Auto merge of #141875 - nnethercote:ByteSymbol, r=petrochenkov

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.

1 files changed, 6 insertions, 2 deletions

diff --git a/compiler/rustc_expand/src/proc_macro_server.rs b/compiler/rustc_expand/src/proc_macro_server.rs
index fb5abaefb57..af91c8b8f00 100644
--- a/compiler/rustc_expand/src/proc_macro_server.rs
+++ b/compiler/rustc_expand/src/proc_macro_server.rs
@@ -599,8 +599,12 @@ impl server::TokenStream for Rustc<'_, '_> {
             ast::ExprKind::Lit(token_lit) => {
                 Ok(tokenstream::TokenStream::token_alone(token::Literal(*token_lit), expr.span))
             }
-            ast::ExprKind::IncludedBytes(bytes) => {
-                let lit = token::Lit::new(token::ByteStr, escape_byte_str_symbol(bytes), None);
+            ast::ExprKind::IncludedBytes(byte_sym) => {
+                let lit = token::Lit::new(
+                    token::ByteStr,
+                    escape_byte_str_symbol(byte_sym.as_byte_str()),
+                    None,
+                );
                 Ok(tokenstream::TokenStream::token_alone(token::TokenKind::Literal(lit), expr.span))
             }
             ast::ExprKind::Unary(ast::UnOp::Neg, e) => match &e.kind {