Add a Cursor::ins() method which constructs a Builder.

Rewrite Builder uses in test cases to use this method and construct a
new builder for each instruction. This pattern allows us to change the
InstBuilder trait to a one-shot implementation that can only create a
single instruction.

Don't re-export the Builder struct, it is less important than the
InstBuilder trait, and we may get more implementations.

lib/cretonne/src/cfg.rs

@@ -139,7 +139,7 @@ impl ControlFlowGraph {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use ir::{Function, Builder, InstBuilder, Cursor, VariableArgs, types};
+    use ir::{Function, InstBuilder, Cursor, VariableArgs, types};
 
     #[test]
     fn empty() {
@@ -184,18 +184,18 @@ mod tests {
         let jmp_ebb1_ebb2;
 
         {
-            let mut cursor = Cursor::new(&mut func.layout);
-            let mut b = Builder::new(&mut func.dfg, &mut cursor);
+            let mut cur = Cursor::new(&mut func.layout);
+            let dfg = &mut func.dfg;
 
-            b.insert_ebb(ebb0);
-            br_ebb0_ebb2 = b.brnz(cond, ebb2, VariableArgs::new());
-            jmp_ebb0_ebb1 = b.jump(ebb1, VariableArgs::new());
+            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());
 
-            b.insert_ebb(ebb1);
-            br_ebb1_ebb1 = b.brnz(cond, ebb1, VariableArgs::new());
-            jmp_ebb1_ebb2 = b.jump(ebb2, 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());
 
-            b.insert_ebb(ebb2);
+            cur.insert_ebb(ebb2);
         }
 
         let cfg = ControlFlowGraph::new(&func);

lib/cretonne/src/dominator_tree.rs

@@ -116,7 +116,7 @@ impl DominatorTree {
 #[cfg(test)]
 mod test {
     use super::*;
-    use ir::{Function, Builder, InstBuilder, Cursor, VariableArgs, types};
+    use ir::{Function, InstBuilder, Cursor, VariableArgs, types};
     use ir::entities::NO_INST;
     use cfg::ControlFlowGraph;
 
@@ -142,20 +142,20 @@ mod test {
         let jmp_ebb1_ebb2;
 
         {
-            let mut cursor = Cursor::new(&mut func.layout);
-            let mut b = Builder::new(&mut func.dfg, &mut cursor);
+            let mut cur = Cursor::new(&mut func.layout);
+            let dfg = &mut func.dfg;
 
-            b.insert_ebb(ebb3);
-            jmp_ebb3_ebb1 = b.jump(ebb1, VariableArgs::new());
+            cur.insert_ebb(ebb3);
+            jmp_ebb3_ebb1 = cur.ins(dfg).jump(ebb1, VariableArgs::new());
 
-            b.insert_ebb(ebb1);
-            br_ebb1_ebb0 = b.brnz(cond, ebb0, VariableArgs::new());
-            jmp_ebb1_ebb2 = b.jump(ebb2, 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());
 
-            b.insert_ebb(ebb2);
-            b.jump(ebb0, VariableArgs::new());
+            cur.insert_ebb(ebb2);
+            cur.ins(dfg).jump(ebb0, VariableArgs::new());
 
-            b.insert_ebb(ebb0);
+            cur.insert_ebb(ebb0);
         }
 
         let cfg = ControlFlowGraph::new(&func);

lib/cretonne/src/ir/layout.rs

@@ -6,6 +6,8 @@
 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::Builder;
 
 /// 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
@@ -615,6 +617,11 @@ 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) -> Builder<'c, 'f, 'fd> {
+        Builder::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

lib/cretonne/src/ir/mod.rs

@@ -24,4 +24,4 @@ pub use ir::jumptable::JumpTableData;
 pub use ir::dfg::{DataFlowGraph, ValueDef};
 pub use ir::layout::{Layout, Cursor};
 pub use ir::function::Function;
-pub use ir::builder::{Builder, InstBuilder};
+pub use ir::builder::InstBuilder;