nir: add an SSA-based dead code elimination pass

v2: Jason Ekstrand <jason.ekstrand@intel.com>:
   whitespace fixes

src/glsl/Makefile.sources

@@ -26,6 +26,7 @@ NIR_FILES = \
 	$(GLSL_SRCDIR)/nir/nir_opcodes.c \
 	$(GLSL_SRCDIR)/nir/nir_opcodes.h \
 	$(GLSL_SRCDIR)/nir/nir_opt_copy_propagate.c \
+	$(GLSL_SRCDIR)/nir/nir_opt_dce.c \
 	$(GLSL_SRCDIR)/nir/nir_opt_global_to_local.c \
 	$(GLSL_SRCDIR)/nir/nir_print.c \
 	$(GLSL_SRCDIR)/nir/nir_remove_dead_variables.c \

src/glsl/nir/nir.h

@@ -397,6 +397,9 @@ typedef struct {
    struct exec_node node;
    nir_instr_type type;
    struct nir_block *block;
+
+   /* flag for dead code elimination (see nir_opt_dce.c) */
+   bool live;
 } nir_instr;
 
 #define nir_instr_next(instr) \
@@ -1296,6 +1299,9 @@ bool nir_opt_global_to_local(nir_shader *shader);
 bool nir_copy_prop_impl(nir_function_impl *impl);
 bool nir_copy_prop(nir_shader *shader);
 
+bool nir_opt_dce_impl(nir_function_impl *impl);
+bool nir_opt_dce(nir_shader *shader);
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif

src/glsl/nir/nir_opt_dce.c

@@ -0,0 +1,184 @@
+/*
+ * 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:
+ *    Connor Abbott (cwabbott0@gmail.com)
+ *
+ */
+
+#include "nir.h"
+
+/* SSA-based mark-and-sweep dead code elimination */
+
+typedef struct {
+   struct exec_node node;
+   nir_instr *instr;
+} worklist_elem;
+
+static void
+worklist_push(struct exec_list *worklist, nir_instr *instr)
+{
+   worklist_elem *elem = ralloc(worklist, worklist_elem);
+   elem->instr = instr;
+   instr->live = true;
+   exec_list_push_tail(worklist, &elem->node);
+}
+
+static nir_instr *
+worklist_pop(struct exec_list *worklist)
+{
+   struct exec_node *node = exec_list_pop_head(worklist);
+   worklist_elem *elem = exec_node_data(worklist_elem, node, node);
+   return elem->instr;
+}
+
+static bool
+mark_live_cb(nir_src *src, void *_state)
+{
+   struct exec_list *worklist = (struct exec_list *) _state;
+
+   if (src->is_ssa && !src->ssa->parent_instr->live) {
+      worklist_push(worklist, src->ssa->parent_instr);
+   }
+
+   return true;
+}
+
+static void
+init_instr(nir_instr *instr, struct exec_list *worklist)
+{
+   nir_alu_instr *alu_instr;
+   nir_intrinsic_instr *intrin_instr;
+   nir_tex_instr *tex_instr;
+   nir_load_const_instr *load_const_instr;
+
+   instr->live = false;
+
+   switch (instr->type) {
+   case nir_instr_type_call:
+   case nir_instr_type_jump:
+      worklist_push(worklist, instr);
+      break;
+
+   case nir_instr_type_alu:
+      alu_instr = nir_instr_as_alu(instr);
+      if (!alu_instr->dest.dest.is_ssa)
+         worklist_push(worklist, instr);
+      break;
+
+   case nir_instr_type_intrinsic:
+      intrin_instr = nir_instr_as_intrinsic(instr);
+      if (nir_intrinsic_infos[intrin_instr->intrinsic].flags &
+          NIR_INTRINSIC_CAN_ELIMINATE) {
+         if (nir_intrinsic_infos[intrin_instr->intrinsic].has_dest &&
+             !intrin_instr->dest.is_ssa) {
+            worklist_push(worklist, instr);
+         }
+      } else {
+         worklist_push(worklist, instr);
+      }
+      break;
+
+   case nir_instr_type_texture:
+      tex_instr = nir_instr_as_texture(instr);
+      if (!tex_instr->dest.is_ssa)
+         worklist_push(worklist, instr);
+      break;
+
+   case nir_instr_type_load_const:
+      load_const_instr = nir_instr_as_load_const(instr);
+      if (!load_const_instr->dest.is_ssa)
+         worklist_push(worklist, instr);
+      break;
+
+   default:
+      break;
+   }
+}
+
+static bool
+init_block_cb(nir_block *block, void *_state)
+{
+   struct exec_list *worklist = (struct exec_list *) _state;
+
+   nir_foreach_instr(block, instr)
+      init_instr(instr, worklist);
+
+   if (block->cf_node.node.next != NULL && /* check that we aren't the end node */
+       !nir_cf_node_is_last(&block->cf_node) &&
+       nir_cf_node_next(&block->cf_node)->type == nir_cf_node_if) {
+      nir_if *if_stmt = nir_cf_node_as_if(nir_cf_node_next(&block->cf_node));
+      if (if_stmt->condition.is_ssa &&
+          !if_stmt->condition.ssa->parent_instr->live)
+         worklist_push(worklist, if_stmt->condition.ssa->parent_instr);
+   }
+
+   return true;
+}
+
+static bool
+delete_block_cb(nir_block *block, void *_state)
+{
+   bool *progress = (bool *) _state;
+
+   nir_foreach_instr_safe(block, instr) {
+      if (!instr->live) {
+         nir_instr_remove(instr);
+         *progress = true;
+      }
+   }
+
+   return true;
+}
+
+bool
+nir_opt_dce_impl(nir_function_impl *impl)
+{
+   struct exec_list *worklist = ralloc(NULL, struct exec_list);
+   exec_list_make_empty(worklist);
+
+   nir_foreach_block(impl, init_block_cb, worklist);
+
+   while (!exec_list_is_empty(worklist)) {
+      nir_instr *instr = worklist_pop(worklist);
+      nir_foreach_src(instr, mark_live_cb, worklist);
+   }
+
+   ralloc_free(worklist);
+
+   bool progress = false;
+   nir_foreach_block(impl, delete_block_cb, &progress);
+
+   return progress;
+}
+
+bool
+nir_opt_dce(nir_shader *shader)
+{
+   bool progress = false;
+   nir_foreach_overload(shader, overload) {
+      if (overload->impl && nir_opt_dce_impl(overload->impl))
+         progress = true;
+   }
+
+   return progress;
+}