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. Liveness is tracked per byte per node. Per
  28  * byte granularity is necessary for proper handling of int8 */
  29
  30 static void
  31 liveness_gen(uint16_t *live, unsigned node, unsigned max, uint16_t mask)
  32 {
  33         if (node >= max)
  34                 return;
  35
  36         live[node] |= mask;
  37 }
  38
  39 static void
  40 liveness_kill(uint16_t *live, unsigned node, unsigned max, uint16_t mask)
  41 {
  42         if (node >= max)
  43                 return;
  44
  45         live[node] &= ~mask;
  46 }
  47
  48 static bool
  49 liveness_get(uint16_t *live, unsigned node, uint16_t max) {
  50         if (node >= max)
  51                 return false;
  52
  53         return live[node];
  54 }
  55
  56 /* Updates live_in for a single instruction */
  57
  58 void
  59 mir_liveness_ins_update(uint16_t *live, midgard_instruction *ins, unsigned max)
  60 {
  61         /* live_in[s] = GEN[s] + (live_out[s] - KILL[s]) */
  62
  63         liveness_kill(live, ins->dest, max, mir_bytemask(ins));
  64
  65         mir_foreach_src(ins, src) {
  66                 unsigned node = ins->src[src];
  67                 unsigned bytemask = mir_bytemask_of_read_components(ins, node);
  68
  69                 liveness_gen(live, node, max, bytemask);
  70         }
  71 }
  72
  73 /* live_out[s] = sum { p in succ[s] } ( live_in[p] ) */
  74
  75 static void
  76 liveness_block_live_out(compiler_context *ctx, midgard_block *blk)
  77 {
  78         mir_foreach_successor(blk, succ) {
  79                 for (unsigned i = 0; i < ctx->temp_count; ++i)
  80                         blk->live_out[i] |= succ->live_in[i];
  81         }
  82 }
  83
  84 /* Liveness analysis is a backwards-may dataflow analysis pass. Within a block,
  85  * we compute live_out from live_in. The intrablock pass is linear-time. It
  86  * returns whether progress was made. */
  87
  88 static bool
  89 liveness_block_update(compiler_context *ctx, midgard_block *blk)
  90 {
  91         bool progress = false;
  92
  93         liveness_block_live_out(ctx, blk);
  94
  95         uint16_t *live = ralloc_array(ctx, uint16_t, ctx->temp_count);
  96         memcpy(live, blk->live_out, ctx->temp_count * sizeof(uint16_t));
  97
  98         mir_foreach_instr_in_block_rev(blk, ins)
  99                 mir_liveness_ins_update(live, ins, ctx->temp_count);
 100
 101         /* To figure out progress, diff live_in */
 102
 103         for (unsigned i = 0; (i < ctx->temp_count) && !progress; ++i)
 104                 progress |= (blk->live_in[i] != live[i]);
 105
 106         ralloc_free(blk->live_in);
 107         blk->live_in = live;
 108
 109         return progress;
 110 }
 111
 112 /* Globally, liveness analysis uses a fixed-point algorithm based on a
 113  * worklist. We initialize a work list with the exit block. We iterate the work
 114  * list to compute live_in from live_out for each block on the work list,
 115  * adding the predecessors of the block to the work list if we made progress.
 116  */
 117
 118 void
 119 mir_compute_liveness(compiler_context *ctx)
 120 {
 121         /* If we already have fresh liveness, nothing to do */
 122         if (ctx->metadata & MIDGARD_METADATA_LIVENESS)
 123                 return;
 124
 125         mir_compute_temp_count(ctx);
 126
 127         /* List of midgard_block */
 128         struct set *work_list = _mesa_set_create(ctx,
 129                         _mesa_hash_pointer,
 130                         _mesa_key_pointer_equal);
 131
 132         struct set *visited = _mesa_set_create(ctx,
 133                         _mesa_hash_pointer,
 134                         _mesa_key_pointer_equal);
 135
 136         /* Allocate */
 137
 138         mir_foreach_block(ctx, block) {
 139                 block->live_in = rzalloc_array(NULL, uint16_t, ctx->temp_count);
 140                 block->live_out = rzalloc_array(NULL, uint16_t, ctx->temp_count);
 141         }
 142
 143         /* Initialize the work list with the exit block */
 144         struct set_entry *cur;
 145
 146         midgard_block *exit = mir_exit_block(ctx);
 147         cur = _mesa_set_add(work_list, exit);
 148
 149         /* Iterate the work list */
 150
 151         do {
 152                 /* Pop off a block */
 153                 midgard_block *blk = (struct midgard_block *) cur->key;
 154                 _mesa_set_remove(work_list, cur);
 155
 156                 /* Update its liveness information */
 157                 bool progress = liveness_block_update(ctx, blk);
 158
 159                 /* If we made progress, we need to process the predecessors */
 160
 161                 if (progress || !_mesa_set_search(visited, blk)) {
 162                         mir_foreach_predecessor(blk, pred)
 163                                 _mesa_set_add(work_list, pred);
 164                 }
 165
 166                 _mesa_set_add(visited, blk);
 167         } while((cur = _mesa_set_next_entry(work_list, NULL)) != NULL);
 168
 169         _mesa_set_destroy(visited, NULL);
 170         _mesa_set_destroy(work_list, NULL);
 171
 172         /* Liveness is now valid */
 173         ctx->metadata |= MIDGARD_METADATA_LIVENESS;
 174 }
 175
 176 /* Once liveness data is no longer valid, call this */
 177
 178 void
 179 mir_invalidate_liveness(compiler_context *ctx)
 180 {
 181         /* If we didn't already compute liveness, there's nothing to do */
 182         if (!(ctx->metadata & MIDGARD_METADATA_LIVENESS))
 183                 return;
 184
 185         /* It's now invalid regardless */
 186         ctx->metadata &= ~MIDGARD_METADATA_LIVENESS;
 187
 188         mir_foreach_block(ctx, block) {
 189                 if (block->live_in)
 190                         ralloc_free(block->live_in);
 191
 192                 if (block->live_out)
 193                         ralloc_free(block->live_out);
 194
 195                 block->live_in = NULL;
 196                 block->live_out = NULL;
 197         }
 198 }
 199
 200 bool
 201 mir_is_live_after(compiler_context *ctx, midgard_block *block, midgard_instruction *start, int src)
 202 {
 203         mir_compute_liveness(ctx);
 204
 205         /* Check whether we're live in the successors */
 206
 207         if (liveness_get(block->live_out, src, ctx->temp_count))
 208                 return true;
 209
 210         /* Check the rest of the block for liveness */
 211
 212         mir_foreach_instr_in_block_from(block, ins, mir_next_op(start)) {
 213                 if (mir_has_arg(ins, src))
 214                         return true;
 215         }
 216
 217         return false;
 218 }