Give Builder a Cursor.

The Builder keeps track of a position in the layout and inserts new
instructions there.

Add insert_ebb() and ebb() methods to Builder.

Use Builder in the cfg tests.

src/libcretonne/ir/builder.rs

@@ -4,20 +4,48 @@
 //! function. Many of its methods are generated from the meta language instruction definitions.
 
 use ir::{types, instructions};
-use ir::{InstructionData, DataFlowGraph};
+use ir::{InstructionData, DataFlowGraph, Cursor};
 use ir::{Opcode, Type, Inst, Value, Ebb, JumpTable, VariableArgs, FuncRef};
 use ir::immediates::{Imm64, Uimm8, Ieee32, Ieee64, ImmVector};
 use ir::condcodes::{IntCC, FloatCC};
 
+/// Instruction builder.
+///
+/// A `Builder` holds mutable references to a data flow graph and a layout cursor. It provides
+/// convenience method for creating and inserting instructions at the current cursor position.
 pub struct Builder<'a> {
-    dfg: &'a mut DataFlowGraph,
+    pub dfg: &'a mut DataFlowGraph,
+    pub pos: &'a mut Cursor<'a>,
 }
 
 impl<'a> Builder<'a> {
+    /// Create a new builder which inserts instructions at `pos`.
+    /// The `dfg` and `pos.layout` references should be from the same `Function`.
+    pub fn new(dfg: &'a mut DataFlowGraph, pos: &'a mut Cursor<'a>) -> Builder<'a> {
+        Builder {
+            dfg: dfg,
+            pos: pos,
+        }
+    }
+
+    /// Create and insert an EBB. Further instructions will be inserted into the new EBB.
+    pub fn ebb(&mut self) -> Ebb {
+        let ebb = self.dfg.make_ebb();
+        self.insert_ebb(ebb);
+        ebb
+    }
+
+    /// Insert an existing EBB at the current position. Further instructions will be inserted into
+    /// the new EBB.
+    pub fn insert_ebb(&mut self, ebb: Ebb) {
+        self.pos.insert_ebb(ebb);
+    }
+
     // Create and insert an instruction.
     // This method is used by the generated format-specific methods.
     fn insert_inst(&mut self, data: InstructionData) -> Inst {
         let inst = self.dfg.make_inst(data);
+        self.pos.insert_inst(inst);
         inst
     }
 }