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 oldmask = ins->mask;
  77
  78                         unsigned rounded = mir_round_bytemask_up(live[ins->dest], type_size);
  79                         unsigned cmask = mir_from_bytemask(rounded, type_size);
  80
  81                         ins->mask &= cmask;
  82                         progress |= (ins->mask != oldmask);
  83                 }
  84
  85                 mir_liveness_ins_update(live, ins, ctx->temp_count);
  86         }
  87
  88         mir_foreach_instr_in_block_safe(block, ins) {
  89                 if (can_dce(ins)) {
  90                         mir_remove_instruction(ins);
  91                         progress = true;
  92                 }
  93         }
  94
  95         free(live);
  96
  97         return progress;
  98 }
  99
 100 bool
 101 midgard_opt_dead_code_eliminate(compiler_context *ctx)
 102 {
 103         /* We track liveness. In fact, it's ok if we assume more things are
 104          * live than they actually are, that just reduces the effectiveness of
 105          * this iterations lightly. And DCE has the effect of strictly reducing
 106          * liveness, so we can run DCE across all blocks while only computing
 107          * liveness at the beginning. */
 108
 109         mir_invalidate_liveness(ctx);
 110         mir_compute_liveness(ctx);
 111
 112         bool progress = false;
 113
 114         mir_foreach_block(ctx, block) {
 115                 progress |= midgard_opt_dead_code_eliminate_block(ctx, (midgard_block *) block);
 116         }
 117
 118         return progress;
 119 }
 120
 121 /* Removes dead moves, that is, moves with a destination overwritten before
 122  * being read. Normally handled implicitly as part of DCE, but this has to run
 123  * after the out-of-SSA pass */
 124
 125 bool
 126 midgard_opt_dead_move_eliminate(compiler_context *ctx, midgard_block *block)
 127 {
 128         bool progress = false;
 129
 130         mir_foreach_instr_in_block_safe(block, ins) {
 131                 if (ins->type != TAG_ALU_4) continue;
 132                 if (ins->compact_branch) continue;
 133                 if (!OP_IS_MOVE(ins->alu.op)) continue;
 134
 135                 /* Check if it's overwritten in this block before being read */
 136                 bool overwritten = false;
 137
 138                 mir_foreach_instr_in_block_from(block, q, mir_next_op(ins)) {
 139                         /* Check if used */
 140                         if (mir_has_arg(q, ins->dest))
 141                                 break;
 142
 143                         /* Check if overwritten */
 144                         if (q->dest == ins->dest) {
 145                                 /* Special case to vec4; component tracking is
 146                                  * harder */
 147
 148                                 overwritten = (q->mask == 0xF);
 149                                 break;
 150                         }
 151                 }
 152
 153                 if (overwritten) {
 154                         mir_remove_instruction(ins);
 155                         progress = true;
 156                 }
 157         }
 158
 159         return progress;
 160 }