nir: Add a pass for lower indirect variable dereferences

This new pass lowers load/store_var intrinsics that act on indirect derefs
to if-ladder of direct load/store_var intrinsics.  The if-ladders perform a
simple binary search on the indirect.

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

4 files changed, 243 insertions, 0 deletions

diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
index c9780d6d6f7..9f3bcf0255b 100644
--- a/src/compiler/Makefile.sources
+++ b/src/compiler/Makefile.sources
@@ -189,6 +189,7 @@ NIR_FILES = \
 	nir/nir_lower_load_const_to_scalar.c \
 	nir/nir_lower_locals_to_regs.c \
 	nir/nir_lower_idiv.c \
+	nir/nir_lower_indirect_derefs.c \
 	nir/nir_lower_io.c \
 	nir/nir_lower_outputs_to_temporaries.c \
 	nir/nir_lower_phis_to_scalar.c \
diff --git a/src/compiler/nir/Makefile.sources b/src/compiler/nir/Makefile.sources
index 0755a100e65..f31547b9aac 100644
--- a/src/compiler/nir/Makefile.sources
+++ b/src/compiler/nir/Makefile.sources
@@ -33,6 +33,7 @@ NIR_FILES = \
 	nir_lower_load_const_to_scalar.c \
 	nir_lower_locals_to_regs.c \
 	nir_lower_idiv.c \
+	nir_lower_indirect_derefs.c \
 	nir_lower_io.c \
 	nir_lower_outputs_to_temporaries.c \
 	nir_lower_phis_to_scalar.c \
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index cccb3a41da5..cfbac81dbb1 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2055,6 +2055,8 @@ void nir_lower_var_copies(nir_shader *shader);
 
 bool nir_lower_global_vars_to_local(nir_shader *shader);
 
+bool nir_lower_indirect_derefs(nir_shader *shader, uint32_t mode_mask);
+
 bool nir_lower_locals_to_regs(nir_shader *shader);
 
 void nir_lower_outputs_to_temporaries(nir_shader *shader);
diff --git a/src/compiler/nir/nir_lower_indirect_derefs.c b/src/compiler/nir/nir_lower_indirect_derefs.c
new file mode 100644
index 00000000000..a4affa7bdcf
--- /dev/null
+++ b/src/compiler/nir/nir_lower_indirect_derefs.c
@@ -0,0 +1,239 @@
+/*
+ * 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"
+
+static void
+emit_load_store(nir_builder *b, nir_intrinsic_instr *orig_instr,
+                nir_deref_var *deref, nir_deref *tail,
+                nir_ssa_def **dest, nir_ssa_def *src);
+
+static void
+emit_indirect_load_store(nir_builder *b, nir_intrinsic_instr *orig_instr,
+                         nir_deref_var *deref, nir_deref *arr_parent,
+                         int start, int end,
+                         nir_ssa_def **dest, nir_ssa_def *src)
+{
+   assert(arr_parent->child &&
+          arr_parent->child->deref_type == nir_deref_type_array);
+   nir_deref_array *arr = nir_deref_as_array(arr_parent->child);
+   assert(arr->deref_array_type == nir_deref_array_type_indirect);
+   assert(arr->indirect.is_ssa);
+
+   assert(start < end);
+   if (start == end - 1) {
+      /* Base case.  Just emit the load/store op */
+      nir_deref_array direct = *arr;
+      direct.deref_array_type = nir_deref_array_type_direct;
+      direct.base_offset += start;
+      direct.indirect = NIR_SRC_INIT;
+
+      arr_parent->child = &direct.deref;
+      emit_load_store(b, orig_instr, deref, &arr->deref, dest, src);
+      arr_parent->child = &arr->deref;
+   } else {
+      int mid = start + (end - start) / 2;
+
+      nir_ssa_def *then_dest, *else_dest;
+
+      nir_if *if_stmt = nir_if_create(b->shader);
+      if_stmt->condition = nir_src_for_ssa(nir_ilt(b, arr->indirect.ssa,
+                                                      nir_imm_int(b, mid)));
+      nir_cf_node_insert(b->cursor, &if_stmt->cf_node);
+
+      b->cursor = nir_after_cf_list(&if_stmt->then_list);
+      emit_indirect_load_store(b, orig_instr, deref, arr_parent,
+                               start, mid, &then_dest, src);
+
+      b->cursor = nir_after_cf_list(&if_stmt->else_list);
+      emit_indirect_load_store(b, orig_instr, deref, arr_parent,
+                               mid, end, &else_dest, src);
+
+      b->cursor = nir_after_cf_node(&if_stmt->cf_node);
+
+      if (src == NULL) {
+         /* We're a load.  We need to insert a phi node */
+         nir_phi_instr *phi = nir_phi_instr_create(b->shader);
+         nir_ssa_dest_init(&phi->instr, &phi->dest,
+                           then_dest->num_components, NULL);
+
+         nir_phi_src *src0 = ralloc(phi, nir_phi_src);
+         src0->pred = nir_cf_node_as_block(nir_if_last_then_node(if_stmt));
+         src0->src = nir_src_for_ssa(then_dest);
+         exec_list_push_tail(&phi->srcs, &src0->node);
+
+         nir_phi_src *src1 = ralloc(phi, nir_phi_src);
+         src1->pred = nir_cf_node_as_block(nir_if_last_else_node(if_stmt));
+         src1->src = nir_src_for_ssa(else_dest);
+         exec_list_push_tail(&phi->srcs, &src1->node);
+
+         nir_builder_instr_insert(b, &phi->instr);
+         *dest = &phi->dest.ssa;
+      }
+   }
+}
+
+static void
+emit_load_store(nir_builder *b, nir_intrinsic_instr *orig_instr,
+                nir_deref_var *deref, nir_deref *tail,
+                nir_ssa_def **dest, nir_ssa_def *src)
+{
+   for (; tail->child; tail = tail->child) {
+      if (tail->child->deref_type != nir_deref_type_array)
+         continue;
+
+      nir_deref_array *arr = nir_deref_as_array(tail->child);
+      if (arr->deref_array_type != nir_deref_array_type_indirect)
+         continue;
+
+      int length = glsl_get_length(tail->type);
+
+      emit_indirect_load_store(b, orig_instr, deref, tail, -arr->base_offset,
+                               length - arr->base_offset, dest, src);
+      return;
+   }
+
+   assert(tail && tail->child == NULL);
+
+   /* We reached the end of the deref chain.  Emit the instruction */
+
+   if (src == NULL) {
+      /* This is a load instruction */
+      nir_intrinsic_instr *load =
+         nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_var);
+      load->num_components = orig_instr->num_components;
+      load->variables[0] =
+         nir_deref_as_var(nir_copy_deref(load, &deref->deref));
+      nir_ssa_dest_init(&load->instr, &load->dest,
+                        load->num_components, NULL);
+      nir_builder_instr_insert(b, &load->instr);
+      *dest = &load->dest.ssa;
+   } else {
+      /* This is a store instruction */
+      nir_intrinsic_instr *store =
+         nir_intrinsic_instr_create(b->shader, nir_intrinsic_store_var);
+      store->num_components = orig_instr->num_components;
+      nir_intrinsic_set_write_mask(store, nir_intrinsic_write_mask(orig_instr));
+      store->variables[0] =
+         nir_deref_as_var(nir_copy_deref(store, &deref->deref));
+      store->src[0] = nir_src_for_ssa(src);
+      nir_builder_instr_insert(b, &store->instr);
+   }
+}
+
+static bool
+deref_has_indirect(nir_deref_var *deref)
+{
+   for (nir_deref *tail = deref->deref.child; tail; tail = tail->child) {
+      if (tail->deref_type != nir_deref_type_array)
+         continue;
+
+      nir_deref_array *arr = nir_deref_as_array(tail);
+      if (arr->deref_array_type == nir_deref_array_type_indirect)
+         return true;
+   }
+
+   return false;
+}
+
+struct lower_indirect_state {
+   nir_builder builder;
+   uint32_t mode_mask;
+   bool progress;
+};
+
+static bool
+lower_indirect_block(nir_block *block, void *void_state)
+{
+   struct lower_indirect_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);
+      if (intrin->intrinsic != nir_intrinsic_load_var &&
+          intrin->intrinsic != nir_intrinsic_store_var)
+         continue;
+
+      if (!deref_has_indirect(intrin->variables[0]))
+         continue;
+
+      /* Only lower variables whose mode is in the mask */
+      if (!(state->mode_mask & (1 << intrin->variables[0]->var->data.mode)))
+         continue;
+
+      state->builder.cursor = nir_before_instr(&intrin->instr);
+
+      if (intrin->intrinsic == nir_intrinsic_load_var) {
+         nir_ssa_def *result;
+         emit_load_store(&state->builder, intrin, intrin->variables[0],
+                         &intrin->variables[0]->deref, &result, NULL);
+         nir_ssa_def_rewrite_uses(&intrin->dest.ssa, nir_src_for_ssa(result));
+      } else {
+         assert(intrin->src[0].is_ssa);
+         emit_load_store(&state->builder, intrin, intrin->variables[0],
+                         &intrin->variables[0]->deref, NULL, intrin->src[0].ssa);
+      }
+      nir_instr_remove(&intrin->instr);
+      state->progress = true;
+   }
+
+   return true;
+}
+
+static bool
+lower_indirects_impl(nir_function_impl *impl, uint32_t mode_mask)
+{
+   struct lower_indirect_state state;
+
+   state.progress = false;
+   state.mode_mask = mode_mask;
+   nir_builder_init(&state.builder, impl);
+
+   nir_foreach_block(impl, lower_indirect_block, &state);
+
+   if (state.progress)
+      nir_metadata_preserve(impl, nir_metadata_none);
+
+   return state.progress;
+}
+
+/** Lowers indirect variable loads/stores to direct loads/stores.
+ *
+ * The pass works by replacing any indirect load or store with an if-ladder
+ * that does a binary search on the array index.
+ */
+bool
+nir_lower_indirect_derefs(nir_shader *shader, uint32_t mode_mask)
+{
+   bool progress = false;
+
+   nir_foreach_function(shader, function) {
+      if (function->impl)
+         progress = lower_indirects_impl(function->impl, mode_mask) || progress;
+   }
+
+   return progress;
+}