diff options
| -rw-r--r-- | src/glsl/nir/nir_lower_variables.c | 106 |
1 files changed, 79 insertions, 27 deletions
diff --git a/src/glsl/nir/nir_lower_variables.c b/src/glsl/nir/nir_lower_variables.c index 76d3979daa0..4844b7c6ed0 100644 --- a/src/glsl/nir/nir_lower_variables.c +++ b/src/glsl/nir/nir_lower_variables.c @@ -53,12 +53,21 @@ struct lower_variables_state { /* A hash table mapping variables to deref_node data */ struct hash_table *deref_var_nodes; - /* A hash table mapping dereference leaves to deref_node data. A deref - * is considered a leaf if it is fully-qualified (no wildcards) and - * direct. In short, these are the derefs we can actually consider - * lowering to SSA values. + /* 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 hash_table *deref_leaves; + struct hash_table *direct_deref_nodes; /* A hash table mapping phi nodes to deref_state data */ struct hash_table *phi_table; @@ -181,14 +190,15 @@ deref_node_create(struct deref_node *parent, } /* Gets the deref_node for the given deref chain and creates it if it - * doesn't yet exist. If the deref is a leaf (fully-qualified and direct) - * and add_to_leaves is true, it will be added to the hash table of leaves. + * doesn't yet exist. If the deref is fully-qualified and direct and + * 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, bool add_to_leaves, +get_deref_node(nir_deref_var *deref, bool add_to_direct_deref_nodes, struct lower_variables_state *state) { - bool is_leaf = true; + bool is_direct = true; struct deref_node *node; @@ -242,7 +252,7 @@ get_deref_node(nir_deref_var *deref, bool add_to_leaves, state->dead_ctx); node = node->indirect; - is_leaf = false; + is_direct = false; break; case nir_deref_array_type_wildcard: @@ -251,7 +261,7 @@ get_deref_node(nir_deref_var *deref, bool add_to_leaves, state->dead_ctx); node = node->wildcard; - is_leaf = false; + is_direct = false; break; default: @@ -266,8 +276,8 @@ get_deref_node(nir_deref_var *deref, bool add_to_leaves, assert(node); - if (is_leaf && add_to_leaves) - _mesa_hash_table_insert(state->deref_leaves, deref, node); + if (is_direct && add_to_direct_deref_nodes) + _mesa_hash_table_insert(state->direct_deref_nodes, deref, node); return node; } @@ -321,7 +331,7 @@ foreach_deref_node_worker(struct deref_node *node, nir_deref *deref, * a[*].foo[*].bar * * The given deref must be a full-length and fully qualified (no wildcards - * or indirexcts) deref chain. + * or indirects) deref chain. */ static bool foreach_deref_node_match(nir_deref_var *deref, @@ -384,13 +394,18 @@ deref_may_be_aliased_node(struct deref_node *node, nir_deref *deref, } /* Returns true if there are no indirects that can ever touch this deref. - * This question can only be asked about fully-qualified derefs. + * + * 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. For example, if the given deref is a[6].foo, then - * any uses of a[i].foo would case 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. + * 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, @@ -940,7 +955,7 @@ rename_variables_block(nir_block *block, struct lower_variables_state *state) def_stack_push(node, &mov->dest.dest.ssa, state); - /* We'll wait to remove the unstruction until the next pass + /* We'll wait to remove the instruction until the next pass * where we pop the node we just pushed back off the stack. */ break; @@ -1012,6 +1027,15 @@ insert_phi_nodes(struct lower_variables_state *state) { unsigned work[state->impl->num_blocks]; unsigned has_already[state->impl->num_blocks]; + + /* + * Since the work flags already prevent us from inserting a node that has + * ever been inserted into W, we don't need to use a set to represent W. + * Also, since no block can ever be inserted into W more than once, we know + * that the maximum size of W is the number of basic blocks in the + * function. So all we need to handle W is an array and a pointer to the + * next element to be inserted and the next element to be removed. + */ nir_block *W[state->impl->num_blocks]; memset(work, 0, sizeof work); @@ -1021,7 +1045,7 @@ insert_phi_nodes(struct lower_variables_state *state) unsigned iter_count = 0; struct hash_entry *deref_entry; - hash_table_foreach(state->deref_leaves, deref_entry) { + hash_table_foreach(state->direct_deref_nodes, deref_entry) { struct deref_node *node = deref_entry->data; if (node->stores == NULL) @@ -1078,6 +1102,34 @@ insert_phi_nodes(struct lower_variables_state *state) } } + +/** 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 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 and, if the deref has a + * constant initializer, we go ahead and add a load_const value at the + * beginning of the function with the initialized value. + * + * 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_variables_impl(nir_function_impl *impl) { @@ -1090,8 +1142,8 @@ nir_lower_variables_impl(nir_function_impl *impl) state.deref_var_nodes = _mesa_hash_table_create(state.dead_ctx, _mesa_hash_pointer, _mesa_key_pointer_equal); - state.deref_leaves = _mesa_hash_table_create(state.dead_ctx, - hash_deref, derefs_equal); + state.direct_deref_nodes = _mesa_hash_table_create(state.dead_ctx, + hash_deref, derefs_equal); state.phi_table = _mesa_hash_table_create(state.dead_ctx, _mesa_hash_pointer, _mesa_key_pointer_equal); @@ -1106,17 +1158,17 @@ nir_lower_variables_impl(nir_function_impl *impl) nir_metadata_require(impl, nir_metadata_block_index); struct hash_entry *entry; - hash_table_foreach(state.deref_leaves, entry) { + hash_table_foreach(state.direct_deref_nodes, entry) { nir_deref_var *deref = (void *)entry->key; struct deref_node *node = entry->data; if (deref->var->data.mode != nir_var_local) { - _mesa_hash_table_remove(state.deref_leaves, entry); + _mesa_hash_table_remove(state.direct_deref_nodes, entry); continue; } if (deref_may_be_aliased(deref, &state)) { - _mesa_hash_table_remove(state.deref_leaves, entry); + _mesa_hash_table_remove(state.direct_deref_nodes, entry); continue; } |