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

pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart

Index: pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart
diff --git a/pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart b/pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart
index 6b4b60e06ab53dae05e9ead2170935c214a39c8a..dc1d7336a274ec57d00653e8bf564677a112cc7c 100644
--- a/pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart
+++ b/pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart
@@ -519,7 +519,8 @@ class ASTEmitter
     // that may occur in expression context, but could not be inlined anywhere.
     if (stmt.variable.element is FunctionElement &&
         stmt.value is tree.FunctionExpression &&
-        !context.declaredVariables.contains(stmt.variable)) {
+        !context.declaredVariables.contains(stmt.variable) &&
+        stmt.variable.writeCount == 1) {
       tree.FunctionExpression functionExp = stmt.value;
       FunctionExpression function =
           makeSubFunction(functionExp.definition, context);