Introduce `ByteSymbol`.

It's like `Symbol` but for byte strings. The interner is now used for
both `Symbol` and `ByteSymbol`. E.g. if you intern `"dog"` and `b"dog"`
you'll get a `Symbol` and a `ByteSymbol` with the same index and the
characters will only be stored once.

The motivation for this is to eliminate the `Arc`s in `ast::LitKind`, to
make `ast::LitKind` impl `Copy`, and to avoid the need to arena-allocate
`ast::LitKind` in HIR. The latter change reduces peak memory by a
non-trivial amount on literal-heavy benchmarks such as `deep-vector` and
`tuple-stress`.

`Encoder`, `Decoder`, `SpanEncoder`, and `SpanDecoder` all get some
changes so that they can handle normal strings and byte strings.

This change does slow down compilation of programs that use
`include_bytes!` on large files, because the contents of those files are
now interned (hashed). This makes `include_bytes!` more similar to
`include_str!`, though `include_bytes!` contents still aren't escaped,
and hashing is still much cheaper than escaping.

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/rustc_middle/src/mir/interpret/mod.rs b/compiler/rustc_middle/src/mir/interpret/mod.rs
index ea2f84d46d7..da9e5bdbadd 100644
--- a/compiler/rustc_middle/src/mir/interpret/mod.rs
+++ b/compiler/rustc_middle/src/mir/interpret/mod.rs
@@ -77,7 +77,7 @@ impl<'tcx> GlobalId<'tcx> {
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, HashStable)]
 pub struct LitToConstInput<'tcx> {
     /// The absolute value of the resultant constant.
-    pub lit: &'tcx LitKind,
+    pub lit: LitKind,
     /// The type of the constant.
     pub ty: Ty<'tcx>,
     /// If the constant is negative.