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/*
* Copyright © 2015 Red Hat
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*
* Authors:
* Rob Clark <robclark@freedesktop.org>
*/
#include "nir.h"
#include "nir_builder.h"
/* Lowers idiv/udiv/umod
* Based on NV50LegalizeSSA::handleDIV()
*
* Note that this is probably not enough precision for compute shaders.
* Perhaps we want a second higher precision (looping) version of this?
* Or perhaps we assume if you can do compute shaders you can also
* branch out to a pre-optimized shader library routine..
*/
static void
convert_instr(nir_builder *bld, nir_alu_instr *alu)
{
nir_ssa_def *numer, *denom, *af, *bf, *a, *b, *q, *r;
nir_op op = alu->op;
bool is_signed;
if ((op != nir_op_idiv) &&
(op != nir_op_udiv) &&
(op != nir_op_umod))
return;
is_signed = (op == nir_op_idiv);
bld->cursor = nir_before_instr(&alu->instr);
numer = nir_ssa_for_alu_src(bld, alu, 0);
denom = nir_ssa_for_alu_src(bld, alu, 1);
if (is_signed) {
af = nir_i2f(bld, numer);
bf = nir_i2f(bld, denom);
af = nir_fabs(bld, af);
bf = nir_fabs(bld, bf);
a = nir_iabs(bld, numer);
b = nir_iabs(bld, denom);
} else {
af = nir_u2f(bld, numer);
bf = nir_u2f(bld, denom);
a = numer;
b = denom;
}
/* get first result: */
bf = nir_frcp(bld, bf);
bf = nir_isub(bld, bf, nir_imm_int(bld, 2)); /* yes, really */
q = nir_fmul(bld, af, bf);
if (is_signed) {
q = nir_f2i(bld, q);
} else {
q = nir_f2u(bld, q);
}
/* get error of first result: */
r = nir_imul(bld, q, b);
r = nir_isub(bld, a, r);
r = nir_u2f(bld, r);
r = nir_fmul(bld, r, bf);
r = nir_f2u(bld, r);
/* add quotients: */
q = nir_iadd(bld, q, r);
/* correction: if modulus >= divisor, add 1 */
r = nir_imul(bld, q, b);
r = nir_isub(bld, a, r);
r = nir_uge(bld, r, b);
r = nir_b2i(bld, r);
q = nir_iadd(bld, q, r);
if (is_signed) {
/* fix the sign: */
r = nir_ixor(bld, numer, denom);
r = nir_ushr(bld, r, nir_imm_int(bld, 31));
r = nir_i2b(bld, r);
b = nir_ineg(bld, q);
q = nir_bcsel(bld, r, b, q);
}
if (op == nir_op_umod) {
/* division result in q */
r = nir_imul(bld, q, b);
q = nir_isub(bld, a, r);
}
assert(alu->dest.dest.is_ssa);
nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, nir_src_for_ssa(q));
}
static bool
convert_block(nir_block *block, void *state)
{
nir_builder *b = state;
nir_foreach_instr_safe(block, instr) {
if (instr->type == nir_instr_type_alu)
convert_instr(b, nir_instr_as_alu(instr));
}
return true;
}
static void
convert_impl(nir_function_impl *impl)
{
nir_builder b;
nir_builder_init(&b, impl);
nir_foreach_block_call(impl, convert_block, &b);
nir_metadata_preserve(impl, nir_metadata_block_index |
nir_metadata_dominance);
}
void
nir_lower_idiv(nir_shader *shader)
{
nir_foreach_function(shader, function) {
if (function->impl)
convert_impl(function->impl);
}
}
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