Short-circuit embedded cons strings.

test/mjsunit/regress/regress-embedded-cons-string.js

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-// Flags: --allow-natives-syntax
-// Flags: --parallel-recompilation --parallel-recompilation-delay=50
+// Flags: --fold-constants --nodead-code-elimination
+// Flags: --expose-gc --allow-natives-syntax
+// Flags: --parallel-recompilation --parallel-recompilation-delay=300
 
 if (!%IsParallelRecompilationSupported()) {
   print("Parallel recompilation is disabled. Skipping this test.");
   quit();
 }
 
 function assertUnoptimized(fun) {
   assertTrue(%GetOptimizationStatus(fun) != 1);
 }
 
-function f(foo) { return foo.bar(); }
+function f() {
+  return "abcdefghijklmn" + "123456789";  // Constant-folds to a cons string.
+}
 
-var o = {};
-o.__proto__ = { __proto__: { bar: function() { return 1; } } };
+f();
+f();
+%OptimizeFunctionOnNextCall(f, "parallel");
+f();   // Trigger optimization in the background.
+gc();  // Tenure cons string.
+assertUnoptimized(f);      // Compilation not complete yet.
+%CompleteOptimization(f);  // Compilation embeds tenured cons string.
 
-assertEquals(1, f(o));
-assertEquals(1, f(o));
+gc();  // Visit embedded cons string during mark compact.
+assertEquals("abcdefghijklmn123456789", f());
+%FlattenString(f());
+gc();  // Short circuit flattened cons string during visit.
+assertEquals("abcdefghijklmn123456789", f());
 
-%OptimizeFunctionOnNextCall(f, "parallel");
-assertEquals(1, f(o));     // Trigger optimization.
-assertUnoptimized(f);      // Optimization not yet done.
-// Change the prototype chain during optimization to trigger map invalidation.
-o.__proto__.__proto__ = { bar: function() { return 2; } };
-%CompleteOptimization(f);  // Conclude optimization with...
-assertUnoptimized(f);      // ... bailing out due to map dependency.
-assertEquals(2, f(o));