The erase/remove from parent methods now use a switch table to remove
themselves from their appropriate parent ilist.
The copyAttributesFrom method is now completely non-virtual, since we
only ever copy attributes from a global of the appropriate type.
Pre-requisite to de-virtualizing Value to save a vptr
(https://reviews.llvm.org/D31261).
NFC
llvm-svn: 302823
e7c7854cb1