/* * 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_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_vars may correspond to this node, but they * will all be equivalent, so any is as good as the other. */ nir_deref_var *deref; struct exec_node direct_derefs_link; struct set *loads; struct set *stores; struct set *copies; struct nir_phi_builder_value *pb_value; 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, nir_shader *shader) { size_t size = sizeof(struct deref_node) + glsl_get_length(type) * sizeof(struct deref_node *); struct deref_node *node = rzalloc_size(shader, size); node->type = type; node->parent = parent; node->deref = NULL; exec_node_init(&node->direct_derefs_link); 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, 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(nir_deref_var *deref, struct lower_variables_state *state) { bool is_direct = true; /* Start at the base of the chain. */ struct deref_node *node = get_deref_node_for_var(deref->var, state); assert(deref->deref.type == node->type); for (nir_deref *tail = deref->deref.child; tail; tail = tail->child) { switch (tail->deref_type) { case nir_deref_type_struct: { nir_deref_struct *deref_struct = nir_deref_as_struct(tail); assert(deref_struct->index < glsl_get_length(node->type)); if (node->children[deref_struct->index] == NULL) node->children[deref_struct->index] = deref_node_create(node, tail->type, state->dead_ctx); node = node->children[deref_struct->index]; break; } case nir_deref_type_array: { nir_deref_array *arr = nir_deref_as_array(tail); switch (arr->deref_array_type) { case nir_deref_array_type_direct: /* This is possible if a loop unrolls and generates an * out-of-bounds offset. We need to handle this at least * somewhat gracefully. */ if (arr->base_offset >= glsl_get_length(node->type)) return NULL; if (node->children[arr->base_offset] == NULL) node->children[arr->base_offset] = deref_node_create(node, tail->type, state->dead_ctx); node = node->children[arr->base_offset]; break; case nir_deref_array_type_indirect: if (node->indirect == NULL) node->indirect = deref_node_create(node, tail->type, state->dead_ctx); node = node->indirect; is_direct = false; break; case nir_deref_array_type_wildcard: if (node->wildcard == NULL) node->wildcard = deref_node_create(node, tail->type, state->dead_ctx); node = node->wildcard; is_direct = false; break; default: unreachable("Invalid array deref type"); } break; } default: unreachable("Invalid deref type"); } } assert(node); /* Only insert if it isn't already in the list. */ if (is_direct && state->add_to_direct_deref_nodes && node->direct_derefs_link.next == NULL) { node->deref = deref; assert(deref->var != NULL); exec_list_push_tail(&state->direct_deref_nodes, &node->direct_derefs_link); } return node; } /* \sa foreach_deref_node_match */ static bool foreach_deref_node_worker(struct deref_node *node, nir_deref *deref, bool (* cb)(struct deref_node *node, struct lower_variables_state *state), struct lower_variables_state *state) { if (deref->child == NULL) { return cb(node, state); } else { switch (deref->child->deref_type) { case nir_deref_type_array: { nir_deref_array *arr = nir_deref_as_array(deref->child); assert(arr->deref_array_type == nir_deref_array_type_direct); if (node->children[arr->base_offset] && !foreach_deref_node_worker(node->children[arr->base_offset], deref->child, cb, state)) return false; if (node->wildcard && !foreach_deref_node_worker(node->wildcard, deref->child, cb, state)) return false; return true; } case nir_deref_type_struct: { nir_deref_struct *str = nir_deref_as_struct(deref->child); return foreach_deref_node_worker(node->children[str->index], deref->child, cb, state); } default: unreachable("Invalid deref child 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 bool foreach_deref_node_match(nir_deref_var *deref, bool (* cb)(struct deref_node *node, struct lower_variables_state *state), struct lower_variables_state *state) { nir_deref_var var_deref = *deref; var_deref.deref.child = NULL; struct deref_node *node = get_deref_node(&var_deref, state); if (node == NULL) return false; return foreach_deref_node_worker(node, &deref->deref, cb, state); } /* \sa deref_may_be_aliased */ static bool deref_may_be_aliased_node(struct deref_node *node, nir_deref *deref, struct lower_variables_state *state) { if (deref->child == NULL) { return false; } else { switch (deref->child->deref_type) { case nir_deref_type_array: { nir_deref_array *arr = nir_deref_as_array(deref->child); if (arr->deref_array_type == nir_deref_array_type_indirect) return true; /* If there is an indirect at this level, we're aliased. */ if (node->indirect) return true; assert(arr->deref_array_type == nir_deref_array_type_direct); if (node->children[arr->base_offset] && deref_may_be_aliased_node(node->children[arr->base_offset], deref->child, state)) return true; if (node->wildcard && deref_may_be_aliased_node(node->wildcard, deref->child, state)) return true; return false; } case nir_deref_type_struct: { nir_deref_struct *str = nir_deref_as_struct(deref->child); if (node->children[str->index]) { return deref_may_be_aliased_node(node->children[str->index], deref->child, state); } else { return false; } } default: unreachable("Invalid nir_deref child 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 deref_may_be_aliased(nir_deref_var *deref, struct lower_variables_state *state) { return deref_may_be_aliased_node(get_deref_node_for_var(deref->var, state), &deref->deref, state); } static void register_load_instr(nir_intrinsic_instr *load_instr, struct lower_variables_state *state) { struct deref_node *node = get_deref_node(load_instr->variables[0], state); if (node == NULL) return; if (node->loads == NULL) node->loads = _mesa_set_create(state->dead_ctx, _mesa_hash_pointer, _mesa_key_pointer_equal); _mesa_set_add(node->loads, load_instr); } static void register_store_instr(nir_intrinsic_instr *store_instr, struct lower_variables_state *state) { struct deref_node *node = get_deref_node(store_instr->variables[0], state); if (node == NULL) return; if (node->stores == NULL) node->stores = _mesa_set_create(state->dead_ctx, _mesa_hash_pointer, _mesa_key_pointer_equal); _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++) { struct deref_node *node = get_deref_node(copy_instr->variables[idx], state); if (node == NULL) continue; if (node->copies == NULL) node->copies = _mesa_set_create(state->dead_ctx, _mesa_hash_pointer, _mesa_key_pointer_equal); _mesa_set_add(node->copies, copy_instr); } } /* Registers all variable uses in the given block. */ static bool register_variable_uses_block(nir_block *block, struct lower_variables_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_load_var: register_load_instr(intrin, state); break; case nir_intrinsic_store_var: register_store_instr(intrin, state); break; case nir_intrinsic_copy_var: register_copy_instr(intrin, state); break; default: continue; } } return true; } /* Walks over all of the copy instructions to or from the given deref_node * and lowers them to load/store intrinsics. */ static bool lower_copies_to_load_store(struct deref_node *node, struct lower_variables_state *state) { if (!node->copies) return true; struct set_entry *copy_entry; set_foreach(node->copies, copy_entry) { nir_intrinsic_instr *copy = (void *)copy_entry->key; nir_lower_var_copy_instr(copy, state->shader); for (unsigned i = 0; i < 2; ++i) { struct deref_node *arg_node = get_deref_node(copy->variables[i], 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(node->copies, arg_entry); } nir_instr_remove(©->instr); } node->copies = NULL; return true; } /* 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_var: { struct deref_node *node = get_deref_node(intrin->variables[0], 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_var: { struct deref_node *node = get_deref_node(intrin->variables[0], state); 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)); assert(intrin->src[0].is_ssa); 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 intrin->src[0].ssa->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, intrin->src[0].ssa, 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, intrin->src[0].ssa, 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_hash_table_create(state.dead_ctx, _mesa_hash_pointer, _mesa_key_pointer_equal); 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; nir_foreach_block(block, impl) { register_variable_uses_block(block, &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_var *deref = node->deref; if (deref->var->data.mode != nir_var_local) { exec_node_remove(&node->direct_derefs_link); continue; } if (deref_may_be_aliased(deref, &state)) { exec_node_remove(&node->direct_derefs_link); continue; } node->lower_to_ssa = true; progress = true; foreach_deref_node_match(deref, lower_copies_to_load_store, &state); } if (!progress) 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. */ nir_foreach_block(block, impl) { register_variable_uses_block(block, &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->deref->var->constant_initializer == NULL); if (node->stores) { struct set_entry *store_entry; 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; }