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glsl: remove gl_nir_opt_dead_builtin_varyings

Browse source 
It doesn't do anything since IO variables are lowered to intrinsics,
which simplifies and eliminates a lot of variable-specific stuff
like declared but dead builtin varyings and unused components
of builtin varying arrays.

This reduces GLSL compile times by 2.4% with the gallium noop driver.

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Timothy Arceri <tarceri@itqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36023>
This commit is contained in:
Marek Olšák 2025-07-06 09:44:49 -04:00 • committed by Marge Bot
parent 08b522d21e
commit 7a506d0a41
4 changed files with 1 additions and 557 deletions
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11
src/compiler/glsl/gl_nir_link_varyings.c
View file

@ -4416,12 +4416,7 @@ link_varyings(struct gl_shader_program *prog, unsigned first,
return false;
}
if (num_shaders == 1) {
gl_nir_opt_dead_builtin_varyings(consts, api, prog, NULL, linked_shader[0],
0, NULL);
gl_nir_opt_dead_builtin_varyings(consts, api, prog, linked_shader[0], NULL,
num_xfb_decls, xfb_decls);
} else {
if (num_shaders > 1) {
/* Linking the stages in the opposite order (from fragment to vertex)
* ensures that inter-shader outputs written to in an earlier stage
* are eliminated if they are (transitively) not used in a later
@ -4435,10 +4430,6 @@ link_varyings(struct gl_shader_program *prog, unsigned first,
struct gl_linked_shader *const sh_i = prog->_LinkedShaders[i];
struct gl_linked_shader *const sh_next = prog->_LinkedShaders[next];
gl_nir_opt_dead_builtin_varyings(consts, api, prog, sh_i, sh_next,
next == MESA_SHADER_FRAGMENT ? num_xfb_decls : 0,
xfb_decls);
const uint64_t reserved_out_slots =
reserved_varying_slot(sh_i, nir_var_shader_out);
const uint64_t reserved_in_slots =

8
src/compiler/glsl/gl_nir_linker.h
View file

@ -101,14 +101,6 @@ nir_variable * gl_nir_lower_xfb_varying(nir_shader *shader,
const char *old_var_name,
nir_variable *toplevel_var);
void gl_nir_opt_dead_builtin_varyings(const struct gl_constants *consts,
gl_api api,
struct gl_shader_program *prog,
struct gl_linked_shader *producer,
struct gl_linked_shader *consumer,
unsigned num_tfeedback_decls,
struct xfb_decl *tfeedback_decls);
void gl_nir_set_uniform_initializers(const struct gl_constants *consts,
struct gl_shader_program *prog);

538
src/compiler/glsl/gl_nir_opt_dead_builtin_varyings.c
View file

@ -1,538 +0,0 @@
/*
* Copyright © 2013 Marek Olšák <maraeo@gmail.com>
* Copyright © 2022 Valve Corporation
*
* 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.
*/
/**
* This eliminates the built-in shader outputs which are either not written
* at all or not used by the next stage. It also eliminates unused elements
* of gl_TexCoord inputs, which reduces the overall varying usage.
* The varyings handled here are the primary and secondary color, the fog,
* and the texture coordinates (gl_TexCoord).
*
* This pass is necessary, because the Mesa GLSL linker cannot eliminate
* built-in varyings like it eliminates user-defined varyings, because
* the built-in varyings have pre-assigned locations. Also, the elimination
* of unused gl_TexCoord elements requires its own lowering pass anyway.
*
* It's implemented by replacing all occurrences of dead varyings with
* temporary variables, which creates dead code. It is recommended to run
* a dead-code elimination pass after this.
*
* If any texture coordinate slots can be eliminated, the gl_TexCoord array is
* broken down into separate vec4 variables with locations equal to
* VARYING_SLOT_TEX0 + i.
*/
#include "gl_nir_link_varyings.h"
#include "gl_nir_linker.h"
#include "glsl_types.h"
#include "linker_util.h"
#include "nir_builder.h"
#include "main/consts_exts.h"
#include "main/shader_types.h"
#include "util/u_string.h"
struct varying_info {
bool lower_texcoord_array;
nir_variable *texcoord_array;
unsigned texcoord_usage; /* bitmask */
bool find_frag_outputs; /* false if it's looking for varyings */
nir_variable *color[2];
nir_variable *backcolor[2];
unsigned color_usage; /* bitmask */
unsigned tfeedback_color_usage; /* bitmask */
nir_variable *fog;
bool has_fog;
bool tfeedback_has_fog;
nir_variable_mode mode;
};
static void
initialise_varying_info(struct varying_info *info, nir_variable_mode mode,
bool find_frag_outputs)
{
info->find_frag_outputs = find_frag_outputs;
info->lower_texcoord_array = true;
info->texcoord_array = NULL;
info->texcoord_usage = 0;
info->color_usage = 0;
info->tfeedback_color_usage = 0;
info->fog = NULL;
info->has_fog = false;
info->tfeedback_has_fog = false;
info->mode = mode;
memset(info->color, 0, sizeof(info->color));
memset(info->backcolor, 0, sizeof(info->backcolor));
}
static void
gather_info_on_varying_deref(struct varying_info *info, nir_deref_instr *deref)
{
nir_variable *var = nir_deref_instr_get_variable(deref);
if (!glsl_type_is_array(var->type) || !is_gl_identifier(var->name))
return;
if (!info->find_frag_outputs && var->data.location == VARYING_SLOT_TEX0) {
info->texcoord_array = var;
assert(deref->deref_type == nir_deref_type_array);
if (nir_src_is_const(deref->arr.index)) {
info->texcoord_usage |= 1 << nir_src_as_uint(deref->arr.index);
} else {
/* There is variable indexing, we can't lower the texcoord array. */
info->texcoord_usage |= (1 << glsl_array_size(var->type)) - 1;
info->lower_texcoord_array = false;
}
return;
}
}
/**
* This obtains detailed information about built-in varyings from shader code.
*/
static void
get_varying_info(struct varying_info *info, nir_shader *shader,
unsigned num_tfeedback_decls, struct xfb_decl *tfeedback_decls)
{
/* Handle the transform feedback varyings. */
for (unsigned i = 0; i < num_tfeedback_decls; i++) {
if (!xfb_decl_is_varying(&tfeedback_decls[i]))
continue;
unsigned location = tfeedback_decls[i].location;
switch (location) {
case VARYING_SLOT_COL0:
case VARYING_SLOT_BFC0:
info->tfeedback_color_usage |= 1;
break;
case VARYING_SLOT_COL1:
case VARYING_SLOT_BFC1:
info->tfeedback_color_usage |= 2;
break;
case VARYING_SLOT_FOGC:
info->tfeedback_has_fog = true;
break;
default:
if (location >= VARYING_SLOT_TEX0 &&
location <= VARYING_SLOT_TEX7) {
info->lower_texcoord_array = false;
}
}
}
/* Process frag shader vars */
nir_foreach_variable_with_modes(var, shader, info->mode) {
/* Nothing to do here for fragment outputs. */
if (info->find_frag_outputs)
break;
/* Handle colors and fog. */
switch (var->data.location) {
case VARYING_SLOT_COL0:
info->color[0] = var;
info->color_usage |= 1;
break;
case VARYING_SLOT_COL1:
info->color[1] = var;
info->color_usage |= 2;
break;
case VARYING_SLOT_BFC0:
info->backcolor[0] = var;
info->color_usage |= 1;
break;
case VARYING_SLOT_BFC1:
info->backcolor[1] = var;
info->color_usage |= 2;
break;
case VARYING_SLOT_FOGC:
info->fog = var;
info->has_fog = true;
break;
}
}
/* Process the shader. */
assert(shader->info.stage != MESA_SHADER_COMPUTE);
nir_function_impl *impl = nir_shader_get_entrypoint(shader);
/* assert that functions have been inlined before packing is called */
nir_foreach_function(f, shader) {
assert(f->impl == impl);
}
nir_foreach_block(block, impl) {
nir_foreach_instr(instr, block) {
if (instr->type != nir_instr_type_intrinsic)
continue;
nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
/* Copies should have been lowered by nir_split_var_copies() before
* calling this pass.
*/
assert(intrin->intrinsic != nir_intrinsic_copy_deref);
if (intrin->intrinsic != nir_intrinsic_load_deref &&
intrin->intrinsic != nir_intrinsic_store_deref)
continue;
nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
if (!nir_deref_mode_is(deref, info->mode))
continue;
gather_info_on_varying_deref(info, deref);
}
}
if (!info->texcoord_array) {
info->lower_texcoord_array = false;
}
}
struct replace_varyings_data {
const struct gl_constants *consts;
struct gl_shader_program *prog;
struct gl_linked_shader *shader;
const struct varying_info *info;
nir_variable *new_texcoord[MAX_TEXTURE_COORD_UNITS];
nir_variable *new_color[2];
nir_variable *new_backcolor[2];
nir_variable *new_fog;
};
static nir_variable *
create_new_var(nir_shader *shader, char *name, nir_variable_mode mode,
const struct glsl_type *type)
{
nir_variable *var = rzalloc(shader, nir_variable);
var->name = ralloc_strdup(var, name);
var->data.mode = mode;
var->type = type;
nir_shader_add_variable(shader, var);
return var;
}
static void
replace_varying(struct replace_varyings_data *rv_data, nir_variable *var)
{
/* Remove the gl_TexCoord array. */
if (rv_data->info->lower_texcoord_array &&
var == rv_data->info->texcoord_array) {
var->data.mode = nir_var_shader_temp;
}
/* Lower set-but-unused color and fog outputs to shader temps. */
for (int i = 0; i < 2; i++) {
if (var == rv_data->info->color[i] && rv_data->new_color[i]) {
var->data.mode = nir_var_shader_temp;
}
if (var == rv_data->info->backcolor[i] && rv_data->new_backcolor[i]) {
var->data.mode = nir_var_shader_temp;
}
}
if (var == rv_data->info->fog && rv_data->new_fog) {
var->data.mode = nir_var_shader_temp;
}
}
static void
rewrite_varying_deref(nir_builder *b, struct replace_varyings_data *rv_data,
nir_deref_instr *deref)
{
if (deref->deref_type != nir_deref_type_array)
return;
nir_variable *var = nir_deref_instr_get_variable(deref);
const struct varying_info *info = rv_data->info;
b->cursor = nir_before_instr(&deref->instr);
/* Replace an array dereference gl_TexCoord[i] with a single
* variable dereference representing gl_TexCoord[i].
*/
if (info->lower_texcoord_array && info->texcoord_array == var) {
/* gl_TexCoord[i] occurrence */
unsigned i = nir_src_as_uint(deref->arr.index);
nir_deref_instr *new_deref =
nir_build_deref_var(b, rv_data->new_texcoord[i]);
nir_def_rewrite_uses(&deref->def, &new_deref->def);
return;
}
}
static void
prepare_array(struct replace_varyings_data *rv_data,
nir_shader *shader, nir_variable **new_var,
int max_elements, unsigned start_location,
const char *var_name, const char *mode_str,
unsigned usage, unsigned external_usage)
{
for (int i = max_elements - 1; i >= 0; i--) {
if (usage & (1 << i)) {
char name[32];
if (!(external_usage & (1 << i))) {
/* This varying is unused in the next stage. Declare
* a temporary instead of an output. */
snprintf(name, 32, "gl_%s_%s%i_dummy", mode_str, var_name, i);
new_var[i] = create_new_var(shader, name, nir_var_shader_temp,
glsl_vec4_type());
} else {
snprintf(name, 32, "gl_%s_%s%i", mode_str, var_name, i);
new_var[i] = create_new_var(shader, name, rv_data->info->mode,
glsl_vec4_type());
new_var[i]->data.location = start_location + i;
new_var[i]->data.explicit_location = true;
}
}
}
}
/**
* This replaces unused varyings with temporary variables.
*
* If "ir" is the producer, the "external" usage should come from
* the consumer. It also works the other way around. If either one is
* missing, set the "external" usage to a full mask.
*/
static void
replace_varyings(const struct gl_constants *consts,
struct gl_linked_shader *shader,
struct gl_shader_program *prog,
const struct varying_info *info,
unsigned external_texcoord_usage,
unsigned external_color_usage, bool external_has_fog)
{
struct replace_varyings_data rv_data;
rv_data.shader = shader;
rv_data.info = info;
rv_data.consts = consts;
rv_data.prog = prog;
memset(rv_data.new_texcoord, 0, sizeof(rv_data.new_texcoord));
memset(rv_data.new_color, 0, sizeof(rv_data.new_color));
memset(rv_data.new_backcolor, 0, sizeof(rv_data.new_backcolor));
rv_data.new_fog = NULL;
const char *mode_str = info->mode == nir_var_shader_in ? "in" : "out";
/* Handle texcoord outputs.
*
* We're going to break down the gl_TexCoord array into separate
* variables. First, add declarations of the new variables all
* occurrences of gl_TexCoord will be replaced with.
*/
if (info->lower_texcoord_array) {
prepare_array(&rv_data, shader->Program->nir, rv_data.new_texcoord,
ARRAY_SIZE(rv_data.new_texcoord),
VARYING_SLOT_TEX0, "TexCoord", mode_str,
info->texcoord_usage, external_texcoord_usage);
}
/* Create dummy variables which will replace set-but-unused color and
* fog outputs.
*/
external_color_usage |= info->tfeedback_color_usage;
for (int i = 0; i < 2; i++) {
char name[32];
if (!(external_color_usage & (1 << i))) {
if (info->color[i]) {
snprintf(name, 32, "gl_%s_FrontColor%i_dummy", mode_str, i);
rv_data.new_color[i] =
create_new_var(shader->Program->nir, name, nir_var_shader_temp,
glsl_vec4_type());
}
if (info->backcolor[i]) {
snprintf(name, 32, "gl_%s_BackColor%i_dummy", mode_str, i);
rv_data.new_backcolor[i] =
create_new_var(shader->Program->nir, name, nir_var_shader_temp,
glsl_vec4_type());
}
}
}
if (!external_has_fog && !info->tfeedback_has_fog && info->fog) {
char name[32];
snprintf(name, 32, "gl_%s_FogFragCoord_dummy", mode_str);
rv_data.new_fog =
create_new_var(shader->Program->nir, name, nir_var_shader_temp,
glsl_float_type());
}
/* Now do the replacing. */
nir_foreach_variable_with_modes_safe(var, shader->Program->nir, info->mode) {
replace_varying(&rv_data, var);
}
nir_function_impl *impl = nir_shader_get_entrypoint(shader->Program->nir);
nir_builder b = nir_builder_create(impl);
/* assert that functions have been inlined before packing is called */
nir_foreach_function(f, shader->Program->nir) {
assert(f->impl == impl);
}
/* Rewrite the derefs to use the new vars */
nir_foreach_block(block, impl) {
nir_foreach_instr(instr, block) {
if (instr->type != nir_instr_type_intrinsic)
continue;
nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
/* Copies should have been lowered by nir_split_var_copies() before
* calling this pass.
*/
assert(intrin->intrinsic != nir_intrinsic_copy_deref);
if (intrin->intrinsic != nir_intrinsic_load_deref &&
intrin->intrinsic != nir_intrinsic_store_deref)
continue;
nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
if (!nir_deref_mode_is(deref, info->mode))
continue;
rewrite_varying_deref(&b, &rv_data, deref);
}
}
}
static void
lower_texcoord_array(const struct gl_constants *consts,
struct gl_linked_shader *shader,
struct gl_shader_program *prog,
const struct varying_info *info)
{
replace_varyings(consts, shader, prog, info,
(1 << MAX_TEXTURE_COORD_UNITS) - 1, 1 | 2, true);
}
void
gl_nir_opt_dead_builtin_varyings(const struct gl_constants *consts, gl_api api,
struct gl_shader_program *prog,
struct gl_linked_shader *producer,
struct gl_linked_shader *consumer,
unsigned num_tfeedback_decls,
struct xfb_decl *tfeedback_decls)
{
/* Lowering of built-in varyings has no effect with the core context and
* GLES2, because they are not available there.
*/
if (api == API_OPENGL_CORE ||
api == API_OPENGLES2) {
goto done;
}
/* Information about built-in varyings. */
struct varying_info producer_info;
struct varying_info consumer_info;
initialise_varying_info(&producer_info, nir_var_shader_out, false);
initialise_varying_info(&consumer_info, nir_var_shader_in, false);
if (producer) {
get_varying_info(&producer_info, producer->Program->nir,
num_tfeedback_decls, tfeedback_decls);
if (producer->Stage == MESA_SHADER_TESS_CTRL)
producer_info.lower_texcoord_array = false;
if (!consumer) {
/* At least eliminate unused gl_TexCoord elements. */
if (producer_info.lower_texcoord_array) {
lower_texcoord_array(consts, producer, prog, &producer_info);
}
goto done;
}
}
if (consumer) {
get_varying_info(&consumer_info, consumer->Program->nir,
num_tfeedback_decls, tfeedback_decls);
if (consumer->Stage != MESA_SHADER_FRAGMENT)
consumer_info.lower_texcoord_array = false;
if (!producer) {
/* At least eliminate unused gl_TexCoord elements. */
if (consumer_info.lower_texcoord_array) {
lower_texcoord_array(consts, consumer, prog, &consumer_info);
}
goto done;
}
}
/* Eliminate the outputs unused by the consumer. */
if (producer_info.lower_texcoord_array ||
producer_info.color_usage ||
producer_info.has_fog) {
replace_varyings(consts, producer, prog, &producer_info,
consumer_info.texcoord_usage,
consumer_info.color_usage,
consumer_info.has_fog);
}
/* The gl_TexCoord fragment shader inputs can be initialized
* by GL_COORD_REPLACE, so we can't eliminate them.
*
* This doesn't prevent elimination of the gl_TexCoord elements which
* are not read by the fragment shader. We want to eliminate those anyway.
*/
if (consumer->Stage == MESA_SHADER_FRAGMENT) {
producer_info.texcoord_usage = (1 << MAX_TEXTURE_COORD_UNITS) - 1;
}
/* Eliminate the inputs uninitialized by the producer. */
if (consumer_info.lower_texcoord_array ||
consumer_info.color_usage ||
consumer_info.has_fog) {
replace_varyings(consts, consumer, prog, &consumer_info,
producer_info.texcoord_usage,
producer_info.color_usage,
producer_info.has_fog);
}
done:
if (producer)
nir_fixup_deref_modes(producer->Program->nir);
if (consumer)
nir_fixup_deref_modes(consumer->Program->nir);
}

1
src/compiler/glsl/meson.build
View file

@ -130,7 +130,6 @@ files_libglsl = files(
'gl_nir_link_xfb.c',
'gl_nir_linker.c',
'gl_nir_linker.h',
'gl_nir_opt_dead_builtin_varyings.c',
'gl_nir.h',
'glsl_parser_extras.cpp',
'glsl_parser_extras.h',