These changes make const translation use adjustments (autodereference, autoreference, bare-fn-to-closure), like normal code does, replacing some ad-hoc logic that wasn't always right.
As a convenient side-effect, explicit dereference (both of pointers and of newtypes) is also supported in const expressions.
There is also a “bonus fix” for a bug in the pretty-printer exposed by one of the added tests.
Struct and enum representations have some complicatedness that's no longer needed. Now that everything's in one place and has access to anything we'd want to know about the type, flatten some of that out. Slight changes to representations in some cases.
The only thing we really lose is that C-like enums with one variant and a
non-zero discriminant now take up space, but I do not think this is a
common usage. As previously noted, that was mostly there for
transitional compatibility with the pre-adt.rs codebase.
Out goes the extra layer of struct wrapping; the destructedness flag is
added to the end of the struct. This means that, if the struct
previously had alignment padding at the end, the flag will live there
instead of increasing the struct size.
Changes the ad-hoc closure adjustment into using adjustment info instead
of being separately driven from types, and likewise for autoderef.
Also takes care of autoref (the cases we should be seeing in consts,
at least, since we can't be doing method calls which would need the
ref-to-vec mode), which didn't quite work right previously.
However, "dereference" of a newtype isn't handled yet....
Also converts const cast-from-enum, because it used the same routine to
get the discriminant as what's renovated to construct the enums.
Also fixes ICE on struct-like variants as consts, and provides a slightly
less bad ICE for functional-update-like struct expressions in consts.
Note that in the ByValue case (which can't happen? yet?) we're still
effectively bitcasting, I think. So this change adds a way to assert
that that's safe.
Note also, for future reference, that LLVM's instcombine pass will turn
a bitcast into a GEP(0, 0, ...) if possible.
