src/compiler/nir/nir_lower_idiv.c

   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 void
  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;
  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_ushr(bld, r, nir_imm_int(bld, 31));
 105       r = nir_i2b(bld, r);
 106       b = nir_ineg(bld, q);
 107       q = nir_bcsel(bld, r, b, q);
 108    }
 109
 110    if (op == nir_op_umod) {
 111       /* division result in q */
 112       r = nir_imul(bld, q, b);
 113       q = nir_isub(bld, a, r);
 114    }
 115
 116    assert(alu->dest.dest.is_ssa);
 117    nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, nir_src_for_ssa(q));
 118 }
 119
 120 static bool
 121 convert_block(nir_block *block, void *state)
 122 {
 123    nir_builder *b = state;
 124
 125    nir_foreach_instr_safe(block, instr) {
 126       if (instr->type == nir_instr_type_alu)
 127          convert_instr(b, nir_instr_as_alu(instr));
 128    }
 129
 130    return true;
 131 }
 132
 133 static void
 134 convert_impl(nir_function_impl *impl)
 135 {
 136    nir_builder b;
 137    nir_builder_init(&b, impl);
 138
 139    nir_foreach_block(impl, convert_block, &b);
 140    nir_metadata_preserve(impl, nir_metadata_block_index |
 141                                nir_metadata_dominance);
 142 }
 143
 144 void
 145 nir_lower_idiv(nir_shader *shader)
 146 {
 147    nir_foreach_function(shader, function) {
 148       if (function->impl)
 149          convert_impl(function->impl);
 150    }
 151 }