src/panfrost/midgard/midgard_liveness.c

   1 /*
   2  * Copyright (C) 2018-2019 Alyssa Rosenzweig <alyssa@rosenzweig.io>
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  20  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  21  * SOFTWARE.
  22  */
  23
  24 #include "compiler.h"
  25 #include "util/u_memory.h"
  26
  27 /* Routines for liveness analysis */
  28
  29 static void
  30 liveness_gen(uint8_t *live, unsigned node, unsigned max, unsigned mask)
  31 {
  32         if (node >= max)
  33                 return;
  34
  35         live[node] |= mask;
  36 }
  37
  38 static void
  39 liveness_kill(uint8_t *live, unsigned node, unsigned max, unsigned mask)
  40 {
  41         if (node >= max)
  42                 return;
  43
  44         live[node] &= ~mask;
  45 }
  46
  47 static bool
  48 liveness_get(uint8_t *live, unsigned node, unsigned max) {
  49         if (node >= max)
  50                 return false;
  51
  52         return live[node];
  53 }
  54
  55 /* Updates live_in for a single instruction */
  56
  57 void
  58 mir_liveness_ins_update(uint8_t *live, midgard_instruction *ins, unsigned max)
  59 {
  60         /* live_in[s] = GEN[s] + (live_out[s] - KILL[s]) */
  61
  62         liveness_kill(live, ins->dest, max, ins->mask);
  63
  64         mir_foreach_src(ins, src) {
  65                 unsigned node = ins->src[src];
  66                 unsigned mask = mir_mask_of_read_components(ins, node);
  67
  68                 liveness_gen(live, node, max, mask);
  69         }
  70 }
  71
  72 /* live_out[s] = sum { p in succ[s] } ( live_in[p] ) */
  73
  74 static void
  75 liveness_block_live_out(compiler_context *ctx, midgard_block *blk)
  76 {
  77         mir_foreach_successor(blk, succ) {
  78                 for (unsigned i = 0; i < ctx->temp_count; ++i)
  79                         blk->live_out[i] |= succ->live_in[i];
  80         }
  81 }
  82
  83 /* Liveness analysis is a backwards-may dataflow analysis pass. Within a block,
  84  * we compute live_out from live_in. The intrablock pass is linear-time. It
  85  * returns whether progress was made. */
  86
  87 static bool
  88 liveness_block_update(compiler_context *ctx, midgard_block *blk)
  89 {
  90         bool progress = false;
  91
  92         liveness_block_live_out(ctx, blk);
  93
  94         uint8_t *live = mem_dup(blk->live_out, ctx->temp_count);
  95
  96         mir_foreach_instr_in_block_rev(blk, ins)
  97                 mir_liveness_ins_update(live, ins, ctx->temp_count);
  98
  99         /* To figure out progress, diff live_in */
 100
 101         for (unsigned i = 0; (i < ctx->temp_count) && !progress; ++i)
 102                 progress |= (blk->live_in[i] != live[i]);
 103
 104         free(blk->live_in);
 105         blk->live_in = live;
 106
 107         return progress;
 108 }
 109
 110 /* Globally, liveness analysis uses a fixed-point algorithm based on a
 111  * worklist. We initialize a work list with the exit block. We iterate the work
 112  * list to compute live_in from live_out for each block on the work list,
 113  * adding the predecessors of the block to the work list if we made progress.
 114  */
 115
 116 void
 117 mir_compute_liveness(compiler_context *ctx)
 118 {
 119         /* If we already have fresh liveness, nothing to do */
 120         if (ctx->metadata & MIDGARD_METADATA_LIVENESS)
 121                 return;
 122
 123         mir_compute_temp_count(ctx);
 124
 125         /* List of midgard_block */
 126         struct set *work_list = _mesa_set_create(ctx,
 127                         _mesa_hash_pointer,
 128                         _mesa_key_pointer_equal);
 129
 130         /* Allocate */
 131
 132         mir_foreach_block(ctx, block) {
 133                 block->live_in = calloc(ctx->temp_count, 1);
 134                 block->live_out = calloc(ctx->temp_count, 1);
 135         }
 136
 137         /* Initialize the work list with the exit block */
 138         struct set_entry *cur;
 139
 140         midgard_block *exit = mir_exit_block(ctx);
 141         cur = _mesa_set_add(work_list, exit);
 142
 143         /* Iterate the work list */
 144
 145         do {
 146                 /* Pop off a block */
 147                 midgard_block *blk = (struct midgard_block *) cur->key;
 148                 _mesa_set_remove(work_list, cur);
 149
 150                 /* Update its liveness information */
 151                 bool progress = liveness_block_update(ctx, blk);
 152
 153                 /* If we made progress, we need to process the predecessors */
 154
 155                 if (progress || (blk == exit)) {
 156                         mir_foreach_predecessor(blk, pred)
 157                                 _mesa_set_add(work_list, pred);
 158                 }
 159         } while((cur = _mesa_set_next_entry(work_list, NULL)) != NULL);
 160
 161         /* Liveness is now valid */
 162         ctx->metadata |= MIDGARD_METADATA_LIVENESS;
 163 }
 164
 165 /* Once liveness data is no longer valid, call this */
 166
 167 void
 168 mir_invalidate_liveness(compiler_context *ctx)
 169 {
 170         /* If we didn't already compute liveness, there's nothing to do */
 171         if (!(ctx->metadata & MIDGARD_METADATA_LIVENESS))
 172                 return;
 173
 174         /* It's now invalid regardless */
 175         ctx->metadata &= ~MIDGARD_METADATA_LIVENESS;
 176
 177         mir_foreach_block(ctx, block) {
 178                 if (block->live_in)
 179                         free(block->live_in);
 180
 181                 if (block->live_out)
 182                         free(block->live_out);
 183
 184                 block->live_in = NULL;
 185                 block->live_out = NULL;
 186         }
 187 }
 188
 189 bool
 190 mir_is_live_after(compiler_context *ctx, midgard_block *block, midgard_instruction *start, int src)
 191 {
 192         mir_compute_liveness(ctx);
 193
 194         /* Check whether we're live in the successors */
 195
 196         if (liveness_get(block->live_out, src, ctx->temp_count))
 197                 return true;
 198
 199         /* Check the rest of the block for liveness */
 200
 201         mir_foreach_instr_in_block_from(block, ins, mir_next_op(start)) {
 202                 if (mir_has_arg(ins, src))
 203                         return true;
 204         }
 205
 206         return false;
 207 }