src/gallium/drivers/vc4/vc4_opt_copy_propagation.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_copy_propagation.c
  26  *
  27  * This implements simple copy propagation for QIR without control flow.
  28  *
  29  * For each temp, it keeps a qreg of which source it was MOVed from, if it
  30  * was.  If we see that used later, we can just reuse the source value, since
  31  * we know we don't have control flow, and we have SSA for our values so
  32  * there's no killing to worry about.
  33  */
  34
  35 #include "vc4_qir.h"
  36
  37 static bool
  38 is_copy_mov(struct qinst *inst)
  39 {
  40         if (!inst)
  41                 return false;
  42
  43         if (inst->op != QOP_MOV &&
  44             inst->op != QOP_FMOV &&
  45             inst->op != QOP_MMOV) {
  46                 return false;
  47         }
  48
  49         if (inst->dst.file != QFILE_TEMP)
  50                 return false;
  51
  52         if (inst->src[0].file != QFILE_TEMP &&
  53             inst->src[0].file != QFILE_UNIF) {
  54                 return false;
  55         }
  56
  57         if (inst->dst.pack || inst->cond != QPU_COND_ALWAYS)
  58                 return false;
  59
  60         return true;
  61
  62 }
  63
  64 static bool
  65 try_copy_prop(struct vc4_compile *c, struct qinst *inst, struct qinst **movs)
  66 {
  67         bool debug = false;
  68         bool progress = false;
  69
  70         for (int i = 0; i < qir_get_op_nsrc(inst->op); i++) {
  71                 if (inst->src[i].file != QFILE_TEMP)
  72                         continue;
  73
  74                 /* We have two ways of finding MOVs we can copy propagate
  75                  * from.  One is if it's an SSA def: then we can reuse it from
  76                  * any block in the program, as long as its source is also an
  77                  * SSA def.  Alternatively, if it's in the "movs" array
  78                  * tracked within the block, then we know the sources for it
  79                  * haven't been changed since we saw the instruction within
  80                  * our block.
  81                  */
  82                 struct qinst *mov = movs[inst->src[i].index];
  83                 if (!mov) {
  84                         if (!is_copy_mov(c->defs[inst->src[i].index]))
  85                                 continue;
  86                         mov = c->defs[inst->src[i].index];
  87
  88                         if (mov->src[0].file == QFILE_TEMP &&
  89                             !c->defs[mov->src[0].index])
  90                                 continue;
  91                 }
  92
  93                 uint8_t unpack;
  94                 if (mov->src[0].pack) {
  95                         /* Make sure that the meaning of the unpack
  96                          * would be the same between the two
  97                          * instructions.
  98                          */
  99                         if (qir_is_float_input(inst) !=
 100                             qir_is_float_input(mov)) {
 101                                 continue;
 102                         }
 103
 104                         /* There's only one unpack field, so make sure
 105                          * this instruction doesn't already use it.
 106                          */
 107                         bool already_has_unpack = false;
 108                         for (int j = 0; j < qir_get_op_nsrc(inst->op); j++) {
 109                                 if (inst->src[j].pack)
 110                                         already_has_unpack = true;
 111                         }
 112                         if (already_has_unpack)
 113                                 continue;
 114
 115                         /* A destination pack requires the PM bit to
 116                          * be set to a specific value already, which
 117                          * may be different from ours.
 118                          */
 119                         if (inst->dst.pack)
 120                                 continue;
 121
 122                         unpack = mov->src[0].pack;
 123                 } else {
 124                         unpack = inst->src[i].pack;
 125                 }
 126
 127                 if (debug) {
 128                         fprintf(stderr, "Copy propagate: ");
 129                         qir_dump_inst(c, inst);
 130                         fprintf(stderr, "\n");
 131                 }
 132
 133                 inst->src[i] = mov->src[0];
 134                 inst->src[i].pack = unpack;
 135
 136                 if (debug) {
 137                         fprintf(stderr, "to: ");
 138                         qir_dump_inst(c, inst);
 139                         fprintf(stderr, "\n");
 140                 }
 141
 142                 progress = true;
 143         }
 144
 145         return progress;
 146 }
 147
 148 static void
 149 apply_kills(struct vc4_compile *c, struct qinst **movs, struct qinst *inst)
 150 {
 151         if (inst->dst.file != QFILE_TEMP)
 152                 return;
 153
 154         for (int i = 0; i < c->num_temps; i++) {
 155                 if (movs[i] &&
 156                     (movs[i]->dst.index == inst->dst.index ||
 157                      (movs[i]->src[0].file == QFILE_TEMP &&
 158                       movs[i]->src[0].index == inst->dst.index))) {
 159                         movs[i] = NULL;
 160                 }
 161         }
 162 }
 163
 164 bool
 165 qir_opt_copy_propagation(struct vc4_compile *c)
 166 {
 167         bool progress = false;
 168         struct qinst **movs;
 169
 170         movs = ralloc_array(c, struct qinst *, c->num_temps);
 171         if (!movs)
 172                 return false;
 173
 174         qir_for_each_block(block, c) {
 175                 /* The MOVs array tracks only available movs within the
 176                  * block.
 177                  */
 178                 memset(movs, 0, sizeof(struct qinst *) * c->num_temps);
 179
 180                 qir_for_each_inst(inst, block) {
 181                         progress = try_copy_prop(c, inst, movs) || progress;
 182
 183                         apply_kills(c, movs, inst);
 184
 185                         if (is_copy_mov(inst))
 186                                 movs[inst->dst.index] = inst;
 187                 }
 188         }
 189
 190         ralloc_free(movs);
 191
 192         return progress;
 193 }