src/gallium/drivers/vc4/vc4_opt_dead_code.c

   1 /*
   2  * Copyright © 2014 Broadcom
   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
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  21  * IN THE SOFTWARE.
  22  */
  23
  24 /**
  25  * @file vc4_opt_dead_code.c
  26  *
  27  * This is a simmple dead code eliminator for QIR with no control flow.
  28  *
  29  * It walks from the bottom of the instruction list, removing instructions
  30  * with a destination that is never used, and marking the sources of non-dead
  31  * instructions as used.
  32  */
  33
  34 #include "vc4_qir.h"
  35
  36 static bool debug;
  37
  38 static void
  39 dce(struct vc4_compile *c, struct qinst *inst)
  40 {
  41         if (debug) {
  42                 fprintf(stderr, "Removing: ");
  43                 qir_dump_inst(c, inst);
  44                 fprintf(stderr, "\n");
  45         }
  46         assert(!inst->sf);
  47         qir_remove_instruction(c, inst);
  48 }
  49
  50 static bool
  51 has_nonremovable_reads(struct vc4_compile *c, struct qinst *inst)
  52 {
  53         for (int i = 0; i < qir_get_op_nsrc(inst->op); i++) {
  54                 if (inst->src[i].file == QFILE_VPM) {
  55                         uint32_t attr = inst->src[i].index / 4;
  56                         uint32_t offset = (inst->src[i].index % 4) * 4;
  57
  58                         if (c->vattr_sizes[attr] != offset + 4)
  59                                 return true;
  60
  61                         /* Can't get rid of the last VPM read, or the
  62                          * simulator (at least) throws an error.
  63                          */
  64                         uint32_t total_size = 0;
  65                         for (uint32_t i = 0; i < ARRAY_SIZE(c->vattr_sizes); i++)
  66                                 total_size += c->vattr_sizes[i];
  67                         if (total_size == 4)
  68                                 return true;
  69                 }
  70
  71                 if (inst->src[i].file == QFILE_VARY &&
  72                     c->input_slots[inst->src[i].index].slot == 0xff) {
  73                         return true;
  74                 }
  75         }
  76
  77         return false;
  78 }
  79
  80 bool
  81 qir_opt_dead_code(struct vc4_compile *c)
  82 {
  83         bool progress = false;
  84         bool *used = calloc(c->num_temps, sizeof(bool));
  85         bool sf_used = false;
  86
  87         list_for_each_entry_safe_rev(struct qinst, inst, &c->instructions,
  88                                      link) {
  89                 if (inst->dst.file == QFILE_TEMP &&
  90                     !used[inst->dst.index] &&
  91                     !inst->sf &&
  92                     !qir_has_side_effects(c, inst) &&
  93                     !has_nonremovable_reads(c, inst)) {
  94                         for (int i = 0; i < qir_get_op_nsrc(inst->op); i++) {
  95                                 if (inst->src[i].file != QFILE_VPM)
  96                                         continue;
  97                                 uint32_t attr = inst->src[i].index / 4;
  98                                 uint32_t offset = (inst->src[i].index % 4) * 4;
  99
 100                                 if (c->vattr_sizes[attr] == offset + 4) {
 101                                         c->num_inputs--;
 102                                         c->vattr_sizes[attr] -= 4;
 103                                 }
 104                         }
 105
 106                         dce(c, inst);
 107                         progress = true;
 108                         continue;
 109                 }
 110
 111                 if (qir_depends_on_flags(inst))
 112                         sf_used = true;
 113                 if (inst->sf) {
 114                         if (!sf_used) {
 115                                 if (debug) {
 116                                         fprintf(stderr, "Removing SF on: ");
 117                                         qir_dump_inst(c, inst);
 118                                         fprintf(stderr, "\n");
 119                                 }
 120
 121                                 inst->sf = false;
 122                                 progress = true;
 123                         }
 124                         sf_used = false;
 125                 }
 126
 127                 for (int i = 0; i < qir_get_op_nsrc(inst->op); i++) {
 128                         if (inst->src[i].file == QFILE_TEMP)
 129                                 used[inst->src[i].index] = true;
 130                 }
 131         }
 132
 133         free(used);
 134
 135         return progress;
 136 }