Fix LookupCode for the DatePrototype_GetField builtin

src/builtins/mips/builtins-mips.cc

Index: src/builtins/mips/builtins-mips.cc
diff --git a/src/builtins/mips/builtins-mips.cc b/src/builtins/mips/builtins-mips.cc
index 003eeb22e01db4b13bbb10e14380944083d4bc36..0a439cfb43d75223f53dc6d4dbee728c793a33ac 100644
--- a/src/builtins/mips/builtins-mips.cc
+++ b/src/builtins/mips/builtins-mips.cc
@@ -1856,6 +1856,16 @@ void Builtins::Generate_DatePrototype_GetField(MacroAssembler* masm,
     __ Move(a0, Smi::FromInt(0));
     __ EnterBuiltinFrame(cp, a1, a0);
     __ 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();
   }
 }