bi_opt_cse.c

/*
 * Copyright (C) 2021 Collabora, Ltd.
 * Copyright (C) 2014 Valve Corporation
 *
 * 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 "bi_builder.h"

#define XXH_INLINE_ALL
#include "xxhash.h"

/* This pass handles CSE'ing repeated expressions created in the process of
 * translating from NIR. Also, currently this is intra-block only, to make it
 * work over multiple block we'd need to bring forward dominance calculation.
 */

static inline uint32_t
HASH(uint32_t hash, unsigned data)
{
        return XXH32(&data, sizeof(data), hash);
}

static uint32_t
hash_index(uint32_t hash, bi_index index)
{
        hash = HASH(hash, index.value);
        hash = HASH(hash, index.abs);
        hash = HASH(hash, index.neg);
        hash = HASH(hash, index.swizzle);
        hash = HASH(hash, index.offset);
        hash = HASH(hash, index.reg);
        hash = HASH(hash, index.type);
        return hash;
}

/* Hash an ALU instruction. */
static uint32_t
hash_instr(const void *data)
{
        const bi_instr *I = data;
        uint32_t hash = 0;

        hash = HASH(hash, I->op);

        /* Explcitly skip destinations, except for size details */
        bi_foreach_dest(I, d) {
                hash = HASH(hash, I->dest[d].swizzle);
        }

        bi_foreach_src(I, s) {
                hash = hash_index(hash, I->src[s]);
        }

        /* Explicitly skip branch, regfmt, vecsize, no_spill, tdd, table */
        hash = HASH(hash, I->dest_mod);

        /* Explicitly skip other immediates */
        hash = HASH(hash, I->shift);

        for (unsigned i = 0; i < ARRAY_SIZE(I->flags); ++i)
                hash = HASH(hash, I->flags[i]);

        return hash;
}

static bool
instrs_equal(const void *_i1, const void *_i2)
{
        const bi_instr *i1 = _i1, *i2 = _i2;

	if (i1->op != i2->op)
		return false;

        /* Explicitly skip destinations */

        bi_foreach_src(i1, s) {
                bi_index s1 = i1->src[s], s2 = i2->src[s];

                if (memcmp(&s1, &s2, sizeof(s1)) != 0)
                        return false;
	}

        if (i1->dest_mod != i2->dest_mod)
                return false;

        if (i1->shift != i2->shift)
                return false;

        for (unsigned i = 0; i < ARRAY_SIZE(i1->flags); ++i) {
                if (i1->flags[i] != i2->flags[i])
                        return false;
        }

	return true;
}

/* Determines what instructions the above routines have to handle */

static bool
instr_can_cse(const bi_instr *I)
{
        switch (I->op)  {
        case BI_OPCODE_DTSEL_IMM:
        case BI_OPCODE_DISCARD_F32:
                return false;
        default:
                break;
        }

        if (bi_opcode_props[I->op].message)
                return false;

        if (I->branch_target)
                return false;

        /* Refuse to CSE non-SSA destinations since the data flow analysis
         * required is nontrivial */
        bi_foreach_dest(I, d) {
                if (!bi_is_null(I->dest[d]) && !bi_is_ssa(I->dest[d]))
                        return false;
        }

        /* Similar refuse to CSE non-SSA sources */
        bi_foreach_src(I, s) {
                if (I->src[s].reg || I->src[s].type == BI_INDEX_REGISTER)
                        return false;
        }

        return true;
}

void
bi_opt_cse(bi_context *ctx)
{
        struct set *instr_set = _mesa_set_create(NULL, hash_instr, instrs_equal);

        bi_foreach_block(ctx, block) {
                bi_index *replacement = calloc(sizeof(bi_index), ((ctx->ssa_alloc + 1) << 2));
                _mesa_set_clear(instr_set, NULL);

                bi_foreach_instr_in_block((bi_block *) block, instr) {
                        /* Rewrite before trying to CSE anything so we converge
                         * locally in one iteration */
                        bi_foreach_src(instr, s) {
                                if (s == 0 && bi_opcode_props[instr->op].sr_read)
                                        continue;

                                if (!bi_is_ssa(instr->src[s]))
                                        continue;

                                bi_index repl = replacement[bi_word_node(instr->src[s])];
                                if (!bi_is_null(repl))
                                        instr->src[s] = bi_replace_index(instr->src[s], repl);
                        }

                        if (!instr_can_cse(instr))
                                continue;

                        bool found;
                        struct set_entry *entry =
                                _mesa_set_search_or_add(instr_set, instr, &found);
                        if (found) {
                                const bi_instr *match = entry->key;

                                bi_foreach_dest(instr, d) {
                                        if (!bi_is_null(instr->dest[d]))
                                                replacement[bi_word_node(instr->dest[d])] = match->dest[d];
                                }
                        }
                }

                free(replacement);
        }

        _mesa_set_destroy(instr_set, NULL);
}