d7144b39a8d6744f0d6ac7a1e18615a53f8dff54
[mesa.git] / src / compiler / nir / nir_inline_functions.c
1 /*
2 * Copyright © 2015 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
24 #include "nir.h"
25 #include "nir_builder.h"
26 #include "nir_control_flow.h"
27 #include "nir_vla.h"
28
29 void nir_inline_function_impl(struct nir_builder *b,
30 const nir_function_impl *impl,
31 nir_ssa_def **params)
32 {
33 nir_function_impl *copy = nir_function_impl_clone(b->shader, impl);
34
35 /* Insert a nop at the cursor so we can keep track of where things are as
36 * we add/remove stuff from the CFG.
37 */
38 nir_intrinsic_instr *nop =
39 nir_intrinsic_instr_create(b->shader, nir_intrinsic_nop);
40 nir_builder_instr_insert(b, &nop->instr);
41
42 exec_list_append(&b->impl->locals, &copy->locals);
43 exec_list_append(&b->impl->registers, &copy->registers);
44
45 nir_foreach_block(block, copy) {
46 nir_foreach_instr_safe(instr, block) {
47 /* Returns have to be lowered for this to work */
48 assert(instr->type != nir_instr_type_jump ||
49 nir_instr_as_jump(instr)->type != nir_jump_return);
50
51 if (instr->type != nir_instr_type_intrinsic)
52 continue;
53
54 nir_intrinsic_instr *load = nir_instr_as_intrinsic(instr);
55 if (load->intrinsic != nir_intrinsic_load_param)
56 continue;
57
58 unsigned param_idx = nir_intrinsic_param_idx(load);
59 assert(param_idx < impl->function->num_params);
60 assert(load->dest.is_ssa);
61 nir_ssa_def_rewrite_uses(&load->dest.ssa,
62 nir_src_for_ssa(params[param_idx]));
63
64 /* Remove any left-over load_param intrinsics because they're soon
65 * to be in another function and therefore no longer valid.
66 */
67 nir_instr_remove(&load->instr);
68 }
69 }
70
71 /* Pluck the body out of the function and place it here */
72 nir_cf_list body;
73 nir_cf_list_extract(&body, &copy->body);
74 nir_cf_reinsert(&body, nir_before_instr(&nop->instr));
75
76 b->cursor = nir_instr_remove(&nop->instr);
77 }
78
79 static bool inline_function_impl(nir_function_impl *impl, struct set *inlined);
80
81 static bool
82 inline_functions_block(nir_block *block, nir_builder *b,
83 struct set *inlined)
84 {
85 bool progress = false;
86 /* This is tricky. We're iterating over instructions in a block but, as
87 * we go, the block and its instruction list are being split into
88 * pieces. However, this *should* be safe since foreach_safe always
89 * stashes the next thing in the iteration. That next thing will
90 * properly get moved to the next block when it gets split, and we
91 * continue iterating there.
92 */
93 nir_foreach_instr_safe(instr, block) {
94 if (instr->type != nir_instr_type_call)
95 continue;
96
97 progress = true;
98
99 nir_call_instr *call = nir_instr_as_call(instr);
100 assert(call->callee->impl);
101
102 /* Make sure that the function we're calling is already inlined */
103 inline_function_impl(call->callee->impl, inlined);
104
105 b->cursor = nir_instr_remove(&call->instr);
106
107 /* Rewrite all of the uses of the callee's parameters to use the call
108 * instructions sources. In order to ensure that the "load" happens
109 * here and not later (for register sources), we make sure to convert it
110 * to an SSA value first.
111 */
112 const unsigned num_params = call->num_params;
113 NIR_VLA(nir_ssa_def *, params, num_params);
114 for (unsigned i = 0; i < num_params; i++) {
115 params[i] = nir_ssa_for_src(b, call->params[i],
116 call->callee->params[i].num_components);
117 }
118
119 nir_inline_function_impl(b, call->callee->impl, params);
120 }
121
122 return progress;
123 }
124
125 static bool
126 inline_function_impl(nir_function_impl *impl, struct set *inlined)
127 {
128 if (_mesa_set_search(inlined, impl))
129 return false; /* Already inlined */
130
131 nir_builder b;
132 nir_builder_init(&b, impl);
133
134 bool progress = false;
135 nir_foreach_block_safe(block, impl) {
136 progress |= inline_functions_block(block, &b, inlined);
137 }
138
139 if (progress) {
140 /* SSA and register indices are completely messed up now */
141 nir_index_ssa_defs(impl);
142 nir_index_local_regs(impl);
143
144 nir_metadata_preserve(impl, nir_metadata_none);
145 } else {
146 nir_metadata_preserve(impl, nir_metadata_all);
147 }
148
149 _mesa_set_add(inlined, impl);
150
151 return progress;
152 }
153
154 /** A pass to inline all functions in a shader into their callers
155 *
156 * For most use-cases, function inlining is a multi-step process. The general
157 * pattern employed by SPIR-V consumers and others is as follows:
158 *
159 * 1. nir_lower_variable_initializers(shader, nir_var_function_temp)
160 *
161 * This is needed because local variables from the callee are simply added
162 * to the locals list for the caller and the information about where the
163 * constant initializer logically happens is lost. If the callee is
164 * called in a loop, this can cause the variable to go from being
165 * initialized once per loop iteration to being initialized once at the
166 * top of the caller and values to persist from one invocation of the
167 * callee to the next. The simple solution to this problem is to get rid
168 * of constant initializers before function inlining.
169 *
170 * 2. nir_lower_returns(shader)
171 *
172 * nir_inline_functions assumes that all functions end "naturally" by
173 * execution reaching the end of the function without any return
174 * instructions causing instant jumps to the end. Thanks to NIR being
175 * structured, we can't represent arbitrary jumps to various points in the
176 * program which is what an early return in the callee would have to turn
177 * into when we inline it into the caller. Instead, we require returns to
178 * be lowered which lets us just copy+paste the callee directly into the
179 * caller.
180 *
181 * 3. nir_inline_functions(shader)
182 *
183 * This does the actual function inlining and the resulting shader will
184 * contain no call instructions.
185 *
186 * 4. nir_opt_deref(shader)
187 *
188 * Most functions contain pointer parameters where the result of a deref
189 * instruction is passed in as a parameter, loaded via a load_param
190 * intrinsic, and then turned back into a deref via a cast. Function
191 * inlining will get rid of the load_param but we are still left with a
192 * cast. Running nir_opt_deref gets rid of the intermediate cast and
193 * results in a whole deref chain again. This is currently required by a
194 * number of optimizations and lowering passes at least for certain
195 * variable modes.
196 *
197 * 5. Loop over the functions and delete all but the main entrypoint.
198 *
199 * In the Intel Vulkan driver this looks like this:
200 *
201 * foreach_list_typed_safe(nir_function, func, node, &nir->functions) {
202 * if (func != entry_point)
203 * exec_node_remove(&func->node);
204 * }
205 * assert(exec_list_length(&nir->functions) == 1);
206 *
207 * While nir_inline_functions does get rid of all call instructions, it
208 * doesn't get rid of any functions because it doesn't know what the "root
209 * function" is. Instead, it's up to the individual driver to know how to
210 * decide on a root function and delete the rest. With SPIR-V,
211 * spirv_to_nir returns the root function and so we can just use == whereas
212 * with GL, you may have to look for a function named "main".
213 *
214 * 6. nir_lower_variable_initializers(shader, ~nir_var_function_temp)
215 *
216 * Lowering constant initializers on inputs, outputs, global variables,
217 * etc. requires that we know the main entrypoint so that we know where to
218 * initialize them. Otherwise, we would have to assume that anything
219 * could be a main entrypoint and initialize them at the start of every
220 * function but that would clearly be wrong if any of those functions were
221 * ever called within another function. Simply requiring a single-
222 * entrypoint function shader is the best way to make it well-defined.
223 */
224 bool
225 nir_inline_functions(nir_shader *shader)
226 {
227 struct set *inlined = _mesa_pointer_set_create(NULL);
228 bool progress = false;
229
230 nir_foreach_function(function, shader) {
231 if (function->impl)
232 progress = inline_function_impl(function->impl, inlined) || progress;
233 }
234
235 _mesa_set_destroy(inlined, NULL);
236
237 return progress;
238 }