panfrost/bifrost/bi_pack.c

/*
 * Copyright (C) 2020 Collabora, Ltd.
 *
 * 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"

/* This file contains the final passes of the compiler. Running after
 * scheduling and RA, the IR is now finalized, so we need to emit it to actual
 * bits on the wire (as well as fixup branches) */

static uint64_t
bi_pack_header(bi_clause *clause, bi_clause *next_1, bi_clause *next_2)
{
        /* next_dependencies are the union of the dependencies of successors'
         * dependencies */

        unsigned dependency_wait = next_1 ? next_1->dependencies : 0;
        dependency_wait |= next_2 ? next_2->dependencies : 0;

        bool staging_barrier = next_1 ? next_1->staging_barrier : false;
        staging_barrier |= next_2 ? next_2->staging_barrier : 0;

        struct bifrost_header header = {
                .flow_control =
                        (next_1 == NULL && next_2 == NULL) ?
                        BIFROST_FLOW_END :  clause->flow_control,
                .terminate_discarded_threads = clause->td,
                .next_clause_prefetch = clause->next_clause_prefetch && next_1,
                .staging_barrier = staging_barrier,
                .staging_register = clause->staging_register,
                .dependency_wait = dependency_wait,
                .dependency_slot = clause->scoreboard_id,
                .message_type = clause->message_type,
                .next_message_type = next_1 ? next_1->message_type : 0,
        };

        uint64_t u = 0;
        memcpy(&u, &header, sizeof(header));
        return u;
}

/* Assigns a slot for reading, before anything is written */

static void
bi_assign_slot_read(bi_registers *regs, bi_index src)
{
        /* We only assign for registers */
        if (src.type != BI_INDEX_REGISTER)
                return;

        /* Check if we already assigned the slot */
        for (unsigned i = 0; i <= 1; ++i) {
                if (regs->slot[i] == src.value && regs->enabled[i])
                        return;
        }

        if (regs->slot[2] == src.value && regs->slot23.slot2 == BIFROST_OP_READ)
                return;

        /* Assign it now */

        for (unsigned i = 0; i <= 1; ++i) {
                if (!regs->enabled[i]) {
                        regs->slot[i] = src.value;
                        regs->enabled[i] = true;
                        return;
                }
        }

        if (!regs->slot23.slot3) {
                regs->slot[2] = src.value;
                regs->slot23.slot2 = BIFROST_OP_READ;
                return;
        }

        bi_print_slots(regs, stderr);
        unreachable("Failed to find a free slot for src");
}

static bi_registers
bi_assign_slots(bi_tuple *now, bi_tuple *prev)
{
        /* We assign slots for the main register mechanism. Special ops
         * use the data registers, which has its own mechanism entirely
         * and thus gets skipped over here. */

        bool read_dreg = now->add && bi_opcode_props[now->add->op].sr_read;
        bool write_dreg = prev->add && bi_opcode_props[prev->add->op].sr_write;

        /* First, assign reads */

        if (now->fma)
                bi_foreach_src(now->fma, src)
                        bi_assign_slot_read(&now->regs, (now->fma)->src[src]);

        if (now->add) {
                bi_foreach_src(now->add, src) {
                        if (!(src == 0 && read_dreg))
                                bi_assign_slot_read(&now->regs, (now->add)->src[src]);
                }
        }

        /* Next, assign writes. Staging writes are assigned separately, but
         * +ATEST wants its destination written to both a staging register
         * _and_ a regular write, because it may not generate a message */

        if (prev->add && (!write_dreg || prev->add->op == BI_OPCODE_ATEST)) {
                bi_index idx = prev->add->dest[0];

                if (idx.type == BI_INDEX_REGISTER) {
                        now->regs.slot[3] = idx.value;
                        now->regs.slot23.slot3 = BIFROST_OP_WRITE;
                }
        }

        if (prev->fma) {
                bi_index idx = (prev->fma)->dest[0];

                if (idx.type == BI_INDEX_REGISTER) {
                        if (now->regs.slot23.slot3) {
                                /* Scheduler constraint: cannot read 3 and write 2 */
                                assert(!now->regs.slot23.slot2);
                                now->regs.slot[2] = idx.value;
                                now->regs.slot23.slot2 = BIFROST_OP_WRITE;
                        } else {
                                now->regs.slot[3] = idx.value;
                                now->regs.slot23.slot3 = BIFROST_OP_WRITE;
                                now->regs.slot23.slot3_fma = true;
                        }
                }
        }

        return now->regs;
}

static enum bifrost_reg_mode
bi_pack_register_mode(bi_registers r)
{
        /* Handle idle as a special case */
        if (!(r.slot23.slot2 | r.slot23.slot3))
                return r.first_instruction ? BIFROST_IDLE_1 : BIFROST_IDLE;

        /* Otherwise, use the LUT */
        for (unsigned i = 0; i < ARRAY_SIZE(bifrost_reg_ctrl_lut); ++i) {
                if (memcmp(bifrost_reg_ctrl_lut + i, &r.slot23, sizeof(r.slot23)) == 0)
                        return i;
        }

        bi_print_slots(&r, stderr);
        unreachable("Invalid slot assignment");
}

static uint64_t
bi_pack_registers(bi_registers regs)
{
        enum bifrost_reg_mode mode = bi_pack_register_mode(regs);
        struct bifrost_regs s = { 0 };
        uint64_t packed = 0;

        /* Need to pack 5-bit mode as a 4-bit field. The decoder moves bit 3 to bit 4 for
         * first instruction and adds 16 when reg 2 == reg 3 */

        unsigned ctrl;
        bool r2_equals_r3 = false;

        if (regs.first_instruction) {
                /* Bit 3 implicitly must be clear for first instructions.
                 * The affected patterns all write both ADD/FMA, but that
                 * is forbidden for the last instruction (whose writes are
                 * encoded by the first), so this does not add additional
                 * encoding constraints */
                assert(!(mode & 0x8));

                /* Move bit 4 to bit 3, since bit 3 is clear */
                ctrl = (mode & 0x7) | ((mode & 0x10) >> 1);

                /* If we can let r2 equal r3, we have to or the hardware raises
                 * INSTR_INVALID_ENC (it's unclear why). */
                if (!(regs.slot23.slot2 && regs.slot23.slot3))
                        r2_equals_r3 = true;
        } else {
                /* We force r2=r3 or not for the upper bit */
                ctrl = (mode & 0xF);
                r2_equals_r3 = (mode & 0x10);
        }

        if (regs.enabled[1]) {
                /* Gotta save that bit!~ Required by the 63-x trick */
                assert(regs.slot[1] > regs.slot[0]);
                assert(regs.enabled[0]);

                /* Do the 63-x trick, see docs/disasm */
                if (regs.slot[0] > 31) {
                        regs.slot[0] = 63 - regs.slot[0];
                        regs.slot[1] = 63 - regs.slot[1];
                }

                assert(regs.slot[0] <= 31);
                assert(regs.slot[1] <= 63);

                s.ctrl = ctrl;
                s.reg1 = regs.slot[1];
                s.reg0 = regs.slot[0];
        } else {
                /* slot 1 disabled, so set to zero and use slot 1 for ctrl */
                s.ctrl = 0;
                s.reg1 = ctrl << 2;

                if (regs.enabled[0]) {
                        /* Bit 0 upper bit of slot 0 */
                        s.reg1 |= (regs.slot[0] >> 5);

                        /* Rest of slot 0 in usual spot */
                        s.reg0 = (regs.slot[0] & 0b11111);
                } else {
                        /* Bit 1 set if slot 0 also disabled */
                        s.reg1 |= (1 << 1);
                }
        }

        /* Force r2 =/!= r3 as needed */
        if (r2_equals_r3) {
                assert(regs.slot[3] == regs.slot[2] || !(regs.slot23.slot2 && regs.slot23.slot3));

                if (regs.slot23.slot2)
                        regs.slot[3] = regs.slot[2];
                else
                        regs.slot[2] = regs.slot[3];
        } else if (!regs.first_instruction) {
                /* Enforced by the encoding anyway */
                assert(regs.slot[2] != regs.slot[3]);
        }

        s.reg2 = regs.slot[2];
        s.reg3 = regs.slot[3];
        s.fau_idx = regs.fau_idx;

        memcpy(&packed, &s, sizeof(s));
        return packed;
}

/* We must ensure slot 1 > slot 0 for the 63-x trick to function, so we fix
 * this up at pack time. (Scheduling doesn't care.) */

static void
bi_flip_slots(bi_registers *regs)
{
        if (regs->enabled[0] && regs->enabled[1] && regs->slot[1] < regs->slot[0]) {
                unsigned temp = regs->slot[0];
                regs->slot[0] = regs->slot[1];
                regs->slot[1] = temp;
        }

}

static inline enum bifrost_packed_src
bi_get_src_slot(bi_registers *regs, unsigned reg)
{
        if (regs->slot[0] == reg && regs->enabled[0])
                return BIFROST_SRC_PORT0;
        else if (regs->slot[1] == reg && regs->enabled[1])
                return BIFROST_SRC_PORT1;
        else if (regs->slot[2] == reg && regs->slot23.slot2 == BIFROST_OP_READ)
                return BIFROST_SRC_PORT2;
        else
                unreachable("Tried to access register with no port");
}

static inline enum bifrost_packed_src
bi_get_src_new(bi_instr *ins, bi_registers *regs, unsigned s)
{
        if (!ins)
                return 0;

        bi_index src = ins->src[s];

        if (src.type == BI_INDEX_REGISTER)
                return bi_get_src_slot(regs, src.value);
        else if (src.type == BI_INDEX_PASS)
                return src.value;
        else if (bi_is_null(src) && ins->op == BI_OPCODE_ZS_EMIT && s < 2)
                return BIFROST_SRC_STAGE;
        else {
                /* TODO make safer */
                return BIFROST_SRC_STAGE;
        }
}

static struct bi_packed_tuple
bi_pack_tuple(bi_clause *clause, bi_tuple *tuple, bi_tuple *prev, bool first_tuple, gl_shader_stage stage)
{
        bi_assign_slots(tuple, prev);
        tuple->regs.fau_idx = tuple->fau_idx;
        tuple->regs.first_instruction = first_tuple;

        bi_flip_slots(&tuple->regs);

        bool sr_read = tuple->add &&
                bi_opcode_props[(tuple->add)->op].sr_read;

        uint64_t reg = bi_pack_registers(tuple->regs);
        uint64_t fma = bi_pack_fma(tuple->fma,
                        bi_get_src_new(tuple->fma, &tuple->regs, 0),
                        bi_get_src_new(tuple->fma, &tuple->regs, 1),
                        bi_get_src_new(tuple->fma, &tuple->regs, 2),
                        bi_get_src_new(tuple->fma, &tuple->regs, 3));

        uint64_t add = bi_pack_add(tuple->add,
                        bi_get_src_new(tuple->add, &tuple->regs, sr_read + 0),
                        bi_get_src_new(tuple->add, &tuple->regs, sr_read + 1),
                        bi_get_src_new(tuple->add, &tuple->regs, sr_read + 2),
                        0);

        if (tuple->add) {
                bi_instr *add = tuple->add;

                bool sr_write = bi_opcode_props[add->op].sr_write &&
                        !bi_is_null(add->dest[0]);

                if (sr_read && !bi_is_null(add->src[0])) {
                        assert(add->src[0].type == BI_INDEX_REGISTER);
                        clause->staging_register = add->src[0].value;

                        if (sr_write)
                                assert(bi_is_equiv(add->src[0], add->dest[0]));
                } else if (sr_write) {
                        assert(add->dest[0].type == BI_INDEX_REGISTER);
                        clause->staging_register = add->dest[0].value;
                }
        }

        struct bi_packed_tuple packed = {
                .lo = reg | (fma << 35) | ((add & 0b111111) << 58),
                .hi = add >> 6
        };

        return packed;
}

/* A block contains at most one PC-relative constant, from a terminal branch.
 * Find the last instruction and if it is a relative branch, fix up the
 * PC-relative constant to contain the absolute offset. This occurs at pack
 * time instead of schedule time because the number of quadwords between each
 * block is not known until after all other passes have finished.
 */

static void
bi_assign_branch_offset(bi_context *ctx, bi_block *block)
{
        if (list_is_empty(&block->clauses))
                return;

        bi_clause *clause = list_last_entry(&block->clauses, bi_clause, link);
        bi_instr *br = bi_last_instr_in_clause(clause);

        if (!br->branch_target)
                return;

        /* Put it in the high place */
        int32_t qwords = bi_block_offset(ctx, clause, br->branch_target);
        int32_t bytes = qwords * 16;

        /* Copy so we can toy with the sign without undefined behaviour */
        uint32_t raw = 0;
        memcpy(&raw, &bytes, sizeof(raw));

        /* Clear off top bits for A1/B1 bits */
        raw &= ~0xF0000000;

        /* Put in top 32-bits */
        assert(clause->pcrel_idx < 8);
        clause->constants[clause->pcrel_idx] |= ((uint64_t) raw) << 32ull;
}

static void
bi_pack_constants(unsigned tuple_count, uint64_t *constants,
                unsigned word_idx, unsigned constant_words, bool ec0_packed,
                struct util_dynarray *emission)
{
        unsigned index = (word_idx << 1) + ec0_packed;

        /* Do more constants follow */
        bool more = (word_idx + 1) < constant_words;

        /* Indexed first by tuple count and second by constant word number,
         * indicates the position in the clause */
        unsigned pos_lookup[8][3] = {
                { 0 },
                { 1 },
                { 3 },
                { 2, 5 },
                { 4, 8 },
                { 7, 11, 14 },
                { 6, 10, 13 },
                { 9, 12 }
        };

        /* Compute the pos, and check everything is reasonable */
        assert((tuple_count - 1) < 8);
        assert(word_idx < 3);
        unsigned pos = pos_lookup[tuple_count - 1][word_idx];
        assert(pos != 0 || (tuple_count == 1 && word_idx == 0));

        struct bifrost_fmt_constant quad = {
                .pos = pos,
                .tag = more ? BIFROST_FMTC_CONSTANTS : BIFROST_FMTC_FINAL,
                .imm_1 = constants[index + 0] >> 4,
                .imm_2 = constants[index + 1] >> 4,
        };

        util_dynarray_append(emission, struct bifrost_fmt_constant, quad);
}

uint8_t
bi_pack_literal(enum bi_clause_subword literal)
{
        assert(literal >= BI_CLAUSE_SUBWORD_LITERAL_0);
        assert(literal <= BI_CLAUSE_SUBWORD_LITERAL_7);

        return (literal - BI_CLAUSE_SUBWORD_LITERAL_0);
}

static inline uint8_t
bi_clause_upper(unsigned val,
                struct bi_packed_tuple *tuples,
                ASSERTED unsigned tuple_count)
{
        assert(val < tuple_count);

        /* top 3-bits of 78-bits is tuple >> 75 == (tuple >> 64) >> 11 */
        struct bi_packed_tuple tuple = tuples[val];
        return (tuple.hi >> 11);
}

uint8_t
bi_pack_upper(enum bi_clause_subword upper,
                struct bi_packed_tuple *tuples,
                ASSERTED unsigned tuple_count)
{
        assert(upper >= BI_CLAUSE_SUBWORD_UPPER_0);
        assert(upper <= BI_CLAUSE_SUBWORD_UPPER_7);

        return bi_clause_upper(upper - BI_CLAUSE_SUBWORD_UPPER_0, tuples,
                        tuple_count);
}

uint64_t
bi_pack_tuple_bits(enum bi_clause_subword idx,
                struct bi_packed_tuple *tuples,
                ASSERTED unsigned tuple_count,
                unsigned offset, unsigned nbits)
{
        assert(idx >= BI_CLAUSE_SUBWORD_TUPLE_0);
        assert(idx <= BI_CLAUSE_SUBWORD_TUPLE_7);

        unsigned val = (idx - BI_CLAUSE_SUBWORD_TUPLE_0);
        assert(val < tuple_count);

        struct bi_packed_tuple tuple = tuples[val];

        assert(offset + nbits < 78);
        assert(nbits <= 64);

        /* (X >> start) & m
         * = (((hi << 64) | lo) >> start) & m
         * = (((hi << 64) >> start) | (lo >> start)) & m
         * = { ((hi << (64 - start)) | (lo >> start)) & m if start <= 64
         *   { ((hi >> (start - 64)) | (lo >> start)) & m if start >= 64
         * = { ((hi << (64 - start)) & m) | ((lo >> start) & m) if start <= 64
         *   { ((hi >> (start - 64)) & m) | ((lo >> start) & m) if start >= 64
         *
         * By setting m = 2^64 - 1, we justify doing the respective shifts as
         * 64-bit integers. Zero special cased to avoid undefined behaviour.
         */

        uint64_t lo = (tuple.lo >> offset);
        uint64_t hi = (offset == 0) ? 0
                : (offset > 64) ? (tuple.hi >> (offset - 64))
                : (tuple.hi << (64 - offset));

        return (lo | hi) & ((1ULL << nbits) - 1);
}

static inline uint16_t
bi_pack_lu(enum bi_clause_subword word,
                struct bi_packed_tuple *tuples,
                ASSERTED unsigned tuple_count)
{
        return (word >= BI_CLAUSE_SUBWORD_UPPER_0) ?
                bi_pack_upper(word, tuples, tuple_count) :
                bi_pack_literal(word);
}

uint8_t
bi_pack_sync(enum bi_clause_subword t1,
             enum bi_clause_subword t2,
             enum bi_clause_subword t3,
             struct bi_packed_tuple *tuples,
             ASSERTED unsigned tuple_count,
             bool z)
{
        uint8_t sync =
                (bi_pack_lu(t3, tuples, tuple_count) << 0) |
                (bi_pack_lu(t2, tuples, tuple_count) << 3);

        if (t1 == BI_CLAUSE_SUBWORD_Z)
                sync |= z << 6;
        else
                sync |= bi_pack_literal(t1) << 6;

        return sync;
}

static inline uint64_t
bi_pack_t_ec(enum bi_clause_subword word,
                struct bi_packed_tuple *tuples,
                ASSERTED unsigned tuple_count,
                uint64_t ec0)
{
        if (word == BI_CLAUSE_SUBWORD_CONSTANT)
                return ec0;
        else
                return bi_pack_tuple_bits(word, tuples, tuple_count, 0, 60);
}

static uint32_t
bi_pack_subwords_56(enum bi_clause_subword t,
                struct bi_packed_tuple *tuples,
                ASSERTED unsigned tuple_count,
                uint64_t header, uint64_t ec0,
                unsigned tuple_subword)
{
        switch (t) {
        case BI_CLAUSE_SUBWORD_HEADER:
                return (header & ((1 << 30) - 1));
        case BI_CLAUSE_SUBWORD_RESERVED:
                return 0;
        case BI_CLAUSE_SUBWORD_CONSTANT:
                return (ec0 >> 15) & ((1 << 30) - 1);
        default:
                return bi_pack_tuple_bits(t, tuples, tuple_count, tuple_subword * 15, 30);
        }
}

static uint16_t
bi_pack_subword(enum bi_clause_subword t, unsigned format,
                struct bi_packed_tuple *tuples,
                ASSERTED unsigned tuple_count,
                uint64_t header, uint64_t ec0, unsigned m0,
                unsigned tuple_subword)
{
        switch (t) {
        case BI_CLAUSE_SUBWORD_HEADER:
                return header >> 30;
        case BI_CLAUSE_SUBWORD_M:
                return m0;
        case BI_CLAUSE_SUBWORD_CONSTANT:
                return (format == 5 || format == 10) ?
                        (ec0 & ((1 << 15) - 1)) :
                        (ec0 >> (15 + 30));
        case BI_CLAUSE_SUBWORD_UPPER_23:
                return (bi_clause_upper(2, tuples, tuple_count) << 12) |
                        (bi_clause_upper(3, tuples, tuple_count) << 9);
        case BI_CLAUSE_SUBWORD_UPPER_56:
                return (bi_clause_upper(5, tuples, tuple_count) << 12) |
                        (bi_clause_upper(6, tuples, tuple_count) << 9);
        case BI_CLAUSE_SUBWORD_UPPER_0 ... BI_CLAUSE_SUBWORD_UPPER_7:
                return bi_pack_upper(t, tuples, tuple_count) << 12;
        default:
                return bi_pack_tuple_bits(t, tuples, tuple_count, tuple_subword * 15, 15);
        }
}

/* EC0 is 60-bits (bottom 4 already shifted off) */
void
bi_pack_format(struct util_dynarray *emission,
                unsigned index,
                struct bi_packed_tuple *tuples,
                ASSERTED unsigned tuple_count,
                uint64_t header, uint64_t ec0,
                unsigned m0, bool z)
{
        struct bi_clause_format format = bi_clause_formats[index];

        uint8_t sync = bi_pack_sync(format.tag_1, format.tag_2, format.tag_3,
                        tuples, tuple_count, z);

        uint64_t s0_s3 = bi_pack_t_ec(format.s0_s3, tuples, tuple_count, ec0);

        uint16_t s4 = bi_pack_subword(format.s4, format.format, tuples, tuple_count, header, ec0, m0, 4);

        uint32_t s5_s6 = bi_pack_subwords_56(format.s5_s6,
                        tuples, tuple_count, header, ec0,
                        (format.format == 2 || format.format == 7) ? 0 : 3);

        uint64_t s7 = bi_pack_subword(format.s7, format.format, tuples, tuple_count, header, ec0, m0, 2);

        /* Now that subwords are packed, split into 64-bit halves and emit */
        uint64_t lo = sync | ((s0_s3 & ((1ull << 56) - 1)) << 8);
        uint64_t hi = (s0_s3 >> 56) | ((uint64_t) s4 << 4) | ((uint64_t) s5_s6 << 19) | ((uint64_t) s7 << 49);

        util_dynarray_append(emission, uint64_t, lo);
        util_dynarray_append(emission, uint64_t, hi);
}

static void
bi_pack_clause(bi_context *ctx, bi_clause *clause,
                bi_clause *next_1, bi_clause *next_2,
                struct util_dynarray *emission, gl_shader_stage stage)
{
        struct bi_packed_tuple ins[8] = { 0 };

        for (unsigned i = 0; i < clause->tuple_count; ++i) {
                unsigned prev = ((i == 0) ? clause->tuple_count : i) - 1;
                ins[i] = bi_pack_tuple(clause, &clause->tuples[i],
                                &clause->tuples[prev], i == 0, stage);
        }

        bool ec0_packed = bi_ec0_packed(clause->tuple_count);

        if (ec0_packed)
                clause->constant_count = MAX2(clause->constant_count, 1);

        unsigned constant_quads =
                DIV_ROUND_UP(clause->constant_count - (ec0_packed ? 1 : 0), 2);

        uint64_t header = bi_pack_header(clause, next_1, next_2);
        uint64_t ec0 = (clause->constants[0] >> 4);
        unsigned m0 = (clause->pcrel_idx == 0) ? 4 : 0;

        unsigned counts[8] = {
                1, 2, 3, 3, 4, 5, 5, 6
        };

        unsigned indices[8][6] = {
                { 1 },
                { 0, 2 },
                { 0, 3, 4 },
                { 0, 3, 6 },
                { 0, 3, 7, 8 },
                { 0, 3, 5, 9, 10 },
                { 0, 3, 5, 9, 11 },
                { 0, 3, 5, 9, 12, 13 },
        };

        unsigned count = counts[clause->tuple_count - 1];

        for (unsigned pos = 0; pos < count; ++pos) {
                ASSERTED unsigned idx = indices[clause->tuple_count - 1][pos];
                assert(bi_clause_formats[idx].pos == pos);
                assert((bi_clause_formats[idx].tag_1 == BI_CLAUSE_SUBWORD_Z) ==
                                (pos == count - 1));

                /* Whether to end the clause immediately after the last tuple */
                bool z = (constant_quads == 0);

                bi_pack_format(emission, indices[clause->tuple_count - 1][pos],
                                ins, clause->tuple_count, header, ec0, m0,
                                z);
        }

        /* Pack the remaining constants */

        for (unsigned pos = 0; pos < constant_quads; ++pos) {
                bi_pack_constants(clause->tuple_count, clause->constants,
                                pos, constant_quads, ec0_packed, emission);
        }
}

static void
bi_collect_blend_ret_addr(bi_context *ctx, struct util_dynarray *emission,
                          const bi_clause *clause)
{
        /* No need to collect return addresses when we're in a blend shader. */
        if (ctx->inputs->is_blend)
                return;

        const bi_tuple *tuple = &clause->tuples[clause->tuple_count - 1];
        const bi_instr *ins = tuple->add;

        if (!ins || ins->op != BI_OPCODE_BLEND)
                return;


        unsigned loc = tuple->regs.fau_idx - BIR_FAU_BLEND_0;
        assert(loc < ARRAY_SIZE(ctx->info->bifrost.blend));
        assert(!ctx->info->bifrost.blend[loc].return_offset);
        ctx->info->bifrost.blend[loc].return_offset =
                util_dynarray_num_elements(emission, uint8_t);
        assert(!(ctx->info->bifrost.blend[loc].return_offset & 0x7));
}

unsigned
bi_pack(bi_context *ctx, struct util_dynarray *emission)
{
        unsigned previous_size = emission->size;

        bi_foreach_block(ctx, block) {
                bi_assign_branch_offset(ctx, block);

                bi_foreach_clause_in_block(block, clause) {
                        bool is_last = (clause->link.next == &block->clauses);

                        /* Get the succeeding clauses, either two successors of
                         * the block for the last clause in the block or just
                         * the next clause within the block */

                        bi_clause *next = NULL, *next_2 = NULL;

                        if (is_last) {
                                next = bi_next_clause(ctx, block->successors[0], NULL);
                                next_2 = bi_next_clause(ctx, block->successors[1], NULL);
                        } else {
                                next = bi_next_clause(ctx, block, clause);
                        }


                        previous_size = emission->size;

                        bi_pack_clause(ctx, clause, next, next_2, emission, ctx->stage);

                        if (!is_last)
                                bi_collect_blend_ret_addr(ctx, emission, clause);
                }
        }

        return emission->size - previous_size;
}