Add ir_loop to represent loops

This touches a lot of files because everything derived from ir_visitor
has to be updated.  This is the primary disadvantage of the visitor pattern.

ir.h

@@ -287,6 +287,44 @@ public:
 };
 
 
+/**
+ * IR instruction representing a high-level loop structure.
+ */
+class ir_loop : public ir_instruction {
+public:
+   ir_loop() : from(NULL), to(NULL), increment(NULL), counter(NULL)
+   {
+      /* empty */
+   }
+
+   virtual void accept(ir_visitor *v)
+   {
+      v->visit(this);
+   }
+
+   /**
+    * Get an iterator for the instructions of the loop body
+    */
+   exec_list_iterator iterator()
+   {
+      return body_instructions.iterator();
+   }
+
+   /** List of instructions that make up the body of the loop. */
+   exec_list body_instructions;
+
+   /**
+    * \name Loop counter and controls
+    */
+   /*@{*/
+   ir_rvalue *from;
+   ir_rvalue *to;
+   ir_rvalue *increment;
+   ir_variable *counter;
+   /*@}*/
+};
+
+
 class ir_assignment : public ir_rvalue {
 public:
    ir_assignment(ir_rvalue *lhs, ir_rvalue *rhs, ir_rvalue *condition);

ir_constant_expression.cpp

@@ -74,6 +74,7 @@ public:
    virtual void visit(ir_call *);
    virtual void visit(ir_return *);
    virtual void visit(ir_if *);
+   virtual void visit(ir_loop *);
    /*@}*/
 
    /**
@@ -464,3 +465,11 @@ ir_constant_visitor::visit(ir_if *ir)
    (void) ir;
    value = NULL;
 }
+
+
+void
+ir_constant_visitor::visit(ir_loop *ir)
+{
+   (void) ir;
+   value = NULL;
+}

ir_constant_folding.cpp

@@ -145,3 +145,10 @@ ir_constant_folding_visitor::visit(ir_if *ir)
    visit_exec_list(&ir->then_instructions, this);
    visit_exec_list(&ir->else_instructions, this);
 }
+
+
+void
+ir_constant_folding_visitor::visit(ir_loop *ir)
+{
+   (void) ir;
+}

ir_constant_folding.h

@@ -58,5 +58,6 @@ public:
    virtual void visit(ir_call *);
    virtual void visit(ir_return *);
    virtual void visit(ir_if *);
+   virtual void visit(ir_loop *);
    /*@}*/
 };

ir_print_visitor.cpp

@@ -294,3 +294,28 @@ ir_print_visitor::visit(ir_if *ir)
    }
    printf("))\n");
 }
+
+
+void
+ir_print_visitor::visit(ir_loop *ir)
+{
+   printf("(loop (");
+   if (ir->counter != NULL)
+      ir->counter->accept(this);
+   printf(") (");
+   if (ir->from != NULL)
+      ir->from->accept(this);
+   printf(") (");
+   if (ir->to != NULL)
+      ir->to->accept(this);
+   printf(") (");
+   if (ir->increment != NULL)
+      ir->increment->accept(this);
+   printf(") (");
+   foreach_iter(exec_list_iterator, iter, ir->body_instructions) {
+      ir_instruction *const inst = (ir_instruction *) iter.get();
+
+      inst->accept(this);
+   }
+   printf("))\n");
+}

ir_print_visitor.h

@@ -65,6 +65,7 @@ public:
    virtual void visit(ir_call *);
    virtual void visit(ir_return *);
    virtual void visit(ir_if *);
+   virtual void visit(ir_loop *);
    /*@}*/
 
 private:

ir_visitor.h

@@ -56,6 +56,7 @@ public:
    virtual void visit(class ir_call *) = 0;
    virtual void visit(class ir_return *) = 0;
    virtual void visit(class ir_if *) = 0;
+   virtual void visit(class ir_loop *) = 0;
    /*@}*/
 };