Check for phi-uses of arguments object before eliminating dead phi's.

test/mjsunit/regress/regress-1582.js

+// Copyright 2011 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
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+//     * Redistributions in binary form must reproduce the above
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+
+// Flags: --allow-natives-syntax
+
+function f(restIsArray, rest) {
+  var arr;
+  if (typeof rest === "object" && (rest instanceof Array)) {
+    arr = rest;
+  } else {
+    arr = arguments;
+  }
+  var i = arr.length;
+  while (--i >= 0) arr[i];
+  var arrIsArguments = (arr[1] !== rest);
+  assertEquals(restIsArray, arrIsArguments);
+}
+
+f(false, 'b', 'c');
+f(false, 'b', 'c');
+f(false, 'b', 'c');
+%OptimizeFunctionOnNextCall(f);
+f(true, ['b', 'c']);