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_is_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_mov:
54      case nir_op_fneg:
55      case nir_op_fabs:
56         assert(use_alu->dest.dest.is_ssa);
57         if (!are_all_uses_fadd(&use_alu->dest.dest.ssa))
58            return false;
59         break;
60
61      default:
62         return false;
63      }
64   }
65
66   return true;
67}
68
69static nir_alu_instr *
70get_mul_for_src(nir_alu_src *src, unsigned num_components,
71                uint8_t swizzle[4], bool *negate, bool *abs)
72{
73   uint8_t swizzle_tmp[4];
74   assert(src->src.is_ssa && !src->abs && !src->negate);
75
76   nir_instr *instr = src->src.ssa->parent_instr;
77   if (instr->type != nir_instr_type_alu)
78      return NULL;
79
80   nir_alu_instr *alu = nir_instr_as_alu(instr);
81
82   /* We want to bail if any of the other ALU operations involved is labled
83    * exact.  One reason for this is that, while the value that is changing is
84    * actually the result of the add and not the multiply, the intention of
85    * the user when they specify an exact multiply is that they want *that*
86    * value and what they don't care about is the add.  Another reason is that
87    * SPIR-V explicitly requires this behaviour.
88    */
89   if (alu->exact)
90      return NULL;
91
92   switch (alu->op) {
93   case nir_op_mov:
94      alu = get_mul_for_src(&alu->src[0], alu->dest.dest.ssa.num_components,
95                            swizzle, negate, abs);
96      break;
97
98   case nir_op_fneg:
99      alu = get_mul_for_src(&alu->src[0], alu->dest.dest.ssa.num_components,
100                            swizzle, negate, abs);
101      *negate = !*negate;
102      break;
103
104   case nir_op_fabs:
105      alu = get_mul_for_src(&alu->src[0], alu->dest.dest.ssa.num_components,
106                            swizzle, negate, abs);
107      *negate = false;
108      *abs = true;
109      break;
110
111   case nir_op_fmul:
112      /* Only absorb a fmul into a ffma if the fmul is only used in fadd
113       * operations.  This prevents us from being too aggressive with our
114       * fusing which can actually lead to more instructions.
115       */
116      if (!are_all_uses_fadd(&alu->dest.dest.ssa))
117         return NULL;
118      break;
119
120   default:
121      return NULL;
122   }
123
124   if (!alu)
125      return NULL;
126
127   /* Copy swizzle data before overwriting it to avoid setting a wrong swizzle.
128    *
129    * Example:
130    *   Former swizzle[] = xyzw
131    *   src->swizzle[] = zyxx
132    *
133    *   Expected output swizzle = zyxx
134    *   If we reuse swizzle in the loop, then output swizzle would be zyzz.
135    */
136   memcpy(swizzle_tmp, swizzle, 4*sizeof(uint8_t));
137   for (int i = 0; i < num_components; i++)
138      swizzle[i] = swizzle_tmp[src->swizzle[i]];
139
140   return alu;
141}
142
143/**
144 * Given a list of (at least two) nir_alu_src's, tells if any of them is a
145 * constant value and is used only once.
146 */
147static bool
148any_alu_src_is_a_constant(nir_alu_src srcs[])
149{
150   for (unsigned i = 0; i < 2; i++) {
151      if (srcs[i].src.ssa->parent_instr->type == nir_instr_type_load_const) {
152         nir_load_const_instr *load_const =
153            nir_instr_as_load_const (srcs[i].src.ssa->parent_instr);
154
155         if (list_is_singular(&load_const->def.uses) &&
156             list_is_empty(&load_const->def.if_uses)) {
157            return true;
158         }
159      }
160   }
161
162   return false;
163}
164
165static bool
166brw_nir_opt_peephole_ffma_instr(nir_builder *b,
167                                nir_instr *instr,
168                                UNUSED void *cb_data)
169{
170   if (instr->type != nir_instr_type_alu)
171      return false;
172
173   nir_alu_instr *add = nir_instr_as_alu(instr);
174   if (add->op != nir_op_fadd)
175      return false;
176
177   assert(add->dest.dest.is_ssa);
178   if (add->exact)
179      return false;
180
181   assert(add->src[0].src.is_ssa && add->src[1].src.is_ssa);
182
183   /* This, is the case a + a.  We would rather handle this with an
184    * algebraic reduction than fuse it.  Also, we want to only fuse
185    * things where the multiply is used only once and, in this case,
186    * it would be used twice by the same instruction.
187    */
188   if (add->src[0].src.ssa == add->src[1].src.ssa)
189      return false;
190
191   nir_alu_instr *mul;
192   uint8_t add_mul_src, swizzle[4];
193   bool negate, abs;
194   for (add_mul_src = 0; add_mul_src < 2; add_mul_src++) {
195      for (unsigned i = 0; i < 4; i++)
196         swizzle[i] = i;
197
198      negate = false;
199      abs = false;
200
201      mul = get_mul_for_src(&add->src[add_mul_src],
202                            add->dest.dest.ssa.num_components,
203                            swizzle, &negate, &abs);
204
205      if (mul != NULL)
206         break;
207   }
208
209   if (mul == NULL)
210      return false;
211
212   unsigned bit_size = add->dest.dest.ssa.bit_size;
213
214   nir_ssa_def *mul_src[2];
215   mul_src[0] = mul->src[0].src.ssa;
216   mul_src[1] = mul->src[1].src.ssa;
217
218   /* If any of the operands of the fmul and any of the fadd is a constant,
219    * we bypass because it will be more efficient as the constants will be
220    * propagated as operands, potentially saving two load_const instructions.
221    */
222   if (any_alu_src_is_a_constant(mul->src) &&
223       any_alu_src_is_a_constant(add->src)) {
224      return false;
225   }
226
227   b->cursor = nir_before_instr(&add->instr);
228
229   if (abs) {
230      for (unsigned i = 0; i < 2; i++)
231         mul_src[i] = nir_fabs(b, mul_src[i]);
232   }
233
234   if (negate)
235      mul_src[0] = nir_fneg(b, mul_src[0]);
236
237   nir_alu_instr *ffma = nir_alu_instr_create(b->shader, nir_op_ffma);
238   ffma->dest.saturate = add->dest.saturate;
239   ffma->dest.write_mask = add->dest.write_mask;
240
241   for (unsigned i = 0; i < 2; i++) {
242      ffma->src[i].src = nir_src_for_ssa(mul_src[i]);
243      for (unsigned j = 0; j < add->dest.dest.ssa.num_components; j++)
244         ffma->src[i].swizzle[j] = mul->src[i].swizzle[swizzle[j]];
245   }
246   nir_alu_src_copy(&ffma->src[2], &add->src[1 - add_mul_src]);
247
248   assert(add->dest.dest.is_ssa);
249
250   nir_ssa_dest_init(&ffma->instr, &ffma->dest.dest,
251                     add->dest.dest.ssa.num_components,
252                     bit_size, NULL);
253   nir_ssa_def_rewrite_uses(&add->dest.dest.ssa, &ffma->dest.dest.ssa);
254
255   nir_builder_instr_insert(b, &ffma->instr);
256   assert(list_is_empty(&add->dest.dest.ssa.uses));
257   nir_instr_remove(&add->instr);
258
259   return true;
260}
261
262bool
263brw_nir_opt_peephole_ffma(nir_shader *shader)
264{
265   return nir_shader_instructions_pass(shader, brw_nir_opt_peephole_ffma_instr,
266                                       nir_metadata_block_index |
267                                       nir_metadata_dominance,
268                                       NULL);
269}
270