diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/expression-autopsy.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/expression-autopsy.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,116 @@
+load(libdir + "asserts.js");
+
+function check_one(expected, f, err) {
+    var failed = true;
+    try {
+        f();
+        failed = false;
+    } catch (ex) {
+        var s = ex.toString();
+        assertEq(s.slice(0, 11), "TypeError: ");
+        assertEq(s.slice(-err.length), err, "" + f);
+        assertEq(s.slice(11, -err.length), expected);
+    }
+    if (!failed)
+        throw new Error("didn't fail");
+}
+ieval = eval;
+function check(expr, expected=expr) {
+    var end, err;
+    for ([end, err] of [[".random_prop", " is undefined"], ["()", " is not a function"]]) {
+        var statement = "o = {};" + expr + end, f;
+        var cases = [
+            // Global scope
+            function () {
+                ieval("var o, undef;\n" + statement);
+            },
+            // Function scope
+            Function("o", "undef", statement),
+            // Function scope with variables
+            Function("var o, undef;\n" + statement),
+            // Function scope with some different arugments
+            Function("arg1", "arg2", "var o, undef;\n" + statement),
+            // Deoptimized function scope
+            Function("o", "undef", "with (Object) {}\n" + statement),
+            // Inside with
+            Function("with (Object) { " + statement + " }"),
+            // Closure
+            Function("o", "undef", "function myfunc() { return o + undef; }\n" + statement),
+            // Let definitions in a block
+            Function("{ let o, undef;\n" + statement + "}"),
+            // Let block
+            Function("let (o, undef) { " + statement + " }"),
+            // Let block with some other variables
+            Function("var v1, v2; let (o, undef) { " + statement + " }"),
+            // Shadowed let block
+            Function("o", "undef", "let (o, undef) { " + statement + " }"),
+            // Let in a switch
+            Function("var x = 4; switch (x) { case 4: let o, undef;" + statement + "\ncase 6: break;}"),
+            // The more lets the merrier
+            Function("let (x=4, y=5) { x + y; }\nlet (a, b, c) { a + b - c; }\nlet (o, undef) {" + statement + " }"),
+            // Let destructuring
+            Function("o", "undef", "let ([] = 4) {} let (o, undef) { " + statement + " }"),
+            // Try-catch blocks
+            Function("o", "undef", "try { let q = 4; try { let p = 4; } catch (e) {} } catch (e) {} let (o, undef) { " + statement + " }")
+        ];
+
+        try {
+            // Let in for-in
+            check_one(expected,
+                      Function("var undef, o; for (let z in [1, 2]) { " + statement + " }"),
+                      err);
+        } catch (ex) {
+            // Bug 831120.  See bug 942804 comment 5.
+            if (expected == 'undef' && err == ' is undefined')
+                check_one(expected + end,
+                          Function("var undef, o; for (let z in [1, 2]) { " + statement + " }"),
+                          err);
+            else
+                throw ex;
+        }
+
+        for (var f of cases) {
+            check_one(expected, f, err);
+        }
+    }
+}
+
+check("undef");
+check("o.b");
+check("o.length");
+check("o[true]");
+check("o[false]");
+check("o[null]");
+check("o[0]");
+check("o[1]");
+check("o[3]");
+check("o[256]");
+check("o[65536]");
+check("o[268435455]");
+check("o['1.1']");
+check("o[4 + 'h']", "o['4h']");
+check("this.x");
+check("ieval(undef)", "ieval(...)");
+check("ieval.call()", "ieval.call(...)");
+check("ieval(...[])", "ieval(...)");
+check("ieval(...[undef])", "ieval(...)");
+check("ieval(...[undef, undef])", "ieval(...)");
+
+for (let tok of ["|", "^", "&", "==", "!==", "===", "!==", "<", "<=", ">", ">=",
+                 ">>", "<<", ">>>", "+", "-", "*", "/", "%"]) {
+    check("o[(undef " + tok + " 4)]");
+}
+
+check("o[!(o)]");
+check("o[~(o)]");
+check("o[+ (o)]");
+check("o[- (o)]");
+
+// A few one off tests
+check_one("6", (function () { 6() }), " is not a function");
+check_one("Array.prototype.reverse.call(...)", (function () { Array.prototype.reverse.call('123'); }), " is read-only");
+check_one("null", function () { var [{ x }] = [null, {}]; }, " has no properties");
+check_one("x", function () { ieval("let (x) { var [a, b, [c0, c1]] = [x, x, x]; }") }, " is undefined");
+
+// Check fallback behavior
+assertThrowsInstanceOf(function () { for (let x of undefined) {} }, TypeError);