Allow `GenericDebugNode` construction directly from `MDString`, rather
than requiring `StringRef`s. I've refactored the `StringRef`
constructors to use these. There's no real functionality change here,
except for exposing the lower-level API.
The purpose of this is to simplify construction of string operands when
reading bitcode. It's unnecessarily indirect to parse an `MDString` ID,
lookup the `MDString` in the bitcode reader list, get the `StringRef`
out of that, and then have `GenericDebugNode::getImpl()` use
`MDString::get()` to acquire the original `MDString`. Instead, this
allows the bitcode reader to directly pass in the `MDString`.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227848 91177308-0d34-0410-b5e6-96231b3b80d8
Move debug-info-centred `Metadata` subclasses into their own
header/source file. A couple of private template functions are needed
from both `Metadata.cpp` and `DebugInfoMetadata.cpp`, so I've moved them
to `lib/IR/MetadataImpl.h`.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227835 91177308-0d34-0410-b5e6-96231b3b80d8
