nir: Add a local variable-based copy propagation pass

Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>

src/compiler/Makefile.sources

@@ -236,6 +236,7 @@ NIR_FILES = \
 	nir/nir_normalize_cubemap_coords.c \
 	nir/nir_opt_conditional_discard.c \
 	nir/nir_opt_constant_folding.c \
+	nir/nir_opt_copy_prop_vars.c \
 	nir/nir_opt_copy_propagate.c \
 	nir/nir_opt_cse.c \
 	nir/nir_opt_dce.c \

src/compiler/nir/nir.h

@@ -2549,6 +2549,8 @@ bool nir_opt_global_to_local(nir_shader *shader);
 
 bool nir_copy_prop(nir_shader *shader);
 
+bool nir_opt_copy_prop_vars(nir_shader *shader);
+
 bool nir_opt_cse(nir_shader *shader);
 
 bool nir_opt_dce(nir_shader *shader);

src/compiler/nir/nir_opt_copy_prop_vars.c

@@ -0,0 +1,813 @@
+/*
+ * Copyright © 2016 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.
+ */
+
+#include "nir.h"
+#include "nir_builder.h"
+
+#include "util/bitscan.h"
+
+/**
+ * Variable-based copy propagation
+ *
+ * Normally, NIR trusts in SSA form for most of its copy-propagation needs.
+ * However, there are cases, especially when dealing with indirects, where SSA
+ * won't help you.  This pass is for those times.  Specifically, it handles
+ * the following things that the rest of NIR can't:
+ *
+ *  1) Copy-propagation on variables that have indirect access.  This includes
+ *     propagating from indirect stores into indirect loads.
+ *
+ *  2) Dead code elimination of store_var and copy_var intrinsics based on
+ *     killed destination values.
+ *
+ *  3) Removal of redundant load_var intrinsics.  We can't trust regular CSE
+ *     to do this because it isn't aware of variable writes that may alias the
+ *     value and make the former load invalid.
+ *
+ * Unfortunately, properly handling all of those cases makes this path rather
+ * complex.  In order to avoid additional complexity, this pass is entirely
+ * block-local.  If we tried to make it global, the data-flow analysis would
+ * rapidly get out of hand.  Fortunately, for anything that is only ever
+ * accessed directly, we get SSA based copy-propagation which is extremely
+ * powerful so this isn't that great a loss.
+ */
+
+struct value {
+   bool is_ssa;
+   union {
+      nir_ssa_def *ssa[4];
+      nir_deref_var *deref;
+   };
+};
+
+struct copy_entry {
+   struct list_head link;
+
+   nir_instr *store_instr[4];
+
+   unsigned comps_may_be_read;
+   struct value src;
+
+   nir_deref_var *dst;
+};
+
+struct copy_prop_var_state {
+   nir_shader *shader;
+
+   void *mem_ctx;
+
+   struct list_head copies;
+
+   /* We're going to be allocating and deleting a lot of copy entries so we'll
+    * keep a free list to avoid thrashing malloc too badly.
+    */
+   struct list_head copy_free_list;
+
+   bool progress;
+};
+
+static struct copy_entry *
+copy_entry_create(struct copy_prop_var_state *state,
+                  nir_deref_var *dst_deref)
+{
+   struct copy_entry *entry;
+   if (!list_empty(&state->copy_free_list)) {
+      struct list_head *item = state->copy_free_list.next;
+      list_del(item);
+      entry = LIST_ENTRY(struct copy_entry, item, link);
+      memset(entry, 0, sizeof(*entry));
+   } else {
+      entry = rzalloc(state->mem_ctx, struct copy_entry);
+   }
+
+   entry->dst = dst_deref;
+   list_add(&entry->link, &state->copies);
+
+   return entry;
+}
+
+static void
+copy_entry_remove(struct copy_prop_var_state *state, struct copy_entry *entry)
+{
+   list_del(&entry->link);
+   list_add(&entry->link, &state->copy_free_list);
+}
+
+enum deref_compare_result {
+   derefs_equal_bit = (1 << 0),
+   derefs_may_alias_bit = (1 << 1),
+   derefs_a_contains_b_bit = (1 << 2),
+   derefs_b_contains_a_bit = (1 << 3),
+};
+
+/** Returns true if the storage referrenced to by deref completely contains
+ * the storage referenced by sub.
+ *
+ * NOTE: This is fairly general and could be moved to core NIR if someone else
+ * ever needs it.
+ */
+static enum deref_compare_result
+compare_derefs(nir_deref_var *a, nir_deref_var *b)
+{
+   if (a->var != b->var)
+      return 0;
+
+   /* Start off assuming they fully compare.  We ignore equality for now.  In
+    * the end, we'll determine that by containment.
+    */
+   enum deref_compare_result result = derefs_may_alias_bit |
+                                      derefs_a_contains_b_bit |
+                                      derefs_b_contains_a_bit;
+
+   nir_deref *a_tail = &a->deref;
+   nir_deref *b_tail = &b->deref;
+   while (a_tail->child && b_tail->child) {
+      a_tail = a_tail->child;
+      b_tail = b_tail->child;
+
+      assert(a_tail->deref_type == b_tail->deref_type);
+      switch (a_tail->deref_type) {
+      case nir_deref_type_array: {
+         nir_deref_array *a_arr = nir_deref_as_array(a_tail);
+         nir_deref_array *b_arr = nir_deref_as_array(b_tail);
+
+         if (a_arr->deref_array_type == nir_deref_array_type_direct &&
+             b_arr->deref_array_type == nir_deref_array_type_direct) {
+            /* If they're both direct and have different offsets, they
+             * don't even alias much less anything else.
+             */
+            if (a_arr->base_offset != b_arr->base_offset)
+               return 0;
+         } else if (a_arr->deref_array_type == nir_deref_array_type_wildcard) {
+            if (b_arr->deref_array_type != nir_deref_array_type_wildcard)
+               result &= ~derefs_b_contains_a_bit;
+         } else if (b_arr->deref_array_type == nir_deref_array_type_wildcard) {
+            if (a_arr->deref_array_type != nir_deref_array_type_wildcard)
+               result &= ~derefs_a_contains_b_bit;
+         } else if (a_arr->deref_array_type == nir_deref_array_type_indirect &&
+                    b_arr->deref_array_type == nir_deref_array_type_indirect) {
+            assert(a_arr->indirect.is_ssa && b_arr->indirect.is_ssa);
+            if (a_arr->indirect.ssa == b_arr->indirect.ssa) {
+               /* If they're different constant offsets from the same indirect
+                * then they don't alias at all.
+                */
+               if (a_arr->base_offset != b_arr->base_offset)
+                  return 0;
+               /* Otherwise the indirect and base both match */
+            } else {
+               /* If they're have different indirect offsets then we can't
+                * prove anything about containment.
+                */
+               result &= ~(derefs_a_contains_b_bit | derefs_b_contains_a_bit);
+            }
+         } else {
+            /* In this case, one is indirect and the other direct so we can't
+             * prove anything about containment.
+             */
+            result &= ~(derefs_a_contains_b_bit | derefs_b_contains_a_bit);
+         }
+         break;
+      }
+
+      case nir_deref_type_struct: {
+         nir_deref_struct *a_struct = nir_deref_as_struct(a_tail);
+         nir_deref_struct *b_struct = nir_deref_as_struct(b_tail);
+
+         /* If they're different struct members, they don't even alias */
+         if (a_struct->index != b_struct->index)
+            return 0;
+         break;
+      }
+
+      default:
+         unreachable("Invalid deref type");
+      }
+   }
+
+   /* If a is longer than b, then it can't contain b */
+   if (a_tail->child)
+      result &= ~derefs_a_contains_b_bit;
+   if (b_tail->child)
+      result &= ~derefs_b_contains_a_bit;
+
+   /* If a contains b and b contains a they must be equal. */
+   if ((result & derefs_a_contains_b_bit) && (result & derefs_b_contains_a_bit))
+      result |= derefs_equal_bit;
+
+   return result;
+}
+
+static void
+remove_dead_writes(struct copy_prop_var_state *state,
+                   struct copy_entry *entry, unsigned write_mask)
+{
+   /* We're overwriting another entry.  Some of it's components may not
+    * have been read yet and, if that's the case, we may be able to delete
+    * some instructions but we have to be careful.
+    */
+   unsigned dead_comps = write_mask & ~entry->comps_may_be_read;
+
+   for (unsigned mask = dead_comps; mask;) {
+      unsigned i = u_bit_scan(&mask);
+
+      nir_instr *instr = entry->store_instr[i];
+
+      /* We may have already deleted it on a previous iteration */
+      if (!instr)
+         continue;
+
+      /* See if this instr is used anywhere that it's not dead */
+      bool keep = false;
+      for (unsigned j = 0; j < 4; j++) {
+         if (entry->store_instr[j] == instr) {
+            if (dead_comps & (1 << j)) {
+               entry->store_instr[j] = NULL;
+            } else {
+               keep = true;
+            }
+         }
+      }
+
+      if (!keep) {
+         nir_instr_remove(instr);
+         state->progress = true;
+      }
+   }
+}
+
+static struct copy_entry *
+lookup_entry_for_deref(struct copy_prop_var_state *state,
+                       nir_deref_var *deref,
+                       enum deref_compare_result allowed_comparisons)
+{
+   list_for_each_entry(struct copy_entry, iter, &state->copies, link) {
+      if (compare_derefs(iter->dst, deref) & allowed_comparisons)
+         return iter;
+   }
+
+   return NULL;
+}
+
+static void
+mark_aliased_entries_as_read(struct copy_prop_var_state *state,
+                             nir_deref_var *deref, unsigned components)
+{
+   list_for_each_entry(struct copy_entry, iter, &state->copies, link) {
+      if (compare_derefs(iter->dst, deref) & derefs_may_alias_bit)
+         iter->comps_may_be_read |= components;
+   }
+}
+
+static struct copy_entry *
+get_entry_and_kill_aliases(struct copy_prop_var_state *state,
+                           nir_deref_var *deref,
+                           unsigned write_mask)
+{
+   struct copy_entry *entry = NULL;
+   list_for_each_entry_safe(struct copy_entry, iter, &state->copies, link) {
+      if (!iter->src.is_ssa) {
+         /* If this write aliases the source of some entry, get rid of it */
+         if (compare_derefs(iter->src.deref, deref) & derefs_may_alias_bit) {
+            copy_entry_remove(state, iter);
+            continue;
+         }
+      }
+
+      enum deref_compare_result comp = compare_derefs(iter->dst, deref);
+      /* This is a store operation.  If we completely overwrite some value, we
+       * want to delete any dead writes that may be present.
+       */
+      if (comp & derefs_b_contains_a_bit)
+         remove_dead_writes(state, iter, write_mask);
+
+      if (comp & derefs_equal_bit) {
+         assert(entry == NULL);
+         entry = iter;
+      } else if (comp & derefs_may_alias_bit) {
+         copy_entry_remove(state, iter);
+      }
+   }
+
+   if (entry == NULL)
+      entry = copy_entry_create(state, deref);
+
+   return entry;
+}
+
+static void
+apply_barrier_for_modes(struct copy_prop_var_state *state,
+                        nir_variable_mode modes)
+{
+   list_for_each_entry_safe(struct copy_entry, iter, &state->copies, link) {
+      if ((iter->dst->var->data.mode & modes) ||
+          (!iter->src.is_ssa && (iter->src.deref->var->data.mode & modes)))
+         copy_entry_remove(state, iter);
+   }
+}
+
+static void
+store_to_entry(struct copy_prop_var_state *state, struct copy_entry *entry,
+               const struct value *value, unsigned write_mask,
+               nir_instr *store_instr)
+{
+   entry->comps_may_be_read &= ~write_mask;
+   if (value->is_ssa) {
+      entry->src.is_ssa = true;
+      /* Only overwrite the written components */
+      for (unsigned i = 0; i < 4; i++) {
+         if (write_mask & (1 << i)) {
+            entry->store_instr[i] = store_instr;
+            entry->src.ssa[i] = value->ssa[i];
+         }
+      }
+   } else {
+      /* Non-ssa stores always write everything */
+      entry->src.is_ssa = false;
+      entry->src.deref = value->deref;
+      for (unsigned i = 0; i < 4; i++)
+         entry->store_instr[i] = store_instr;
+   }
+}
+
+/* Remove an instruction and return a cursor pointing to where it was */
+static nir_cursor
+instr_remove_cursor(nir_instr *instr)
+{
+   nir_cursor cursor;
+   nir_instr *prev = nir_instr_prev(instr);
+   if (prev) {
+      cursor = nir_after_instr(prev);
+   } else {
+      cursor = nir_before_block(instr->block);
+   }
+   nir_instr_remove(instr);
+   return cursor;
+}
+
+/* Do a "load" from an SSA-based entry return it in "value" as a value with a
+ * single SSA def.  Because an entry could reference up to 4 different SSA
+ * defs, a vecN operation may be inserted to combine them into a single SSA
+ * def before handing it back to the caller.  If the load instruction is no
+ * longer needed, it is removed and nir_instr::block is set to NULL.  (It is
+ * possible, in some cases, for the load to be used in the vecN operation in
+ * which case it isn't deleted.)
+ */
+static bool
+load_from_ssa_entry_value(struct copy_prop_var_state *state,
+                          struct copy_entry *entry,
+                          nir_builder *b, nir_intrinsic_instr *intrin,
+                          struct value *value)
+{
+   *value = entry->src;
+   assert(value->is_ssa);
+
+   const struct glsl_type *type = nir_deref_tail(&entry->dst->deref)->type;
+   unsigned num_components = glsl_get_vector_elements(type);
+
+   uint8_t available = 0;
+   bool all_same = true;
+   for (unsigned i = 0; i < num_components; i++) {
+      if (value->ssa[i])
+         available |= (1 << i);
+
+      if (value->ssa[i] != value->ssa[0])
+         all_same = false;
+   }
+
+   if (all_same) {
+      /* Our work here is done */
+      b->cursor = instr_remove_cursor(&intrin->instr);
+      intrin->instr.block = NULL;
+      return true;
+   }
+
+   if (available != (1 << num_components) - 1 &&
+       intrin->intrinsic == nir_intrinsic_load_var &&
+       (available & nir_ssa_def_components_read(&intrin->dest.ssa)) == 0) {
+      /* If none of the components read are available as SSA values, then we
+       * should just bail.  Otherwise, we would end up replacing the uses of
+       * the load_var a vecN() that just gathers up its components.
+       */
+      return false;
+   }
+
+   b->cursor = nir_after_instr(&intrin->instr);
+
+   nir_ssa_def *load_def =
+      intrin->intrinsic == nir_intrinsic_load_var ? &intrin->dest.ssa : NULL;
+
+   bool keep_intrin = false;
+   nir_ssa_def *comps[4];
+   for (unsigned i = 0; i < num_components; i++) {
+      if (value->ssa[i]) {
+         comps[i] = nir_channel(b, value->ssa[i], i);
+      } else {
+         /* We don't have anything for this component in our
+          * list.  Just re-use a channel from the load.
+          */
+         if (load_def == NULL)
+            load_def = nir_load_deref_var(b, entry->dst);
+
+         if (load_def->parent_instr == &intrin->instr)
+            keep_intrin = true;
+
+         comps[i] = nir_channel(b, load_def, i);
+      }
+   }
+
+   nir_ssa_def *vec = nir_vec(b, comps, num_components);
+   for (unsigned i = 0; i < num_components; i++)
+      value->ssa[i] = vec;
+
+   if (!keep_intrin) {
+      /* Removing this instruction should not touch the cursor because we
+       * created the cursor after the intrinsic and have added at least one
+       * instruction (the vec) since then.
+       */
+      assert(b->cursor.instr != &intrin->instr);
+      nir_instr_remove(&intrin->instr);
+      intrin->instr.block = NULL;
+   }
+
+   return true;
+}
+
+/**
+ * Specialize the wildcards in a deref chain
+ *
+ * This function returns a deref chain identical to \param deref except that
+ * some of its wildcards are replaced with indices from \param specific.  The
+ * process is guided by \param guide which references the same type as \param
+ * specific but has the same wildcard array lengths as \param deref.
+ */
+static nir_deref_var *
+specialize_wildcards(nir_deref_var *deref,
+                     nir_deref_var *guide,
+                     nir_deref_var *specific,
+                     void *mem_ctx)
+{
+   nir_deref_var *ret = nir_deref_var_create(mem_ctx, deref->var);
+
+   nir_deref *deref_tail = deref->deref.child;
+   nir_deref *guide_tail = guide->deref.child;
+   nir_deref *spec_tail = specific->deref.child;
+   nir_deref *ret_tail = &ret->deref;
+   while (deref_tail) {
+      switch (deref_tail->deref_type) {
+      case nir_deref_type_array: {
+         nir_deref_array *deref_arr = nir_deref_as_array(deref_tail);
+
+         nir_deref_array *ret_arr = nir_deref_array_create(ret_tail);
+         ret_arr->deref.type = deref_arr->deref.type;
+         ret_arr->deref_array_type = deref_arr->deref_array_type;
+
+         switch (deref_arr->deref_array_type) {
+         case nir_deref_array_type_direct:
+            ret_arr->base_offset = deref_arr->base_offset;
+            break;
+         case nir_deref_array_type_indirect:
+            ret_arr->base_offset = deref_arr->base_offset;
+            assert(deref_arr->indirect.is_ssa);
+            ret_arr->indirect = deref_arr->indirect;
+            break;
+         case nir_deref_array_type_wildcard:
+            /* This is where things get tricky.  We have to search through
+             * the entry deref to find its corresponding wildcard and fill
+             * this slot in with the value from the src.
+             */
+            while (guide_tail) {
+               if (guide_tail->deref_type == nir_deref_type_array &&
+                   nir_deref_as_array(guide_tail)->deref_array_type ==
+                   nir_deref_array_type_wildcard)
+                  break;
+
+               guide_tail = guide_tail->child;
+               spec_tail = spec_tail->child;
+            }
+
+            nir_deref_array *spec_arr = nir_deref_as_array(spec_tail);
+            ret_arr->deref_array_type = spec_arr->deref_array_type;
+            ret_arr->base_offset = spec_arr->base_offset;
+            ret_arr->indirect = spec_arr->indirect;
+         }
+
+         ret_tail->child = &ret_arr->deref;
+         break;
+      }
+      case nir_deref_type_struct: {
+         nir_deref_struct *deref_struct = nir_deref_as_struct(deref_tail);
+
+         nir_deref_struct *ret_struct =
+            nir_deref_struct_create(ret_tail, deref_struct->index);
+         ret_struct->deref.type = deref_struct->deref.type;
+
+         ret_tail->child = &ret_struct->deref;
+         break;
+      }
+      case nir_deref_type_var:
+         unreachable("Invalid deref type");
+      }
+
+      deref_tail = deref_tail->child;
+      ret_tail = ret_tail->child;
+   }
+
+   return ret;
+}
+
+/* Do a "load" from an deref-based entry return it in "value" as a value.  The
+ * deref returned in "value" will always be a fresh copy so the caller can
+ * steal it and assign it to the instruction directly without copying it
+ * again.
+ */
+static bool
+load_from_deref_entry_value(struct copy_prop_var_state *state,
+                            struct copy_entry *entry,
+                            nir_builder *b, nir_intrinsic_instr *intrin,
+                            nir_deref_var *src, struct value *value)
+{
+   *value = entry->src;
+
+   /* Walk the deref to get the two tails and also figure out if we need to
+    * specialize any wildcards.
+    */
+   bool need_to_specialize_wildcards = false;
+   nir_deref *entry_tail = &entry->dst->deref;
+   nir_deref *src_tail = &src->deref;
+   while (entry_tail->child && src_tail->child) {
+      assert(src_tail->child->deref_type == entry_tail->child->deref_type);
+      if (src_tail->child->deref_type == nir_deref_type_array) {
+         nir_deref_array *entry_arr = nir_deref_as_array(entry_tail->child);
+         nir_deref_array *src_arr = nir_deref_as_array(src_tail->child);
+
+         if (src_arr->deref_array_type != nir_deref_array_type_wildcard &&
+             entry_arr->deref_array_type == nir_deref_array_type_wildcard)
+            need_to_specialize_wildcards = true;
+      }
+
+      entry_tail = entry_tail->child;
+      src_tail = src_tail->child;
+   }
+
+   /* If the entry deref is longer than the source deref then it refers to a
+    * smaller type and we can't source from it.
+    */
+   assert(entry_tail->child == NULL);
+
+   if (need_to_specialize_wildcards) {
+      /* The entry has some wildcards that are not in src.  This means we need
+       * to construct a new deref based on the entry but using the wildcards
+       * from the source and guided by the entry dst.  Oof.
+       */
+      value->deref = specialize_wildcards(entry->src.deref, entry->dst, src,
+                                          state->mem_ctx);
+   } else {
+      /* We're going to need to make a copy in case we modify it below */
+      value->deref = nir_deref_var_clone(value->deref, state->mem_ctx);
+   }
+
+   if (src_tail->child) {
+      /* If our source deref is longer than the entry deref, that's ok because
+       * it just means the entry deref needs to be extended a bit.
+       */
+      nir_deref *value_tail = nir_deref_tail(&value->deref->deref);
+      value_tail->child = nir_deref_clone(src_tail->child, value_tail);
+   }
+
+   b->cursor = instr_remove_cursor(&intrin->instr);
+
+   return true;
+}
+
+static bool
+try_load_from_entry(struct copy_prop_var_state *state, struct copy_entry *entry,
+                    nir_builder *b, nir_intrinsic_instr *intrin,
+                    nir_deref_var *src, struct value *value)
+{
+   if (entry == NULL)
+      return false;
+
+   if (entry->src.is_ssa) {
+      return load_from_ssa_entry_value(state, entry, b, intrin, value);
+   } else {
+      return load_from_deref_entry_value(state, entry, b, intrin, src, value);
+   }
+}
+
+static void
+copy_prop_vars_block(struct copy_prop_var_state *state,
+                     nir_builder *b, nir_block *block)
+{
+   /* Start each block with a blank slate */
+   list_for_each_entry_safe(struct copy_entry, iter, &state->copies, link)
+      copy_entry_remove(state, iter);
+
+   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_barrier:
+      case nir_intrinsic_memory_barrier:
+         /* If we hit a barrier, we need to trash everything that may possibly
+          * be accessible to another thread.  Locals, globals, and things of
+          * the like are safe, however.
+          */
+         apply_barrier_for_modes(state, ~(nir_var_local | nir_var_global |
+                                          nir_var_shader_in | nir_var_uniform));
+         break;
+
+      case nir_intrinsic_emit_vertex:
+      case nir_intrinsic_emit_vertex_with_counter:
+         apply_barrier_for_modes(state, nir_var_shader_out);
+         break;
+
+      case nir_intrinsic_load_var: {
+         nir_deref_var *src = intrin->variables[0];
+
+         uint8_t comps_read = nir_ssa_def_components_read(&intrin->dest.ssa);
+         mark_aliased_entries_as_read(state, src, comps_read);
+
+         struct copy_entry *src_entry =
+            lookup_entry_for_deref(state, src, derefs_a_contains_b_bit);
+         struct value value;
+         if (try_load_from_entry(state, src_entry, b, intrin, src, &value)) {
+            if (value.is_ssa) {
+               /* lookup_load has already ensured that we get a single SSA
+                * value that has all of the channels.  We just have to do the
+                * rewrite operation.
+                */
+               if (intrin->instr.block) {
+                  /* The lookup left our instruction in-place.  This means it
+                   * must have used it to vec up a bunch of different sources.
+                   * We need to be careful when rewriting uses so we don't
+                   * rewrite the vecN itself.
+                   */
+                  nir_ssa_def_rewrite_uses_after(&intrin->dest.ssa,
+                                                 nir_src_for_ssa(value.ssa[0]),
+                                                 value.ssa[0]->parent_instr);
+               } else {
+                  nir_ssa_def_rewrite_uses(&intrin->dest.ssa,
+                                           nir_src_for_ssa(value.ssa[0]));
+               }
+            } else {
+               /* We're turning it into a load of a different variable */
+               ralloc_steal(intrin, value.deref);
+               intrin->variables[0] = value.deref;
+
+               /* Put it back in again. */
+               nir_builder_instr_insert(b, instr);
+
+               value.is_ssa = true;
+               for (unsigned i = 0; i < intrin->num_components; i++)
+                  value.ssa[i] = &intrin->dest.ssa;
+            }
+            state->progress = true;
+         } else {
+            value.is_ssa = true;
+            for (unsigned i = 0; i < intrin->num_components; i++)
+               value.ssa[i] = &intrin->dest.ssa;
+         }
+
+         /* Now that we have a value, we're going to store it back so that we
+          * have the right value next time we come looking for it.  In order
+          * to do this, we need an exact match, not just something that
+          * contains what we're looking for.
+          */
+         struct copy_entry *store_entry =
+            lookup_entry_for_deref(state, src, derefs_equal_bit);
+         if (!store_entry)
+            store_entry = copy_entry_create(state, src);
+
+         /* Set up a store to this entry with the value of the load.  This way
+          * we can potentially remove subsequent loads.  However, we use a
+          * NULL instruction so we don't try and delete the load on a
+          * subsequent store.
+          */
+         store_to_entry(state, store_entry, &value,
+                        ((1 << intrin->num_components) - 1), NULL);
+         break;
+      }
+
+      case nir_intrinsic_store_var: {
+         struct value value = {
+            .is_ssa = true
+         };
+
+         for (unsigned i = 0; i < intrin->num_components; i++)
+            value.ssa[i] = intrin->src[0].ssa;
+
+         nir_deref_var *dst = intrin->variables[0];
+         unsigned wrmask = nir_intrinsic_write_mask(intrin);
+         struct copy_entry *entry =
+            get_entry_and_kill_aliases(state, dst, wrmask);
+         store_to_entry(state, entry, &value, wrmask, &intrin->instr);
+         break;
+      }
+
+      case nir_intrinsic_copy_var: {
+         nir_deref_var *dst = intrin->variables[0];
+         nir_deref_var *src = intrin->variables[1];
+
+         if (compare_derefs(src, dst) & derefs_equal_bit) {
+            /* This is a no-op self-copy.  Get rid of it */
+            nir_instr_remove(instr);
+            continue;
+         }
+
+         mark_aliased_entries_as_read(state, src, 0xf);
+
+         struct copy_entry *src_entry =
+            lookup_entry_for_deref(state, src, derefs_a_contains_b_bit);
+         struct value value;
+         if (try_load_from_entry(state, src_entry, b, intrin, src, &value)) {
+            if (value.is_ssa) {
+               nir_store_deref_var(b, dst, value.ssa[0], 0xf);
+               intrin = nir_instr_as_intrinsic(nir_builder_last_instr(b));
+            } else {
+               /* If this would be a no-op self-copy, don't bother. */
+               if (compare_derefs(value.deref, dst) & derefs_equal_bit)
+                  continue;
+
+               /* Just turn it into a copy of a different deref */
+               ralloc_steal(intrin, value.deref);
+               intrin->variables[1] = value.deref;
+
+               /* Put it back in again. */
+               nir_builder_instr_insert(b, instr);
+            }
+
+            state->progress = true;
+         } else {
+            value = (struct value) {
+               .is_ssa = false,
+               .deref = src,
+            };
+         }
+
+         struct copy_entry *dst_entry =
+            get_entry_and_kill_aliases(state, dst, 0xf);
+         store_to_entry(state, dst_entry, &value, 0xf, &intrin->instr);
+         break;
+      }
+
+      default:
+         break;
+      }
+   }
+}
+
+bool
+nir_opt_copy_prop_vars(nir_shader *shader)
+{
+   struct copy_prop_var_state state;
+
+   state.shader = shader;
+   state.mem_ctx = ralloc_context(NULL);
+   list_inithead(&state.copies);
+   list_inithead(&state.copy_free_list);
+
+   bool global_progress = false;
+   nir_foreach_function(function, shader) {
+      if (!function->impl)
+         continue;
+
+      nir_builder b;
+      nir_builder_init(&b, function->impl);
+
+      state.progress = false;
+      nir_foreach_block(block, function->impl)
+         copy_prop_vars_block(&state, &b, block);
+
+      if (state.progress) {
+         nir_metadata_preserve(function->impl, nir_metadata_block_index |
+                                               nir_metadata_dominance);
+         global_progress = true;
+      }
+   }
+
+   ralloc_free(state.mem_ctx);
+
+   return global_progress;
+}