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 /* mir_is_live_after performs liveness analysis on the MIR, used primarily
  25  * as part of register allocation. TODO: Algorithmic improvements for
  26  * compiler performance (this is the worst algorithm possible -- see
  27  * backlog with Connor on IRC) */
  28
  29 #include "compiler.h"
  30
  31 static bool
  32 midgard_is_live_in_instr(midgard_instruction *ins, int src)
  33 {
  34         if (ins->compact_branch)
  35                 return false;
  36
  37         if (ins->ssa_args.src0 == src)
  38                 return true;
  39
  40         if (!ins->ssa_args.inline_constant && ins->ssa_args.src1 == src)
  41                 return true;
  42
  43         return false;
  44 }
  45
  46 /* Determine if a variable is live in the successors of a block */
  47 static bool
  48 is_live_after_successors(compiler_context *ctx, midgard_block *bl, int src)
  49 {
  50         for (unsigned i = 0; i < bl->nr_successors; ++i) {
  51                 midgard_block *succ = bl->successors[i];
  52
  53                 /* If we already visited, the value we're seeking
  54                  * isn't down this path (or we would have short
  55                  * circuited */
  56
  57                 if (succ->visited) continue;
  58
  59                 /* Otherwise (it's visited *now*), check the block */
  60
  61                 succ->visited = true;
  62
  63                 /* Within this block, check if it's overwritten first */
  64                 bool block_done = false;
  65
  66                 mir_foreach_instr_in_block(succ, ins) {
  67                         if (midgard_is_live_in_instr(ins, src))
  68                                 return true;
  69
  70                         /* If written-before-use, we're gone */
  71
  72                         if (ins->ssa_args.dest == src && ins->type == TAG_LOAD_STORE_4 && ins->load_store.op == midgard_op_ld_int4 && ins->load_store.unknown == 0x1EEA) {
  73                                 block_done = true;
  74                                 break;
  75                         }
  76                 }
  77
  78                 if (block_done)
  79                         continue;
  80
  81                 /* ...and also, check *its* successors */
  82                 if (is_live_after_successors(ctx, succ, src))
  83                         return true;
  84
  85         }
  86
  87         /* Welp. We're really not live. */
  88
  89         return false;
  90 }
  91
  92 bool
  93 mir_is_live_after(compiler_context *ctx, midgard_block *block, midgard_instruction *start, int src)
  94 {
  95         /* Check the rest of the block for liveness */
  96
  97         mir_foreach_instr_in_block_from(block, ins, mir_next_op(start)) {
  98                 if (midgard_is_live_in_instr(ins, src))
  99                         return true;
 100         }
 101
 102         /* Check the rest of the blocks for liveness recursively */
 103
 104         bool succ = is_live_after_successors(ctx, block, src);
 105
 106         mir_foreach_block(ctx, block) {
 107                 block->visited = false;
 108         }
 109
 110         return succ;
 111 }
 112
 113 /* Just a quick check -- is it written more than once? (I.e. are we definitely
 114  * not SSA?) */
 115
 116 bool
 117 mir_has_multiple_writes(compiler_context *ctx, int dest)
 118 {
 119         unsigned write_count = 0;
 120
 121         mir_foreach_instr_global(ctx, ins) {
 122                 if (ins->ssa_args.dest == dest)
 123                         write_count++;
 124         }
 125
 126         return write_count > 1;
 127 }