1 /* 2 * Copyright 2015 Intel Corporation 3 * 4 * Permission is hereby granted, free of charge, to any person obtaining a 5 * copy of this software and associated documentation files (the "Software"), 6 * to deal in the Software without restriction, including without limitation 7 * the rights to use, copy, modify, merge, publish, distribute, sublicense, 8 * and/or sell copies of the Software, and to permit persons to whom the 9 * Software is furnished to do so, subject to the following conditions: 10 * 11 * The above copyright notice and this permission notice (including the next 12 * paragraph) shall be included in all copies or substantial portions of the 13 * Software. 14 * 15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS 21 * IN THE SOFTWARE. 22 */ 23 24 #include "nir.h" 25 #include "nir_builder.h" 26 27 /** 28 * \file nir_lower_gs_intrinsics.c 29 * 30 * Geometry Shaders can call EmitVertex()/EmitStreamVertex() to output an 31 * arbitrary number of vertices. However, the shader must declare the maximum 32 * number of vertices that it will ever output - further attempts to emit 33 * vertices result in undefined behavior according to the GLSL specification. 34 * 35 * Drivers might use this maximum number of vertices to allocate enough space 36 * to hold the geometry shader's output. Some drivers (such as i965) need to 37 * implement "safety checks" which ensure that the shader hasn't emitted too 38 * many vertices, to avoid overflowing that space and trashing other memory. 39 * 40 * The count of emitted vertices can also be useful in buffer offset 41 * calculations, so drivers know where to write the GS output. 42 * 43 * However, for simple geometry shaders that emit a statically determinable 44 * number of vertices, this extra bookkeeping is unnecessary and inefficient. 45 * By tracking the vertex count in NIR, we allow constant folding/propagation 46 * and dead control flow optimizations to eliminate most of it where possible. 47 * 48 * This pass introduces a new global variable which stores the current vertex 49 * count (initialized to 0), and converts emit_vertex/end_primitive intrinsics 50 * to their *_with_counter variants. emit_vertex is also wrapped in a safety 51 * check to avoid buffer overflows. Finally, it adds a set_vertex_count 52 * intrinsic at the end of the program, informing the driver of the final 53 * vertex count. 54 */ 55 56 struct state { 57 nir_builder *builder; 58 nir_variable *vertex_count_var; 59 bool progress; 60 }; 61 62 /** 63 * Replace emit_vertex intrinsics with: 64 * 65 * if (vertex_count < max_vertices) { 66 * emit_vertex_with_counter vertex_count ... 67 * vertex_count += 1 68 * } 69 */ 70 static void 71 rewrite_emit_vertex(nir_intrinsic_instr *intrin, struct state *state) 72 { 73 nir_builder *b = state->builder; 74 75 /* Load the vertex count */ 76 b->cursor = nir_before_instr(&intrin->instr); 77 nir_ssa_def *count = nir_load_var(b, state->vertex_count_var); 78 79 nir_ssa_def *max_vertices = 80 nir_imm_int(b, b->shader->info.gs.vertices_out); 81 82 /* Create: if (vertex_count < max_vertices) and insert it. 83 * 84 * The new if statement needs to be hooked up to the control flow graph 85 * before we start inserting instructions into it. 86 */ 87 nir_push_if(b, nir_ilt(b, count, max_vertices)); 88 89 nir_intrinsic_instr *lowered = 90 nir_intrinsic_instr_create(b->shader, 91 nir_intrinsic_emit_vertex_with_counter); 92 nir_intrinsic_set_stream_id(lowered, nir_intrinsic_stream_id(intrin)); 93 lowered->src[0] = nir_src_for_ssa(count); 94 nir_builder_instr_insert(b, &lowered->instr); 95 96 /* Increment the vertex count by 1 */ 97 nir_store_var(b, state->vertex_count_var, 98 nir_iadd(b, count, nir_imm_int(b, 1)), 99 0x1); /* .x */ 100 101 nir_pop_if(b, NULL); 102 103 nir_instr_remove(&intrin->instr); 104 105 state->progress = true; 106 } 107 108 /** 109 * Replace end_primitive with end_primitive_with_counter. 110 */ 111 static void 112 rewrite_end_primitive(nir_intrinsic_instr *intrin, struct state *state) 113 { 114 nir_builder *b = state->builder; 115 116 b->cursor = nir_before_instr(&intrin->instr); 117 nir_ssa_def *count = nir_load_var(b, state->vertex_count_var); 118 119 nir_intrinsic_instr *lowered = 120 nir_intrinsic_instr_create(b->shader, 121 nir_intrinsic_end_primitive_with_counter); 122 nir_intrinsic_set_stream_id(lowered, nir_intrinsic_stream_id(intrin)); 123 lowered->src[0] = nir_src_for_ssa(count); 124 nir_builder_instr_insert(b, &lowered->instr); 125 126 nir_instr_remove(&intrin->instr); 127 128 state->progress = true; 129 } 130 131 static bool 132 rewrite_intrinsics(nir_block *block, struct state *state) 133 { 134 nir_foreach_instr_safe(instr, block) { 135 if (instr->type != nir_instr_type_intrinsic) 136 continue; 137 138 nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr); 139 switch (intrin->intrinsic) { 140 case nir_intrinsic_emit_vertex: 141 rewrite_emit_vertex(intrin, state); 142 break; 143 case nir_intrinsic_end_primitive: 144 rewrite_end_primitive(intrin, state); 145 break; 146 default: 147 /* not interesting; skip this */ 148 break; 149 } 150 } 151 152 return true; 153 } 154 155 /** 156 * Add a set_vertex_count intrinsic at the end of the program 157 * (representing the final vertex count). 158 */ 159 static void 160 append_set_vertex_count(nir_block *end_block, struct state *state) 161 { 162 nir_builder *b = state->builder; 163 nir_shader *shader = state->builder->shader; 164 165 /* Insert the new intrinsic in all of the predecessors of the end block, 166 * but before any jump instructions (return). 167 */ 168 struct set_entry *entry; 169 set_foreach(end_block->predecessors, entry) { 170 nir_block *pred = (nir_block *) entry->key; 171 b->cursor = nir_after_block_before_jump(pred); 172 173 nir_ssa_def *count = nir_load_var(b, state->vertex_count_var); 174 175 nir_intrinsic_instr *set_vertex_count = 176 nir_intrinsic_instr_create(shader, nir_intrinsic_set_vertex_count); 177 set_vertex_count->src[0] = nir_src_for_ssa(count); 178 179 nir_builder_instr_insert(b, &set_vertex_count->instr); 180 } 181 } 182 183 bool 184 nir_lower_gs_intrinsics(nir_shader *shader) 185 { 186 struct state state; 187 state.progress = false; 188 189 nir_function_impl *impl = nir_shader_get_entrypoint(shader); 190 assert(impl); 191 192 nir_builder b; 193 nir_builder_init(&b, impl); 194 state.builder = &b; 195 196 /* Create the counter variable */ 197 state.vertex_count_var = 198 nir_local_variable_create(impl, glsl_uint_type(), "vertex_count"); 199 /* initialize to 0 */ 200 b.cursor = nir_before_cf_list(&impl->body); 201 nir_store_var(&b, state.vertex_count_var, nir_imm_int(&b, 0), 0x1); 202 203 nir_foreach_block_safe(block, impl) 204 rewrite_intrinsics(block, &state); 205 206 /* This only works because we have a single main() function. */ 207 append_set_vertex_count(impl->end_block, &state); 208 209 nir_metadata_preserve(impl, 0); 210 211 return state.progress; 212 } 213
