Fix LookupCode for the DatePrototype_GetField builtin

src/builtins/ppc/builtins-ppc.cc

Index: src/builtins/ppc/builtins-ppc.cc
diff --git a/src/builtins/ppc/builtins-ppc.cc b/src/builtins/ppc/builtins-ppc.cc
index af1e624ca07f8a2a9e2d13eab015852dae0b23e8..756aeedf9104aa6cd43670b868c1d5337150e14b 100644
--- a/src/builtins/ppc/builtins-ppc.cc
+++ b/src/builtins/ppc/builtins-ppc.cc
@@ -1892,6 +1892,16 @@ void Builtins::Generate_DatePrototype_GetField(MacroAssembler* masm,
     __ LoadSmiLiteral(r3, Smi::FromInt(0));
     __ EnterBuiltinFrame(cp, r4, r3);
     __ CallRuntime(Runtime::kThrowNotDateError);
+
+    // It's far from obvious, but this final trailing instruction after the call
+    // is required for StackFrame::LookupCode to work correctly. To illustrate
+    // why: if call were the final instruction in the code object, then the pc
+    // (== return address) would point beyond the code object when the stack is
+    // traversed. When we then try to look up the code object through
+    // StackFrame::LookupCode, we actually return the next code object that
+    // happens to be on the same page in memory.
+    // TODO(jgruber): A proper fix for this would be nice.
+    __ nop();
   }
 }