cps-ir: Merge variables based on set-based liveness and graph coloring.

pkg/analyzer2dart/test/end2end_data.dart

Index: pkg/analyzer2dart/test/end2end_data.dart
diff --git a/pkg/analyzer2dart/test/end2end_data.dart b/pkg/analyzer2dart/test/end2end_data.dart
index b1cb1db2687731529c69e0f5b143a75dfc27dddd..2ad4598b970b3da3b22c0cf97881395a4a9cb37e 100644
--- a/pkg/analyzer2dart/test/end2end_data.dart
+++ b/pkg/analyzer2dart/test/end2end_data.dart
@@ -256,6 +256,14 @@ main() {
   print(a);
   return a;
 }
+''', '''
+main() {
+  var a;
+  print(0);
+  a = "";
+  print(a);
+  return a;
+}
 '''),
 
     const TestSpec('''
@@ -275,6 +283,12 @@ main(a) {
   print(a);
   return a;
 }
+''', '''
+main(a) {
+  a = a ? "" : a;
+  print(a);
+  return a;
+}
 '''),
   ]),
 
@@ -741,12 +755,10 @@ main(a) {
 }
 ''', '''
 main(a) {
-  var v0 = a.iterator, i;
+  var v0 = a.iterator;
   while (v0.moveNext()) {
-    i = v0.current;
-    print(i);
-    i = 0;
-    print(i);
+    print(v0.current);
+    print(0);
   }
 }
 '''),