nir: Add a copy splitting pass

Reviewed-by: Connor Abbott <[email protected]>

3 files changed, 288 insertions, 0 deletions

diff --git a/src/glsl/Makefile.sources b/src/glsl/Makefile.sources
index 20496ff5843..84245bcb3c6 100644
--- a/src/glsl/Makefile.sources
+++ b/src/glsl/Makefile.sources
@@ -37,6 +37,7 @@ NIR_FILES = \
 	$(GLSL_SRCDIR)/nir/nir_opt_peephole_select.c \
 	$(GLSL_SRCDIR)/nir/nir_print.c \
 	$(GLSL_SRCDIR)/nir/nir_remove_dead_variables.c \
+	$(GLSL_SRCDIR)/nir/nir_split_var_copies.c \
 	$(GLSL_SRCDIR)/nir/nir_to_ssa.c \
 	$(GLSL_SRCDIR)/nir/nir_validate.c \
 	$(GLSL_SRCDIR)/nir/nir_types.cpp \
diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
index ac2329fbbc8..8664fc8d47a 100644
--- a/src/glsl/nir/nir.h
+++ b/src/glsl/nir/nir.h
@@ -1356,6 +1356,8 @@ void nir_dump_dom_frontier(nir_shader *shader, FILE *fp);
 void nir_dump_cfg_impl(nir_function_impl *impl, FILE *fp);
 void nir_dump_cfg(nir_shader *shader, FILE *fp);
 
+void nir_split_var_copies(nir_shader *shader);
+
 void nir_lower_variables_scalar(nir_shader *shader, bool lower_globals,
                                 bool lower_io, bool add_names,
                                 bool native_integers);
diff --git a/src/glsl/nir/nir_split_var_copies.c b/src/glsl/nir/nir_split_var_copies.c
new file mode 100644
index 00000000000..edabfb7e5c3
--- /dev/null
+++ b/src/glsl/nir/nir_split_var_copies.c
@@ -0,0 +1,285 @@
+/*
+ * 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 ([email protected])
+ *
+ */
+
+#include "nir.h"
+
+/*
+ * Implements "copy splitting" which is similar to structure splitting only
+ * it works on copy operations rather than the datatypes themselves.  The
+ * GLSL language allows you to copy one variable to another an entire
+ * structure (which may contain arrays or other structures) at a time.
+ * Normally, in a language such as C this would be handled by a "structure
+ * splitting" pass that breaks up the structures.  Unfortunately for us,
+ * structures used in inputs or outputs can't be split.  Therefore,
+ * regardlesss of what we do, we have to be able to copy to/from
+ * structures.
+ *
+ * The primary purpose of structure splitting is to allow you to better
+ * optimize variable access and lower things to registers where you can.
+ * The primary issue here is that, if you lower the copy to a bunch of
+ * loads and stores, you loose a lot of information about the copy
+ * operation that you would like to keep around.  To solve this problem, we
+ * have a "copy splitting" pass that, instead of splitting the structures
+ * or lowering the copy into loads and storres, splits the copy operation
+ * into a bunch of copy operations one for each leaf of the structure tree.
+ * If an intermediate array is encountered, it is referenced with a
+ * wildcard reference to indicate that the entire array is to be copied.
+ *
+ * As things become direct, array copies may be able to be losslessly
+ * lowered to having fewer and fewer wildcards.  However, until that
+ * happens we want to keep the information about the arrays intact.
+ *
+ * Prior to the copy splitting pass, there are no wildcard references but
+ * there may be incomplete references where the tail of the deref chain is
+ * an array or a structure and not a specific element.  After the copy
+ * splitting pass has completed, every variable deref will be a full-length
+ * dereference pointing to a single leaf in the structure type tree with
+ * possibly a few wildcard array dereferences.
+ */
+
+struct split_var_copies_state {
+   void *mem_ctx;
+   void *dead_ctx;
+};
+
+static nir_deref *
+get_deref_tail(nir_deref *deref)
+{
+   while (deref->child != NULL)
+      deref = deref->child;
+   return deref;
+}
+
+/* Recursively constructs deref chains to split a copy instruction into
+ * multiple (if needed) copy instructions with full-length deref chains.
+ * External callers of this function should pass the tail and head of the
+ * deref chains found as the source and destination of the copy instruction
+ * into this function.
+ *
+ * \param  old_copy  The copy instruction we are splitting
+ * \param  dest_head The head of the destination deref chain we are building
+ * \param  src_head  The head of the source deref chain we are building
+ * \param  dest_tail The tail of the destination deref chain we are building
+ * \param  src_tail  The tail of the source deref chain we are building
+ * \param  state     The current split_var_copies_state object
+ */
+static void
+split_var_copy_instr(nir_intrinsic_instr *old_copy,
+                     nir_deref *dest_head, nir_deref *src_head,
+                     nir_deref *dest_tail, nir_deref *src_tail,
+                     struct split_var_copies_state *state)
+{
+   assert(src_tail->type == dest_tail->type);
+
+   /* Make sure these really are the tails of the deref chains */
+   assert(dest_tail->child == NULL);
+   assert(src_tail->child == NULL);
+
+   switch (glsl_get_base_type(src_tail->type)) {
+   case GLSL_TYPE_ARRAY: {
+      /* Make a wildcard dereference */
+      nir_deref_array *deref = nir_deref_array_create(state->dead_ctx);
+      deref->deref.type = glsl_get_array_element(src_tail->type);
+      deref->deref_array_type = nir_deref_array_type_wildcard;
+
+      /* Set the tail of both as the newly created wildcard deref.  It is
+       * safe to use the same wildcard in both places because a) we will be
+       * copying it before we put it in an actual instruction and b)
+       * everything that will potentially add another link in the deref
+       * chain will also add the same thing to both chains.
+       */
+      src_tail->child = &deref->deref;
+      dest_tail->child = &deref->deref;
+
+      split_var_copy_instr(old_copy, dest_head, src_head,
+                           dest_tail->child, src_tail->child, state);
+
+      /* Set it back to the way we found it */
+      src_tail->child = NULL;
+      dest_tail->child = NULL;
+      break;
+   }
+
+   case GLSL_TYPE_STRUCT:
+      /* This is the only part that actually does any interesting
+       * splitting.  For array types, we just use wildcards and resolve
+       * them later.  For structure types, we need to emit one copy
+       * instruction for every structure element.  Because we may have
+       * structs inside structs, we just recurse and let the next level
+       * take care of any additional structures.
+       */
+      for (unsigned i = 0; i < glsl_get_length(src_tail->type); i++) {
+         nir_deref_struct *deref = nir_deref_struct_create(state->dead_ctx, i);
+         deref->deref.type = glsl_get_struct_field(src_tail->type, i);
+
+         /* Set the tail of both as the newly created structure deref.  It
+          * is safe to use the same wildcard in both places because a) we
+          * will be copying it before we put it in an actual instruction
+          * and b) everything that will potentially add another link in the
+          * deref chain will also add the same thing to both chains.
+          */
+         src_tail->child = &deref->deref;
+         dest_tail->child = &deref->deref;
+
+         split_var_copy_instr(old_copy, dest_head, src_head,
+                              dest_tail->child, src_tail->child, state);
+      }
+      /* Set it back to the way we found it */
+      src_tail->child = NULL;
+      dest_tail->child = NULL;
+      break;
+
+   case GLSL_TYPE_UINT:
+   case GLSL_TYPE_INT:
+   case GLSL_TYPE_FLOAT:
+   case GLSL_TYPE_BOOL:
+      if (glsl_type_is_matrix(src_tail->type)) {
+         nir_deref_array *deref = nir_deref_array_create(state->dead_ctx);
+         deref->deref.type = glsl_get_column_type(src_tail->type);
+         deref->deref_array_type = nir_deref_array_type_wildcard;
+
+         /* Set the tail of both as the newly created wildcard deref.  It
+          * is safe to use the same wildcard in both places because a) we
+          * will be copying it before we put it in an actual instruction
+          * and b) everything that will potentially add another link in the
+          * deref chain will also add the same thing to both chains.
+          */
+         src_tail->child = &deref->deref;
+         dest_tail->child = &deref->deref;
+
+         split_var_copy_instr(old_copy, dest_head, src_head,
+                              dest_tail->child, src_tail->child, state);
+
+         /* Set it back to the way we found it */
+         src_tail->child = NULL;
+         dest_tail->child = NULL;
+      } else {
+         /* At this point, we have fully built our deref chains and can
+          * actually add the new copy instruction.
+          */
+         nir_intrinsic_instr *new_copy =
+            nir_intrinsic_instr_create(state->mem_ctx, nir_intrinsic_copy_var);
+
+         if (old_copy->has_predicate) {
+            new_copy->has_predicate = true;
+            new_copy->predicate = nir_src_copy(old_copy->predicate,
+                                               state->mem_ctx);
+         }
+
+         /* We need to make copies because a) this deref chain actually
+          * belongs to the copy instruction and b) the deref chains may
+          * have some of the same links due to the way we constructed them
+          */
+         nir_deref *src = nir_copy_deref(state->mem_ctx, src_head);
+         nir_deref *dest = nir_copy_deref(state->mem_ctx, dest_head);
+
+         new_copy->variables[0] = nir_deref_as_var(dest);
+         new_copy->variables[1] = nir_deref_as_var(src);
+
+         /* Emit the copy instruction after the old instruction.  We'll
+          * remove the old one later.
+          */
+         nir_instr_insert_after(&old_copy->instr, &new_copy->instr);
+      }
+      break;
+
+   case GLSL_TYPE_SAMPLER:
+   case GLSL_TYPE_IMAGE:
+   case GLSL_TYPE_ATOMIC_UINT:
+   case GLSL_TYPE_INTERFACE:
+   default:
+      unreachable("Cannot copy these types");
+   }
+}
+
+static bool
+split_var_copies_block(nir_block *block, void *void_state)
+{
+   struct split_var_copies_state *state = void_state;
+
+   nir_foreach_instr_safe(block, instr) {
+      if (instr->type != nir_instr_type_intrinsic)
+         continue;
+
+      nir_intrinsic_instr *intrinsic = nir_instr_as_intrinsic(instr);
+      if (intrinsic->intrinsic != nir_intrinsic_copy_var)
+         continue;
+
+      nir_deref *dest_head = &intrinsic->variables[0]->deref;
+      nir_deref *src_head = &intrinsic->variables[1]->deref;
+      nir_deref *dest_tail = get_deref_tail(dest_head);
+      nir_deref *src_tail = get_deref_tail(src_head);
+
+      switch (glsl_get_base_type(src_tail->type)) {
+      case GLSL_TYPE_ARRAY:
+      case GLSL_TYPE_STRUCT:
+         split_var_copy_instr(intrinsic, dest_head, src_head,
+                              dest_tail, src_tail, state);
+         nir_instr_remove(&intrinsic->instr);
+         ralloc_steal(state->dead_ctx, instr);
+         break;
+      case GLSL_TYPE_FLOAT:
+      case GLSL_TYPE_INT:
+      case GLSL_TYPE_UINT:
+      case GLSL_TYPE_BOOL:
+         if (glsl_type_is_matrix(src_tail->type)) {
+            split_var_copy_instr(intrinsic, dest_head, src_head,
+                                 dest_tail, src_tail, state);
+            nir_instr_remove(&intrinsic->instr);
+            ralloc_steal(state->dead_ctx, instr);
+         }
+         break;
+      default:
+         unreachable("Invalid type");
+         break;
+      }
+   }
+
+   return true;
+}
+
+static void
+split_var_copies_impl(nir_function_impl *impl)
+{
+   struct split_var_copies_state state;
+
+   state.mem_ctx = ralloc_parent(impl);
+   state.dead_ctx = ralloc_context(NULL);
+
+   nir_foreach_block(impl, split_var_copies_block, &state);
+
+   ralloc_free(state.dead_ctx);
+}
+
+void
+nir_split_var_copies(nir_shader *shader)
+{
+   nir_foreach_overload(shader, overload) {
+      if (overload->impl)
+         split_var_copies_impl(overload->impl);
+   }
+}