summaryrefslogtreecommitdiff
path: root/src/compiler/nir/nir_opt_conditional_discard.c
blob: 781438df06ea63945097bd540b58d1b82a44de82 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
/*
 * Copyright © 2016 Red Hat
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include "nir.h"
#include "nir_builder.h"

/** @file nir_opt_conditional_discard.c
 *
 * Handles optimization of lowering of
 *  - if (cond) discard to discard_if(cond) and
 *  - if (cond) demote to demote_if(cond)
 */

static bool
nir_opt_conditional_discard_block(nir_builder *b, nir_block *block)
{
   if (nir_cf_node_is_first(&block->cf_node))
      return false;

   nir_cf_node *prev_node = nir_cf_node_prev(&block->cf_node);
   if (prev_node->type != nir_cf_node_if)
      return false;

   nir_if *if_stmt = nir_cf_node_as_if(prev_node);
   nir_block *then_block = nir_if_first_then_block(if_stmt);
   nir_block *else_block = nir_if_first_else_block(if_stmt);

   /* check there is only one else block and it is empty */
   if (nir_if_last_else_block(if_stmt) != else_block)
      return false;
   if (!exec_list_is_empty(&else_block->instr_list))
      return false;

   /* check there is only one then block and it has only one instruction in it */
   if (nir_if_last_then_block(if_stmt) != then_block)
      return false;
   if (exec_list_is_empty(&then_block->instr_list))
      return false;
   if (exec_list_length(&then_block->instr_list) > 1)
      return false;
   /*
    * make sure no subsequent phi nodes point at this if.
    */
   nir_block *after = nir_cf_node_as_block(nir_cf_node_next(&if_stmt->cf_node));
   nir_foreach_instr_safe(instr, after) {
      if (instr->type != nir_instr_type_phi)
         break;
      nir_phi_instr *phi = nir_instr_as_phi(instr);

      nir_foreach_phi_src(phi_src, phi) {
         if (phi_src->pred == then_block ||
             phi_src->pred == else_block)
            return false;
      }
   }

   /* Get the first instruction in the then block and confirm it is
    * a discard or a demote instruction.
    */
   nir_instr *instr = nir_block_first_instr(then_block);
   if (instr->type != nir_instr_type_intrinsic)
      return false;

   nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
   nir_intrinsic_op op = intrin->intrinsic;
   assert(if_stmt->condition.is_ssa);
   nir_ssa_def *cond = if_stmt->condition.ssa;
   b->cursor = nir_before_cf_node(prev_node);

   switch (intrin->intrinsic) {
   case nir_intrinsic_discard:
      op = nir_intrinsic_discard_if;
      break;
   case nir_intrinsic_demote:
      op = nir_intrinsic_demote_if;
      break;
   case nir_intrinsic_discard_if:
   case nir_intrinsic_demote_if:
      assert(intrin->src[0].is_ssa);
      cond = nir_iand(b, cond, intrin->src[0].ssa);
      break;
   default:
      return false;
   }

   nir_intrinsic_instr *discard_if =
      nir_intrinsic_instr_create(b->shader, op);
   discard_if->src[0] = nir_src_for_ssa(cond);

   nir_instr_insert_before_cf(prev_node, &discard_if->instr);
   nir_instr_remove(&intrin->instr);
   nir_cf_node_remove(&if_stmt->cf_node);

   return true;
}

bool
nir_opt_conditional_discard(nir_shader *shader)
{
   bool progress = false;

   nir_builder builder;

   nir_foreach_function(function, shader) {
      if (function->impl) {
         nir_builder_init(&builder, function->impl);
         nir_foreach_block_safe(block, function->impl) {
            progress |= nir_opt_conditional_discard_block(&builder, block);
         }
      }
   }
   return progress;
}