depth(instr, &ctx->depth_list);
                }
        }

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

                instr = find_eligible_instr(ctx, &notes, true);
                if (!instr)
                        instr = find_eligible_instr(ctx, &notes, false);

                if (instr) {
                        unsigned delay = delay_calc(ctx->block, instr, false, false);

                        /* 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;

                        /* 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.addr_conflict) {
                                new_instr = split_addr(ctx);
                        } else if (notes.pred_conflict) {
                                new_instr = split_pred(ctx);
                        } else {
                                debug_assert(0);
                                ctx->error = true;
                                return;
                        }

                        if (new_instr) {
                                /* clearing current addr/pred can change what is
                                 * available to schedule, so clear cache..
                                 */
                                clear_cache(ctx, NULL);

                                ir3_insert_by_depth(new_instr, &ctx->depth_list);
                                /* the original instr that wrote addr/pred may have
                                 * originated from a different block:
                                 */
                                new_instr->block = block;
                        }
                }
        }

        /* And lastly, insert branch/jump instructions to take us to
         * the next block.  Later we'll strip back out the branches
         * that simply jump to next instruction.
         */
        if (block->successors[1]) {
                /* if/else, conditional branches to "then" or "else": */
                struct ir3_instruction *br;
                unsigned delay = 6;

                debug_assert(ctx->pred);
                debug_assert(block->condition);

                delay -= distance(ctx->block, ctx->pred, delay, false);

                while (delay > 0) {
                        ir3_NOP(block);
                        delay--;
                }

                /* create "else" branch first (since "then" block should
                 * frequently/always end up being a fall-thru):
                 */
                br = ir3_BR(block);
                br->cat0.inv = true;
                br->cat0.target = block->successors[1];

                /* NOTE: we have to hard code delay of 6 above, since
                 * we want to insert the nop's before constructing the
                 * branch.  Throw in an assert so we notice if this
                 * ever breaks on future generation:
                 */
                debug_assert(ir3_delayslots(ctx->pred, br, 0) == 6);

                br = ir3_BR(block);
                br->cat0.target = block->successors[0];

        } else if (block->successors[0]) {
                /* otherwise unconditional jump to next block: */
                struct ir3_instruction *jmp;

                jmp = ir3_JUMP(block);
                jmp->cat0.target = block->successors[0];
        }

        /* NOTE: if we kept track of the predecessors, we could do a better
         * job w/ (jp) flags.. every node w/ > predecessor is a join point.
         * Note that as we eliminate blocks which contain only an unconditional
         * jump we probably need to propagate (jp) flag..
         */
}

/* After scheduling individual blocks, we still could have cases where
 * one (or more) paths into a block, a value produced by a previous
 * has too few delay slots to be legal.  We can't deal with this in the
 * first pass, because loops (ie. we can't ensure all predecessor blocks
 * are already scheduled in the first pass).  All we can really do at
 * this point is stuff in extra nop's until things are legal.
 */
static void
sched_intra_block(struct ir3_sched_ctx *ctx, struct ir3_block *block)
{
        unsigned n = 0;

        ctx->block = block;

        list_for_each_entry_safe (struct ir3_instruction, instr, &block->instr_list, node) {
                unsigned delay = 0;

                set_foreach(block->predecessors, entry) {
                        struct ir3_block *pred = (struct ir3_block *)entry->key;
                        unsigned d = delay_calc(pred, instr, false, true);
                        delay = MAX2(d, delay);
                }

                while (delay > n) {
                        struct ir3_instruction *nop = ir3_NOP(block);

                        /* move to before instr: */
                        list_delinit(&nop->node);
                        list_addtail(&nop->node, &instr->node);

                        n++;
                }

                /* we can bail once we hit worst case delay: */
                if (++n > 6)
                        break;
        }
}

int ir3_sched(struct ir3 *ir)
{
        struct ir3_sched_ctx ctx = {0};

        ir3_clear_mark(ir);
        update_use_count(ir);

        list_for_each_entry (struct ir3_block, block, &ir->block_list, node) {
                ctx.live_values = 0;
                sched_block(&ctx, block);
        }

        list_for_each_entry (struct ir3_block, block, &ir->block_list, node) {
                sched_intra_block(&ctx, block);
        }

        if (ctx.error)
                return -1;

        return 0;
}

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)
{
        list_for_each_entry (struct ir3_instruction, instr, &block->instr_list, node) {
                if (instr->barrier_class) {
                        add_barrier_deps(block, instr);
                }
        }
}

void
ir3_sched_add_deps(struct ir3 *ir)
{
        list_for_each_entry (struct ir3_block, block, &ir->block_list, node) {
                calculate_deps(block);
        }
}