src/panfrost/midgard/midgard_address.c

/*
 * Copyright (C) 2019 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.
 *
 * Authors (Collabora):
 *    Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
 */

#include "compiler.h"

/* Midgard's generic load/store instructions, particularly to implement SSBOs
 * and globals, have support for address arithmetic natively. In particularly,
 * they take two indirect arguments A, B and two immediates #s, #c, calculating
 * the address:
 *
 *      A + (zext?(B) << #s) + #c
 *
 * This allows for fast indexing into arrays. This file tries to pattern match the offset in NIR with this form to reduce pressure on the ALU pipe.
 */

struct mir_address {
        nir_ssa_scalar A;
        nir_ssa_scalar B;

        bool zext;
        unsigned shift;
        unsigned bias;
};

static bool
mir_args_ssa(nir_ssa_scalar s, unsigned count)
{
        nir_alu_instr *alu = nir_instr_as_alu(s.def->parent_instr);
        assert(count <= nir_op_infos[alu->op].num_inputs);

        for (unsigned i = 0; i < count; ++i) {
                if (!alu->src[i].src.is_ssa)
                        return false;
        }

        return true;
}

/* Matches a constant in either slot and moves it to the bias */

static void
mir_match_constant(struct mir_address *address)
{
        if (address->A.def && nir_ssa_scalar_is_const(address->A)) {
                address->bias += nir_ssa_scalar_as_uint(address->A);
                address->A.def = NULL;
        }

        if (address->B.def && nir_ssa_scalar_is_const(address->B)) {
                address->bias += nir_ssa_scalar_as_uint(address->B);
                address->B.def = NULL;
        }
}

/* Matches an iadd when there is a free slot or constant */

static void
mir_match_iadd(struct mir_address *address, bool first_free)
{
        if (!address->B.def || !nir_ssa_scalar_is_alu(address->B))
                return;

        if (!mir_args_ssa(address->B, 2))
                return;

        nir_op op = nir_ssa_scalar_alu_op(address->B);

        if (op != nir_op_iadd) return;

        nir_ssa_scalar op1 = nir_ssa_scalar_chase_alu_src(address->B, 0);
        nir_ssa_scalar op2 = nir_ssa_scalar_chase_alu_src(address->B, 1);

        if (nir_ssa_scalar_is_const(op1)) {
                address->bias += nir_ssa_scalar_as_uint(op1);
                address->B = op2;
        } else if (nir_ssa_scalar_is_const(op2)) {
                address->bias += nir_ssa_scalar_as_uint(op2);
                address->B = op1;
        } else if (first_free && !address->A.def) {
                address->A = op1;
                address->B = op2;
        }
}

/* Matches u2u64 and sets zext */

static void
mir_match_u2u64(struct mir_address *address)
{
        if (!address->B.def || !nir_ssa_scalar_is_alu(address->B))
                return;

        if (!mir_args_ssa(address->B, 1))
                return;

        nir_op op = nir_ssa_scalar_alu_op(address->B);
        if (op != nir_op_u2u64) return;
        nir_ssa_scalar arg = nir_ssa_scalar_chase_alu_src(address->B, 0);

        address->B = arg;
        address->zext = true;
}

/* Matches ishl to shift */

static void
mir_match_ishl(struct mir_address *address)
{
        if (!address->B.def || !nir_ssa_scalar_is_alu(address->B))
                return;

        if (!mir_args_ssa(address->B, 2))
                return;

        nir_op op = nir_ssa_scalar_alu_op(address->B);
        if (op != nir_op_ishl) return;
        nir_ssa_scalar op1 = nir_ssa_scalar_chase_alu_src(address->B, 0);
        nir_ssa_scalar op2 = nir_ssa_scalar_chase_alu_src(address->B, 1);

        if (!nir_ssa_scalar_is_const(op2)) return;

        unsigned shift = nir_ssa_scalar_as_uint(op2);
        if (shift > 0x7) return;

        address->B = op1;
        address->shift = shift;
}

/* Strings through mov which can happen from NIR vectorization */

static void
mir_match_mov(struct mir_address *address)
{
        if (address->A.def && nir_ssa_scalar_is_alu(address->A)) {
                nir_op op = nir_ssa_scalar_alu_op(address->A);

                if (op == nir_op_mov && mir_args_ssa(address->A, 1))
                        address->A = nir_ssa_scalar_chase_alu_src(address->A, 0);
        }

        if (address->B.def && nir_ssa_scalar_is_alu(address->B)) {
                nir_op op = nir_ssa_scalar_alu_op(address->B);

                if (op == nir_op_mov && mir_args_ssa(address->B, 1))
                        address->B = nir_ssa_scalar_chase_alu_src(address->B, 0);
        }
}

/* Tries to pattern match into mir_address */

static struct mir_address
mir_match_offset(nir_ssa_def *offset, bool first_free)
{
        struct mir_address address = {
                .B = { .def = offset }
        };

        mir_match_mov(&address);
        mir_match_constant(&address);
        mir_match_mov(&address);
        mir_match_iadd(&address, first_free);
        mir_match_mov(&address);
        mir_match_u2u64(&address);
        mir_match_mov(&address);
        mir_match_ishl(&address);

        return address;
}

void
mir_set_offset(compiler_context *ctx, midgard_instruction *ins, nir_src *offset, bool is_shared)
{
        for(unsigned i = 0; i < 16; ++i) {
                ins->swizzle[1][i] = 0;
                ins->swizzle[2][i] = 0;
        }

        bool force_zext = (nir_src_bit_size(*offset) < 64);

        if (!offset->is_ssa) {
                ins->load_store.arg_1 |= is_shared ? 0x6E : 0x7E;
                ins->src[2] = nir_src_index(ctx, offset);
                ins->src_types[2] = nir_type_uint | nir_src_bit_size(*offset);

                if (force_zext)
                        ins->load_store.arg_1 |= 0x80;

                return;
        }

        struct mir_address match = mir_match_offset(offset->ssa, !is_shared);

        if (match.A.def) {
                ins->src[1] = nir_ssa_index(match.A.def);
                ins->swizzle[1][0] = match.A.comp;
                ins->src_types[1] = nir_type_uint | match.A.def->bit_size;
        } else
                ins->load_store.arg_1 |= is_shared ? 0x6E : 0x7E;

        if (match.B.def) {
                ins->src[2] = nir_ssa_index(match.B.def);
                ins->swizzle[2][0] = match.B.comp;
                ins->src_types[2] = nir_type_uint | match.B.def->bit_size;
        } else
                ins->load_store.arg_2 = 0x1E;

        if (match.zext || force_zext)
                ins->load_store.arg_1 |= 0x80;

        assert(match.shift <= 7);
        ins->load_store.arg_2 |= (match.shift) << 5;

        ins->constants.u32[0] = match.bias;
}