[turbofan] Initial support for escape analysis.

test/mjsunit/compiler/escape-analysis-7.js

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-if (this.Worker) {
-  var workerScript =
-    `var w = new Worker('postMessage(42)');
-     onmessage = function(parentMsg) {
-       w.postMessage(parentMsg);
-       var childMsg = w.getMessage();
-       postMessage(childMsg);
-     };`;
+// Flags: --allow-natives-syntax --turbo-escape
+//
 
-  var w = new Worker(workerScript);
-  w.postMessage(9);
-  assertEquals(42, w.getMessage());
+function f(a) {
+  "use strict";
+  return arguments;
 }
+
+function g(a) {
+  "use strict";
+  var x = f(1,2,3);
+  if (a) {
+    x[1] = 5;
+  } else {
+    x[1] = 7;
+  }
+
+  return x[1];
+}
+
+assertEquals(7, g());
+assertEquals(7, g());
+%OptimizeFunctionOnNextCall(g);
+assertEquals(7, g());