Auto merge of #34652 - jseyfried:fix_expansion_perf, r=nrc

Fix expansion performance regression

**syntax-[breaking-change] cc #31645**

This fixes #34630 by reverting commit 5bf7970 of PR #33943, which landed in #34424.

By removing the `Rc<_>` wrapping around `Delimited` and `SequenceRepetition` in `TokenTree`, 5bf7970 made cloning `TokenTree`s more expensive. While this had no measurable performance impact on the compiler's crates, it caused an order of magnitude performance regression on some macro-heavy code in the wild. I believe this is due to clones of `TokenTree`s in `macro_parser.rs` and/or `macro_rules.rs`.

r? @nrc

2 files changed, 7 insertions, 6 deletions

diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index 23f0b1fff0a..84572b84963 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -28,6 +28,7 @@ use util::small_vector::SmallVector;
 use std::cell::RefCell;
 use std::collections::{HashMap};
 use std::collections::hash_map::{Entry};
+use std::rc::Rc;
 
 struct ParserAnyMacro<'a> {
     parser: RefCell<Parser<'a>>,
@@ -262,7 +263,7 @@ pub fn compile<'cx>(cx: &'cx mut ExtCtxt,
     let match_lhs_tok = MatchNt(lhs_nm, token::str_to_ident("tt"));
     let match_rhs_tok = MatchNt(rhs_nm, token::str_to_ident("tt"));
     let argument_gram = vec![
-        TokenTree::Sequence(DUMMY_SP, tokenstream::SequenceRepetition {
+        TokenTree::Sequence(DUMMY_SP, Rc::new(tokenstream::SequenceRepetition {
             tts: vec![
                 TokenTree::Token(DUMMY_SP, match_lhs_tok),
                 TokenTree::Token(DUMMY_SP, token::FatArrow),
@@ -271,14 +272,14 @@ pub fn compile<'cx>(cx: &'cx mut ExtCtxt,
             separator: Some(token::Semi),
             op: tokenstream::KleeneOp::OneOrMore,
             num_captures: 2,
-        }),
+        })),
         // to phase into semicolon-termination instead of semicolon-separation
-        TokenTree::Sequence(DUMMY_SP, tokenstream::SequenceRepetition {
+        TokenTree::Sequence(DUMMY_SP, Rc::new(tokenstream::SequenceRepetition {
             tts: vec![TokenTree::Token(DUMMY_SP, token::Semi)],
             separator: None,
             op: tokenstream::KleeneOp::ZeroOrMore,
             num_captures: 0
-        }),
+        })),
     ];
 
     // Parse the macro_rules! invocation (`none` is for no interpolations):
diff --git a/src/libsyntax/ext/tt/transcribe.rs b/src/libsyntax/ext/tt/transcribe.rs
index 40944a9a1c2..7c0d10669f3 100644
--- a/src/libsyntax/ext/tt/transcribe.rs
+++ b/src/libsyntax/ext/tt/transcribe.rs
@@ -79,11 +79,11 @@ pub fn new_tt_reader_with_doc_flag(sp_diag: &Handler,
     let mut r = TtReader {
         sp_diag: sp_diag,
         stack: vec!(TtFrame {
-            forest: TokenTree::Sequence(DUMMY_SP, tokenstream::SequenceRepetition {
+            forest: TokenTree::Sequence(DUMMY_SP, Rc::new(tokenstream::SequenceRepetition {
                 tts: src,
                 // doesn't matter. This merely holds the root unzipping.
                 separator: None, op: tokenstream::KleeneOp::ZeroOrMore, num_captures: 0
-            }),
+            })),
             idx: 0,
             dotdotdoted: false,
             sep: None,