Sink down the null Decl printing into
`printDeclDescription` such that all callers
benefit from it.
This is an attempt at fixing at least the secondary
crash in rdar://113491294, it does not address the
underlying crash.
My goal was to reduce the size of SILLocation. It now contains only of a storage union, which is basically a pointer and a bitfield containing the Kind, StorageKind and flags. By far, most locations are only single pointers to an AST node. For the few cases where more data needs to be stored, this data is allocated separately: with the SILModule's bump pointer allocator.
While working on this, I couldn't resist to do a major refactoring to simplify the code:
* removed unused stuff
* The term "DebugLoc" was used for 3 completely different things:
- for `struct SILLocation::DebugLoc` -> renamed it to `FilePosition`
- for `hasDebugLoc()`/`getDebugSourceLoc()` -> renamed it to `hasASTNodeForDebugging()`/`getSourceLocForDebugging()`
- for `class SILDebugLocation` -> kept it as it is (though, `SILScopedLocation` would be a better name, IMO)
* made SILLocation more "functional", i.e. replaced some setters with corresponding constructors
* replaced the hand-written bitfield `KindData` with C bitfields
* updated and improved comments
Specifically, I split it into 3 initial categories: IR, Utils, Verifier. I just
did this quickly, we can always split it more later if we want.
I followed the model that we use in SILOptimizer: ./lib/SIL/CMakeLists.txt vends
a macro (sil_register_sources) to the sub-folders that register the sources of
the subdirectory with a global state variable that ./lib/SIL/CMakeLists.txt
defines. Then after including those subdirs, the parent cmake declares the SIL
library. So the output is the same, but we have the flexibility of having
subdirectories to categorize source files.
