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         return true;
  60 }
  61
  62 bool
  63 midgard_opt_dead_code_eliminate(compiler_context *ctx, midgard_block *block)
  64 {
  65         bool progress = false;
  66
  67         mir_invalidate_liveness(ctx);
  68         mir_compute_liveness(ctx);
  69
  70         uint16_t *live = mem_dup(block->live_out, ctx->temp_count * sizeof(uint16_t));
  71
  72         mir_foreach_instr_in_block_rev(block, ins) {
  73                 if (can_cull_mask(ctx, ins)) {
  74                         midgard_reg_mode mode = mir_typesize(ins);
  75                         unsigned oldmask = ins->mask;
  76
  77                         unsigned rounded = mir_round_bytemask_down(live[ins->dest], mode);
  78                         unsigned cmask = mir_from_bytemask(rounded, mode);
  79
  80                         ins->mask &= cmask;
  81                         progress |= (ins->mask != oldmask);
  82                 }
  83
  84                 mir_liveness_ins_update(live, ins, ctx->temp_count);
  85         }
  86
  87         mir_foreach_instr_in_block_safe(block, ins) {
  88                 if (can_dce(ins)) {
  89                         mir_remove_instruction(ins);
  90                         progress = true;
  91                 }
  92         }
  93
  94         free(live);
  95
  96         return progress;
  97 }
  98
  99 /* Removes dead moves, that is, moves with a destination overwritten before
 100  * being read. Normally handled implicitly as part of DCE, but this has to run
 101  * after the out-of-SSA pass */
 102
 103 bool
 104 midgard_opt_dead_move_eliminate(compiler_context *ctx, midgard_block *block)
 105 {
 106         bool progress = false;
 107
 108         mir_foreach_instr_in_block_safe(block, ins) {
 109                 if (ins->type != TAG_ALU_4) continue;
 110                 if (ins->compact_branch) continue;
 111                 if (!OP_IS_MOVE(ins->alu.op)) continue;
 112
 113                 /* Check if it's overwritten in this block before being read */
 114                 bool overwritten = false;
 115
 116                 mir_foreach_instr_in_block_from(block, q, mir_next_op(ins)) {
 117                         /* Check if used */
 118                         if (mir_has_arg(q, ins->dest))
 119                                 break;
 120
 121                         /* Check if overwritten */
 122                         if (q->dest == ins->dest) {
 123                                 /* Special case to vec4; component tracking is
 124                                  * harder */
 125
 126                                 overwritten = (q->mask == 0xF);
 127                                 break;
 128                         }
 129                 }
 130
 131                 if (overwritten) {
 132                         mir_remove_instruction(ins);
 133                         progress = true;
 134                 }
 135         }
 136
 137         return progress;
 138 }