[Mesa-dev] [PATCH 4/4] RFC: nir: add lowering for idiv/udiv/umod
Roland Scheidegger
sroland at vmware.com
Tue Mar 31 18:03:55 PDT 2015
Am 01.04.2015 um 00:57 schrieb Rob Clark:
> From: Rob Clark <robclark at freedesktop.org>
>
> Based on the algo from NV50LegalizeSSA::handleDIV() and handleMOD().
> See also trans_idiv() in freedreno/ir3/ir3_compiler.c (which was an
> adaptation of the nv50 code from Ilia).
>
> Just sending as an rfc right now, since I'm not quite at the point to be
> able to test it on actual hw.
>
> Signed-off-by: Rob Clark <robclark at freedesktop.org>
> ---
> src/glsl/Makefile.sources | 1 +
> src/glsl/nir/nir.h | 1 +
> src/glsl/nir/nir_lower_idiv.c | 212 ++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 214 insertions(+)
> create mode 100644 src/glsl/nir/nir_lower_idiv.c
>
> diff --git a/src/glsl/Makefile.sources b/src/glsl/Makefile.sources
> index 18fff38..e426970 100644
> --- a/src/glsl/Makefile.sources
> +++ b/src/glsl/Makefile.sources
> @@ -32,6 +32,7 @@ NIR_FILES = \
> nir/nir_lower_atomics.c \
> nir/nir_lower_global_vars_to_local.c \
> nir/nir_lower_locals_to_regs.c \
> + nir/nir_lower_idiv.c \
> nir/nir_lower_io.c \
> nir/nir_lower_phis_to_scalar.c \
> nir/nir_lower_samplers.cpp \
> diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
> index cd03d6b..e002d6f 100644
> --- a/src/glsl/nir/nir.h
> +++ b/src/glsl/nir/nir.h
> @@ -1605,6 +1605,7 @@ void nir_lower_samplers(nir_shader *shader,
>
> void nir_lower_system_values(nir_shader *shader);
> void nir_lower_tex_projector(nir_shader *shader);
> +void nir_lower_idiv(nir_shader *shader);
>
> void nir_lower_atomics(nir_shader *shader);
> void nir_lower_to_source_mods(nir_shader *shader);
> diff --git a/src/glsl/nir/nir_lower_idiv.c b/src/glsl/nir/nir_lower_idiv.c
> new file mode 100644
> index 0000000..e95c57e
> --- /dev/null
> +++ b/src/glsl/nir/nir_lower_idiv.c
> @@ -0,0 +1,212 @@
> +/*
> + * 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 at 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..
So if this is not enough precision, maybe should state how large the
error can be?
Roland
> + *
> + * vec4 af, bf, a, b, q, r;
> + *
> + * if (op == idiv) {
> + * af = i2f numerator
> + * bf = i2f denominator
> + * af = fabs af
> + * bf = fabs bf
> + * a = iabs numerator
> + * b = iabs denominator
> + * } else {
> + * af = u2f numerator
> + * bf = u2f denominator
> + * a = numerator
> + * b = denominator
> + * }
> + *
> + * ; get first result
> + * bf = frcp bf
> + * bf = iadd bf, -2 ; yes, subtract 2 as integer from float
> + * q = fmul af, bf
> + *
> + * if (op == idiv) {
> + * q = f2i q
> + * } else {
> + * q = f2u q
> + * }
> + *
> + * ; get error of first result:
> + * r = imul q, b
> + * r = isub a, r
> + * r = u2f r
> + *
> + * r = fmul r, bf
> + * r = f2u r
> + * q = iadd q, r
> + *
> + * ; correction: if modulus >= divisor, add 1
> + * t = imul q, b
> + * r = isub a, t
> + *
> + * r = fge r, b
> + * r = b2i r
> + *
> + * q = isub q, r
> + * if (op == idiv) {
> + * r = ixor a, b
> + * r = ushr r, 31
> + * r = i2b r
> + * b = ineg q
> + * q = bcsel r, b, q
> + * }
> + *
> + * if (op == umod) {
> + * ; division result in q
> + * r = imul q, b
> + * q = isub a, r
> + * }
> + *
> + * dst = q
> + */
> +
> +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;
> +
> + if ((op != nir_op_idiv) &&
> + (op != nir_op_udiv) &&
> + (op != nir_op_umod))
> + return;
> +
> + nir_builder_insert_before_instr(bld, &alu->instr);
> +
> + numer = nir_ssa_for_src(bld, alu->src[0].src,
> + nir_ssa_alu_instr_src_components(alu, 0));
> + denom = nir_ssa_for_src(bld, alu->src[1].src,
> + nir_ssa_alu_instr_src_components(alu, 1));
> +
> + if (op == nir_op_idiv) {
> + 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_iadd(bld, bf, nir_imm_int(bld, -2)); /* yes, sub 2 as int from float */
> + q = nir_fmul(bld, af, bf);
> +
> + if (op == nir_op_idiv) {
> + 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);
> +
> + /* correction: if modulus >= divisor, add 1 */
> + r = nir_imul(bld, q, b);
> + r = nir_isub(bld, a, r);
> +
> + r = nir_fge(bld, r, b);
> + r = nir_b2i(bld, r);
> +
> + q = nir_isub(bld, q, r);
> + if (op == nir_op_idiv) { /* ie. udiv or umod */
> + r = nir_ixor(bld, a, b);
> + 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);
> + }
> +
> + /* not quite sure if frob'ing the existing instr is what we
> + * are *supposed* to do.. but wasn't sure a better way:
> + */
> + alu->op = nir_op_imov;
> + nir_instr_rewrite_src(&alu->instr, &alu->src[0].src, 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(impl, convert_block, &b);
> + nir_metadata_preserve(impl, nir_metadata_block_index |
> + nir_metadata_dominance);
> +}
> +
> +void
> +nir_lower_idiv(nir_shader *shader)
> +{
> + nir_foreach_overload(shader, overload) {
> + if (overload->impl)
> + convert_impl(overload->impl);
> + }
> +
> + exec_list_make_empty(&shader->system_values);
> +}
>
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