1/*
2 * Copyright © 2014 Intel Corporation
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#include "brw_fs.h"
25#include "brw_fs_live_variables.h"
26#include "brw_cfg.h"
27
28/** @file brw_fs_dead_code_eliminate.cpp
29 *
30 * Dataflow-aware dead code elimination.
31 *
32 * Walks the instruction list from the bottom, removing instructions that
33 * have results that both aren't used in later blocks and haven't been read
34 * yet in the tail end of this block.
35 */
36
37/**
38 * Is it safe to eliminate the instruction?
39 */
40static bool
41can_eliminate(const fs_inst *inst, BITSET_WORD *flag_live)
42{
43    return !inst->is_control_flow() &&
44           !inst->has_side_effects() &&
45           !(flag_live[0] & inst->flags_written()) &&
46           !inst->writes_accumulator;
47}
48
49/**
50 * Is it safe to omit the write, making the destination ARF null?
51 */
52static bool
53can_omit_write(const fs_inst *inst)
54{
55   switch (inst->opcode) {
56   case SHADER_OPCODE_UNTYPED_ATOMIC_LOGICAL:
57   case SHADER_OPCODE_UNTYPED_ATOMIC_FLOAT_LOGICAL:
58   case SHADER_OPCODE_TYPED_ATOMIC_LOGICAL:
59      return true;
60   default:
61      /* We can eliminate the destination write for ordinary instructions,
62       * but not most SENDs.
63       */
64      if (inst->opcode < 128 && inst->mlen == 0)
65         return true;
66
67      /* It might not be safe for other virtual opcodes. */
68      return false;
69   }
70}
71
72bool
73fs_visitor::dead_code_eliminate()
74{
75   bool progress = false;
76
77   calculate_live_intervals();
78
79   int num_vars = live_intervals->num_vars;
80   BITSET_WORD *live = rzalloc_array(NULL, BITSET_WORD, BITSET_WORDS(num_vars));
81   BITSET_WORD *flag_live = rzalloc_array(NULL, BITSET_WORD, 1);
82
83   foreach_block_reverse_safe(block, cfg) {
84      memcpy(live, live_intervals->block_data[block->num].liveout,
85             sizeof(BITSET_WORD) * BITSET_WORDS(num_vars));
86      memcpy(flag_live, live_intervals->block_data[block->num].flag_liveout,
87             sizeof(BITSET_WORD));
88
89      foreach_inst_in_block_reverse_safe(fs_inst, inst, block) {
90         if (inst->dst.file == VGRF) {
91            const unsigned var = live_intervals->var_from_reg(inst->dst);
92            bool result_live = false;
93
94            for (unsigned i = 0; i < regs_written(inst); i++)
95               result_live |= BITSET_TEST(live, var + i);
96
97            if (!result_live &&
98                (can_omit_write(inst) || can_eliminate(inst, flag_live))) {
99               inst->dst = fs_reg(retype(brw_null_reg(), inst->dst.type));
100               progress = true;
101            }
102         }
103
104         if (inst->dst.is_null() && can_eliminate(inst, flag_live)) {
105            inst->opcode = BRW_OPCODE_NOP;
106            progress = true;
107         }
108
109         if (inst->dst.file == VGRF) {
110            if (!inst->is_partial_write()) {
111               int var = live_intervals->var_from_reg(inst->dst);
112               for (unsigned i = 0; i < regs_written(inst); i++) {
113                  BITSET_CLEAR(live, var + i);
114               }
115            }
116         }
117
118         if (!inst->predicate && inst->exec_size >= 8)
119            flag_live[0] &= ~inst->flags_written();
120
121         if (inst->opcode == BRW_OPCODE_NOP) {
122            inst->remove(block);
123            continue;
124         }
125
126         for (int i = 0; i < inst->sources; i++) {
127            if (inst->src[i].file == VGRF) {
128               int var = live_intervals->var_from_reg(inst->src[i]);
129
130               for (unsigned j = 0; j < regs_read(inst, i); j++) {
131                  BITSET_SET(live, var + j);
132               }
133            }
134         }
135
136         flag_live[0] |= inst->flags_read(devinfo);
137      }
138   }
139
140   ralloc_free(live);
141   ralloc_free(flag_live);
142
143   if (progress)
144      invalidate_live_intervals();
145
146   return progress;
147}
148