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 *    Jason Ekstrand (jason@jlekstrand.net)
25 *
26 */
27
28#include "brw_nir.h"
29#include "compiler/nir/nir_builder.h"
30
31/*
32 * Implements a small peephole optimization that looks for a multiply that
33 * is only ever used in an add and replaces both with an fma.
34 */
35
36static inline bool
37are_all_uses_fadd(nir_ssa_def *def)
38{
39   if (!list_empty(&def->if_uses))
40      return false;
41
42   nir_foreach_use(use_src, def) {
43      nir_instr *use_instr = use_src->parent_instr;
44
45      if (use_instr->type != nir_instr_type_alu)
46         return false;
47
48      nir_alu_instr *use_alu = nir_instr_as_alu(use_instr);
49      switch (use_alu->op) {
50      case nir_op_fadd:
51         break; /* This one's ok */
52
53      case nir_op_imov:
54      case nir_op_fmov:
55      case nir_op_fneg:
56      case nir_op_fabs:
57         assert(use_alu->dest.dest.is_ssa);
58         if (!are_all_uses_fadd(&use_alu->dest.dest.ssa))
59            return false;
60         break;
61
62      default:
63         return false;
64      }
65   }
66
67   return true;
68}
69
70static nir_alu_instr *
71get_mul_for_src(nir_alu_src *src, unsigned num_components,
72                uint8_t swizzle[4], bool *negate, bool *abs)
73{
74   uint8_t swizzle_tmp[4];
75   assert(src->src.is_ssa && !src->abs && !src->negate);
76
77   nir_instr *instr = src->src.ssa->parent_instr;
78   if (instr->type != nir_instr_type_alu)
79      return NULL;
80
81   nir_alu_instr *alu = nir_instr_as_alu(instr);
82
83   /* We want to bail if any of the other ALU operations involved is labled
84    * exact.  One reason for this is that, while the value that is changing is
85    * actually the result of the add and not the multiply, the intention of
86    * the user when they specify an exact multiply is that they want *that*
87    * value and what they don't care about is the add.  Another reason is that
88    * SPIR-V explicitly requires this behaviour.
89    */
90   if (alu->exact)
91      return NULL;
92
93   switch (alu->op) {
94   case nir_op_imov:
95   case nir_op_fmov:
96      alu = get_mul_for_src(&alu->src[0], alu->dest.dest.ssa.num_components,
97                            swizzle, negate, abs);
98      break;
99
100   case nir_op_fneg:
101      alu = get_mul_for_src(&alu->src[0], alu->dest.dest.ssa.num_components,
102                            swizzle, negate, abs);
103      *negate = !*negate;
104      break;
105
106   case nir_op_fabs:
107      alu = get_mul_for_src(&alu->src[0], alu->dest.dest.ssa.num_components,
108                            swizzle, negate, abs);
109      *negate = false;
110      *abs = true;
111      break;
112
113   case nir_op_fmul:
114      /* Only absorb a fmul into a ffma if the fmul is only used in fadd
115       * operations.  This prevents us from being too aggressive with our
116       * fusing which can actually lead to more instructions.
117       */
118      if (!are_all_uses_fadd(&alu->dest.dest.ssa))
119         return NULL;
120      break;
121
122   default:
123      return NULL;
124   }
125
126   if (!alu)
127      return NULL;
128
129   /* Copy swizzle data before overwriting it to avoid setting a wrong swizzle.
130    *
131    * Example:
132    *   Former swizzle[] = xyzw
133    *   src->swizzle[] = zyxx
134    *
135    *   Expected output swizzle = zyxx
136    *   If we reuse swizzle in the loop, then output swizzle would be zyzz.
137    */
138   memcpy(swizzle_tmp, swizzle, 4*sizeof(uint8_t));
139   for (int i = 0; i < num_components; i++)
140      swizzle[i] = swizzle_tmp[src->swizzle[i]];
141
142   return alu;
143}
144
145/**
146 * Given a list of (at least two) nir_alu_src's, tells if any of them is a
147 * constant value and is used only once.
148 */
149static bool
150any_alu_src_is_a_constant(nir_alu_src srcs[])
151{
152   for (unsigned i = 0; i < 2; i++) {
153      if (srcs[i].src.ssa->parent_instr->type == nir_instr_type_load_const) {
154         nir_load_const_instr *load_const =
155            nir_instr_as_load_const (srcs[i].src.ssa->parent_instr);
156
157         if (list_is_singular(&load_const->def.uses) &&
158             list_empty(&load_const->def.if_uses)) {
159            return true;
160         }
161      }
162   }
163
164   return false;
165}
166
167static bool
168brw_nir_opt_peephole_ffma_block(nir_builder *b, nir_block *block)
169{
170   bool progress = false;
171
172   nir_foreach_instr_safe(instr, block) {
173      if (instr->type != nir_instr_type_alu)
174         continue;
175
176      nir_alu_instr *add = nir_instr_as_alu(instr);
177      if (add->op != nir_op_fadd)
178         continue;
179
180      assert(add->dest.dest.is_ssa);
181      if (add->exact)
182         continue;
183
184      assert(add->src[0].src.is_ssa && add->src[1].src.is_ssa);
185
186      /* This, is the case a + a.  We would rather handle this with an
187       * algebraic reduction than fuse it.  Also, we want to only fuse
188       * things where the multiply is used only once and, in this case,
189       * it would be used twice by the same instruction.
190       */
191      if (add->src[0].src.ssa == add->src[1].src.ssa)
192         continue;
193
194      nir_alu_instr *mul;
195      uint8_t add_mul_src, swizzle[4];
196      bool negate, abs;
197      for (add_mul_src = 0; add_mul_src < 2; add_mul_src++) {
198         for (unsigned i = 0; i < 4; i++)
199            swizzle[i] = i;
200
201         negate = false;
202         abs = false;
203
204         mul = get_mul_for_src(&add->src[add_mul_src],
205                               add->dest.dest.ssa.num_components,
206                               swizzle, &negate, &abs);
207
208         if (mul != NULL)
209            break;
210      }
211
212      if (mul == NULL)
213         continue;
214
215      unsigned bit_size = add->dest.dest.ssa.bit_size;
216
217      nir_ssa_def *mul_src[2];
218      mul_src[0] = mul->src[0].src.ssa;
219      mul_src[1] = mul->src[1].src.ssa;
220
221      /* If any of the operands of the fmul and any of the fadd is a constant,
222       * we bypass because it will be more efficient as the constants will be
223       * propagated as operands, potentially saving two load_const instructions.
224       */
225      if (any_alu_src_is_a_constant(mul->src) &&
226          any_alu_src_is_a_constant(add->src)) {
227         continue;
228      }
229
230      b->cursor = nir_before_instr(&add->instr);
231
232      if (abs) {
233         for (unsigned i = 0; i < 2; i++)
234            mul_src[i] = nir_fabs(b, mul_src[i]);
235      }
236
237      if (negate)
238         mul_src[0] = nir_fneg(b, mul_src[0]);
239
240      nir_alu_instr *ffma = nir_alu_instr_create(b->shader, nir_op_ffma);
241      ffma->dest.saturate = add->dest.saturate;
242      ffma->dest.write_mask = add->dest.write_mask;
243
244      for (unsigned i = 0; i < 2; i++) {
245         ffma->src[i].src = nir_src_for_ssa(mul_src[i]);
246         for (unsigned j = 0; j < add->dest.dest.ssa.num_components; j++)
247            ffma->src[i].swizzle[j] = mul->src[i].swizzle[swizzle[j]];
248      }
249      nir_alu_src_copy(&ffma->src[2], &add->src[1 - add_mul_src], ffma);
250
251      assert(add->dest.dest.is_ssa);
252
253      nir_ssa_dest_init(&ffma->instr, &ffma->dest.dest,
254                        add->dest.dest.ssa.num_components,
255                        bit_size,
256                        add->dest.dest.ssa.name);
257      nir_ssa_def_rewrite_uses(&add->dest.dest.ssa,
258                               nir_src_for_ssa(&ffma->dest.dest.ssa));
259
260      nir_builder_instr_insert(b, &ffma->instr);
261      assert(list_empty(&add->dest.dest.ssa.uses));
262      nir_instr_remove(&add->instr);
263
264      progress = true;
265   }
266
267   return progress;
268}
269
270static bool
271brw_nir_opt_peephole_ffma_impl(nir_function_impl *impl)
272{
273   bool progress = false;
274
275   nir_builder builder;
276   nir_builder_init(&builder, impl);
277
278   nir_foreach_block(block, impl) {
279      progress |= brw_nir_opt_peephole_ffma_block(&builder, block);
280   }
281
282   if (progress)
283      nir_metadata_preserve(impl, nir_metadata_block_index |
284                                  nir_metadata_dominance);
285
286   return progress;
287}
288
289bool
290brw_nir_opt_peephole_ffma(nir_shader *shader)
291{
292   bool progress = false;
293
294   nir_foreach_function(function, shader) {
295      if (function->impl)
296         progress |= brw_nir_opt_peephole_ffma_impl(function->impl);
297   }
298
299   return progress;
300}
301