Move the 'ins' method to DataFlowGraph.

This given us better symmetry between the replace and insert builder operations:

    dfg.replace(inst).iadd(x, y)
    dfg.ins(cursor).imul(x, y)

lib/cretonne/src/cfg.rs

@@ -184,16 +184,16 @@ mod tests {
         let jmp_ebb1_ebb2;
 
         {
-            let mut cur = Cursor::new(&mut func.layout);
             let dfg = &mut func.dfg;
+            let cur = &mut Cursor::new(&mut func.layout);
 
             cur.insert_ebb(ebb0);
-            br_ebb0_ebb2 = cur.ins(dfg).brnz(cond, ebb2, VariableArgs::new());
-            jmp_ebb0_ebb1 = cur.ins(dfg).jump(ebb1, VariableArgs::new());
+            br_ebb0_ebb2 = dfg.ins(cur).brnz(cond, ebb2, VariableArgs::new());
+            jmp_ebb0_ebb1 = dfg.ins(cur).jump(ebb1, VariableArgs::new());
 
             cur.insert_ebb(ebb1);
-            br_ebb1_ebb1 = cur.ins(dfg).brnz(cond, ebb1, VariableArgs::new());
-            jmp_ebb1_ebb2 = cur.ins(dfg).jump(ebb2, VariableArgs::new());
+            br_ebb1_ebb1 = dfg.ins(cur).brnz(cond, ebb1, VariableArgs::new());
+            jmp_ebb1_ebb2 = dfg.ins(cur).jump(ebb2, VariableArgs::new());
 
             cur.insert_ebb(ebb2);
         }

lib/cretonne/src/dominator_tree.rs

@@ -142,18 +142,18 @@ mod test {
         let jmp_ebb1_ebb2;
 
         {
-            let mut cur = Cursor::new(&mut func.layout);
             let dfg = &mut func.dfg;
+            let cur = &mut Cursor::new(&mut func.layout);
 
             cur.insert_ebb(ebb3);
-            jmp_ebb3_ebb1 = cur.ins(dfg).jump(ebb1, VariableArgs::new());
+            jmp_ebb3_ebb1 = dfg.ins(cur).jump(ebb1, VariableArgs::new());
 
             cur.insert_ebb(ebb1);
-            br_ebb1_ebb0 = cur.ins(dfg).brnz(cond, ebb0, VariableArgs::new());
-            jmp_ebb1_ebb2 = cur.ins(dfg).jump(ebb2, VariableArgs::new());
+            br_ebb1_ebb0 = dfg.ins(cur).brnz(cond, ebb0, VariableArgs::new());
+            jmp_ebb1_ebb2 = dfg.ins(cur).jump(ebb2, VariableArgs::new());
 
             cur.insert_ebb(ebb2);
-            cur.ins(dfg).jump(ebb0, VariableArgs::new());
+            dfg.ins(cur).jump(ebb0, VariableArgs::new());
 
             cur.insert_ebb(ebb0);
         }

lib/cretonne/src/ir/dfg.rs

@@ -5,7 +5,8 @@ use ir::entities::{NO_VALUE, ExpandedValue};
 use ir::instructions::{InstructionData, CallInfo};
 use ir::extfunc::ExtFuncData;
 use entity_map::{EntityMap, PrimaryEntityData};
-use ir::builder::ReplaceBuilder;
+use ir::builder::{InsertBuilder, ReplaceBuilder};
+use ir::layout::Cursor;
 
 use std::mem;
 use std::ops::{Index, IndexMut};
@@ -271,6 +272,13 @@ impl DataFlowGraph {
         total_results
     }
 
+    /// Create an `InsertBuilder` that will insert an instruction at the cursor's current position.
+    pub fn ins<'c, 'fc: 'c, 'fd>(&'fd mut self,
+                                 at: &'c mut Cursor<'fc>)
+                                 -> InsertBuilder<'c, 'fc, 'fd> {
+        InsertBuilder::new(self, at)
+    }
+
     /// Create a `ReplaceBuilder` that will replace `inst` with a new instruction in place.
     pub fn replace(&mut self, inst: Inst) -> ReplaceBuilder {
         ReplaceBuilder::new(self, inst)

lib/cretonne/src/ir/layout.rs

@@ -6,8 +6,6 @@
 use std::iter::{Iterator, IntoIterator};
 use entity_map::{EntityMap, EntityRef};
 use ir::entities::{Ebb, NO_EBB, Inst, NO_INST};
-use ir::dfg::DataFlowGraph;
-use ir::builder::InsertBuilder;
 
 /// The `Layout` struct determines the layout of EBBs and instructions in a function. It does not
 /// contain definitions of instructions or EBBs, but depends on `Inst` and `Ebb` entity references
@@ -617,11 +615,6 @@ impl<'f> Cursor<'f> {
         }
     }
 
-    /// Create a builder for inserting an instruction at the current position.
-    pub fn ins<'c, 'fd>(&'c mut self, dfg: &'fd mut DataFlowGraph) -> InsertBuilder<'c, 'f, 'fd> {
-        InsertBuilder::new(dfg, self)
-    }
-
     /// Insert an EBB at the current position and switch to it.
     ///
     /// As far as possible, this method behaves as if the EBB header were an instruction inserted