1/*
2 * Copyright © 2019 Red Hat
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 "compiler/nir/nir_builder.h"
25#include "ir3_nir.h"
26
27/**
28 * This pass moves varying fetches (and the instructions they depend on
29 * into the start block.
30 *
31 * We need to set the (ei) "end input" flag on the last varying fetch.
32 * And we want to ensure that all threads execute the instruction that
33 * sets (ei).  The easiest way to ensure this is to move all varying
34 * fetches into the start block.  Which is something we used to get for
35 * free by using lower_all_io_to_temps=true.
36 *
37 * This may come at the cost of additional register usage.  OTOH setting
38 * the (ei) flag earlier probably frees up more VS to run.
39 *
40 * Not all varying fetches could be pulled into the start block.
41 * If there are fetches we couldn't pull, like load_interpolated_input
42 * with offset which depends on a non-reorderable ssbo load or on a
43 * phi node, this pass is skipped since it would be hard to find a place
44 * to set (ei) flag (beside at the very end).
45 * a5xx and a6xx do automatically release varying storage at the end.
46 */
47
48typedef struct {
49   nir_block *start_block;
50   bool precondition_failed;
51} precond_state;
52
53typedef struct {
54   nir_shader *shader;
55   nir_block *start_block;
56} state;
57
58static void check_precondition_instr(precond_state *state, nir_instr *instr);
59static void move_instruction_to_start_block(state *state, nir_instr *instr);
60
61static bool
62check_precondition_src(nir_src *src, void *state)
63{
64   check_precondition_instr(state, src->ssa->parent_instr);
65   return true;
66}
67
68/* Recursively check if there is even a single dependency which
69 * cannot be moved.
70 */
71static void
72check_precondition_instr(precond_state *state, nir_instr *instr)
73{
74   if (instr->block == state->start_block)
75      return;
76
77   switch (instr->type) {
78   case nir_instr_type_alu:
79   case nir_instr_type_deref:
80   case nir_instr_type_load_const:
81   case nir_instr_type_ssa_undef:
82      /* These could be safely moved around */
83      break;
84   case nir_instr_type_intrinsic: {
85      nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
86      if (!nir_intrinsic_can_reorder(intr)) {
87         state->precondition_failed = true;
88         return;
89      }
90      break;
91   }
92   default:
93      state->precondition_failed = true;
94      return;
95   }
96
97   nir_foreach_src(instr, check_precondition_src, state);
98}
99
100static void
101check_precondition_block(precond_state *state, nir_block *block)
102{
103   nir_foreach_instr_safe (instr, block) {
104      if (instr->type != nir_instr_type_intrinsic)
105         continue;
106
107      nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
108
109      switch (intr->intrinsic) {
110      case nir_intrinsic_load_interpolated_input:
111      case nir_intrinsic_load_input:
112         break;
113      default:
114         continue;
115      }
116
117      check_precondition_instr(state, instr);
118
119      if (state->precondition_failed)
120         return;
121   }
122}
123
124static bool
125move_src(nir_src *src, void *state)
126{
127   /* At this point we shouldn't have any non-ssa src: */
128   debug_assert(src->is_ssa);
129   move_instruction_to_start_block(state, src->ssa->parent_instr);
130   return true;
131}
132
133static void
134move_instruction_to_start_block(state *state, nir_instr *instr)
135{
136   /* nothing to do if the instruction is already in the start block */
137   if (instr->block == state->start_block)
138      return;
139
140   /* first move (recursively) all src's to ensure they appear before
141    * load*_input that we are trying to move:
142    */
143   nir_foreach_src(instr, move_src, state);
144
145   /* and then move the instruction itself:
146    */
147   exec_node_remove(&instr->node);
148   exec_list_push_tail(&state->start_block->instr_list, &instr->node);
149   instr->block = state->start_block;
150}
151
152static bool
153move_varying_inputs_block(state *state, nir_block *block)
154{
155   bool progress = false;
156
157   nir_foreach_instr_safe (instr, block) {
158      if (instr->type != nir_instr_type_intrinsic)
159         continue;
160
161      nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
162
163      switch (intr->intrinsic) {
164      case nir_intrinsic_load_interpolated_input:
165      case nir_intrinsic_load_input:
166         /* TODO any others to handle? */
167         break;
168      default:
169         continue;
170      }
171
172      debug_assert(intr->dest.is_ssa);
173
174      move_instruction_to_start_block(state, instr);
175
176      progress = true;
177   }
178
179   return progress;
180}
181
182bool
183ir3_nir_move_varying_inputs(nir_shader *shader)
184{
185   bool progress = false;
186
187   debug_assert(shader->info.stage == MESA_SHADER_FRAGMENT);
188
189   nir_foreach_function (function, shader) {
190      precond_state state;
191
192      if (!function->impl)
193         continue;
194
195      state.precondition_failed = false;
196      state.start_block = nir_start_block(function->impl);
197
198      nir_foreach_block (block, function->impl) {
199         if (block == state.start_block)
200            continue;
201
202         check_precondition_block(&state, block);
203
204         if (state.precondition_failed)
205            return false;
206      }
207   }
208
209   nir_foreach_function (function, shader) {
210      state state;
211
212      if (!function->impl)
213         continue;
214
215      state.shader = shader;
216      state.start_block = nir_start_block(function->impl);
217
218      bool progress = false;
219      nir_foreach_block (block, function->impl) {
220         /* don't need to move anything that is already in the first block */
221         if (block == state.start_block)
222            continue;
223         progress |= move_varying_inputs_block(&state, block);
224      }
225
226      if (progress) {
227         nir_metadata_preserve(
228            function->impl, nir_metadata_block_index | nir_metadata_dominance);
229      }
230   }
231
232   return progress;
233}
234