Add #[loop_match] for improved DFA codegen

Co-authored-by: Folkert de Vries <folkert@folkertdev.nl>

compiler/rustc_feature/src/builtin_attrs.rs

@@ -657,6 +657,19 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         EncodeCrossCrate::Yes, min_generic_const_args, experimental!(type_const),
     ),
 
+    // The `#[loop_match]` and `#[const_continue]` attributes are part of the
+    // lang experiment for RFC 3720 tracked in:
+    //
+    // - https://github.com/rust-lang/rust/issues/132306
+    gated!(
+        const_continue, Normal, template!(Word), ErrorFollowing,
+        EncodeCrossCrate::No, loop_match, experimental!(const_continue)
+    ),
+    gated!(
+        loop_match, Normal, template!(Word), ErrorFollowing,
+        EncodeCrossCrate::No, loop_match, experimental!(loop_match)
+    ),
+
     // ==========================================================================
     // Internal attributes: Stability, deprecation, and unsafe:
     // ==========================================================================

compiler/rustc_feature/src/unstable.rs

@@ -557,6 +557,8 @@ declare_features! (
     /// Allows using `#[link(kind = "link-arg", name = "...")]`
     /// to pass custom arguments to the linker.
     (unstable, link_arg_attribute, "1.76.0", Some(99427)),
+    /// Allows fused `loop`/`match` for direct intraprocedural jumps.
+    (incomplete, loop_match, "CURRENT_RUSTC_VERSION", Some(132306)),
     /// Give access to additional metadata about declarative macro meta-variables.
     (unstable, macro_metavar_expr, "1.61.0", Some(83527)),
     /// Provides a way to concatenate identifiers using metavariable expressions.