pan_liveness.c

/*
 * Copyright (C) 2019-2020 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 "pan_ir.h"
#include "util/u_memory.h"
#include "util/list.h"
#include "util/set.h"

/* Routines for liveness analysis. Liveness is tracked per byte per node. Per
 * byte granularity is necessary for proper handling of int8 */

void
pan_liveness_gen(uint16_t *live, unsigned node, unsigned max, uint16_t mask)
{
        if (node >= max)
                return;

        live[node] |= mask;
}

void
pan_liveness_kill(uint16_t *live, unsigned node, unsigned max, uint16_t mask)
{
        if (node >= max)
                return;

        live[node] &= ~mask;
}

bool
pan_liveness_get(uint16_t *live, unsigned node, uint16_t max)
{
        if (node >= max)
                return false;

        return live[node];
}

/* live_out[s] = sum { p in succ[s] } ( live_in[p] ) */

static void
liveness_block_live_out(pan_block *blk, unsigned temp_count)
{
        pan_foreach_successor(blk, succ) {
                for (unsigned i = 0; i < temp_count; ++i)
                        blk->live_out[i] |= succ->live_in[i];
        }
}

/* Liveness analysis is a backwards-may dataflow analysis pass. Within a block,
 * we compute live_out from live_in. The intrablock pass is linear-time. It
 * returns whether progress was made. */

static bool
liveness_block_update(
                pan_block *blk, unsigned temp_count,
                pan_liveness_update callback)
{
        bool progress = false;

        liveness_block_live_out(blk, temp_count);

        uint16_t *live = ralloc_array(blk, uint16_t, temp_count);
        memcpy(live, blk->live_out, temp_count * sizeof(uint16_t));

        pan_foreach_instr_in_block_rev(blk, ins)
                callback(live, (void *) ins, temp_count);

        /* To figure out progress, diff live_in */

        for (unsigned i = 0; (i < temp_count) && !progress; ++i)
                progress |= (blk->live_in[i] != live[i]);

        ralloc_free(blk->live_in);
        blk->live_in = live;

        return progress;
}


/* Globally, liveness analysis uses a fixed-point algorithm based on a
 * worklist. We initialize a work list with the exit block. We iterate the work
 * list to compute live_in from live_out for each block on the work list,
 * adding the predecessors of the block to the work list if we made progress.
 */

void
pan_compute_liveness(
                struct list_head *blocks,
                unsigned temp_count,
                pan_liveness_update callback)
{

        /* Set of pan_block */
        struct set *work_list = _mesa_set_create(NULL,
                        _mesa_hash_pointer,
                        _mesa_key_pointer_equal);

        struct set *visited = _mesa_set_create(NULL,
                        _mesa_hash_pointer,
                        _mesa_key_pointer_equal);

        /* Free any previous liveness, and allocate */

        pan_free_liveness(blocks);

        list_for_each_entry(pan_block, block, blocks, link) {
                block->live_in = rzalloc_array(block, uint16_t, temp_count);
                block->live_out = rzalloc_array(block, uint16_t, temp_count);
        }

        /* Initialize the work list with the exit block */
        struct set_entry *cur;

        cur = _mesa_set_add(work_list, pan_exit_block(blocks));

        /* Iterate the work list */

        do {
                /* Pop off a block */
                pan_block *blk = (struct pan_block *) cur->key;
                _mesa_set_remove(work_list, cur);

                /* Update its liveness information */
                bool progress = liveness_block_update(blk, temp_count, callback);

                /* If we made progress, we need to process the predecessors */

                if (progress || !_mesa_set_search(visited, blk)) {
                        pan_foreach_predecessor(blk, pred)
                                _mesa_set_add(work_list, pred);
                }

                _mesa_set_add(visited, blk);
        } while((cur = _mesa_set_next_entry(work_list, NULL)) != NULL);

        _mesa_set_destroy(visited, NULL);
        _mesa_set_destroy(work_list, NULL);
}

void
pan_free_liveness(struct list_head *blocks)
{
        list_for_each_entry(pan_block, block, blocks, link) {
                if (block->live_in)
                        ralloc_free(block->live_in);

                if (block->live_out)
                        ralloc_free(block->live_out);

                block->live_in = NULL;
                block->live_out = NULL;
        }
}