Tool selection is primarily done by checking the executable (= symlink) name.
But sometimes (e.g. if the tool symlink is not there) it's useful to have an option for selecting the tool.
The selection option (e.g. -sil-opt) must be the first argument of swift-frontend.
Constructors and methods had two parameter lists, one for self and one
for the formal parameters. Destructors only had one parameter list,
which introduced an annoying corner case.
This converts the instances of the pattern for which we have a proper
substitution in lit. This will make it easier to replace it
appropriately with Windows equivalents.
Conformance manglings, which are used for witness tables and related witness
thunks, mangle the generic signature of the conformance. Since conformances
also describe the conforming type, mangle the conformances's generic signature
relative to the conforming type's generic signature.
In practice, this means that we don't mangle any part of the generic signature
into a conformance mangling now, so we see a decent win: 2.3% smaller
trie and 6.4% smaller strings section in the standard library binary.
When conditional conformances land, we'll see some generic signatures
mangling again (for the additional requirements of the constrained
extension).
Static initializers are now represented by a list of literal and aggregate instructions in a SILGlobalVariable.
For details see SIL.rst.
This representation is cleaner than what we did so far (point to the initializer function and do some pattern matching).
One implication of that change is that now (a subset of) instructions not necessarily have a parent function.
Regarding the generated code it's a NFC.
Also the swift module format didn't change because so far we don't serializer global variables.
Also, add a third [serializable] state for functions whose bodies we
*can* serialize, but only do so if they're referenced from another
serialized function.
This will be used for bodies synthesized for imported definitions,
such as init(rawValue:), etc, and various thunks, but for now this
change is NFC.
