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->dest == ctx->blend_src1)
  40                 return false;
  41
  42         if (ins->type == TAG_LOAD_STORE_4)
  43                 if (load_store_opcode_props[ins->load_store.op].props & LDST_SPECIAL_MASK)
  44                         return false;
  45
  46         return true;
  47 }
  48
  49 static bool
  50 can_dce(midgard_instruction *ins)
  51 {
  52         if (ins->mask)
  53                 return false;
  54
  55         if (ins->compact_branch)
  56                 return false;
  57
  58         if (ins->type == TAG_LOAD_STORE_4)
  59                 if (load_store_opcode_props[ins->load_store.op].props & LDST_SIDE_FX)
  60                         return false;
  61
  62         if (ins->type == TAG_TEXTURE_4)
  63                 if (ins->op == TEXTURE_OP_BARRIER)
  64                         return false;
  65
  66         return true;
  67 }
  68
  69 static bool
  70 midgard_opt_dead_code_eliminate_block(compiler_context *ctx, midgard_block *block)
  71 {
  72         bool progress = false;
  73
  74         uint16_t *live = mem_dup(block->base.live_out, ctx->temp_count * sizeof(uint16_t));
  75
  76         mir_foreach_instr_in_block_rev(block, ins) {
  77                 if (can_cull_mask(ctx, ins)) {
  78                         unsigned type_size = nir_alu_type_get_type_size(ins->dest_type);
  79                         unsigned round_size = type_size;
  80                         unsigned oldmask = ins->mask;
  81
  82                         /* Make sure we're packable */
  83                         if (type_size == 16 && ins->type == TAG_LOAD_STORE_4)
  84                                 round_size = 32;
  85
  86                         unsigned rounded = mir_round_bytemask_up(live[ins->dest], round_size);
  87                         unsigned cmask = mir_from_bytemask(rounded, type_size);
  88
  89                         ins->mask &= cmask;
  90                         progress |= (ins->mask != oldmask);
  91                 }
  92
  93                 mir_liveness_ins_update(live, ins, ctx->temp_count);
  94         }
  95
  96         mir_foreach_instr_in_block_safe(block, ins) {
  97                 if (can_dce(ins)) {
  98                         mir_remove_instruction(ins);
  99                         progress = true;
 100                 }
 101         }
 102
 103         free(live);
 104
 105         return progress;
 106 }
 107
 108 bool
 109 midgard_opt_dead_code_eliminate(compiler_context *ctx)
 110 {
 111         /* We track liveness. In fact, it's ok if we assume more things are
 112          * live than they actually are, that just reduces the effectiveness of
 113          * this iterations lightly. And DCE has the effect of strictly reducing
 114          * liveness, so we can run DCE across all blocks while only computing
 115          * liveness at the beginning. */
 116
 117         mir_invalidate_liveness(ctx);
 118         mir_compute_liveness(ctx);
 119
 120         bool progress = false;
 121
 122         mir_foreach_block(ctx, block) {
 123                 progress |= midgard_opt_dead_code_eliminate_block(ctx, (midgard_block *) block);
 124         }
 125
 126         return progress;
 127 }
 128
 129 /* Removes dead moves, that is, moves with a destination overwritten before
 130  * being read. Normally handled implicitly as part of DCE, but this has to run
 131  * after the out-of-SSA pass */
 132
 133 bool
 134 midgard_opt_dead_move_eliminate(compiler_context *ctx, midgard_block *block)
 135 {
 136         bool progress = false;
 137
 138         mir_foreach_instr_in_block_safe(block, ins) {
 139                 if (ins->type != TAG_ALU_4) continue;
 140                 if (ins->compact_branch) continue;
 141                 if (!OP_IS_MOVE(ins->op)) continue;
 142
 143                 /* Check if it's overwritten in this block before being read */
 144                 bool overwritten = false;
 145
 146                 mir_foreach_instr_in_block_from(block, q, mir_next_op(ins)) {
 147                         /* Check if used */
 148                         if (mir_has_arg(q, ins->dest))
 149                                 break;
 150
 151                         /* Check if overwritten */
 152                         if (q->dest == ins->dest) {
 153                                 /* Special case to vec4; component tracking is
 154                                  * harder */
 155
 156                                 overwritten = (q->mask == 0xF);
 157                                 break;
 158                         }
 159                 }
 160
 161                 if (overwritten) {
 162                         mir_remove_instruction(ins);
 163                         progress = true;
 164                 }
 165         }
 166
 167         return progress;
 168 }