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/*
* 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 "util/u_memory.h"
/* Routines for liveness analysis. Liveness is tracked per byte per node. Per
* byte granularity is necessary for proper handling of int8 */
static void
liveness_gen(uint16_t *live, unsigned node, unsigned max, uint16_t mask)
{
if (node >= max)
return;
live[node] |= mask;
}
static void
liveness_kill(uint16_t *live, unsigned node, unsigned max, uint16_t mask)
{
if (node >= max)
return;
live[node] &= ~mask;
}
static bool
liveness_get(uint16_t *live, unsigned node, uint16_t max) {
if (node >= max)
return false;
return live[node];
}
/* Updates live_in for a single instruction */
void
mir_liveness_ins_update(uint16_t *live, midgard_instruction *ins, unsigned max)
{
/* live_in[s] = GEN[s] + (live_out[s] - KILL[s]) */
liveness_kill(live, ins->dest, max, mir_bytemask(ins));
mir_foreach_src(ins, src) {
unsigned node = ins->src[src];
unsigned bytemask = mir_bytemask_of_read_components(ins, node);
liveness_gen(live, node, max, bytemask);
}
}
/* live_out[s] = sum { p in succ[s] } ( live_in[p] ) */
static void
liveness_block_live_out(compiler_context *ctx, midgard_block *blk)
{
mir_foreach_successor(blk, succ) {
for (unsigned i = 0; i < ctx->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(compiler_context *ctx, midgard_block *blk)
{
bool progress = false;
liveness_block_live_out(ctx, blk);
uint16_t *live = mem_dup(blk->live_out, ctx->temp_count * sizeof(uint16_t));
mir_foreach_instr_in_block_rev(blk, ins)
mir_liveness_ins_update(live, ins, ctx->temp_count);
/* To figure out progress, diff live_in */
for (unsigned i = 0; (i < ctx->temp_count) && !progress; ++i)
progress |= (blk->live_in[i] != live[i]);
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
mir_compute_liveness(compiler_context *ctx)
{
/* If we already have fresh liveness, nothing to do */
if (ctx->metadata & MIDGARD_METADATA_LIVENESS)
return;
mir_compute_temp_count(ctx);
/* List of midgard_block */
struct set *work_list = _mesa_set_create(ctx,
_mesa_hash_pointer,
_mesa_key_pointer_equal);
/* Allocate */
mir_foreach_block(ctx, block) {
block->live_in = calloc(ctx->temp_count, sizeof(uint16_t));
block->live_out = calloc(ctx->temp_count, sizeof(uint16_t));
}
/* Initialize the work list with the exit block */
struct set_entry *cur;
midgard_block *exit = mir_exit_block(ctx);
cur = _mesa_set_add(work_list, exit);
/* Iterate the work list */
do {
/* Pop off a block */
midgard_block *blk = (struct midgard_block *) cur->key;
_mesa_set_remove(work_list, cur);
/* Update its liveness information */
bool progress = liveness_block_update(ctx, blk);
/* If we made progress, we need to process the predecessors */
if (progress || !blk->visited) {
mir_foreach_predecessor(blk, pred)
_mesa_set_add(work_list, pred);
}
blk->visited = true;
} while((cur = _mesa_set_next_entry(work_list, NULL)) != NULL);
/* Liveness is now valid */
ctx->metadata |= MIDGARD_METADATA_LIVENESS;
mir_foreach_block(ctx, block) {
block->visited = false;
}
}
/* Once liveness data is no longer valid, call this */
void
mir_invalidate_liveness(compiler_context *ctx)
{
/* If we didn't already compute liveness, there's nothing to do */
if (!(ctx->metadata & MIDGARD_METADATA_LIVENESS))
return;
/* It's now invalid regardless */
ctx->metadata &= ~MIDGARD_METADATA_LIVENESS;
mir_foreach_block(ctx, block) {
if (block->live_in)
free(block->live_in);
if (block->live_out)
free(block->live_out);
block->live_in = NULL;
block->live_out = NULL;
}
}
bool
mir_is_live_after(compiler_context *ctx, midgard_block *block, midgard_instruction *start, int src)
{
mir_compute_liveness(ctx);
/* Check whether we're live in the successors */
if (liveness_get(block->live_out, src, ctx->temp_count))
return true;
/* Check the rest of the block for liveness */
mir_foreach_instr_in_block_from(block, ins, mir_next_op(start)) {
if (mir_has_arg(ins, src))
return true;
}
return false;
}
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