1 /*
2 * Copyright © 2015 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 * Authors:
24 * Rob Clark <robclark@freedesktop.org>
25 */
26
27 #include "nir.h"
28 #include "nir_builder.h"
29
30 /* Lowers idiv/udiv/umod
31 * Based on NV50LegalizeSSA::handleDIV()
32 *
33 * Note that this is probably not enough precision for compute shaders.
34 * Perhaps we want a second higher precision (looping) version of this?
35 * Or perhaps we assume if you can do compute shaders you can also
36 * branch out to a pre-optimized shader library routine..
37 */
38
39 static bool
convert_instr(nir_builder * bld,nir_alu_instr * alu)40 convert_instr(nir_builder *bld, nir_alu_instr *alu)
41 {
42 nir_ssa_def *numer, *denom, *af, *bf, *a, *b, *q, *r;
43 nir_op op = alu->op;
44 bool is_signed;
45
46 if ((op != nir_op_idiv) &&
47 (op != nir_op_udiv) &&
48 (op != nir_op_umod))
49 return false;
50
51 is_signed = (op == nir_op_idiv);
52
53 bld->cursor = nir_before_instr(&alu->instr);
54
55 numer = nir_ssa_for_alu_src(bld, alu, 0);
56 denom = nir_ssa_for_alu_src(bld, alu, 1);
57
58 if (is_signed) {
59 af = nir_i2f(bld, numer);
60 bf = nir_i2f(bld, denom);
61 af = nir_fabs(bld, af);
62 bf = nir_fabs(bld, bf);
63 a = nir_iabs(bld, numer);
64 b = nir_iabs(bld, denom);
65 } else {
66 af = nir_u2f(bld, numer);
67 bf = nir_u2f(bld, denom);
68 a = numer;
69 b = denom;
70 }
71
72 /* get first result: */
73 bf = nir_frcp(bld, bf);
74 bf = nir_isub(bld, bf, nir_imm_int(bld, 2)); /* yes, really */
75 q = nir_fmul(bld, af, bf);
76
77 if (is_signed) {
78 q = nir_f2i(bld, q);
79 } else {
80 q = nir_f2u(bld, q);
81 }
82
83 /* get error of first result: */
84 r = nir_imul(bld, q, b);
85 r = nir_isub(bld, a, r);
86 r = nir_u2f(bld, r);
87 r = nir_fmul(bld, r, bf);
88 r = nir_f2u(bld, r);
89
90 /* add quotients: */
91 q = nir_iadd(bld, q, r);
92
93 /* correction: if modulus >= divisor, add 1 */
94 r = nir_imul(bld, q, b);
95 r = nir_isub(bld, a, r);
96
97 r = nir_uge(bld, r, b);
98 r = nir_b2i(bld, r);
99
100 q = nir_iadd(bld, q, r);
101 if (is_signed) {
102 /* fix the sign: */
103 r = nir_ixor(bld, numer, denom);
104 r = nir_ishr(bld, r, nir_imm_int(bld, 31));
105 b = nir_ineg(bld, q);
106 q = nir_bcsel(bld, r, b, q);
107 }
108
109 if (op == nir_op_umod) {
110 /* division result in q */
111 r = nir_imul(bld, q, b);
112 q = nir_isub(bld, a, r);
113 }
114
115 assert(alu->dest.dest.is_ssa);
116 nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, nir_src_for_ssa(q));
117
118 return true;
119 }
120
121 static bool
convert_impl(nir_function_impl * impl)122 convert_impl(nir_function_impl *impl)
123 {
124 nir_builder b;
125 nir_builder_init(&b, impl);
126 bool progress = false;
127
128 nir_foreach_block(block, impl) {
129 nir_foreach_instr_safe(instr, block) {
130 if (instr->type == nir_instr_type_alu)
131 progress |= convert_instr(&b, nir_instr_as_alu(instr));
132 }
133 }
134
135 nir_metadata_preserve(impl, nir_metadata_block_index |
136 nir_metadata_dominance);
137
138 return progress;
139 }
140
141 bool
nir_lower_idiv(nir_shader * shader)142 nir_lower_idiv(nir_shader *shader)
143 {
144 bool progress = false;
145
146 nir_foreach_function(function, shader) {
147 if (function->impl)
148 progress |= convert_impl(function->impl);
149 }
150
151 return progress;
152 }
153