nir: Add an array copy optimization

This peephole optimization looks for a series of load/store_deref or
copy_deref instructions that copy an array from one variable to another
and turns it into a copy_deref that copies the entire array.  The
pattern it looks for is extremely specific but it's good enough to pick
up on the input array copies in DXVK and should also be able to pick up
the sequence generated by spirv_to_nir for a OpLoad of a large composite
followed by OpStore.  It can always be improved later if needed.

Reviewed-by: Caio Marcelo de Oliveira Filho <[email protected]>

4 files changed, 415 insertions, 0 deletions

diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
index c6daf4d9c8f..d3b06564832 100644
--- a/src/compiler/Makefile.sources
+++ b/src/compiler/Makefile.sources
@@ -274,6 +274,7 @@ NIR_FILES = \
 	nir/nir_opt_cse.c \
 	nir/nir_opt_dce.c \
 	nir/nir_opt_dead_cf.c \
+	nir/nir_opt_find_array_copies.c \
 	nir/nir_opt_gcm.c \
 	nir/nir_opt_global_to_local.c \
 	nir/nir_opt_if.c \
diff --git a/src/compiler/nir/meson.build b/src/compiler/nir/meson.build
index b32ae75f76b..090aa7a628f 100644
--- a/src/compiler/nir/meson.build
+++ b/src/compiler/nir/meson.build
@@ -158,6 +158,7 @@ files_libnir = files(
   'nir_opt_cse.c',
   'nir_opt_dce.c',
   'nir_opt_dead_cf.c',
+  'nir_opt_find_array_copies.c',
   'nir_opt_gcm.c',
   'nir_opt_global_to_local.c',
   'nir_opt_if.c',
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index 442a1c9c79f..45a8c2c64cc 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2971,6 +2971,8 @@ bool nir_opt_dce(nir_shader *shader);
 
 bool nir_opt_dead_cf(nir_shader *shader);
 
+bool nir_opt_find_array_copies(nir_shader *shader);
+
 bool nir_opt_gcm(nir_shader *shader, bool value_number);
 
 bool nir_opt_if(nir_shader *shader);
diff --git a/src/compiler/nir/nir_opt_find_array_copies.c b/src/compiler/nir/nir_opt_find_array_copies.c
new file mode 100644
index 00000000000..417ad9c55c3
--- /dev/null
+++ b/src/compiler/nir/nir_opt_find_array_copies.c
@@ -0,0 +1,411 @@
+/*
+ * Copyright © 2018 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 "nir_deref.h"
+
+static bool
+index_ssa_def_cb(nir_ssa_def *def, void *state)
+{
+   unsigned *index = (unsigned *) state;
+   def->index = (*index)++;
+
+   return true;
+}
+
+static nir_deref_instr *
+get_deref_for_load_src(nir_src src, unsigned first_valid_load)
+{
+   if (!src.is_ssa)
+      return NULL;
+
+   if (src.ssa->parent_instr->type != nir_instr_type_intrinsic)
+      return NULL;
+
+   nir_intrinsic_instr *load = nir_instr_as_intrinsic(src.ssa->parent_instr);
+   if (load->intrinsic != nir_intrinsic_load_deref)
+      return NULL;
+
+   if (load->dest.ssa.index < first_valid_load)
+      return NULL;
+
+   return nir_src_as_deref(load->src[0]);
+}
+
+struct match_state {
+   /* Index into the array of the last copy or -1 for no ongoing copy. */
+   unsigned next_array_idx;
+
+   /* Length of the array we're copying */
+   unsigned array_len;
+
+   /* Index into the deref path to the array we think is being copied */
+   int src_deref_array_idx;
+   int dst_deref_array_idx;
+
+   /* Deref paths of the first load/store pair or copy */
+   nir_deref_path first_src_path;
+   nir_deref_path first_dst_path;
+};
+
+static void
+match_state_init(struct match_state *state)
+{
+   state->next_array_idx = 0;
+   state->array_len = 0;
+   state->src_deref_array_idx = -1;
+   state->dst_deref_array_idx = -1;
+}
+
+static void
+match_state_finish(struct match_state *state)
+{
+   if (state->next_array_idx > 0) {
+      nir_deref_path_finish(&state->first_src_path);
+      nir_deref_path_finish(&state->first_dst_path);
+   }
+}
+
+static void
+match_state_reset(struct match_state *state)
+{
+   match_state_finish(state);
+   match_state_init(state);
+}
+
+static bool
+try_match_deref(nir_deref_path *base_path, int *path_array_idx,
+                nir_deref_instr *deref, int arr_idx, void *mem_ctx)
+{
+   nir_deref_path deref_path;
+   nir_deref_path_init(&deref_path, deref, mem_ctx);
+
+   bool found = false;
+   for (int i = 0; ; i++) {
+      nir_deref_instr *b = base_path->path[i];
+      nir_deref_instr *d = deref_path.path[i];
+      /* They have to be the same length */
+      if ((b == NULL) != (d == NULL))
+         goto fail;
+
+      if (b == NULL)
+         break;
+
+      /* This can happen if one is a deref_array and the other a wildcard */
+      if (b->deref_type != d->deref_type)
+         goto fail;
+
+      switch (b->deref_type) {
+      case nir_deref_type_var:
+         if (b->var != d->var)
+            goto fail;
+         continue;
+
+      case nir_deref_type_array:
+         assert(b->arr.index.is_ssa && d->arr.index.is_ssa);
+         nir_const_value *const_b_idx = nir_src_as_const_value(b->arr.index);
+         nir_const_value *const_d_idx = nir_src_as_const_value(d->arr.index);
+
+         /* If we don't have an index into the path yet or if this entry in
+          * the path is at the array index, see if this is a candidate.  We're
+          * looking for an index which is zero in the base deref and arr_idx
+          * in the search deref.
+          */
+         if ((*path_array_idx < 0 || *path_array_idx == i) &&
+             const_b_idx && const_b_idx->u32[0] == 0 &&
+             const_d_idx && const_d_idx->u32[0] == arr_idx) {
+            *path_array_idx = i;
+            continue;
+         }
+
+         /* We're at the array index but not a candidate */
+         if (*path_array_idx == i)
+            goto fail;
+
+         /* If we're not the path array index, we must match exactly.  We
+          * could probably just compare SSA values and trust in copy
+          * propagation but doing it ourselves means this pass can run a bit
+          * earlier.
+          */
+         if (b->arr.index.ssa == d->arr.index.ssa ||
+             (const_b_idx && const_d_idx &&
+              const_b_idx->u32[0] == const_d_idx->u32[0]))
+            continue;
+
+         goto fail;
+
+      case nir_deref_type_array_wildcard:
+         continue;
+
+      case nir_deref_type_struct:
+         if (b->strct.index != d->strct.index)
+            goto fail;
+         continue;
+
+      default:
+         unreachable("Invalid deref type in a path");
+      }
+   }
+
+   /* If we got here without failing, we've matched.  However, it isn't an
+    * array match unless we found an altered array index.
+    */
+   found = *path_array_idx > 0;
+
+fail:
+   nir_deref_path_finish(&deref_path);
+   return found;
+}
+
+static nir_deref_instr *
+build_wildcard_deref(nir_builder *b, nir_deref_path *path,
+                     unsigned wildcard_idx)
+{
+   assert(path->path[wildcard_idx]->deref_type == nir_deref_type_array);
+
+   nir_deref_instr *tail =
+      nir_build_deref_array_wildcard(b, path->path[wildcard_idx - 1]);
+
+   for (unsigned i = wildcard_idx + 1; path->path[i]; i++)
+      tail = nir_build_deref_follower(b, tail, path->path[i]);
+
+   return tail;
+}
+
+static bool
+opt_find_array_copies_block(nir_builder *b, nir_block *block,
+                            unsigned *num_ssa_defs, void *mem_ctx)
+{
+   bool progress = false;
+
+   struct match_state s;
+   match_state_init(&s);
+
+   nir_variable *dst_var = NULL;
+   unsigned prev_dst_var_last_write = *num_ssa_defs;
+   unsigned dst_var_last_write = *num_ssa_defs;
+
+   nir_foreach_instr(instr, block) {
+      /* Index the SSA defs before we do anything else. */
+      nir_foreach_ssa_def(instr, index_ssa_def_cb, num_ssa_defs);
+
+      if (instr->type != nir_instr_type_intrinsic)
+         continue;
+
+      nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+      if (intrin->intrinsic != nir_intrinsic_copy_deref &&
+          intrin->intrinsic != nir_intrinsic_store_deref)
+         continue;
+
+      nir_deref_instr *dst_deref = nir_src_as_deref(intrin->src[0]);
+
+      /* The destination must be local.  If we see a non-local store, we
+       * continue on because it won't affect local stores or read-only
+       * variables.
+       */
+      if (dst_deref->mode != nir_var_local)
+         continue;
+
+      /* We keep track of the SSA indices where the two last-written
+       * variables are written.  The prev_dst_var_last_write tells us when
+       * the last store_deref to something other than dst happened.  If the
+       * SSA def index from a load is greater than or equal to this number
+       * then we know it happened afterwards and no writes to anything other
+       * than dst occur between the load and the current instruction.
+       */
+      if (nir_deref_instr_get_variable(dst_deref) != dst_var) {
+         prev_dst_var_last_write = dst_var_last_write;
+         dst_var = nir_deref_instr_get_variable(dst_deref);
+      }
+      dst_var_last_write = *num_ssa_defs;
+
+      /* If it's a full variable store or copy, reset.  This will trigger
+       * eventually because we'll fail to match an array element.  However,
+       * it's a cheap early-exit.
+       */
+      if (dst_deref->deref_type == nir_deref_type_var)
+         goto reset;
+
+      nir_deref_instr *src_deref;
+      if (intrin->intrinsic == nir_intrinsic_copy_deref) {
+         src_deref = nir_src_as_deref(intrin->src[1]);
+      } else {
+         assert(intrin->intrinsic == nir_intrinsic_store_deref);
+         src_deref = get_deref_for_load_src(intrin->src[1],
+                                            prev_dst_var_last_write);
+
+         /* We can only handle full writes */
+         if (nir_intrinsic_write_mask(intrin) !=
+             (1 << glsl_get_components(dst_deref->type)) - 1)
+            goto reset;
+      }
+
+      /* If we didn't find a valid src, then we have an unknown store and it
+       * could mess things up.
+       */
+      if (src_deref == NULL)
+         goto reset;
+
+      /* The source must be either local or something that's guaranteed to be
+       * read-only.
+       */
+      const nir_variable_mode read_only_modes =
+         nir_var_shader_in | nir_var_uniform | nir_var_system_value;
+      if (!(src_deref->mode & (nir_var_local | read_only_modes)))
+         goto reset;
+
+      /* If we don't yet have an active copy, then make this instruction the
+       * active copy.
+       */
+      if (s.next_array_idx == 0) {
+         /* We can't combine a copy if there is any chance the source and
+          * destination will end up aliasing.  Just bail if they're the same
+          * variable.
+          */
+         if (nir_deref_instr_get_variable(src_deref) == dst_var)
+            goto reset;
+
+         /* The load/store pair is enough to guarantee the same bit size and
+          * number of components but a copy_var requires the actual types to
+          * match.
+          */
+         if (dst_deref->type != src_deref->type)
+            continue;
+
+         /* The first time we see a store, we don't know which array in the
+          * deref path is the one being copied so we just record the paths
+          * as-is and continue.  On the next iteration, it will try to match
+          * based on which array index changed.
+          */
+         nir_deref_path_init(&s.first_dst_path, dst_deref, mem_ctx);
+         nir_deref_path_init(&s.first_src_path, src_deref, mem_ctx);
+         s.next_array_idx = 1;
+         continue;
+      }
+
+      if (!try_match_deref(&s.first_dst_path, &s.dst_deref_array_idx,
+                           dst_deref, s.next_array_idx, mem_ctx) ||
+          !try_match_deref(&s.first_src_path, &s.src_deref_array_idx,
+                           src_deref, s.next_array_idx, mem_ctx))
+         goto reset;
+
+      if (s.next_array_idx == 1) {
+         /* This is our first non-trivial match.  We now have indices into
+          * the search paths so we can do a couple more checks.
+          */
+         assert(s.dst_deref_array_idx > 0 && s.src_deref_array_idx > 0);
+         const struct glsl_type *dst_arr_type =
+            s.first_dst_path.path[s.dst_deref_array_idx - 1]->type;
+         const struct glsl_type *src_arr_type =
+            s.first_src_path.path[s.src_deref_array_idx - 1]->type;
+
+         assert(glsl_type_is_array(dst_arr_type) ||
+                glsl_type_is_matrix(dst_arr_type));
+         assert(glsl_type_is_array(src_arr_type) ||
+                glsl_type_is_matrix(src_arr_type));
+
+         /* They must be the same length */
+         s.array_len = glsl_get_length(dst_arr_type);
+         if (s.array_len != glsl_get_length(src_arr_type))
+            goto reset;
+      }
+
+      s.next_array_idx++;
+
+      if (s.next_array_idx == s.array_len) {
+         /* Hooray, We found a copy! */
+         b->cursor = nir_after_instr(instr);
+         nir_copy_deref(b, build_wildcard_deref(b, &s.first_dst_path,
+                                                s.dst_deref_array_idx),
+                           build_wildcard_deref(b, &s.first_src_path,
+                                                s.src_deref_array_idx));
+         match_state_reset(&s);
+         progress = true;
+      }
+
+      continue;
+
+   reset:
+      match_state_reset(&s);
+   }
+
+   return progress;
+}
+
+static bool
+opt_find_array_copies_impl(nir_function_impl *impl)
+{
+   nir_builder b;
+   nir_builder_init(&b, impl);
+
+   bool progress = false;
+
+   void *mem_ctx = ralloc_context(NULL);
+
+   /* We re-index the SSA defs as we go; it makes it easier to handle
+    * resetting the state machine.
+    */
+   unsigned num_ssa_defs = 0;
+
+   nir_foreach_block(block, impl) {
+      if (opt_find_array_copies_block(&b, block, &num_ssa_defs, mem_ctx))
+         progress = true;
+   }
+
+   impl->ssa_alloc = num_ssa_defs;
+
+   ralloc_free(mem_ctx);
+
+   if (progress) {
+      nir_metadata_preserve(impl, nir_metadata_block_index |
+                                  nir_metadata_dominance);
+   }
+
+   return progress;
+}
+
+/**
+ * This peephole optimization looks for a series of load/store_deref or
+ * copy_deref instructions that copy an array from one variable to another and
+ * turns it into a copy_deref that copies the entire array.  The pattern it
+ * looks for is extremely specific but it's good enough to pick up on the
+ * input array copies in DXVK and should also be able to pick up the sequence
+ * generated by spirv_to_nir for a OpLoad of a large composite followed by
+ * OpStore.
+ *
+ * TODO: Use a hash table approach to support out-of-order and interleaved
+ * copies.
+ */
+bool
+nir_opt_find_array_copies(nir_shader *shader)
+{
+   bool progress = false;
+
+   nir_foreach_function(function, shader) {
+      if (function->impl && opt_find_array_copies_impl(function->impl))
+         progress = true;
+   }
+
+   return progress;
+}