This series of changes moves the representation details of algebraic datatypes (enums, and special cases like structs and tuples and (until they're fully removed) records) from various places around rustc::middle::trans into a single module, to enable future improvements in this area.
r?(@nikomatsakis), and the core developers in general; this seems like a “super-review” kind of change.
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.
The first is reduced from a case in rustdoc (originally involving an
ARC); the other is related. No committed version has gotten these
wrong, but when I broke them it showed up only in rustdoc; there was
nothing in the test suite (or the compiler!) that failed.
The general issue is that the statics and trans have to agree on order
of evaluation, or else you get use-after-move-out-of errors at runtime.
This change remains separate from the addition of adt.rs, even though
it's necessary for compatibility with pre-trans::adt representation,
to serve as an example of a change to the representation logic.
Later changes on this branch adapt the rest of rustc::middle::trans
to use this module instead of scattered hard-coded knowledge of
representations; a few of them also have improvements or cleanup for
adt.rs (and many added comments) that weren't drastic enough to justify
changing history to move them into this commit.
After the removal of the "restricted keyword" feature in 0c82c00dc4 , there's no longer any difference between parse_ident() and parse_value_ident(), and therefore no difference between parse parse_path_without_tps() and parse_value_path(). I've collapsed all of these, removing the redundant functions and eliminating the need for two higher-order arguments.
