Remove layout::Cursor from the legalizer::split API.

We still use the cursor internally, but don't require callers to use it
too.

lib/cretonne/meta/gen_legalizer.py

@@ -264,12 +264,12 @@ def emit_dst_inst(node, fmt):
         # Split instructions are not emitted with the builder, but by calling
         # special functions in the `legalizer::split` module. These functions
         # will eliminate concat-split patterns.
-        fmt.line(
-                'let {} = split::{}(dfg, cfg, pos, {});'
-                .format(
-                    wrap_tup(node.defs),
-                    node.expr.inst.snake_name(),
-                    node.expr.args[0]))
+        fmt.line('let curpos = pos.position();')
+        fmt.format(
+                'let {} = split::{}(dfg, pos.layout, cfg, curpos, {});',
+                wrap_tup(node.defs),
+                node.expr.inst.snake_name(),
+                node.expr.args[0])
     else:
         if len(node.defs) == 0:
             # This node doesn't define any values, so just insert the new

lib/cretonne/src/ir/layout.rs

@@ -709,6 +709,15 @@ pub trait CursorBase {
     /// Borrow a mutable reference to the function layout that this cursor is navigating.
     fn layout_mut(&mut self) -> &mut Layout;
 
+    /// Rebuild this cursor positioned at `pos`.
+    fn at_position(mut self, pos: CursorPosition) -> Self
+    where
+        Self: Sized,
+    {
+        self.set_position(pos);
+        self
+    }
+
     /// Rebuild this cursor positioned at `inst`.
     ///
     /// This is intended to be used as a builder method:

lib/cretonne/src/legalizer/boundary.rs

@@ -331,12 +331,14 @@ fn convert_to_abi<PutArg>(
     let ty = dfg.value_type(value);
     match legalize_abi_value(ty, &arg_type) {
         ValueConversion::IntSplit => {
-            let (lo, hi) = isplit(dfg, cfg, pos, value);
+            let curpos = pos.position();
+            let (lo, hi) = isplit(dfg, pos.layout, cfg, curpos, value);
             convert_to_abi(dfg, cfg, pos, lo, put_arg);
             convert_to_abi(dfg, cfg, pos, hi, put_arg);
         }
         ValueConversion::VectorSplit => {
-            let (lo, hi) = vsplit(dfg, cfg, pos, value);
+            let curpos = pos.position();
+            let (lo, hi) = vsplit(dfg, pos.layout, cfg, curpos, value);
             convert_to_abi(dfg, cfg, pos, lo, put_arg);
             convert_to_abi(dfg, cfg, pos, hi, put_arg);
         }

lib/cretonne/src/legalizer/split.rs

@@ -64,31 +64,33 @@
 //! It is possible to have circular dependencies of EBB arguments that are never used by any real
 //! instructions. These loops will remain in the program.
 
+use cursor::{Cursor, CursorPosition};
 use flowgraph::ControlFlowGraph;
-use ir::{DataFlowGraph, Ebb, Inst, Cursor, CursorBase, Value, Type, Opcode, ValueDef,
-         InstructionData, InstBuilder};
+use ir::{self, Ebb, Inst, Value, Type, Opcode, ValueDef, InstructionData, InstBuilder};
 use std::iter;
 
 /// Split `value` into two values using the `isplit` semantics. Do this by reusing existing values
 /// if possible.
 pub fn isplit(
-    dfg: &mut DataFlowGraph,
+    dfg: &mut ir::DataFlowGraph,
+    layout: &mut ir::Layout,
     cfg: &ControlFlowGraph,
-    pos: &mut Cursor,
+    pos: CursorPosition,
     value: Value,
 ) -> (Value, Value) {
-    split_any(dfg, cfg, pos, value, Opcode::Iconcat)
+    split_any(dfg, layout, cfg, pos, value, Opcode::Iconcat)
 }
 
 /// Split `value` into halves using the `vsplit` semantics. Do this by reusing existing values if
 /// possible.
 pub fn vsplit(
-    dfg: &mut DataFlowGraph,
+    dfg: &mut ir::DataFlowGraph,
+    layout: &mut ir::Layout,
     cfg: &ControlFlowGraph,
-    pos: &mut Cursor,
+    pos: CursorPosition,
     value: Value,
 ) -> (Value, Value) {
-    split_any(dfg, cfg, pos, value, Opcode::Vconcat)
+    split_any(dfg, layout, cfg, pos, value, Opcode::Vconcat)
 }
 
 /// After splitting an EBB argument, we need to go back and fix up all of the predecessor
@@ -110,15 +112,16 @@ struct Repair {
 
 /// Generic version of `isplit` and `vsplit` controlled by the `concat` opcode.
 fn split_any(
-    dfg: &mut DataFlowGraph,
+    dfg: &mut ir::DataFlowGraph,
+    layout: &mut ir::Layout,
     cfg: &ControlFlowGraph,
-    pos: &mut Cursor,
+    pos: CursorPosition,
     value: Value,
     concat: Opcode,
 ) -> (Value, Value) {
-    let saved_pos = pos.position();
     let mut repairs = Vec::new();
-    let result = split_value(dfg, pos, value, concat, &mut repairs);
+    let mut pos = ir::Cursor::new(layout).at_position(pos);
+    let result = split_value(dfg, &mut pos, value, concat, &mut repairs);
 
     // We have split the value requested, and now we may need to fix some EBB predecessors.
     while let Some(repair) = repairs.pop() {
@@ -147,7 +150,7 @@ fn split_any(
 
             // Split the old argument, possibly causing more repairs to be scheduled.
             pos.goto_inst(inst);
-            let (lo, hi) = split_value(dfg, pos, old_arg, repair.concat, &mut repairs);
+            let (lo, hi) = split_value(dfg, &mut pos, old_arg, repair.concat, &mut repairs);
 
             // The `lo` part replaces the original argument.
             *args.get_mut(fixed_args + repair.num, &mut dfg.value_lists)
@@ -173,7 +176,6 @@ fn split_any(
         }
     }
 
-    pos.set_position(saved_pos);
     result
 }
 
@@ -184,8 +186,8 @@ fn split_any(
 ///
 /// Return the two new values representing the parts of `value`.
 fn split_value(
-    dfg: &mut DataFlowGraph,
-    pos: &mut Cursor,
+    dfg: &mut ir::DataFlowGraph,
+    pos: &mut ir::Cursor,
     value: Value,
     concat: Opcode,
     repairs: &mut Vec<Repair>,
@@ -292,7 +294,7 @@ fn add_repair(
 /// ```
 ///
 /// This function resolves `v11` to `v1` and `v12` to `v2`.
-fn resolve_splits(dfg: &DataFlowGraph, value: Value) -> Value {
+fn resolve_splits(dfg: &ir::DataFlowGraph, value: Value) -> Value {
     let value = dfg.resolve_copies(value);
 
     // Deconstruct a split instruction.
@@ -330,7 +332,7 @@ fn resolve_splits(dfg: &DataFlowGraph, value: Value) -> Value {
 ///
 /// After legalizing the instructions computing the value that was split, it is likely that we can
 /// avoid depending on the split instruction. Its input probably comes from a concatenation.
-pub fn simplify_branch_arguments(dfg: &mut DataFlowGraph, branch: Inst) {
+pub fn simplify_branch_arguments(dfg: &mut ir::DataFlowGraph, branch: Inst) {
     let mut new_args = Vec::new();
 
     for &arg in dfg.inst_args(branch) {