nir_propagate_invariant.c revision 7e102996 
1/*
2 * Copyright © 2016 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
21 * DEALINGS IN THE SOFTWARE.
22 */
23
24#include "nir.h"
25
26static void
27add_src(nir_src *src, struct set *invariants)
28{
29   if (src->is_ssa) {
30      _mesa_set_add(invariants, src->ssa);
31   } else {
32      _mesa_set_add(invariants, src->reg.reg);
33   }
34}
35
36static bool
37add_src_cb(nir_src *src, void *state)
38{
39   add_src(src, state);
40   return true;
41}
42
43static bool
44dest_is_invariant(nir_dest *dest, struct set *invariants)
45{
46   if (dest->is_ssa) {
47      return _mesa_set_search(invariants, &dest->ssa);
48   } else {
49      return _mesa_set_search(invariants, dest->reg.reg);
50   }
51}
52
53static void
54add_cf_node(nir_cf_node *cf, struct set *invariants)
55{
56   if (cf->type == nir_cf_node_if) {
57      nir_if *if_stmt = nir_cf_node_as_if(cf);
58      add_src(&if_stmt->condition, invariants);
59   }
60
61   if (cf->parent)
62      add_cf_node(cf->parent, invariants);
63}
64
65static void
66add_var(nir_variable *var, struct set *invariants)
67{
68   /* Because we pass the result of nir_intrinsic_get_var directly to this
69    * function, it's possible for var to be NULL if, for instance, there's a
70    * cast somewhere in the chain.
71    */
72   if (var != NULL)
73      _mesa_set_add(invariants, var);
74}
75
76static bool
77var_is_invariant(nir_variable *var, struct set * invariants)
78{
79   /* Because we pass the result of nir_intrinsic_get_var directly to this
80    * function, it's possible for var to be NULL if, for instance, there's a
81    * cast somewhere in the chain.
82    */
83   return var && (var->data.invariant || _mesa_set_search(invariants, var));
84}
85
86static void
87propagate_invariant_instr(nir_instr *instr, struct set *invariants)
88{
89   switch (instr->type) {
90   case nir_instr_type_alu: {
91      nir_alu_instr *alu = nir_instr_as_alu(instr);
92      if (!dest_is_invariant(&alu->dest.dest, invariants))
93         break;
94
95      alu->exact = true;
96      nir_foreach_src(instr, add_src_cb, invariants);
97      break;
98   }
99
100   case nir_instr_type_tex: {
101      nir_tex_instr *tex = nir_instr_as_tex(instr);
102      if (dest_is_invariant(&tex->dest, invariants))
103         nir_foreach_src(instr, add_src_cb, invariants);
104      break;
105   }
106
107   case nir_instr_type_intrinsic: {
108      nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
109      switch (intrin->intrinsic) {
110      case nir_intrinsic_copy_deref:
111         /* If the destination is invariant then so is the source */
112         if (var_is_invariant(nir_intrinsic_get_var(intrin, 0), invariants))
113            add_var(nir_intrinsic_get_var(intrin, 1), invariants);
114         break;
115
116      case nir_intrinsic_load_deref:
117         if (dest_is_invariant(&intrin->dest, invariants))
118            add_var(nir_intrinsic_get_var(intrin, 0), invariants);
119         break;
120
121      case nir_intrinsic_store_deref:
122         if (var_is_invariant(nir_intrinsic_get_var(intrin, 0), invariants))
123            add_src(&intrin->src[1], invariants);
124         break;
125
126      default:
127         /* Nothing to do */
128         break;
129      }
130   }
131
132   case nir_instr_type_deref:
133   case nir_instr_type_jump:
134   case nir_instr_type_ssa_undef:
135   case nir_instr_type_load_const:
136      break; /* Nothing to do */
137
138   case nir_instr_type_phi: {
139      nir_phi_instr *phi = nir_instr_as_phi(instr);
140      if (!dest_is_invariant(&phi->dest, invariants))
141         break;
142
143      nir_foreach_phi_src(src, phi) {
144         add_src(&src->src, invariants);
145         add_cf_node(&src->pred->cf_node, invariants);
146      }
147      break;
148   }
149
150   case nir_instr_type_call:
151      unreachable("This pass must be run after function inlining");
152
153   case nir_instr_type_parallel_copy:
154   default:
155      unreachable("Cannot have this instruction type");
156   }
157}
158
159static bool
160propagate_invariant_impl(nir_function_impl *impl, struct set *invariants)
161{
162   bool progress = false;
163
164   while (true) {
165      uint32_t prev_entries = invariants->entries;
166
167      nir_foreach_block_reverse(block, impl) {
168         nir_foreach_instr_reverse(instr, block)
169            propagate_invariant_instr(instr, invariants);
170      }
171
172      /* Keep running until we make no more progress. */
173      if (invariants->entries > prev_entries) {
174         progress = true;
175         continue;
176      } else {
177         break;
178      }
179   }
180
181   if (progress) {
182      nir_metadata_preserve(impl, nir_metadata_block_index |
183                                  nir_metadata_dominance |
184                                  nir_metadata_live_ssa_defs);
185   }
186
187   return progress;
188}
189
190bool
191nir_propagate_invariant(nir_shader *shader)
192{
193   /* Hash set of invariant things */
194   struct set *invariants = _mesa_pointer_set_create(NULL);
195
196   bool progress = false;
197   nir_foreach_function(function, shader) {
198      if (function->impl && propagate_invariant_impl(function->impl, invariants))
199         progress = true;
200   }
201
202   _mesa_set_destroy(invariants, NULL);
203
204   return progress;
205}
206