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

4 files changed, 22 insertions, 15 deletions

diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 877293bac54..b2b63d0dbb4 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -237,7 +237,7 @@ fn expand_mac_invoc<T>(mac: ast::Mac, ident: Option<Ident>, attrs: Vec<ast::Attr
                     },
                 });
 
-                let marked_tts = mark_tts(tts, mark);
+                let marked_tts = mark_tts(&tts, mark);
                 Some(expandfun.expand(fld.cx, call_site, &marked_tts))
             }
 
@@ -257,7 +257,7 @@ fn expand_mac_invoc<T>(mac: ast::Mac, ident: Option<Ident>, attrs: Vec<ast::Attr
                     }
                 });
 
-                let marked_tts = mark_tts(tts, mark);
+                let marked_tts = mark_tts(&tts, mark);
                 Some(expander.expand(fld.cx, call_site, ident, marked_tts))
             }
 
@@ -1130,7 +1130,7 @@ impl Folder for Marker {
         Spanned {
             node: Mac_ {
                 path: self.fold_path(node.path),
-                tts: self.fold_tts(node.tts),
+                tts: self.fold_tts(&node.tts),
             },
             span: self.new_span(span),
         }
@@ -1145,7 +1145,7 @@ impl Folder for Marker {
 }
 
 // apply a given mark to the given token trees. Used prior to expansion of a macro.
-fn mark_tts(tts: Vec<TokenTree>, m: Mrk) -> Vec<TokenTree> {
+fn mark_tts(tts: &[TokenTree], m: Mrk) -> Vec<TokenTree> {
     noop_fold_tts(tts, &mut Marker{mark:m, expn_id: None})
 }
 
diff --git a/src/libsyntax/ext/quote.rs b/src/libsyntax/ext/quote.rs
index 68527b0797d..ffc950d76dd 100644
--- a/src/libsyntax/ext/quote.rs
+++ b/src/libsyntax/ext/quote.rs
@@ -32,6 +32,7 @@ pub mod rt {
     use ext::base::ExtCtxt;
     use parse::{self, token, classify};
     use ptr::P;
+    use std::rc::Rc;
 
     use tokenstream::{self, TokenTree};
 
@@ -215,12 +216,12 @@ pub mod rt {
             if self.node.style == ast::AttrStyle::Inner {
                 r.push(TokenTree::Token(self.span, token::Not));
             }
-            r.push(TokenTree::Delimited(self.span, tokenstream::Delimited {
+            r.push(TokenTree::Delimited(self.span, Rc::new(tokenstream::Delimited {
                 delim: token::Bracket,
                 open_span: self.span,
                 tts: self.node.value.to_tokens(cx),
                 close_span: self.span,
-            }));
+            })));
             r
         }
     }
@@ -235,12 +236,12 @@ pub mod rt {
 
     impl ToTokens for () {
         fn to_tokens(&self, _cx: &ExtCtxt) -> Vec<TokenTree> {
-            vec![TokenTree::Delimited(DUMMY_SP, tokenstream::Delimited {
+            vec![TokenTree::Delimited(DUMMY_SP, Rc::new(tokenstream::Delimited {
                 delim: token::Paren,
                 open_span: DUMMY_SP,
                 tts: vec![],
                 close_span: DUMMY_SP,
-            })]
+            }))]
         }
     }
 
@@ -791,9 +792,14 @@ fn statements_mk_tt(cx: &ExtCtxt, tt: &TokenTree, matcher: bool) -> Vec<ast::Stm
                                 id_ext("tokenstream"),
                                 id_ext("SequenceRepetition")];
             let e_seq_struct = cx.expr_struct(sp, cx.path_global(sp, seq_path), fields);
+            let e_rc_new = cx.expr_call_global(sp, vec![id_ext("std"),
+                                                        id_ext("rc"),
+                                                        id_ext("Rc"),
+                                                        id_ext("new")],
+                                                   vec![e_seq_struct]);
             let e_tok = cx.expr_call(sp,
                                      mk_tt_path(cx, sp, "Sequence"),
-                                     vec!(e_sp, e_seq_struct));
+                                     vec!(e_sp, e_rc_new));
             let e_push =
                 cx.expr_method_call(sp,
                                     cx.expr_ident(sp, id_ext("tt")),
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,