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 * Authors:
24 *    Connor Abbott (cwabbott0@gmail.com)
25 *
26 */
27
28#include "nir.h"
29
30static bool
31deref_used_for_not_store(nir_deref_instr *deref)
32{
33   nir_foreach_use(src, &deref->dest.ssa) {
34      switch (src->parent_instr->type) {
35      case nir_instr_type_deref:
36         if (deref_used_for_not_store(nir_instr_as_deref(src->parent_instr)))
37            return true;
38         break;
39
40      case nir_instr_type_intrinsic: {
41         nir_intrinsic_instr *intrin =
42            nir_instr_as_intrinsic(src->parent_instr);
43         /* The first source of copy and store intrinsics is the deref to
44          * write.  Don't record those.
45          */
46         if ((intrin->intrinsic != nir_intrinsic_store_deref &&
47              intrin->intrinsic != nir_intrinsic_copy_deref) ||
48             src != &intrin->src[0])
49            return true;
50         break;
51      }
52
53      default:
54         /* If it's used by any other instruction type (most likely a texture
55          * or call instruction), consider it used.
56          */
57         return true;
58      }
59   }
60
61   return false;
62}
63
64static void
65add_var_use_deref(nir_deref_instr *deref, struct set *live)
66{
67   if (deref->deref_type != nir_deref_type_var)
68      return;
69
70   /* Since these local variables don't escape the shader, writing doesn't
71    * make them live.  Only keep them if they are used by some intrinsic.
72    */
73   if ((deref->var->data.mode & (nir_var_function_temp |
74                                 nir_var_shader_temp)) &&
75       !deref_used_for_not_store(deref))
76      return;
77
78   /*
79    * Shared memory blocks (interface type) alias each other, so be
80    * conservative in that case.
81    */
82   if ((deref->var->data.mode & nir_var_mem_shared) &&
83       !glsl_type_is_interface(deref->var->type) &&
84       !deref_used_for_not_store(deref))
85      return;
86
87   nir_variable *var = deref->var;
88   do {
89      _mesa_set_add(live, var);
90      /* Also mark the chain of variables used to initialize it. */
91      var = var->pointer_initializer;
92   } while (var);
93}
94
95static void
96add_var_use_shader(nir_shader *shader, struct set *live, nir_variable_mode modes)
97{
98   nir_foreach_function(function, shader) {
99      if (function->impl) {
100         nir_foreach_block(block, function->impl) {
101            nir_foreach_instr(instr, block) {
102               if (instr->type == nir_instr_type_deref)
103                  add_var_use_deref(nir_instr_as_deref(instr), live);
104            }
105         }
106      }
107   }
108}
109
110static void
111remove_dead_var_writes(nir_shader *shader)
112{
113   nir_foreach_function(function, shader) {
114      if (!function->impl)
115         continue;
116
117      nir_foreach_block(block, function->impl) {
118         nir_foreach_instr_safe(instr, block) {
119            switch (instr->type) {
120            case nir_instr_type_deref: {
121               nir_deref_instr *deref = nir_instr_as_deref(instr);
122               if (deref->deref_type == nir_deref_type_cast &&
123                   !nir_deref_instr_parent(deref))
124                  continue;
125
126               nir_variable_mode parent_modes;
127               if (deref->deref_type == nir_deref_type_var)
128                  parent_modes = deref->var->data.mode;
129               else
130                  parent_modes = nir_deref_instr_parent(deref)->modes;
131
132               /* If the parent mode is 0, then it references a dead variable.
133                * Flag this deref as dead and remove it.
134                */
135               if (parent_modes == 0) {
136                  deref->modes = 0;
137                  nir_instr_remove(&deref->instr);
138               }
139               break;
140            }
141
142            case nir_instr_type_intrinsic: {
143               nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
144               if (intrin->intrinsic != nir_intrinsic_copy_deref &&
145                   intrin->intrinsic != nir_intrinsic_store_deref)
146                  break;
147
148               if (nir_src_as_deref(intrin->src[0])->modes == 0)
149                  nir_instr_remove(instr);
150               break;
151            }
152
153            default:
154               break; /* Nothing to do */
155            }
156         }
157      }
158   }
159}
160
161static bool
162remove_dead_vars(struct exec_list *var_list, nir_variable_mode modes,
163                 struct set *live, const nir_remove_dead_variables_options *opts)
164{
165   bool progress = false;
166
167   nir_foreach_variable_in_list_safe(var, var_list) {
168      if (!(var->data.mode & modes))
169         continue;
170
171      if (opts && opts->can_remove_var &&
172          !opts->can_remove_var(var, opts->can_remove_var_data))
173         continue;
174
175      struct set_entry *entry = _mesa_set_search(live, var);
176      if (entry == NULL) {
177         /* Mark this variable as used by setting the mode to 0 */
178         var->data.mode = 0;
179         exec_node_remove(&var->node);
180         progress = true;
181      }
182   }
183
184   return progress;
185}
186
187bool
188nir_remove_dead_variables(nir_shader *shader, nir_variable_mode modes,
189                          const nir_remove_dead_variables_options *opts)
190{
191   bool progress = false;
192   struct set *live = _mesa_pointer_set_create(NULL);
193
194   add_var_use_shader(shader, live, modes);
195
196   if (modes & ~nir_var_function_temp) {
197      progress = remove_dead_vars(&shader->variables, modes,
198                                  live, opts) || progress;
199   }
200
201   if (modes & nir_var_function_temp) {
202      nir_foreach_function(function, shader) {
203         if (function->impl) {
204            if (remove_dead_vars(&function->impl->locals,
205                                 nir_var_function_temp,
206                                 live, opts))
207               progress = true;
208         }
209      }
210   }
211
212   _mesa_set_destroy(live, NULL);
213
214   nir_foreach_function(function, shader) {
215      if (!function->impl)
216         continue;
217
218      if (progress) {
219         remove_dead_var_writes(shader);
220         nir_metadata_preserve(function->impl, nir_metadata_block_index |
221                                               nir_metadata_dominance);
222      } else {
223         nir_metadata_preserve(function->impl, nir_metadata_all);
224      }
225   }
226
227   return progress;
228}
229