/* * Copyright © 2014 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. * * Authors: * Jason Ekstrand (jason@jlekstrand.net) * */ #include "nir.h" #include "nir_builder.h" #include "nir_deref.h" #include "nir_phi_builder.h" #include "nir_vla.h" struct deref_node { struct deref_node *parent; const struct glsl_type *type; bool lower_to_ssa; /* Only valid for things that end up in the direct list. * Note that multiple nir_deref_instrs may correspond to this node, but * they will all be equivalent, so any is as good as the other. */ nir_deref_path path; struct exec_node direct_derefs_link; struct set *loads; struct set *stores; struct set *copies; struct nir_phi_builder_value *pb_value; /* True if this node is fully direct. If set, it must be in the children * array of its parent. */ bool is_direct; struct deref_node *wildcard; struct deref_node *indirect; struct deref_node *children[0]; }; struct lower_variables_state { nir_shader *shader; void *dead_ctx; nir_function_impl *impl; /* A hash table mapping variables to deref_node data */ struct hash_table *deref_var_nodes; /* A hash table mapping fully-qualified direct dereferences, i.e. * dereferences with no indirect or wildcard array dereferences, to * deref_node data. * * At the moment, we only lower loads, stores, and copies that can be * trivially lowered to loads and stores, i.e. copies with no indirects * and no wildcards. If a part of a variable that is being loaded from * and/or stored into is also involved in a copy operation with * wildcards, then we lower that copy operation to loads and stores, but * otherwise we leave copies with wildcards alone. Since the only derefs * used in these loads, stores, and trivial copies are ones with no * wildcards and no indirects, these are precisely the derefs that we * can actually consider lowering. */ struct exec_list direct_deref_nodes; /* Controls whether get_deref_node will add variables to the * direct_deref_nodes table. This is turned on when we are initially * scanning for load/store instructions. It is then turned off so we * don't accidentally change the direct_deref_nodes table while we're * iterating throug it. */ bool add_to_direct_deref_nodes; struct nir_phi_builder *phi_builder; }; static struct deref_node * deref_node_create(struct deref_node *parent, const struct glsl_type *type, bool is_direct, void *mem_ctx) { size_t size = sizeof(struct deref_node) + glsl_get_length(type) * sizeof(struct deref_node *); struct deref_node *node = rzalloc_size(mem_ctx, size); node->type = type; node->parent = parent; exec_node_init(&node->direct_derefs_link); node->is_direct = is_direct; return node; } /* Returns the deref node associated with the given variable. This will be * the root of the tree representing all of the derefs of the given variable. */ static struct deref_node * get_deref_node_for_var(nir_variable *var, struct lower_variables_state *state) { struct deref_node *node; struct hash_entry *var_entry = _mesa_hash_table_search(state->deref_var_nodes, var); if (var_entry) { return var_entry->data; } else { node = deref_node_create(NULL, var->type, true, state->dead_ctx); _mesa_hash_table_insert(state->deref_var_nodes, var, node); return node; } } /* Gets the deref_node for the given deref chain and creates it if it * doesn't yet exist. If the deref is fully-qualified and direct and * state->add_to_direct_deref_nodes is true, it will be added to the hash * table of of fully-qualified direct derefs. */ static struct deref_node * get_deref_node_recur(nir_deref_instr *deref, struct lower_variables_state *state) { if (deref->deref_type == nir_deref_type_var) return get_deref_node_for_var(deref->var, state); struct deref_node *parent = get_deref_node_recur(nir_deref_instr_parent(deref), state); switch (deref->deref_type) { case nir_deref_type_struct: assert(glsl_type_is_struct(parent->type)); assert(deref->strct.index < glsl_get_length(parent->type)); if (parent->children[deref->strct.index] == NULL) { parent->children[deref->strct.index] = deref_node_create(parent, deref->type, parent->is_direct, state->dead_ctx); } return parent->children[deref->strct.index]; case nir_deref_type_array: { if (nir_src_is_const(deref->arr.index)) { uint32_t index = nir_src_as_uint(deref->arr.index); /* This is possible if a loop unrolls and generates an * out-of-bounds offset. We need to handle this at least * somewhat gracefully. */ if (index >= glsl_get_length(parent->type)) return NULL; if (parent->children[index] == NULL) { parent->children[index] = deref_node_create(parent, deref->type, parent->is_direct, state->dead_ctx); } return parent->children[index]; } else { if (parent->indirect == NULL) { parent->indirect = deref_node_create(parent, deref->type, false, state->dead_ctx); } return parent->indirect; } break; } case nir_deref_type_array_wildcard: if (parent->wildcard == NULL) { parent->wildcard = deref_node_create(parent, deref->type, false, state->dead_ctx); } return parent->wildcard; default: unreachable("Invalid deref type"); } } static struct deref_node * get_deref_node(nir_deref_instr *deref, struct lower_variables_state *state) { /* This pass only works on local variables. Just ignore any derefs with * a non-local mode. */ if (deref->mode != nir_var_function_temp) return NULL; struct deref_node *node = get_deref_node_recur(deref, state); if (!node) return NULL; /* Insert the node in the direct derefs list. We only do this if it's not * already in the list and we only bother for deref nodes which are used * directly in a load or store. */ if (node->is_direct && state->add_to_direct_deref_nodes && node->direct_derefs_link.next == NULL) { nir_deref_path_init(&node->path, deref, state->dead_ctx); assert(deref->var != NULL); exec_list_push_tail(&state->direct_deref_nodes, &node->direct_derefs_link); } return node; } /* \sa foreach_deref_node_match */ static void foreach_deref_node_worker(struct deref_node *node, nir_deref_instr **path, void (* cb)(struct deref_node *node, struct lower_variables_state *state), struct lower_variables_state *state) { if (*path == NULL) { cb(node, state); return; } switch ((*path)->deref_type) { case nir_deref_type_struct: if (node->children[(*path)->strct.index]) { foreach_deref_node_worker(node->children[(*path)->strct.index], path + 1, cb, state); } return; case nir_deref_type_array: { uint32_t index = nir_src_as_uint((*path)->arr.index); if (node->children[index]) { foreach_deref_node_worker(node->children[index], path + 1, cb, state); } if (node->wildcard) { foreach_deref_node_worker(node->wildcard, path + 1, cb, state); } return; } default: unreachable("Unsupported deref type"); } } /* Walks over every "matching" deref_node and calls the callback. A node * is considered to "match" if either refers to that deref or matches up t * a wildcard. In other words, the following would match a[6].foo[3].bar: * * a[6].foo[3].bar * a[*].foo[3].bar * a[6].foo[*].bar * a[*].foo[*].bar * * The given deref must be a full-length and fully qualified (no wildcards * or indirects) deref chain. */ static void foreach_deref_node_match(nir_deref_path *path, void (* cb)(struct deref_node *node, struct lower_variables_state *state), struct lower_variables_state *state) { assert(path->path[0]->deref_type == nir_deref_type_var); struct deref_node *node = get_deref_node_for_var(path->path[0]->var, state); if (node == NULL) return; foreach_deref_node_worker(node, &path->path[1], cb, state); } /* \sa deref_may_be_aliased */ static bool path_may_be_aliased_node(struct deref_node *node, nir_deref_instr **path, struct lower_variables_state *state) { if (*path == NULL) return false; switch ((*path)->deref_type) { case nir_deref_type_struct: if (node->children[(*path)->strct.index]) { return path_may_be_aliased_node(node->children[(*path)->strct.index], path + 1, state); } else { return false; } case nir_deref_type_array: { if (!nir_src_is_const((*path)->arr.index)) return true; uint32_t index = nir_src_as_uint((*path)->arr.index); /* If there is an indirect at this level, we're aliased. */ if (node->indirect) return true; if (node->children[index] && path_may_be_aliased_node(node->children[index], path + 1, state)) return true; if (node->wildcard && path_may_be_aliased_node(node->wildcard, path + 1, state)) return true; return false; } default: unreachable("Unsupported deref type"); } } /* Returns true if there are no indirects that can ever touch this deref. * * For example, if the given deref is a[6].foo, then any uses of a[i].foo * would cause this to return false, but a[i].bar would not affect it * because it's a different structure member. A var_copy involving of * a[*].bar also doesn't affect it because that can be lowered to entirely * direct load/stores. * * We only support asking this question about fully-qualified derefs. * Obviously, it's pointless to ask this about indirects, but we also * rule-out wildcards. Handling Wildcard dereferences would involve * checking each array index to make sure that there aren't any indirect * references. */ static bool path_may_be_aliased(nir_deref_path *path, struct lower_variables_state *state) { assert(path->path[0]->deref_type == nir_deref_type_var); nir_variable *var = path->path[0]->var; return path_may_be_aliased_node(get_deref_node_for_var(var, state), &path->path[1], state); } static void register_load_instr(nir_intrinsic_instr *load_instr, struct lower_variables_state *state) { nir_deref_instr *deref = nir_src_as_deref(load_instr->src[0]); struct deref_node *node = get_deref_node(deref, state); if (node == NULL) return; if (node->loads == NULL) node->loads = _mesa_pointer_set_create(state->dead_ctx); _mesa_set_add(node->loads, load_instr); } static void register_store_instr(nir_intrinsic_instr *store_instr, struct lower_variables_state *state) { nir_deref_instr *deref = nir_src_as_deref(store_instr->src[0]); struct deref_node *node = get_deref_node(deref, state); if (node == NULL) return; if (node->stores == NULL) node->stores = _mesa_pointer_set_create(state->dead_ctx); _mesa_set_add(node->stores, store_instr); } static void register_copy_instr(nir_intrinsic_instr *copy_instr, struct lower_variables_state *state) { for (unsigned idx = 0; idx < 2; idx++) { nir_deref_instr *deref = nir_src_as_deref(copy_instr->src[idx]); struct deref_node *node = get_deref_node(deref, state); if (node == NULL) continue; if (node->copies == NULL) node->copies = _mesa_pointer_set_create(state->dead_ctx); _mesa_set_add(node->copies, copy_instr); } } static void register_variable_uses(nir_function_impl *impl, struct lower_variables_state *state) { nir_foreach_block(block, impl) { 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_deref: register_load_instr(intrin, state); break; case nir_intrinsic_store_deref: register_store_instr(intrin, state); break; case nir_intrinsic_copy_deref: register_copy_instr(intrin, state); break; default: continue; } } } } /* Walks over all of the copy instructions to or from the given deref_node * and lowers them to load/store intrinsics. */ static void lower_copies_to_load_store(struct deref_node *node, struct lower_variables_state *state) { if (!node->copies) return; nir_builder b; nir_builder_init(&b, state->impl); set_foreach(node->copies, copy_entry) { nir_intrinsic_instr *copy = (void *)copy_entry->key; nir_lower_deref_copy_instr(&b, copy); for (unsigned i = 0; i < 2; ++i) { nir_deref_instr *arg_deref = nir_src_as_deref(copy->src[i]); struct deref_node *arg_node = get_deref_node(arg_deref, state); /* Only bother removing copy entries for other nodes */ if (arg_node == NULL || arg_node == node) continue; struct set_entry *arg_entry = _mesa_set_search(arg_node->copies, copy); assert(arg_entry); _mesa_set_remove(arg_node->copies, arg_entry); } nir_instr_remove(©->instr); } node->copies = NULL; } /* Performs variable renaming * * This algorithm is very similar to the one outlined in "Efficiently * Computing Static Single Assignment Form and the Control Dependence * Graph" by Cytron et al. The primary difference is that we only put one * SSA def on the stack per block. */ static bool rename_variables(struct lower_variables_state *state) { nir_builder b; nir_builder_init(&b, state->impl); nir_foreach_block(block, state->impl) { 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_deref: { nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]); if (deref->mode != nir_var_function_temp) continue; struct deref_node *node = get_deref_node(deref, state); if (node == NULL) { /* If we hit this path then we are referencing an invalid * value. Most likely, we unrolled something and are * reading past the end of some array. In any case, this * should result in an undefined value. */ nir_ssa_undef_instr *undef = nir_ssa_undef_instr_create(state->shader, intrin->num_components, intrin->dest.ssa.bit_size); nir_instr_insert_before(&intrin->instr, &undef->instr); nir_instr_remove(&intrin->instr); nir_ssa_def_rewrite_uses(&intrin->dest.ssa, nir_src_for_ssa(&undef->def)); continue; } if (!node->lower_to_ssa) continue; nir_alu_instr *mov = nir_alu_instr_create(state->shader, nir_op_imov); mov->src[0].src = nir_src_for_ssa( nir_phi_builder_value_get_block_def(node->pb_value, block)); for (unsigned i = intrin->num_components; i < 4; i++) mov->src[0].swizzle[i] = 0; assert(intrin->dest.is_ssa); mov->dest.write_mask = (1 << intrin->num_components) - 1; nir_ssa_dest_init(&mov->instr, &mov->dest.dest, intrin->num_components, intrin->dest.ssa.bit_size, NULL); nir_instr_insert_before(&intrin->instr, &mov->instr); nir_instr_remove(&intrin->instr); nir_ssa_def_rewrite_uses(&intrin->dest.ssa, nir_src_for_ssa(&mov->dest.dest.ssa)); break; } case nir_intrinsic_store_deref: { nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]); if (deref->mode != nir_var_function_temp) continue; struct deref_node *node = get_deref_node(deref, state); assert(intrin->src[1].is_ssa); nir_ssa_def *value = intrin->src[1].ssa; if (node == NULL) { /* Probably an out-of-bounds array store. That should be a * no-op. */ nir_instr_remove(&intrin->instr); continue; } if (!node->lower_to_ssa) continue; assert(intrin->num_components == glsl_get_vector_elements(node->type)); nir_ssa_def *new_def; b.cursor = nir_before_instr(&intrin->instr); unsigned wrmask = nir_intrinsic_write_mask(intrin); if (wrmask == (1 << intrin->num_components) - 1) { /* Whole variable store - just copy the source. Note that * intrin->num_components and value->num_components * may differ. */ unsigned swiz[4]; for (unsigned i = 0; i < 4; i++) swiz[i] = i < intrin->num_components ? i : 0; new_def = nir_swizzle(&b, value, swiz, intrin->num_components, false); } else { nir_ssa_def *old_def = nir_phi_builder_value_get_block_def(node->pb_value, block); /* For writemasked store_var intrinsics, we combine the newly * written values with the existing contents of unwritten * channels, creating a new SSA value for the whole vector. */ nir_ssa_def *srcs[4]; for (unsigned i = 0; i < intrin->num_components; i++) { if (wrmask & (1 << i)) { srcs[i] = nir_channel(&b, value, i); } else { srcs[i] = nir_channel(&b, old_def, i); } } new_def = nir_vec(&b, srcs, intrin->num_components); } assert(new_def->num_components == intrin->num_components); nir_phi_builder_value_set_block_def(node->pb_value, block, new_def); nir_instr_remove(&intrin->instr); break; } default: break; } } } return true; } /** Implements a pass to lower variable uses to SSA values * * This path walks the list of instructions and tries to lower as many * local variable load/store operations to SSA defs and uses as it can. * The process involves four passes: * * 1) Iterate over all of the instructions and mark where each local * variable deref is used in a load, store, or copy. While we're at * it, we keep track of all of the fully-qualified (no wildcards) and * fully-direct references we see and store them in the * direct_deref_nodes hash table. * * 2) Walk over the list of fully-qualified direct derefs generated in * the previous pass. For each deref, we determine if it can ever be * aliased, i.e. if there is an indirect reference anywhere that may * refer to it. If it cannot be aliased, we mark it for lowering to an * SSA value. At this point, we lower any var_copy instructions that * use the given deref to load/store operations. * * 3) Walk over the list of derefs we plan to lower to SSA values and * insert phi nodes as needed. * * 4) Perform "variable renaming" by replacing the load/store instructions * with SSA definitions and SSA uses. */ static bool nir_lower_vars_to_ssa_impl(nir_function_impl *impl) { struct lower_variables_state state; state.shader = impl->function->shader; state.dead_ctx = ralloc_context(state.shader); state.impl = impl; state.deref_var_nodes = _mesa_pointer_hash_table_create(state.dead_ctx); exec_list_make_empty(&state.direct_deref_nodes); /* Build the initial deref structures and direct_deref_nodes table */ state.add_to_direct_deref_nodes = true; register_variable_uses(impl, &state); bool progress = false; nir_metadata_require(impl, nir_metadata_block_index); /* We're about to iterate through direct_deref_nodes. Don't modify it. */ state.add_to_direct_deref_nodes = false; foreach_list_typed_safe(struct deref_node, node, direct_derefs_link, &state.direct_deref_nodes) { nir_deref_path *path = &node->path; assert(path->path[0]->deref_type == nir_deref_type_var); /* We don't build deref nodes for non-local variables */ assert(path->path[0]->var->data.mode == nir_var_function_temp); if (path_may_be_aliased(path, &state)) { exec_node_remove(&node->direct_derefs_link); continue; } node->lower_to_ssa = true; progress = true; foreach_deref_node_match(path, lower_copies_to_load_store, &state); } if (!progress) { #ifndef NDEBUG impl->valid_metadata &= ~nir_metadata_not_properly_reset; #endif return false; } nir_metadata_require(impl, nir_metadata_dominance); /* We may have lowered some copy instructions to load/store * instructions. The uses from the copy instructions hav already been * removed but we need to rescan to ensure that the uses from the newly * added load/store instructions are registered. We need this * information for phi node insertion below. */ register_variable_uses(impl, &state); state.phi_builder = nir_phi_builder_create(state.impl); NIR_VLA(BITSET_WORD, store_blocks, BITSET_WORDS(state.impl->num_blocks)); foreach_list_typed(struct deref_node, node, direct_derefs_link, &state.direct_deref_nodes) { if (!node->lower_to_ssa) continue; memset(store_blocks, 0, BITSET_WORDS(state.impl->num_blocks) * sizeof(*store_blocks)); assert(node->path.path[0]->var->constant_initializer == NULL); if (node->stores) { set_foreach(node->stores, store_entry) { nir_intrinsic_instr *store = (nir_intrinsic_instr *)store_entry->key; BITSET_SET(store_blocks, store->instr.block->index); } } node->pb_value = nir_phi_builder_add_value(state.phi_builder, glsl_get_vector_elements(node->type), glsl_get_bit_size(node->type), store_blocks); } rename_variables(&state); nir_phi_builder_finish(state.phi_builder); nir_metadata_preserve(impl, nir_metadata_block_index | nir_metadata_dominance); ralloc_free(state.dead_ctx); return progress; } bool nir_lower_vars_to_ssa(nir_shader *shader) { bool progress = false; nir_foreach_function(function, shader) { if (function->impl) progress |= nir_lower_vars_to_ssa_impl(function->impl); } return progress; }