xref: /aosp_15_r20/external/mesa3d/src/compiler/nir/nir_remove_dead_variables.c (revision 6104692788411f58d303aa86923a9ff6ecaded22)
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  
30  static bool
deref_used_for_not_store(nir_deref_instr * deref)31  deref_used_for_not_store(nir_deref_instr *deref)
32  {
33     nir_foreach_use(src, &deref->def) {
34        switch (nir_src_parent_instr(src)->type) {
35        case nir_instr_type_deref:
36           if (deref_used_for_not_store(nir_instr_as_deref(nir_src_parent_instr(src))))
37              return true;
38           break;
39  
40        case nir_instr_type_intrinsic: {
41           nir_intrinsic_instr *intrin =
42              nir_instr_as_intrinsic(nir_src_parent_instr(src));
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  
64  static void
add_var_use_deref(nir_deref_instr * deref,struct set * live)65  add_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  
95  static void
add_var_use_shader(nir_shader * shader,struct set * live,nir_variable_mode modes)96  add_var_use_shader(nir_shader *shader, struct set *live, nir_variable_mode modes)
97  {
98     nir_foreach_function_impl(impl, shader) {
99        nir_foreach_block(block, impl) {
100           nir_foreach_instr(instr, block) {
101              if (instr->type == nir_instr_type_deref)
102                 add_var_use_deref(nir_instr_as_deref(instr), live);
103           }
104        }
105     }
106  }
107  
108  static void
remove_dead_var_writes(nir_shader * shader)109  remove_dead_var_writes(nir_shader *shader)
110  {
111     nir_foreach_function_impl(impl, shader) {
112        nir_foreach_block(block, impl) {
113           nir_foreach_instr_safe(instr, block) {
114              switch (instr->type) {
115              case nir_instr_type_deref: {
116                 nir_deref_instr *deref = nir_instr_as_deref(instr);
117                 if (deref->deref_type == nir_deref_type_cast &&
118                     !nir_deref_instr_parent(deref))
119                    continue;
120  
121                 nir_variable_mode parent_modes;
122                 if (deref->deref_type == nir_deref_type_var)
123                    parent_modes = deref->var->data.mode;
124                 else
125                    parent_modes = nir_deref_instr_parent(deref)->modes;
126  
127                 /* If the parent mode is 0, then it references a dead variable.
128                  * Flag this deref as dead and remove it.
129                  */
130                 if (parent_modes == 0) {
131                    deref->modes = 0;
132                    nir_instr_remove(&deref->instr);
133                 }
134                 break;
135              }
136  
137              case nir_instr_type_intrinsic: {
138                 nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
139                 if (intrin->intrinsic != nir_intrinsic_copy_deref &&
140                     intrin->intrinsic != nir_intrinsic_store_deref)
141                    break;
142  
143                 if (nir_src_as_deref(intrin->src[0])->modes == 0)
144                    nir_instr_remove(instr);
145                 break;
146              }
147  
148              default:
149                 break; /* Nothing to do */
150              }
151           }
152        }
153     }
154  }
155  
156  static bool
remove_dead_vars(struct exec_list * var_list,nir_variable_mode modes,struct set * live,const nir_remove_dead_variables_options * opts)157  remove_dead_vars(struct exec_list *var_list, nir_variable_mode modes,
158                   struct set *live, const nir_remove_dead_variables_options *opts)
159  {
160     bool progress = false;
161  
162     nir_foreach_variable_in_list_safe(var, var_list) {
163        if (!(var->data.mode & modes))
164           continue;
165  
166        if (opts && opts->can_remove_var &&
167            !opts->can_remove_var(var, opts->can_remove_var_data))
168           continue;
169  
170        struct set_entry *entry = _mesa_set_search(live, var);
171        if (entry == NULL) {
172           /* Mark this variable as dead by setting the mode to 0 */
173           var->data.mode = 0;
174           exec_node_remove(&var->node);
175           progress = true;
176        }
177     }
178  
179     return progress;
180  }
181  
182  bool
nir_remove_dead_variables(nir_shader * shader,nir_variable_mode modes,const nir_remove_dead_variables_options * opts)183  nir_remove_dead_variables(nir_shader *shader, nir_variable_mode modes,
184                            const nir_remove_dead_variables_options *opts)
185  {
186     bool progress = false;
187     struct set *live = _mesa_pointer_set_create(NULL);
188  
189     add_var_use_shader(shader, live, modes);
190  
191     if (modes & ~nir_var_function_temp) {
192        progress = remove_dead_vars(&shader->variables, modes,
193                                    live, opts) ||
194                   progress;
195     }
196  
197     if (modes & nir_var_function_temp) {
198        nir_foreach_function_impl(impl, shader) {
199           if (remove_dead_vars(&impl->locals,
200                                nir_var_function_temp,
201                                live, opts))
202              progress = true;
203        }
204     }
205  
206     _mesa_set_destroy(live, NULL);
207  
208     nir_foreach_function_impl(impl, shader) {
209        if (progress) {
210           remove_dead_var_writes(shader);
211           nir_metadata_preserve(impl, nir_metadata_control_flow);
212        } else {
213           nir_metadata_preserve(impl, nir_metadata_all);
214        }
215     }
216  
217     return progress;
218  }
219