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/*
* Copyright © 2015 Intel 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.
*/
#include "nir.h"
#include "nir_builder.h"
/**
* \file nir_lower_gs_intrinsics.c
*
* Geometry Shaders can call EmitVertex()/EmitStreamVertex() to output an
* arbitrary number of vertices. However, the shader must declare the maximum
* number of vertices that it will ever output - further attempts to emit
* vertices result in undefined behavior according to the GLSL specification.
*
* Drivers might use this maximum number of vertices to allocate enough space
* to hold the geometry shader's output. Some drivers (such as i965) need to
* implement "safety checks" which ensure that the shader hasn't emitted too
* many vertices, to avoid overflowing that space and trashing other memory.
*
* The count of emitted vertices can also be useful in buffer offset
* calculations, so drivers know where to write the GS output.
*
* However, for simple geometry shaders that emit a statically determinable
* number of vertices, this extra bookkeeping is unnecessary and inefficient.
* By tracking the vertex count in NIR, we allow constant folding/propagation
* and dead control flow optimizations to eliminate most of it where possible.
*
* This pass introduces a new global variable which stores the current vertex
* count (initialized to 0), and converts emit_vertex/end_primitive intrinsics
* to their *_with_counter variants. emit_vertex is also wrapped in a safety
* check to avoid buffer overflows. Finally, it adds a set_vertex_count
* intrinsic at the end of the program, informing the driver of the final
* vertex count.
*/
struct state {
nir_builder *builder;
nir_variable *vertex_count_var;
bool progress;
};
/**
* Replace emit_vertex intrinsics with:
*
* if (vertex_count < max_vertices) {
* emit_vertex_with_counter vertex_count ...
* vertex_count += 1
* }
*/
static void
rewrite_emit_vertex(nir_intrinsic_instr *intrin, struct state *state)
{
nir_builder *b = state->builder;
/* Load the vertex count */
b->cursor = nir_before_instr(&intrin->instr);
nir_ssa_def *count = nir_load_var(b, state->vertex_count_var);
nir_ssa_def *max_vertices = nir_imm_int(b, b->shader->gs.vertices_out);
/* Create: if (vertex_count < max_vertices) and insert it.
*
* The new if statement needs to be hooked up to the control flow graph
* before we start inserting instructions into it.
*/
nir_if *if_stmt = nir_if_create(b->shader);
if_stmt->condition = nir_src_for_ssa(nir_ilt(b, count, max_vertices));
nir_builder_cf_insert(b, &if_stmt->cf_node);
/* Fill out the new then-block */
b->cursor = nir_after_cf_list(&if_stmt->then_list);
nir_intrinsic_instr *lowered =
nir_intrinsic_instr_create(b->shader,
nir_intrinsic_emit_vertex_with_counter);
lowered->const_index[0] = intrin->const_index[0];
lowered->src[0] = nir_src_for_ssa(count);
nir_builder_instr_insert(b, &lowered->instr);
/* Increment the vertex count by 1 */
nir_store_var(b, state->vertex_count_var,
nir_iadd(b, count, nir_imm_int(b, 1)));
nir_instr_remove(&intrin->instr);
state->progress = true;
}
/**
* Replace end_primitive with end_primitive_with_counter.
*/
static void
rewrite_end_primitive(nir_intrinsic_instr *intrin, struct state *state)
{
nir_builder *b = state->builder;
b->cursor = nir_before_instr(&intrin->instr);
nir_ssa_def *count = nir_load_var(b, state->vertex_count_var);
nir_intrinsic_instr *lowered =
nir_intrinsic_instr_create(b->shader,
nir_intrinsic_end_primitive_with_counter);
lowered->const_index[0] = intrin->const_index[0];
lowered->src[0] = nir_src_for_ssa(count);
nir_builder_instr_insert(b, &lowered->instr);
nir_instr_remove(&intrin->instr);
state->progress = true;
}
static bool
rewrite_intrinsics(nir_block *block, void *closure)
{
struct state *state = closure;
nir_foreach_instr_safe(block, instr) {
if (instr->type != nir_instr_type_intrinsic)
continue;
nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
switch (intrin->intrinsic) {
case nir_intrinsic_emit_vertex:
rewrite_emit_vertex(intrin, state);
break;
case nir_intrinsic_end_primitive:
rewrite_end_primitive(intrin, state);
break;
default:
/* not interesting; skip this */
break;
}
}
return true;
}
/**
* Add a set_vertex_count intrinsic at the end of the program
* (representing the final vertex count).
*/
static void
append_set_vertex_count(nir_block *end_block, struct state *state)
{
nir_builder *b = state->builder;
nir_shader *shader = state->builder->shader;
/* Insert the new intrinsic in all of the predecessors of the end block,
* but before any jump instructions (return).
*/
struct set_entry *entry;
set_foreach(end_block->predecessors, entry) {
nir_block *pred = (nir_block *) entry->key;
b->cursor = nir_after_block_before_jump(pred);
nir_ssa_def *count = nir_load_var(b, state->vertex_count_var);
nir_intrinsic_instr *set_vertex_count =
nir_intrinsic_instr_create(shader, nir_intrinsic_set_vertex_count);
set_vertex_count->src[0] = nir_src_for_ssa(count);
nir_builder_instr_insert(b, &set_vertex_count->instr);
}
}
bool
nir_lower_gs_intrinsics(nir_shader *shader)
{
struct state state;
state.progress = false;
/* Create the counter variable */
nir_variable *var = rzalloc(shader, nir_variable);
var->data.mode = nir_var_global;
var->type = glsl_uint_type();
var->name = "vertex_count";
var->constant_initializer = rzalloc(shader, nir_constant); /* initialize to 0 */
exec_list_push_tail(&shader->globals, &var->node);
state.vertex_count_var = var;
nir_foreach_overload(shader, overload) {
if (overload->impl) {
nir_builder b;
nir_builder_init(&b, overload->impl);
state.builder = &b;
nir_foreach_block(overload->impl, rewrite_intrinsics, &state);
/* This only works because we have a single main() function. */
append_set_vertex_count(overload->impl->end_block, &state);
nir_metadata_preserve(overload->impl, 0);
}
}
return state.progress;
}
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