/* * Copyright © 2016 Intel Corporation * Copyright © 2020 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. */ #include "nir_control_flow.h" #include "nir_builder.h" /** * This file implements an optimization for multiview. Some GPU's have a * special mode which allows the vertex shader (or last stage in the geometry * pipeline) to create multiple primitives in different layers of the * framebuffer at once by writing multiple copies of gl_Position. The * assumption is that in most uses of multiview, the only use of gl_ViewIndex * is to change the position to implement the parallax effect, and other * varyings will be the same between the different views. We put the body of * the original vertex shader in a loop, writing to a different copy of * gl_Position each loop iteration, and then let other optimizations clean up * the mess. */ static bool shader_writes_to_memory(nir_shader *shader) { /* With multiview, we would need to ensure that memory writes happen either * once or once per view. Since combination of multiview and memory writes * is not expected, we'll just skip this optimization in this case. */ nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader); nir_foreach_block(block, entrypoint) { nir_foreach_instr(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_deref_atomic_add: case nir_intrinsic_deref_atomic_imin: case nir_intrinsic_deref_atomic_umin: case nir_intrinsic_deref_atomic_imax: case nir_intrinsic_deref_atomic_umax: case nir_intrinsic_deref_atomic_and: case nir_intrinsic_deref_atomic_or: case nir_intrinsic_deref_atomic_xor: case nir_intrinsic_deref_atomic_exchange: case nir_intrinsic_deref_atomic_comp_swap: case nir_intrinsic_store_ssbo: case nir_intrinsic_ssbo_atomic_add: case nir_intrinsic_ssbo_atomic_imin: case nir_intrinsic_ssbo_atomic_umin: case nir_intrinsic_ssbo_atomic_imax: case nir_intrinsic_ssbo_atomic_umax: case nir_intrinsic_ssbo_atomic_and: case nir_intrinsic_ssbo_atomic_or: case nir_intrinsic_ssbo_atomic_xor: case nir_intrinsic_ssbo_atomic_exchange: case nir_intrinsic_ssbo_atomic_comp_swap: case nir_intrinsic_store_shared: case nir_intrinsic_shared_atomic_add: case nir_intrinsic_shared_atomic_imin: case nir_intrinsic_shared_atomic_umin: case nir_intrinsic_shared_atomic_imax: case nir_intrinsic_shared_atomic_umax: case nir_intrinsic_shared_atomic_and: case nir_intrinsic_shared_atomic_or: case nir_intrinsic_shared_atomic_xor: case nir_intrinsic_shared_atomic_exchange: case nir_intrinsic_shared_atomic_comp_swap: case nir_intrinsic_image_deref_store: case nir_intrinsic_image_deref_atomic_add: case nir_intrinsic_image_deref_atomic_umin: case nir_intrinsic_image_deref_atomic_umax: case nir_intrinsic_image_deref_atomic_imin: case nir_intrinsic_image_deref_atomic_imax: case nir_intrinsic_image_deref_atomic_and: case nir_intrinsic_image_deref_atomic_or: case nir_intrinsic_image_deref_atomic_xor: case nir_intrinsic_image_deref_atomic_exchange: case nir_intrinsic_image_deref_atomic_comp_swap: return true; default: /* Keep walking. */ break; } } } return false; } bool nir_shader_uses_view_index(nir_shader *shader) { nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader); nir_foreach_block(block, entrypoint) { nir_foreach_instr(instr, block) { if (instr->type != nir_instr_type_intrinsic) continue; nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr); if (intrin->intrinsic == nir_intrinsic_load_view_index) return true; } } return false; } static bool shader_only_position_uses_view_index(nir_shader *shader) { nir_shader *shader_no_position = nir_shader_clone(NULL, shader); nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader_no_position); /* Remove the store position from a cloned shader. */ nir_foreach_block(block, entrypoint) { nir_foreach_instr_safe(instr, block) { if (instr->type != nir_instr_type_intrinsic) continue; nir_intrinsic_instr *store = nir_instr_as_intrinsic(instr); if (store->intrinsic != nir_intrinsic_store_deref) continue; nir_variable *var = nir_intrinsic_get_var(store, 0); if (var->data.location != VARYING_SLOT_POS) continue; nir_instr_remove(&store->instr); } } /* Clean up shader so unused load_view_index intrinsics are removed. */ bool progress; do { progress = false; progress |= nir_opt_dead_cf(shader_no_position); /* Peephole select will drop if-blocks that have then and else empty, * which will remove the usage of an SSA in the condition. */ progress |= nir_opt_peephole_select(shader_no_position, 0, false, false); progress |= nir_opt_dce(shader_no_position); } while (progress); bool uses_view_index = nir_shader_uses_view_index(shader_no_position); ralloc_free(shader_no_position); return !uses_view_index; } /* Return true if it's safe to call nir_lower_multiview() on this vertex * shader. Note that this only handles driver-agnostic checks, i.e. things * which would make nir_lower_multiview() incorrect. Any driver-specific * checks, e.g. for sufficient varying space or performance considerations, * should be handled in the driver. * * Note that we don't handle the more complex checks needed for lowering * pipelines with geometry or tessellation shaders. */ bool nir_can_lower_multiview(nir_shader *shader) { bool writes_position = false; nir_foreach_shader_out_variable(var, shader) { if (var->data.location == VARYING_SLOT_POS) { writes_position = true; break; } } /* Don't bother handling this edge case. */ if (!writes_position) return false; return !shader_writes_to_memory(shader) && shader_only_position_uses_view_index(shader); } /** * The lowering. Call with the last active geometry stage. */ bool nir_lower_multiview(nir_shader *shader, uint32_t view_mask) { assert(shader->info.stage != MESA_SHADER_FRAGMENT); int view_count = util_bitcount(view_mask); nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader); /* Update position to refer to an array. */ nir_variable *pos_var = NULL; nir_foreach_shader_out_variable(var, shader) { if (var->data.location == VARYING_SLOT_POS) { assert(var->type == glsl_vec4_type()); var->type = glsl_array_type(glsl_vec4_type(), view_count, 0); var->data.per_view = true; pos_var = var; break; } } assert(pos_var); nir_cf_list body; nir_cf_list_extract(&body, &entrypoint->body); nir_builder b; nir_builder_init(&b, entrypoint); b.cursor = nir_after_cf_list(&entrypoint->body); /* Loop Index will go from 0 to view_count. */ nir_variable *loop_index_var = nir_local_variable_create(entrypoint, glsl_uint_type(), "loop_index"); nir_deref_instr *loop_index_deref = nir_build_deref_var(&b, loop_index_var); nir_store_deref(&b, loop_index_deref, nir_imm_int(&b, 0), 1); /* Array of view index values that are active in the loop. Note that the * loop index only matches the view index if there are no gaps in the * view_mask. */ nir_variable *view_index_var = nir_local_variable_create( entrypoint, glsl_array_type(glsl_uint_type(), view_count, 0), "view_index"); nir_deref_instr *view_index_deref = nir_build_deref_var(&b, view_index_var); { int array_position = 0; uint32_t view_mask_temp = view_mask; while (view_mask_temp) { uint32_t view_index = u_bit_scan(&view_mask_temp); nir_store_deref(&b, nir_build_deref_array_imm(&b, view_index_deref, array_position), nir_imm_int(&b, view_index), 1); array_position++; } } /* Create the equivalent of * * while (true): * if (loop_index >= view_count): * break * * view_index = active_indices[loop_index] * pos_deref = &pos[loop_index] * * # Placeholder for the body to be reinserted. * * loop_index += 1 * * Later both `view_index` and `pos_deref` will be used to rewrite the * original shader body. */ nir_loop* loop = nir_push_loop(&b); nir_ssa_def *loop_index = nir_load_deref(&b, loop_index_deref); nir_ssa_def *cmp = nir_ige(&b, loop_index, nir_imm_int(&b, view_count)); nir_if *loop_check = nir_push_if(&b, cmp); nir_jump(&b, nir_jump_break); nir_pop_if(&b, loop_check); nir_ssa_def *view_index = nir_load_deref(&b, nir_build_deref_array(&b, view_index_deref, loop_index)); nir_deref_instr *pos_deref = nir_build_deref_array(&b, nir_build_deref_var(&b, pos_var), loop_index); nir_store_deref(&b, loop_index_deref, nir_iadd_imm(&b, loop_index, 1), 1); nir_pop_loop(&b, loop); /* Reinsert the body. */ b.cursor = nir_after_instr(&pos_deref->instr); nir_cf_reinsert(&body, b.cursor); nir_foreach_block(block, entrypoint) { 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_load_view_index: { assert(intrin->dest.is_ssa); nir_ssa_def_rewrite_uses(&intrin->dest.ssa, nir_src_for_ssa(view_index)); break; } case nir_intrinsic_store_deref: { nir_variable *var = nir_intrinsic_get_var(intrin, 0); if (var == pos_var) { nir_deref_instr *old_deref = nir_src_as_deref(intrin->src[0]); nir_instr_rewrite_src(instr, &intrin->src[0], nir_src_for_ssa(&pos_deref->dest.ssa)); /* Remove old deref since it has the wrong type. */ nir_deref_instr_remove_if_unused(old_deref); } break; } case nir_intrinsic_load_deref: if (nir_intrinsic_get_var(intrin, 0) == pos_var) { unreachable("Should have lowered I/O to temporaries " "so no load_deref on position output is expected."); } break; case nir_intrinsic_copy_deref: unreachable("Should have lowered copy_derefs at this point"); break; default: /* Do nothing. */ break; } } } nir_metadata_preserve(entrypoint, nir_metadata_none); return true; }