Promote the BasicBlock tuple to a real struct;

It makes reading code that uses it easier to understand.

lib/codegen/src/licm.rs

@@ -3,7 +3,7 @@
 use cursor::{Cursor, FuncCursor};
 use dominator_tree::DominatorTree;
 use entity::{EntityList, ListPool};
-use flowgraph::ControlFlowGraph;
+use flowgraph::{BasicBlock, ControlFlowGraph};
 use fx::FxHashSet;
 use ir::{DataFlowGraph, Ebb, Function, Inst, InstBuilder, Layout, Opcode, Type, Value};
 use loop_analysis::{Loop, LoopAnalysis};
@@ -77,7 +77,10 @@ fn create_pre_header(
     for typ in header_args_types {
         pre_header_args_value.push(func.dfg.append_ebb_param(pre_header, typ), pool);
     }
-    for (_, last_inst) in cfg.pred_iter(header) {
+    for BasicBlock {
+        inst: last_inst, ..
+    } in cfg.pred_iter(header)
+    {
         // We only follow normal edges (not the back edges)
         if !domtree.dominates(header, last_inst, &func.layout) {
             change_branch_jump_destination(last_inst, pre_header, func);
@@ -106,7 +109,11 @@ fn has_pre_header(
 ) -> Option<(Ebb, Inst)> {
     let mut result = None;
     let mut found = false;
-    for (pred_ebb, last_inst) in cfg.pred_iter(header) {
+    for BasicBlock {
+        ebb: pred_ebb,
+        inst: last_inst,
+    } in cfg.pred_iter(header)
+    {
         // We only count normal edges (not the back edges)
         if !domtree.dominates(header, last_inst, layout) {
             if found {