Fix LFastLiteral to check boilerplate elements kind.

test/mjsunit/regress/regress-fast-literal-transition.js

+// Copyright 2012 the V8 project authors. All rights reserved.
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+
+// Flags: --allow-natives-syntax --always-opt --expose-gc
+
+// Test that the elements kind of the boilerplate object is sufficiently
+// checked in LFastLiteral, so that unoptimized code can transition the
+// boilerplate. The --always-opt flag makes sure that optimized code is
+// not thrown away at deoptimization.
+
+// The switch statement in f() makes sure that f() is not inlined. If we
+// start inlining switch statements, we will still catch the bug on the
+// final --stress-opt run.
+
+function f(x) {
+  switch(x) {
+    case 1: return 1.4;
+    case 2: return 1.5;
+    case 3: return {};
+    default: gc();
+  }
+}
+
+function g(x) {
+  return [1.1, 1.2, 1.3, f(x)];
+}
+
+// Step 1: Optimize g() to contain a FAST_DOUBLE_ELEMENTS boilerplate.
+assertEquals([1.1, 1.2, 1.3, 1.4], g(1));
+assertEquals([1.1, 1.2, 1.3, 1.5], g(2));
+%OptimizeFunctionOnNextCall(g);
+
+// Step 2: Deoptimize g() and transition to FAST_ELEMENTS boilerplate.
+assertEquals([1.1, 1.2, 1.3, {}], g(3));
+
+// Step 3: Cause a GC while broken clone of boilerplate is on the heap,
+// hence causing heap verification to catch it.
+assertEquals([1.1, 1.2, 1.3, undefined], g(4));