[mesa.git] / src / panfrost / midgard / midgard_schedule.c

/*
 * Copyright (C) 2018-2019 Alyssa Rosenzweig <alyssa@rosenzweig.io>
 *
 * 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.
 */

#include "compiler.h"
#include "midgard_ops.h"
#include "midgard_quirks.h"
#include "util/u_memory.h"

/* Scheduling for Midgard is complicated, to say the least. ALU instructions
 * must be grouped into VLIW bundles according to following model:
 *
 * [VMUL] [SADD]
 * [VADD] [SMUL] [VLUT]
 *
 * A given instruction can execute on some subset of the units (or a few can
 * execute on all). Instructions can be either vector or scalar; only scalar
 * instructions can execute on SADD/SMUL units. Units on a given line execute
 * in parallel. Subsequent lines execute separately and can pass results
 * directly via pipeline registers r24/r25, bypassing the register file.
 *
 * A bundle can optionally have 128-bits of embedded constants, shared across
 * all of the instructions within a bundle.
 *
 * Instructions consuming conditionals (branches and conditional selects)
 * require their condition to be written into the conditional register (r31)
 * within the same bundle they are consumed.
 *
 * Fragment writeout requires its argument to be written in full within the
 * same bundle as the branch, with no hanging dependencies.
 *
 * Load/store instructions are also in bundles of simply two instructions, and
 * texture instructions have no bundling.
 *
 * -------------------------------------------------------------------------
 *
 */

/* We create the dependency graph with per-byte granularity */

#define BYTE_COUNT 16

static void
add_dependency(struct util_dynarray *table, unsigned index, uint16_t mask, midgard_instruction **instructions, unsigned child)
{
        for (unsigned i = 0; i < BYTE_COUNT; ++i) {
                if (!(mask & (1 << i)))
                        continue;

                struct util_dynarray *parents = &table[(BYTE_COUNT * index) + i];

                util_dynarray_foreach(parents, unsigned, parent) {
                        BITSET_WORD *dependents = instructions[*parent]->dependents;

                        /* Already have the dependency */
                        if (BITSET_TEST(dependents, child))
                                continue;

                        BITSET_SET(dependents, child);
                        instructions[child]->nr_dependencies++;
                }
        }
}

static void
mark_access(struct util_dynarray *table, unsigned index, uint16_t mask, unsigned parent)
{
        for (unsigned i = 0; i < BYTE_COUNT; ++i) {
                if (!(mask & (1 << i)))
                        continue;

                util_dynarray_append(&table[(BYTE_COUNT * index) + i], unsigned, parent);
        }
}

static void
mir_create_dependency_graph(midgard_instruction **instructions, unsigned count, unsigned node_count)
{
        size_t sz = node_count * BYTE_COUNT;

        struct util_dynarray *last_read = calloc(sizeof(struct util_dynarray), sz);
        struct util_dynarray *last_write = calloc(sizeof(struct util_dynarray), sz);

        for (unsigned i = 0; i < sz; ++i) {
                util_dynarray_init(&last_read[i], NULL);
                util_dynarray_init(&last_write[i], NULL);
        }

        /* Initialize dependency graph */
        for (unsigned i = 0; i < count; ++i) {
                instructions[i]->dependents =
                        calloc(BITSET_WORDS(count), sizeof(BITSET_WORD));

                instructions[i]->nr_dependencies = 0;
        }

        /* Populate dependency graph */
        for (signed i = count - 1; i >= 0; --i) {
                if (instructions[i]->compact_branch)
                        continue;

                unsigned dest = instructions[i]->dest;
                unsigned mask = mir_bytemask(instructions[i]);

                mir_foreach_src((*instructions), s) {
                        unsigned src = instructions[i]->src[s];

                        if (src < node_count) {
                                unsigned readmask = mir_bytemask_of_read_components(instructions[i], src);
                                add_dependency(last_write, src, readmask, instructions, i);
                        }
                }

                if (dest < node_count) {
                        add_dependency(last_read, dest, mask, instructions, i);
                        add_dependency(last_write, dest, mask, instructions, i);
                        mark_access(last_write, dest, mask, i);
                }

                mir_foreach_src((*instructions), s) {
                        unsigned src = instructions[i]->src[s];

                        if (src < node_count) {
                                unsigned readmask = mir_bytemask_of_read_components(instructions[i], src);
                                mark_access(last_read, src, readmask, i);
                        }
                }
        }

        /* If there is a branch, all instructions depend on it, as interblock
         * execution must be purely in-order */

        if (instructions[count - 1]->compact_branch) {
                BITSET_WORD *dependents = instructions[count - 1]->dependents;

                for (signed i = count - 2; i >= 0; --i) {
                        if (BITSET_TEST(dependents, i))
                                continue;

                        BITSET_SET(dependents, i);
                        instructions[i]->nr_dependencies++;
                }
        }

        /* Free the intermediate structures */
        for (unsigned i = 0; i < sz; ++i) {
                util_dynarray_fini(&last_read[i]);
                util_dynarray_fini(&last_write[i]);
        }

        free(last_read);
        free(last_write);
}

/* Does the mask cover more than a scalar? */

static bool
is_single_component_mask(unsigned mask)
{
        int components = 0;

        for (int c = 0; c < 8; ++c) {
                if (mask & (1 << c))
                        components++;
        }

        return components == 1;
}

/* Helpers for scheudling */

static bool
mir_is_scalar(midgard_instruction *ains)
{
        /* Do we try to use it as a vector op? */
        if (!is_single_component_mask(ains->mask))
                return false;

        /* Otherwise, check mode hazards */
        bool could_scalar = true;

        /* Only 16/32-bit can run on a scalar unit */
        could_scalar &= ains->alu.reg_mode != midgard_reg_mode_8;
        could_scalar &= ains->alu.reg_mode != midgard_reg_mode_64;
        could_scalar &= ains->alu.dest_override == midgard_dest_override_none;

        if (ains->alu.reg_mode == midgard_reg_mode_16) {
                /* If we're running in 16-bit mode, we
                 * can't have any 8-bit sources on the
                 * scalar unit (since the scalar unit
                 * doesn't understand 8-bit) */

                midgard_vector_alu_src s1 =
                        vector_alu_from_unsigned(ains->alu.src1);

                could_scalar &= !s1.half;

                midgard_vector_alu_src s2 =
                        vector_alu_from_unsigned(ains->alu.src2);

                could_scalar &= !s2.half;
        }

        return could_scalar;
}

/* How many bytes does this ALU instruction add to the bundle? */

static unsigned
bytes_for_instruction(midgard_instruction *ains)
{
        if (ains->unit & UNITS_ANY_VECTOR)
                return sizeof(midgard_reg_info) + sizeof(midgard_vector_alu);
        else if (ains->unit == ALU_ENAB_BRANCH)
                return sizeof(midgard_branch_extended);
        else if (ains->compact_branch)
                return sizeof(ains->br_compact);
        else
                return sizeof(midgard_reg_info) + sizeof(midgard_scalar_alu);
}

/* We would like to flatten the linked list of midgard_instructions in a bundle
 * to an array of pointers on the heap for easy indexing */

static midgard_instruction **
flatten_mir(midgard_block *block, unsigned *len)
{
        *len = list_length(&block->instructions);

        if (!(*len))
                return NULL;

        midgard_instruction **instructions =
                calloc(sizeof(midgard_instruction *), *len);

        unsigned i = 0;

        mir_foreach_instr_in_block(block, ins)
                instructions[i++] = ins;

        return instructions;
}

/* The worklist is the set of instructions that can be scheduled now; that is,
 * the set of instructions with no remaining dependencies */

static void
mir_initialize_worklist(BITSET_WORD *worklist, midgard_instruction **instructions, unsigned count)
{
        for (unsigned i = 0; i < count; ++i) {
                if (instructions[i]->nr_dependencies == 0)
                        BITSET_SET(worklist, i);
        }
}

/* Update the worklist after an instruction terminates. Remove its edges from
 * the graph and if that causes any node to have no dependencies, add it to the
 * worklist */

static void
mir_update_worklist(
                BITSET_WORD *worklist, unsigned count,
                midgard_instruction **instructions, midgard_instruction *done)
{
        /* Sanity check: if no instruction terminated, there is nothing to do.
         * If the instruction that terminated had dependencies, that makes no
         * sense and means we messed up the worklist. Finally, as the purpose
         * of this routine is to update dependents, we abort early if there are
         * no dependents defined. */

        if (!done)
                return;

        assert(done->nr_dependencies == 0);

        if (!done->dependents)
                return;

        /* We have an instruction with dependents. Iterate each dependent to
         * remove one dependency (`done`), adding dependents to the worklist
         * where possible. */

        unsigned i;
        BITSET_WORD tmp;
        BITSET_FOREACH_SET(i, tmp, done->dependents, count) {
                assert(instructions[i]->nr_dependencies);

                if (!(--instructions[i]->nr_dependencies))
                        BITSET_SET(worklist, i);
        }

        free(done->dependents);
}

/* While scheduling, we need to choose instructions satisfying certain
 * criteria. As we schedule backwards, we choose the *last* instruction in the
 * worklist to simulate in-order scheduling. Chosen instructions must satisfy a
 * given predicate. */

struct midgard_predicate {
        /* TAG or ~0 for dont-care */
        unsigned tag;

        /* True if we want to pop off the chosen instruction */
        bool destructive;

        /* For ALU, choose only this unit */
        unsigned unit;

        /* State for bundle constants. constants is the actual constants
         * for the bundle. constant_count is the number of bytes (up to
         * 16) currently in use for constants. When picking in destructive
         * mode, the constants array will be updated, and the instruction
         * will be adjusted to index into the constants array */

        midgard_constants *constants;
        unsigned constant_mask;
        bool blend_constant;

        /* Exclude this destination (if not ~0) */
        unsigned exclude;

        /* Don't schedule instructions consuming conditionals (since we already
         * scheduled one). Excludes conditional branches and csel */
        bool no_cond;

        /* Require a minimal mask and (if nonzero) given destination. Used for
         * writeout optimizations */

        unsigned mask;
        unsigned dest;
};

/* For an instruction that can fit, adjust it to fit and update the constants
 * array, in destructive mode. Returns whether the fitting was successful. */

static bool
mir_adjust_constants(midgard_instruction *ins,
                struct midgard_predicate *pred,
                bool destructive)
{
        /* Blend constants dominate */
        if (ins->has_blend_constant) {
                if (pred->constant_mask)
                        return false;
                else if (destructive) {
                        pred->blend_constant = true;
                        pred->constant_mask = 0xffff;
                        return true;
                }
        }

        /* No constant, nothing to adjust */
        if (!ins->has_constants)
                return true;

        unsigned r_constant = SSA_FIXED_REGISTER(REGISTER_CONSTANT);
        midgard_reg_mode reg_mode = ins->alu.reg_mode;

        midgard_vector_alu_src const_src = { };

        if (ins->src[0] == r_constant)
                const_src = vector_alu_from_unsigned(ins->alu.src1);
        else if (ins->src[1] == r_constant)
                const_src = vector_alu_from_unsigned(ins->alu.src2);

        unsigned type_size = mir_bytes_for_mode(reg_mode);

        /* If the ALU is converting up we need to divide type_size by 2 */
        if (const_src.half)
                type_size /= 2;

        unsigned max_comp = 16 / type_size;
        unsigned comp_mask = mir_from_bytemask(mir_bytemask_of_read_components(ins, r_constant),
                                               reg_mode);
        unsigned type_mask = (1 << type_size) - 1;
        unsigned bundle_constant_mask = pred->constant_mask;
        unsigned comp_mapping[16] = { };
        uint8_t bundle_constants[16];

        memcpy(bundle_constants, pred->constants, 16);

        /* Let's try to find a place for each active component of the constant
         * register.
         */
        for (unsigned comp = 0; comp < max_comp; comp++) {
                if (!(comp_mask & (1 << comp)))
                        continue;

                uint8_t *constantp = ins->constants.u8 + (type_size * comp);
                unsigned best_reuse_bytes = 0;
                signed best_place = -1;
                unsigned i, j;

                for (i = 0; i < 16; i += type_size) {
                        unsigned reuse_bytes = 0;

                        for (j = 0; j < type_size; j++) {
                                if (!(bundle_constant_mask & (1 << (i + j))))
                                        continue;
                                if (constantp[j] != bundle_constants[i + j])
                                        break;

                                reuse_bytes++;
                        }

                        /* Select the place where existing bytes can be
                         * reused so we leave empty slots to others
                         */
                        if (j == type_size &&
                            (reuse_bytes > best_reuse_bytes || best_place < 0)) {
                                best_reuse_bytes = reuse_bytes;
                                best_place = i;
                                break;
                        }
                }

                /* This component couldn't fit in the remaining constant slot,
                 * no need check the remaining components, bail out now
                 */
                if (best_place < 0)
                        return false;

                memcpy(&bundle_constants[i], constantp, type_size);
                bundle_constant_mask |= type_mask << best_place;
                comp_mapping[comp] = best_place / type_size;
        }

        /* If non-destructive, we're done */
        if (!destructive)
                return true;

        /* Otherwise update the constant_mask and constant values */
        pred->constant_mask = bundle_constant_mask;
        memcpy(pred->constants, bundle_constants, 16);

        /* Use comp_mapping as a swizzle */
        mir_foreach_src(ins, s) {
                if (ins->src[s] == r_constant)
                        mir_compose_swizzle(ins->swizzle[s], comp_mapping, ins->swizzle[s]);
        }

        return true;
}

static midgard_instruction *
mir_choose_instruction(
                midgard_instruction **instructions,
                BITSET_WORD *worklist, unsigned count,
                struct midgard_predicate *predicate)
{
        /* Parse the predicate */
        unsigned tag = predicate->tag;
        bool alu = tag == TAG_ALU_4;
        unsigned unit = predicate->unit;
        bool branch = alu && (unit == ALU_ENAB_BR_COMPACT);
        bool scalar = (unit != ~0) && (unit & UNITS_SCALAR);
        bool no_cond = predicate->no_cond;

        unsigned mask = predicate->mask;
        unsigned dest = predicate->dest;
        bool needs_dest = mask & 0xF;

        /* Iterate to find the best instruction satisfying the predicate */
        unsigned i;
        BITSET_WORD tmp;

        signed best_index = -1;
        bool best_conditional = false;

        /* Enforce a simple metric limiting distance to keep down register
         * pressure. TOOD: replace with liveness tracking for much better
         * results */

        unsigned max_active = 0;
        unsigned max_distance = 6;

        BITSET_FOREACH_SET(i, tmp, worklist, count) {
                max_active = MAX2(max_active, i);
        }

        BITSET_FOREACH_SET(i, tmp, worklist, count) {
                if ((max_active - i) >= max_distance)
                        continue;

                if (tag != ~0 && instructions[i]->type != tag)
                        continue;

                if (predicate->exclude != ~0 && instructions[i]->dest == predicate->exclude)
                        continue;

                if (alu && !branch && !(alu_opcode_props[instructions[i]->alu.op].props & unit))
                        continue;

                if (branch && !instructions[i]->compact_branch)
                        continue;

                if (alu && scalar && !mir_is_scalar(instructions[i]))
                        continue;

                if (alu && !mir_adjust_constants(instructions[i], predicate, false))
                        continue;

                if (needs_dest && instructions[i]->dest != dest)
                        continue;

                if (mask && ((~instructions[i]->mask) & mask))
                        continue;

                bool conditional = alu && !branch && OP_IS_CSEL(instructions[i]->alu.op);
                conditional |= (branch && instructions[i]->branch.conditional);

                if (conditional && no_cond)
                        continue;

                /* Simulate in-order scheduling */
                if ((signed) i < best_index)
                        continue;

                best_index = i;
                best_conditional = conditional;
        }


        /* Did we find anything?  */

        if (best_index < 0)
                return NULL;

        /* If we found something, remove it from the worklist */
        assert(best_index < count);

        if (predicate->destructive) {
                BITSET_CLEAR(worklist, best_index);

                if (alu)
                        mir_adjust_constants(instructions[best_index], predicate, true);

                /* Once we schedule a conditional, we can't again */
                predicate->no_cond |= best_conditional;
        }

        return instructions[best_index];
}

/* Still, we don't choose instructions in a vacuum. We need a way to choose the
 * best bundle type (ALU, load/store, texture). Nondestructive. */

static unsigned
mir_choose_bundle(
                midgard_instruction **instructions,
                BITSET_WORD *worklist, unsigned count)
{
        /* At the moment, our algorithm is very simple - use the bundle of the
         * best instruction, regardless of what else could be scheduled
         * alongside it. This is not optimal but it works okay for in-order */

        struct midgard_predicate predicate = {
                .tag = ~0,
                .destructive = false,
                .exclude = ~0
        };

        midgard_instruction *chosen = mir_choose_instruction(instructions, worklist, count, &predicate);

        if (chosen)
                return chosen->type;
        else
                return ~0;
}

/* We want to choose an ALU instruction filling a given unit */
static void
mir_choose_alu(midgard_instruction **slot,
                midgard_instruction **instructions,
                BITSET_WORD *worklist, unsigned len,
                struct midgard_predicate *predicate,
                unsigned unit)
{
        /* Did we already schedule to this slot? */
        if ((*slot) != NULL)
                return;

        /* Try to schedule something, if not */
        predicate->unit = unit;
        *slot = mir_choose_instruction(instructions, worklist, len, predicate);

        /* Store unit upon scheduling */
        if (*slot && !((*slot)->compact_branch))
                (*slot)->unit = unit;
}

/* When we are scheduling a branch/csel, we need the consumed condition in the
 * same block as a pipeline register. There are two options to enable this:
 *
 *  - Move the conditional into the bundle. Preferred, but only works if the
 *    conditional is used only once and is from this block.
 *  - Copy the conditional.
 *
 * We search for the conditional. If it's in this block, single-use, and
 * without embedded constants, we schedule it immediately. Otherwise, we
 * schedule a move for it.
 *
 * mir_comparison_mobile is a helper to find the moveable condition.
 */

static unsigned
mir_comparison_mobile(
                compiler_context *ctx,
                midgard_instruction **instructions,
                struct midgard_predicate *predicate,
                unsigned count,
                unsigned cond)
{
        if (!mir_single_use(ctx, cond))
                return ~0;

        unsigned ret = ~0;

        for (unsigned i = 0; i < count; ++i) {
                if (instructions[i]->dest != cond)
                        continue;

                /* Must fit in an ALU bundle */
                if (instructions[i]->type != TAG_ALU_4)
                        return ~0;

                /* If it would itself require a condition, that's recursive */
                if (OP_IS_CSEL(instructions[i]->alu.op))
                        return ~0;

                /* We'll need to rewrite to .w but that doesn't work for vector
                 * ops that don't replicate (ball/bany), so bail there */

                if (GET_CHANNEL_COUNT(alu_opcode_props[instructions[i]->alu.op].props))
                        return ~0;

                /* Ensure it will fit with constants */

                if (!mir_adjust_constants(instructions[i], predicate, false))
                        return ~0;

                /* Ensure it is written only once */

                if (ret != ~0)
                        return ~0;
                else
                        ret = i;
        }

        /* Inject constants now that we are sure we want to */
        if (ret != ~0)
                mir_adjust_constants(instructions[ret], predicate, true);

        return ret;
}

/* Using the information about the moveable conditional itself, we either pop
 * that condition off the worklist for use now, or create a move to
 * artificially schedule instead as a fallback */

static midgard_instruction *
mir_schedule_comparison(
                compiler_context *ctx,
                midgard_instruction **instructions,
                struct midgard_predicate *predicate,
                BITSET_WORD *worklist, unsigned count,
                unsigned cond, bool vector, unsigned *swizzle,
                midgard_instruction *user)
{
        /* TODO: swizzle when scheduling */
        unsigned comp_i =
                (!vector && (swizzle[0] == 0)) ?
                mir_comparison_mobile(ctx, instructions, predicate, count, cond) : ~0;

        /* If we can, schedule the condition immediately */
        if ((comp_i != ~0) && BITSET_TEST(worklist, comp_i)) {
                assert(comp_i < count);
                BITSET_CLEAR(worklist, comp_i);
                return instructions[comp_i];
        }

        /* Otherwise, we insert a move */

        midgard_instruction mov = v_mov(cond, cond);
        mov.mask = vector ? 0xF : 0x1;
        memcpy(mov.swizzle[1], swizzle, sizeof(mov.swizzle[1]));

        return mir_insert_instruction_before(ctx, user, mov);
}

/* Most generally, we need instructions writing to r31 in the appropriate
 * components */

static midgard_instruction *
mir_schedule_condition(compiler_context *ctx,
                struct midgard_predicate *predicate,
                BITSET_WORD *worklist, unsigned count,
                midgard_instruction **instructions,
                midgard_instruction *last)
{
        /* For a branch, the condition is the only argument; for csel, third */
        bool branch = last->compact_branch;
        unsigned condition_index = branch ? 0 : 2;

        /* csel_v is vector; otherwise, conditions are scalar */
        bool vector = !branch && OP_IS_CSEL_V(last->alu.op);

        /* Grab the conditional instruction */

        midgard_instruction *cond = mir_schedule_comparison(
                        ctx, instructions, predicate, worklist, count, last->src[condition_index],
                        vector, last->swizzle[2], last);

        /* We have exclusive reign over this (possibly move) conditional
         * instruction. We can rewrite into a pipeline conditional register */

        predicate->exclude = cond->dest;
        cond->dest = SSA_FIXED_REGISTER(31);

        if (!vector) {
                cond->mask = (1 << COMPONENT_W);

                mir_foreach_src(cond, s) {
                        if (cond->src[s] == ~0)
                                continue;

                        for (unsigned q = 0; q < 4; ++q)
                                cond->swizzle[s][q + COMPONENT_W] = cond->swizzle[s][q];
                }
        }

        /* Schedule the unit: csel is always in the latter pipeline, so a csel
         * condition must be in the former pipeline stage (vmul/sadd),
         * depending on scalar/vector of the instruction itself. A branch must
         * be written from the latter pipeline stage and a branch condition is
         * always scalar, so it is always in smul (exception: ball/bany, which
         * will be vadd) */

        if (branch)
                cond->unit = UNIT_SMUL;
        else
                cond->unit = vector ? UNIT_VMUL : UNIT_SADD;

        return cond;
}

/* Schedules a single bundle of the given type */

static midgard_bundle
mir_schedule_texture(
                midgard_instruction **instructions,
                BITSET_WORD *worklist, unsigned len)
{
        struct midgard_predicate predicate = {
                .tag = TAG_TEXTURE_4,
                .destructive = true,
                .exclude = ~0
        };

        midgard_instruction *ins =
                mir_choose_instruction(instructions, worklist, len, &predicate);

        mir_update_worklist(worklist, len, instructions, ins);

        struct midgard_bundle out = {
                .tag = TAG_TEXTURE_4,
                .instruction_count = 1,
                .instructions = { ins }
        };

        return out;
}

static midgard_bundle
mir_schedule_ldst(
                midgard_instruction **instructions,
                BITSET_WORD *worklist, unsigned len)
{
        struct midgard_predicate predicate = {
                .tag = TAG_LOAD_STORE_4,
                .destructive = true,
                .exclude = ~0
        };

        /* Try to pick two load/store ops. Second not gauranteed to exist */

        midgard_instruction *ins =
                mir_choose_instruction(instructions, worklist, len, &predicate);

        midgard_instruction *pair =
                mir_choose_instruction(instructions, worklist, len, &predicate);

        struct midgard_bundle out = {
                .tag = TAG_LOAD_STORE_4,
                .instruction_count = pair ? 2 : 1,
                .instructions = { ins, pair }
        };

        /* We have to update the worklist atomically, since the two
         * instructions run concurrently (TODO: verify it's not pipelined) */

        mir_update_worklist(worklist, len, instructions, ins);
        mir_update_worklist(worklist, len, instructions, pair);

        return out;
}

static midgard_bundle
mir_schedule_alu(
                compiler_context *ctx,
                midgard_instruction **instructions,
                BITSET_WORD *worklist, unsigned len)
{
        struct midgard_bundle bundle = {};

        unsigned bytes_emitted = sizeof(bundle.control);

        struct midgard_predicate predicate = {
                .tag = TAG_ALU_4,
                .destructive = true,
                .exclude = ~0,
                .constants = &bundle.constants
        };

        midgard_instruction *vmul = NULL;
        midgard_instruction *vadd = NULL;
        midgard_instruction *vlut = NULL;
        midgard_instruction *smul = NULL;
        midgard_instruction *sadd = NULL;
        midgard_instruction *branch = NULL;

        mir_choose_alu(&branch, instructions, worklist, len, &predicate, ALU_ENAB_BR_COMPACT);
        mir_update_worklist(worklist, len, instructions, branch);
        bool writeout = branch && branch->writeout;

        if (branch && branch->branch.conditional) {
                midgard_instruction *cond = mir_schedule_condition(ctx, &predicate, worklist, len, instructions, branch);

                if (cond->unit == UNIT_VADD)
                        vadd = cond;
                else if (cond->unit == UNIT_SMUL)
                        smul = cond;
                else
                        unreachable("Bad condition");
        }

        mir_choose_alu(&smul, instructions, worklist, len, &predicate, UNIT_SMUL);

        if (!writeout)
                mir_choose_alu(&vlut, instructions, worklist, len, &predicate, UNIT_VLUT);

        if (writeout) {
                /* Propagate up */
                bundle.last_writeout = branch->last_writeout;

                midgard_instruction add = v_mov(~0, make_compiler_temp(ctx));

                if (!ctx->is_blend) {
                        add.alu.op = midgard_alu_op_iadd;
                        add.src[0] = SSA_FIXED_REGISTER(31);

                        for (unsigned c = 0; c < 16; ++c)
                                add.swizzle[0][c] = COMPONENT_X;

                        add.has_inline_constant = true;
                        add.inline_constant = 0;
                } else {
                        add.src[1] = SSA_FIXED_REGISTER(1);

                        for (unsigned c = 0; c < 16; ++c)
                                add.swizzle[1][c] = COMPONENT_W;
                }

                vadd = mem_dup(&add, sizeof(midgard_instruction));

                vadd->unit = UNIT_VADD;
                vadd->mask = 0x1;
                branch->src[2] = add.dest;
        }

        mir_choose_alu(&vadd, instructions, worklist, len, &predicate, UNIT_VADD);
        
        mir_update_worklist(worklist, len, instructions, vlut);
        mir_update_worklist(worklist, len, instructions, vadd);
        mir_update_worklist(worklist, len, instructions, smul);

        bool vadd_csel = vadd && OP_IS_CSEL(vadd->alu.op);
        bool smul_csel = smul && OP_IS_CSEL(smul->alu.op);

        if (vadd_csel || smul_csel) {
                midgard_instruction *ins = vadd_csel ? vadd : smul;
                midgard_instruction *cond = mir_schedule_condition(ctx, &predicate, worklist, len, instructions, ins);

                if (cond->unit == UNIT_VMUL)
                        vmul = cond;
                else if (cond->unit == UNIT_SADD)
                        sadd = cond;
                else
                        unreachable("Bad condition");
        }

        /* If we have a render target reference, schedule a move for it */

        if (branch && branch->writeout && (branch->constants.u32[0] || ctx->is_blend)) {
                midgard_instruction mov = v_mov(~0, make_compiler_temp(ctx));
                sadd = mem_dup(&mov, sizeof(midgard_instruction));
                sadd->unit = UNIT_SADD;
                sadd->mask = 0x1;
                sadd->has_inline_constant = true;
                sadd->inline_constant = branch->constants.u32[0];
                branch->src[1] = mov.dest;
                /* TODO: Don't leak */
        }

        /* Stage 2, let's schedule sadd before vmul for writeout */
        mir_choose_alu(&sadd, instructions, worklist, len, &predicate, UNIT_SADD);

        /* Check if writeout reads its own register */

        if (branch && branch->writeout) {
                midgard_instruction *stages[] = { sadd, vadd, smul };
                unsigned src = (branch->src[0] == ~0) ? SSA_FIXED_REGISTER(0) : branch->src[0];
                unsigned writeout_mask = 0x0;
                bool bad_writeout = false;

                for (unsigned i = 0; i < ARRAY_SIZE(stages); ++i) {
                        if (!stages[i])
                                continue;

                        if (stages[i]->dest != src)
                                continue;

                        writeout_mask |= stages[i]->mask;
                        bad_writeout |= mir_has_arg(stages[i], branch->src[0]);
                }

                /* It's possible we'll be able to schedule something into vmul
                 * to fill r0. Let's peak into the future, trying to schedule
                 * vmul specially that way. */

                if (!bad_writeout && writeout_mask != 0xF) {
                        predicate.unit = UNIT_VMUL;
                        predicate.dest = src;
                        predicate.mask = writeout_mask ^ 0xF;

                        struct midgard_instruction *peaked =
                                mir_choose_instruction(instructions, worklist, len, &predicate);

                        if (peaked) {
                                vmul = peaked;
                                vmul->unit = UNIT_VMUL;
                                writeout_mask |= predicate.mask;
                                assert(writeout_mask == 0xF);
                        }

                        /* Cleanup */
                        predicate.dest = predicate.mask = 0;
                }

                /* Finally, add a move if necessary */
                if (bad_writeout || writeout_mask != 0xF) {
                        unsigned temp = (branch->src[0] == ~0) ? SSA_FIXED_REGISTER(0) : make_compiler_temp(ctx);
                        midgard_instruction mov = v_mov(src, temp);
                        vmul = mem_dup(&mov, sizeof(midgard_instruction));
                        vmul->unit = UNIT_VMUL;
                        vmul->mask = 0xF ^ writeout_mask;
                        /* TODO: Don't leak */

                        /* Rewrite to use our temp */

                        for (unsigned i = 0; i < ARRAY_SIZE(stages); ++i) {
                                if (stages[i])
                                        mir_rewrite_index_dst_single(stages[i], src, temp);
                        }

                        mir_rewrite_index_src_single(branch, src, temp);
                }
        }

        mir_choose_alu(&vmul, instructions, worklist, len, &predicate, UNIT_VMUL);

        mir_update_worklist(worklist, len, instructions, vmul);
        mir_update_worklist(worklist, len, instructions, sadd);

        bundle.has_blend_constant = predicate.blend_constant;
        bundle.has_embedded_constants = predicate.constant_mask != 0;

        unsigned padding = 0;

        /* Now that we have finished scheduling, build up the bundle */
        midgard_instruction *stages[] = { vmul, sadd, vadd, smul, vlut, branch };

        for (unsigned i = 0; i < ARRAY_SIZE(stages); ++i) {
                if (stages[i]) {
                        bundle.control |= stages[i]->unit;
                        bytes_emitted += bytes_for_instruction(stages[i]);
                        bundle.instructions[bundle.instruction_count++] = stages[i];
                }
        }

        /* Pad ALU op to nearest word */

        if (bytes_emitted & 15) {
                padding = 16 - (bytes_emitted & 15);
                bytes_emitted += padding;
        }

        /* Constants must always be quadwords */
        if (bundle.has_embedded_constants)
                bytes_emitted += 16;

        /* Size ALU instruction for tag */
        bundle.tag = (TAG_ALU_4) + (bytes_emitted / 16) - 1;

        /* MRT capable GPUs use a special writeout procedure */
        if (writeout && !(ctx->quirks & MIDGARD_NO_UPPER_ALU))
                bundle.tag += 4;

        bundle.padding = padding;
        bundle.control |= bundle.tag;

        return bundle;
}

/* Schedule a single block by iterating its instruction to create bundles.
 * While we go, tally about the bundle sizes to compute the block size. */


static void
schedule_block(compiler_context *ctx, midgard_block *block)
{
        /* Copy list to dynamic array */
        unsigned len = 0;
        midgard_instruction **instructions = flatten_mir(block, &len);

        if (!len)
                return;

        /* Calculate dependencies and initial worklist */
        unsigned node_count = ctx->temp_count + 1;
        mir_create_dependency_graph(instructions, len, node_count);

        /* Allocate the worklist */
        size_t sz = BITSET_WORDS(len) * sizeof(BITSET_WORD);
        BITSET_WORD *worklist = calloc(sz, 1);
        mir_initialize_worklist(worklist, instructions, len);

        struct util_dynarray bundles;
        util_dynarray_init(&bundles, NULL);

        block->quadword_count = 0;
        unsigned blend_offset = 0;

        for (;;) {
                unsigned tag = mir_choose_bundle(instructions, worklist, len);
                midgard_bundle bundle;

                if (tag == TAG_TEXTURE_4)
                        bundle = mir_schedule_texture(instructions, worklist, len);
                else if (tag == TAG_LOAD_STORE_4)
                        bundle = mir_schedule_ldst(instructions, worklist, len);
                else if (tag == TAG_ALU_4)
                        bundle = mir_schedule_alu(ctx, instructions, worklist, len);
                else
                        break;

                util_dynarray_append(&bundles, midgard_bundle, bundle);

                if (bundle.has_blend_constant)
                        blend_offset = block->quadword_count;

                block->quadword_count += midgard_word_size[bundle.tag];
        }

        /* We emitted bundles backwards; copy into the block in reverse-order */

        util_dynarray_init(&block->bundles, NULL);
        util_dynarray_foreach_reverse(&bundles, midgard_bundle, bundle) {
                util_dynarray_append(&block->bundles, midgard_bundle, *bundle);
        }

        /* Blend constant was backwards as well. blend_offset if set is
         * strictly positive, as an offset of zero would imply constants before
         * any instructions which is invalid in Midgard. TODO: blend constants
         * are broken if you spill since then quadword_count becomes invalid
         * XXX */

        if (blend_offset)
                ctx->blend_constant_offset = ((ctx->quadword_count + block->quadword_count) - blend_offset - 1) * 0x10;

        block->is_scheduled = true;
        ctx->quadword_count += block->quadword_count;

        /* Reorder instructions to match bundled. First remove existing
         * instructions and then recreate the list */

        mir_foreach_instr_in_block_safe(block, ins) {
                list_del(&ins->link);
        }

        mir_foreach_instr_in_block_scheduled_rev(block, ins) {
                list_add(&ins->link, &block->instructions);
        }

        free(instructions); /* Allocated by flatten_mir() */
        free(worklist);
}

void
midgard_schedule_program(compiler_context *ctx)
{
        midgard_promote_uniforms(ctx);

        /* Must be lowered right before scheduling */
        mir_squeeze_index(ctx);
        mir_lower_special_reads(ctx);
        mir_squeeze_index(ctx);

        /* Lowering can introduce some dead moves */

        mir_foreach_block(ctx, block) {
                midgard_opt_dead_move_eliminate(ctx, block);
                schedule_block(ctx, block);
        }

}