Fix LookupCode for the DatePrototype_GetField builtin

src/builtins/mips64/builtins-mips64.cc

Index: src/builtins/mips64/builtins-mips64.cc
diff --git a/src/builtins/mips64/builtins-mips64.cc b/src/builtins/mips64/builtins-mips64.cc
index cbdb5c32505aef75566fa90d205a330213d971cf..8cb44b3c52403add1ad54cb762de2e96d5222d16 100644
--- a/src/builtins/mips64/builtins-mips64.cc
+++ b/src/builtins/mips64/builtins-mips64.cc
@@ -1850,6 +1850,16 @@ 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();
   }
 }