Add combine-based benchmark that caused a large performance regression

See rust-lang/rust#67454

collector/benchmarks/README.md

@@ -67,6 +67,9 @@ programs.
 - **coercions**: Contains a static array with 65,536 string literals, which
   caused [poor performance](https://github.com/rust-lang/rust/issues/32278) in
   the past.
+- **combine**: Contains a small `combine`-based parser that caused a [large
+  performance regression](https://github.com/rust-lang/rust/issues/67454) in
+  the past.
 - **ctfe-stress-4**: A stress test for compile-time function evaluation.
 - **deeply-nested**: A small program that caused [exponential
   behavior](https://github.com/rust-lang/rust/issues/38528) in the past.

collector/benchmarks/combine/.gitignore

@@ -0,0 +1,2 @@
+/target
+**/*.rs.bk

collector/benchmarks/combine/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "combine-bench"
+license = "MIT"
+version = "0.1.0"
+authors = ["Sebastian Dröge <[email protected]>", "François Laignel <[email protected]>"]
+edition = "2018"
+
+[dependencies]
+combine = "3.8"

collector/benchmarks/combine/src/lib.rs

@@ -0,0 +1,35 @@
+use combine::byte::hex_digit;
+use combine::{choice, token};
+use combine::{ParseError, Parser, RangeStream};
+
+pub fn parse<'a, I: 'a>() -> impl Parser<Input = I, Output = u8>
+where
+    I: RangeStream<Item = u8, Range = &'a [u8]>,
+    I::Error: ParseError<I::Item, I::Range, I::Position>,
+{
+    choice!(
+        token(b'A').map(|_| 1),
+        token(b'B').map(|_| 2),
+        token(b'C').map(|_| 3),
+        token(b'D').map(|_| 4),
+        token(b'E').map(|_| 5),
+        token(b'F').map(|_| 6),
+        token(b'G').map(|_| 7),
+        token(b'H').map(|_| 8),
+        token(b'I').map(|_| 9),
+        token(b'J').map(|_| 10),
+        token(b'K').map(|_| 11),
+        token(b'L').map(|_| 12),
+        token(b'M').map(|_| 13),
+        token(b'N').map(|_| 14),
+        token(b'O').map(|_| 15),
+        token(b'P').map(|_| 16),
+        token(b'Q').map(|_| 17),
+        token(b'R').map(|_| 18),
+        (hex_digit(), hex_digit()).map(|(u, l)| {
+            let val = (u << 4) | l;
+            val
+        })
+    )
+    .message("while parsing")
+}