nir: move to compiler/

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Acked-by: Matt Turner <mattst88@gmail.com>
Acked-by: Jose Fonseca <jfonseca@vmware.com>

1 files changed, 973 insertions, 0 deletions

diff --git a/src/compiler/nir/nir_lower_vars_to_ssa.c b/src/compiler/nir/nir_lower_vars_to_ssa.c
new file mode 100644
index 0000000..75d31ff
--- /dev/null
+++ b/src/compiler/nir/nir_lower_vars_to_ssa.c
@@ -0,0 +1,973 @@
+/*
+ * 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_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;
+
+   nir_ssa_def **def_stack;
+   nir_ssa_def **def_stack_tail;
+
+   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;
+
+   /* A hash table mapping phi nodes to deref_state data */
+   struct hash_table *phi_table;
+};
+
+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, void *void_state)
+{
+   struct lower_variables_state *state = void_state;
+
+   nir_foreach_instr_safe(block, instr) {
+      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(&copy->instr);
+   }
+
+   node->copies = NULL;
+
+   return true;
+}
+
+/** Pushes an SSA def onto the def stack for the given node
+ *
+ * Each node is potentially associated with a stack of SSA definitions.
+ * This stack is used for determining what SSA definition reaches a given
+ * point in the program for variable renaming.  The stack is always kept in
+ * dominance-order with at most one SSA def per block.  If the SSA
+ * definition on the top of the stack is in the same block as the one being
+ * pushed, the top element is replaced.
+ */
+static void
+def_stack_push(struct deref_node *node, nir_ssa_def *def,
+               struct lower_variables_state *state)
+{
+   if (node->def_stack == NULL) {
+      node->def_stack = ralloc_array(state->dead_ctx, nir_ssa_def *,
+                                     state->impl->num_blocks);
+      node->def_stack_tail = node->def_stack - 1;
+   }
+
+   if (node->def_stack_tail >= node->def_stack) {
+      nir_ssa_def *top_def = *node->def_stack_tail;
+
+      if (def->parent_instr->block == top_def->parent_instr->block) {
+         /* They're in the same block, just replace the top */
+         *node->def_stack_tail = def;
+         return;
+      }
+   }
+
+   *(++node->def_stack_tail) = def;
+}
+
+/* Pop the top of the def stack if it's in the given block */
+static void
+def_stack_pop_if_in_block(struct deref_node *node, nir_block *block)
+{
+   /* If we're popping, then we have presumably pushed at some time in the
+    * past so this should exist.
+    */
+   assert(node->def_stack != NULL);
+
+   /* The stack is already empty.  Do nothing. */
+   if (node->def_stack_tail < node->def_stack)
+      return;
+
+   nir_ssa_def *def = *node->def_stack_tail;
+   if (def->parent_instr->block == block)
+      node->def_stack_tail--;
+}
+
+/** Retrieves the SSA definition on the top of the stack for the given
+ * node, if one exists.  If the stack is empty, then we return the constant
+ * initializer (if it exists) or an SSA undef.
+ */
+static nir_ssa_def *
+get_ssa_def_for_block(struct deref_node *node, nir_block *block,
+                      struct lower_variables_state *state)
+{
+   /* If we have something on the stack, go ahead and return it.  We're
+    * assuming that the top of the stack dominates the given block.
+    */
+   if (node->def_stack && node->def_stack_tail >= node->def_stack)
+      return *node->def_stack_tail;
+
+   /* If we got here then we don't have a definition that dominates the
+    * given block.  This means that we need to add an undef and use that.
+    */
+   nir_ssa_undef_instr *undef =
+      nir_ssa_undef_instr_create(state->shader,
+                                 glsl_get_vector_elements(node->type));
+   nir_instr_insert_before_cf_list(&state->impl->body, &undef->instr);
+   def_stack_push(node, &undef->def, state);
+   return &undef->def;
+}
+
+/* Given a block and one of its predecessors, this function fills in the
+ * souces of the phi nodes to take SSA defs from the given predecessor.
+ * This function must be called exactly once per block/predecessor pair.
+ */
+static void
+add_phi_sources(nir_block *block, nir_block *pred,
+                struct lower_variables_state *state)
+{
+   nir_foreach_instr(block, instr) {
+      if (instr->type != nir_instr_type_phi)
+         break;
+
+      nir_phi_instr *phi = nir_instr_as_phi(instr);
+
+      struct hash_entry *entry =
+            _mesa_hash_table_search(state->phi_table, phi);
+      if (!entry)
+         continue;
+
+      struct deref_node *node = entry->data;
+
+      nir_phi_src *src = ralloc(phi, nir_phi_src);
+      src->pred = pred;
+      src->src.parent_instr = &phi->instr;
+      src->src.is_ssa = true;
+      src->src.ssa = get_ssa_def_for_block(node, pred, state);
+
+      list_addtail(&src->src.use_link, &src->src.ssa->uses);
+
+      exec_list_push_tail(&phi->srcs, &src->node);
+   }
+}
+
+/* Performs variable renaming by doing a DFS of the dominance tree
+ *
+ * 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_block(nir_block *block, struct lower_variables_state *state)
+{
+   nir_builder b;
+   nir_builder_init(&b, state->impl);
+
+   nir_foreach_instr_safe(block, instr) {
+      if (instr->type == nir_instr_type_phi) {
+         nir_phi_instr *phi = nir_instr_as_phi(instr);
+
+         struct hash_entry *entry =
+            _mesa_hash_table_search(state->phi_table, phi);
+
+         /* This can happen if we already have phi nodes in the program
+          * that were not created in this pass.
+          */
+         if (!entry)
+            continue;
+
+         struct deref_node *node = entry->data;
+
+         def_stack_push(node, &phi->dest.ssa, state);
+      } else if (instr->type == nir_instr_type_intrinsic) {
+         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);
+
+               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.is_ssa = true;
+            mov->src[0].src.ssa = get_ssa_def_for_block(node, block, state);
+            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, 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);
+
+            if (intrin->const_index[0] == (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 = get_ssa_def_for_block(node, block, state);
+               /* 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 (intrin->const_index[0] & (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);
+
+            def_stack_push(node, new_def, state);
+
+            /* We'll wait to remove the instruction until the next pass
+             * where we pop the node we just pushed back off the stack.
+             */
+            break;
+         }
+
+         default:
+            break;
+         }
+      }
+   }
+
+   if (block->successors[0])
+      add_phi_sources(block->successors[0], block, state);
+   if (block->successors[1])
+      add_phi_sources(block->successors[1], block, state);
+
+   for (unsigned i = 0; i < block->num_dom_children; ++i)
+      rename_variables_block(block->dom_children[i], state);
+
+   /* Now we iterate over the instructions and pop off any SSA defs that we
+    * pushed in the first loop.
+    */
+   nir_foreach_instr_safe(block, instr) {
+      if (instr->type == nir_instr_type_phi) {
+         nir_phi_instr *phi = nir_instr_as_phi(instr);
+
+         struct hash_entry *entry =
+            _mesa_hash_table_search(state->phi_table, phi);
+
+         /* This can happen if we already have phi nodes in the program
+          * that were not created in this pass.
+          */
+         if (!entry)
+            continue;
+
+         struct deref_node *node = entry->data;
+
+         def_stack_pop_if_in_block(node, block);
+      } else if (instr->type == nir_instr_type_intrinsic) {
+         nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+
+         if (intrin->intrinsic != nir_intrinsic_store_var)
+            continue;
+
+         struct deref_node *node = get_deref_node(intrin->variables[0], state);
+         if (!node)
+            continue;
+
+         if (!node->lower_to_ssa)
+            continue;
+
+         def_stack_pop_if_in_block(node, block);
+         nir_instr_remove(&intrin->instr);
+      }
+   }
+
+   return true;
+}
+
+/* Inserts phi nodes for all variables marked lower_to_ssa
+ *
+ * This is the same algorithm as presented in "Efficiently Computing Static
+ * Single Assignment Form and the Control Dependence Graph" by Cytron et.
+ * al.
+ */
+static void
+insert_phi_nodes(struct lower_variables_state *state)
+{
+   NIR_VLA_ZERO(unsigned, work, state->impl->num_blocks);
+   NIR_VLA_ZERO(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_VLA(nir_block *, W, state->impl->num_blocks);
+
+   unsigned w_start, w_end;
+   unsigned iter_count = 0;
+
+   foreach_list_typed(struct deref_node, node, direct_derefs_link,
+                      &state->direct_deref_nodes) {
+      if (node->stores == NULL)
+         continue;
+
+      if (!node->lower_to_ssa)
+         continue;
+
+      w_start = w_end = 0;
+      iter_count++;
+
+      struct set_entry *store_entry;
+      set_foreach(node->stores, store_entry) {
+         nir_intrinsic_instr *store = (nir_intrinsic_instr *)store_entry->key;
+         if (work[store->instr.block->index] < iter_count)
+            W[w_end++] = store->instr.block;
+         work[store->instr.block->index] = iter_count;
+      }
+
+      while (w_start != w_end) {
+         nir_block *cur = W[w_start++];
+         struct set_entry *dom_entry;
+         set_foreach(cur->dom_frontier, dom_entry) {
+            nir_block *next = (nir_block *) dom_entry->key;
+
+            /*
+             * If there's more than one return statement, then the end block
+             * can be a join point for some definitions. However, there are
+             * no instructions in the end block, so nothing would use those
+             * phi nodes. Of course, we couldn't place those phi nodes
+             * anyways due to the restriction of having no instructions in the
+             * end block...
+             */
+            if (next == state->impl->end_block)
+               continue;
+
+            if (has_already[next->index] < iter_count) {
+               nir_phi_instr *phi = nir_phi_instr_create(state->shader);
+               nir_ssa_dest_init(&phi->instr, &phi->dest,
+                                 glsl_get_vector_elements(node->type), NULL);
+               nir_instr_insert_before_block(next, &phi->instr);
+
+               _mesa_hash_table_insert(state->phi_table, phi, node);
+
+               has_already[next->index] = iter_count;
+               if (work[next->index] < iter_count) {
+                  work[next->index] = iter_count;
+                  W[w_end++] = next;
+               }
+            }
+         }
+      }
+   }
+}
+
+
+/** 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_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);
+   state.phi_table = _mesa_hash_table_create(state.dead_ctx,
+                                             _mesa_hash_pointer,
+                                             _mesa_key_pointer_equal);
+
+   /* Build the initial deref structures and direct_deref_nodes table */
+   state.add_to_direct_deref_nodes = true;
+   nir_foreach_block(impl, register_variable_uses_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;
+
+      if (deref->var->constant_initializer) {
+         nir_load_const_instr *load =
+            nir_deref_get_const_initializer_load(state.shader, deref);
+         nir_ssa_def_init(&load->instr, &load->def,
+                          glsl_get_vector_elements(node->type), NULL);
+         nir_instr_insert_before_cf_list(&impl->body, &load->instr);
+         def_stack_push(node, &load->def, &state);
+      }
+
+      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(impl, register_variable_uses_block, &state);
+
+   insert_phi_nodes(&state);
+   rename_variables_block(nir_start_block(impl), &state);
+
+   nir_metadata_preserve(impl, nir_metadata_block_index |
+                               nir_metadata_dominance);
+
+   ralloc_free(state.dead_ctx);
+
+   return progress;
+}
+
+void
+nir_lower_vars_to_ssa(nir_shader *shader)
+{
+   nir_foreach_function(shader, function) {
+      if (function->impl)
+         nir_lower_vars_to_ssa_impl(function->impl);
+   }
+}