[Patch] Fix for bug 15246

[Jyotsna Verma]

>> Yes, the bug is specific to a TG backend, CodeGenMapTable.cpp. All the
>> current tests for TableGen appear to be for the frontend/parser. I
>> don't think we have any backend specific test at this point. In order
>> to have such a test, it would require some basic infrastructure in a
>> test .td file, mostly the classes defined in
>> include/llvm/Target/Target.td. This may result into a test with a couple
of
>hundreds of lines.
>
>Or just include the needed .td file(s)?

Including Target.td file as is has its own set of problems because then
TableGen expects various subclasses to be defined. For instance, you have to
define a subclass of Target and RegisterClass class and many more.

-Jyotsna