/* * 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" #include "nir_xfb_info.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_vars[NIR_MAX_XFB_STREAMS]; 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; unsigned stream = nir_intrinsic_stream_id(intrin); /* Load the vertex count */ b->cursor = nir_before_instr(&intrin->instr); nir_ssa_def *count = nir_load_var(b, state->vertex_count_vars[stream]); nir_ssa_def *max_vertices = nir_imm_int(b, b->shader->info.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_push_if(b, nir_ilt(b, count, max_vertices)); nir_intrinsic_instr *lowered = nir_intrinsic_instr_create(b->shader, nir_intrinsic_emit_vertex_with_counter); nir_intrinsic_set_stream_id(lowered, stream); 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_vars[stream], nir_iadd(b, count, nir_imm_int(b, 1)), 0x1); /* .x */ nir_pop_if(b, NULL); 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; unsigned stream = nir_intrinsic_stream_id(intrin); b->cursor = nir_before_instr(&intrin->instr); nir_ssa_def *count = nir_load_var(b, state->vertex_count_vars[stream]); nir_intrinsic_instr *lowered = nir_intrinsic_instr_create(b->shader, nir_intrinsic_end_primitive_with_counter); nir_intrinsic_set_stream_id(lowered, stream); 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, struct state *state) { nir_foreach_instr_safe(instr, block) { 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). */ 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_vars[0]); 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, bool per_stream) { struct state state; state.progress = false; nir_function_impl *impl = nir_shader_get_entrypoint(shader); assert(impl); nir_builder b; nir_builder_init(&b, impl); state.builder = &b; /* Create the counter variables */ b.cursor = nir_before_cf_list(&impl->body); unsigned num_counters = per_stream && shader->info.gs.uses_streams ? NIR_MAX_XFB_STREAMS : 1; for (unsigned i = 0; i < num_counters; i++) { state.vertex_count_vars[i] = nir_local_variable_create(impl, glsl_uint_type(), "vertex_count"); /* initialize to 0 */ nir_store_var(&b, state.vertex_count_vars[i], nir_imm_int(&b, 0), 0x1); } /* If per_stream is false, we only have one counter which we want to use * for all streams. Duplicate the counter pointer so all streams use the * same counter. */ for (unsigned i = num_counters; i < NIR_MAX_XFB_STREAMS; i++) state.vertex_count_vars[i] = state.vertex_count_vars[0]; nir_foreach_block_safe(block, impl) rewrite_intrinsics(block, &state); /* This only works because we have a single main() function. */ if (!per_stream) append_set_vertex_count(impl->end_block, &state); nir_metadata_preserve(impl, 0); return state.progress; }