src/panfrost/midgard/midgard_opt_dce.c

   1 /*
   2  * Copyright (C) 2018 Alyssa Rosenzweig
   3  * Copyright (C) 2019 Collabora, Ltd.
   4  *
   5  * Permission is hereby granted, free of charge, to any person obtaining a
   6  * copy of this software and associated documentation files (the "Software"),
   7  * to deal in the Software without restriction, including without limitation
   8  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   9  * and/or sell copies of the Software, and to permit persons to whom the
  10  * Software is furnished to do so, subject to the following conditions:
  11  *
  12  * The above copyright notice and this permission notice (including the next
  13  * paragraph) shall be included in all copies or substantial portions of the
  14  * Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22  * SOFTWARE.
  23  */
  24
  25 #include "compiler.h"
  26 #include "util/u_memory.h"
  27 #include "midgard_ops.h"
  28
  29 /* SIMD-aware dead code elimination. Perform liveness analysis step-by-step,
  30  * removing dead components. If an instruction ends up with a zero mask, the
  31  * instruction in total is dead and should be removed. */
  32
  33 static bool
  34 can_cull_mask(compiler_context *ctx, midgard_instruction *ins)
  35 {
  36         if (ins->dest >= ctx->temp_count)
  37                 return false;
  38
  39         if (ins->type == TAG_LOAD_STORE_4)
  40                 if (load_store_opcode_props[ins->load_store.op].props & LDST_SPECIAL_MASK)
  41                         return false;
  42
  43         return true;
  44 }
  45
  46 static bool
  47 can_dce(midgard_instruction *ins)
  48 {
  49         if (ins->mask)
  50                 return false;
  51
  52         if (ins->compact_branch)
  53                 return false;
  54
  55         if (ins->type == TAG_LOAD_STORE_4)
  56                 if (load_store_opcode_props[ins->load_store.op].props & LDST_SIDE_FX)
  57                         return false;
  58
  59         if (ins->type == TAG_TEXTURE_4)
  60                 if (ins->texture.op == TEXTURE_OP_BARRIER)
  61                         return false;
  62
  63         return true;
  64 }
  65
  66 static bool
  67 midgard_opt_dead_code_eliminate_block(compiler_context *ctx, midgard_block *block)
  68 {
  69         bool progress = false;
  70
  71         uint16_t *live = mem_dup(block->base.live_out, ctx->temp_count * sizeof(uint16_t));
  72
  73         mir_foreach_instr_in_block_rev(block, ins) {
  74                 if (can_cull_mask(ctx, ins)) {
  75                         unsigned type_size = nir_alu_type_get_type_size(ins->dest_type);
  76                         unsigned round_size = type_size;
  77                         unsigned oldmask = ins->mask;
  78
  79                         /* Make sure we're packable */
  80                         if (type_size == 16 && ins->type == TAG_LOAD_STORE_4)
  81                                 round_size = 32;
  82
  83                         unsigned rounded = mir_round_bytemask_up(live[ins->dest], round_size);
  84                         unsigned cmask = mir_from_bytemask(rounded, type_size);
  85
  86                         ins->mask &= cmask;
  87                         progress |= (ins->mask != oldmask);
  88                 }
  89
  90                 mir_liveness_ins_update(live, ins, ctx->temp_count);
  91         }
  92
  93         mir_foreach_instr_in_block_safe(block, ins) {
  94                 if (can_dce(ins)) {
  95                         mir_remove_instruction(ins);
  96                         progress = true;
  97                 }
  98         }
  99
 100         free(live);
 101
 102         return progress;
 103 }
 104
 105 bool
 106 midgard_opt_dead_code_eliminate(compiler_context *ctx)
 107 {
 108         /* We track liveness. In fact, it's ok if we assume more things are
 109          * live than they actually are, that just reduces the effectiveness of
 110          * this iterations lightly. And DCE has the effect of strictly reducing
 111          * liveness, so we can run DCE across all blocks while only computing
 112          * liveness at the beginning. */
 113
 114         mir_invalidate_liveness(ctx);
 115         mir_compute_liveness(ctx);
 116
 117         bool progress = false;
 118
 119         mir_foreach_block(ctx, block) {
 120                 progress |= midgard_opt_dead_code_eliminate_block(ctx, (midgard_block *) block);
 121         }
 122
 123         return progress;
 124 }
 125
 126 /* Removes dead moves, that is, moves with a destination overwritten before
 127  * being read. Normally handled implicitly as part of DCE, but this has to run
 128  * after the out-of-SSA pass */
 129
 130 bool
 131 midgard_opt_dead_move_eliminate(compiler_context *ctx, midgard_block *block)
 132 {
 133         bool progress = false;
 134
 135         mir_foreach_instr_in_block_safe(block, ins) {
 136                 if (ins->type != TAG_ALU_4) continue;
 137                 if (ins->compact_branch) continue;
 138                 if (!OP_IS_MOVE(ins->alu.op)) continue;
 139
 140                 /* Check if it's overwritten in this block before being read */
 141                 bool overwritten = false;
 142
 143                 mir_foreach_instr_in_block_from(block, q, mir_next_op(ins)) {
 144                         /* Check if used */
 145                         if (mir_has_arg(q, ins->dest))
 146                                 break;
 147
 148                         /* Check if overwritten */
 149                         if (q->dest == ins->dest) {
 150                                 /* Special case to vec4; component tracking is
 151                                  * harder */
 152
 153                                 overwritten = (q->mask == 0xF);
 154                                 break;
 155                         }
 156                 }
 157
 158                 if (overwritten) {
 159                         mir_remove_instruction(ins);
 160                         progress = true;
 161                 }
 162         }
 163
 164         return progress;
 165 }