Remove dead code assignments and variable declarations.

This pass only works on assignments where the variable is never
referenced.  There is no code flow analysis, so it can't do a better
job of avoiding redundant assignments.

For now, the optimizer only does do_dead_code_unlinked(), so it won't
trim the builtin variable list or initializers outside of the scope of
functions.  This is because we don't have the visibility into other
functions that might get linked in in order to eliminate work on
global variables.

1 files changed, 336 insertions, 0 deletions

diff --git a/ir_dead_code.cpp b/ir_dead_code.cpp
new file mode 100644
index 0000000000..aae45d993e
--- /dev/null
+++ b/ir_dead_code.cpp
@@ -0,0 +1,336 @@
+/*
+ * Copyright © 2010 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.
+ */
+
+/**
+ * \file ir_dead_code.cpp
+ *
+ * Eliminates dead assignments and variable declarations from the code.
+ */
+
+#define NULL 0
+#include "ir.h"
+#include "ir_visitor.h"
+#include "ir_expression_flattening.h"
+#include "glsl_types.h"
+
+class variable_entry : public exec_node
+{
+public:
+   variable_entry(ir_variable *var)
+   {
+      this->var = var;
+      assign = NULL;
+      referenced = false;
+      declaration = false;
+   }
+
+   ir_variable *var; /* The key: the variable's pointer. */
+   ir_assignment *assign; /* An assignment to the variable, if any */
+   bool referenced; /* If the variable has ever been referenced. */
+   bool declaration; /* If the variable had a decl in the instruction stream */
+};
+
+class ir_dead_code_visitor : public ir_visitor {
+public:
+
+   /**
+    * \name Visit methods
+    *
+    * As typical for the visitor pattern, there must be one \c visit method for
+    * each concrete subclass of \c ir_instruction.  Virtual base classes within
+    * the hierarchy should not have \c visit methods.
+    */
+   /*@{*/
+   virtual void visit(ir_variable *);
+   virtual void visit(ir_label *);
+   virtual void visit(ir_loop *);
+   virtual void visit(ir_loop_jump *);
+   virtual void visit(ir_function_signature *);
+   virtual void visit(ir_function *);
+   virtual void visit(ir_expression *);
+   virtual void visit(ir_swizzle *);
+   virtual void visit(ir_dereference *);
+   virtual void visit(ir_assignment *);
+   virtual void visit(ir_constant *);
+   virtual void visit(ir_call *);
+   virtual void visit(ir_return *);
+   virtual void visit(ir_if *);
+   /*@}*/
+
+   variable_entry *get_variable_entry(ir_variable *var);
+
+   bool (*predicate)(ir_instruction *ir);
+   ir_instruction *base_ir;
+
+   /* List of variable_entry */
+   exec_list variable_list;
+};
+
+variable_entry *
+ir_dead_code_visitor::get_variable_entry(ir_variable *var)
+{
+   assert(var);
+   foreach_iter(exec_list_iterator, iter, this->variable_list) {
+      variable_entry *entry = (variable_entry *)iter.get();
+      if (entry->var == var)
+	 return entry;
+   }
+
+   variable_entry *entry = new variable_entry(var);
+   this->variable_list.push_tail(entry);
+   return entry;
+}
+
+void
+find_dead_code(exec_list *instructions, ir_dead_code_visitor *v)
+{
+   foreach_iter(exec_list_iterator, iter, *instructions) {
+      ir_instruction *ir = (ir_instruction *)iter.get();
+
+      ir->accept(v);
+   }
+}
+
+void
+ir_dead_code_visitor::visit(ir_variable *ir)
+{
+   variable_entry *entry = this->get_variable_entry(ir);
+   if (entry) {
+      entry->declaration = true;
+   }
+}
+
+
+void
+ir_dead_code_visitor::visit(ir_label *ir)
+{
+   ir->signature->accept(this);
+}
+
+void
+ir_dead_code_visitor::visit(ir_loop *ir)
+{
+   find_dead_code(&ir->body_instructions, this);
+   if (ir->from)
+      ir->from->accept(this);
+   if (ir->to)
+      ir->to->accept(this);
+   if (ir->increment)
+      ir->increment->accept(this);
+}
+
+void
+ir_dead_code_visitor::visit(ir_loop_jump *ir)
+{
+   (void) ir;
+}
+
+
+void
+ir_dead_code_visitor::visit(ir_function_signature *ir)
+{
+   find_dead_code(&ir->body, this);
+}
+
+void
+ir_dead_code_visitor::visit(ir_function *ir)
+{
+   (void) ir;
+}
+
+void
+ir_dead_code_visitor::visit(ir_expression *ir)
+{
+   unsigned int operand;
+
+   for (operand = 0; operand < ir->get_num_operands(); operand++) {
+      ir->operands[operand]->accept(this);
+   }
+}
+
+
+void
+ir_dead_code_visitor::visit(ir_swizzle *ir)
+{
+   ir->val->accept(this);
+}
+
+
+void
+ir_dead_code_visitor::visit(ir_dereference *ir)
+{
+   ir_variable *var;
+
+   if (ir->mode == ir_dereference::ir_reference_array) {
+      ir->selector.array_index->accept(this);
+   }
+
+   var = ir->var->as_variable();
+   if (var) {
+      variable_entry *entry = this->get_variable_entry(var);
+      entry->referenced = true;
+   } else {
+      ir->var->accept(this);
+   }
+}
+
+void
+ir_dead_code_visitor::visit(ir_assignment *ir)
+{
+   ir_instruction *lhs = ir->lhs;
+
+   /* Walk through the LHS and mark references for variables used in
+    * array indices but not for the assignment dereference.
+    */
+   while (lhs) {
+      if (lhs->as_variable())
+	 break;
+
+      ir_dereference *deref = lhs->as_dereference();
+      if (deref) {
+	 if (deref->mode == ir_dereference::ir_reference_array)
+	    deref->selector.array_index->accept(this);
+	 lhs = deref->var;
+      } else {
+	 ir_swizzle *swiz = lhs->as_swizzle();
+
+	 lhs = swiz->val;
+      }
+   }
+
+   ir->rhs->accept(this);
+   if (ir->condition)
+      ir->condition->accept(this);
+
+   variable_entry *entry;
+   entry = this->get_variable_entry(lhs->as_variable());
+   if (entry) {
+      if (entry->assign == NULL)
+	 entry->assign = ir;
+   }
+}
+
+
+void
+ir_dead_code_visitor::visit(ir_constant *ir)
+{
+   (void) ir;
+}
+
+
+void
+ir_dead_code_visitor::visit(ir_call *ir)
+{
+   foreach_iter(exec_list_iterator, iter, *ir) {
+      ir_rvalue *param = (ir_rvalue *)iter.get();
+
+      /* FINISHME: handle out values. */
+      param->accept(this);
+   }
+
+   /* Ignore the callee.  Function bodies will get handled when they're
+    * encountered at the top level instruction stream and spawn their
+    * own dead code visitor.
+    */
+}
+
+
+void
+ir_dead_code_visitor::visit(ir_return *ir)
+{
+   ir->get_value()->accept(this);
+}
+
+
+void
+ir_dead_code_visitor::visit(ir_if *ir)
+{
+   ir->condition->accept(this);
+
+   find_dead_code(&ir->then_instructions, this);
+   find_dead_code(&ir->else_instructions, this);
+}
+
+/**
+ * Do a dead code pass over instructions and everything that instructions
+ * references.
+ *
+ * Note that this will remove assignments to globals, so it is not suitable
+ * for usage on an unlinked instruction stream.
+ */
+bool
+do_dead_code(exec_list *instructions)
+{
+   ir_dead_code_visitor v;
+   bool progress = false;
+
+   find_dead_code(instructions, &v);
+
+   foreach_iter(exec_list_iterator, iter, v.variable_list) {
+      variable_entry *entry = (variable_entry *)iter.get();
+
+      if (entry->referenced || !entry->declaration)
+	 continue;
+
+      if (entry->assign) {
+	 /* Remove a single dead assignment to the variable we found.
+	  * Don't do so if it's a shader output, though.
+	  */
+	 if (!entry->var->shader_out) {
+	    entry->assign->remove();
+	    progress = true;
+	 }
+      } else {
+	 /* If there are no assignments or references to the variable left,
+	  * then we can remove its declaration.
+	  */
+	 entry->var->remove();
+	 progress = true;
+      }
+   }
+   return progress;
+}
+
+/**
+ * Does a dead code pass on the functions present in the instruction stream.
+ *
+ * This is suitable for use while the program is not linked, as it will
+ * ignore variable declarations (and the assignments to them) for variables
+ * with global scope.
+ */
+bool
+do_dead_code_unlinked(exec_list *instructions)
+{
+   bool progress = false;
+
+   foreach_iter(exec_list_iterator, iter, *instructions) {
+      ir_instruction *ir = (ir_instruction *)iter.get();
+      ir_label *label = ir->as_label();
+      if (label) {
+	 if (do_dead_code(&label->signature->body))
+	    progress = true;
+      }
+   }
+
+   return progress;
+}