Remove the branch merging optimisations for slice patterns

src/librustc/middle/check_match.rs

@@ -28,8 +28,7 @@ use syntax::codemap::{Span, Spanned, DUMMY_SP};
 use syntax::fold::{Folder, noop_fold_pat};
 use syntax::print::pprust::pat_to_string;
 use syntax::parse::token;
-use syntax::visit;
-use syntax::visit::{Visitor, FnKind};
+use syntax::visit::{mod, Visitor, FnKind};
 use util::ppaux::ty_to_string;
 
 struct Matrix(Vec<Vec<Gc<Pat>>>);
@@ -103,7 +102,9 @@ pub enum Constructor {
     /// Ranges of literal values (2..5).
     ConstantRange(const_val, const_val),
     /// Array patterns of length n.
-    Slice(uint)
+    Slice(uint),
+    /// Array patterns with a subslice.
+    SliceWithSubslice(uint, uint)
 }
 
 #[deriving(Clone, PartialEq)]
@@ -270,13 +271,6 @@ fn check_arms(cx: &MatchCheckCtxt, arms: &[Arm]) {
     }
 }
 
-fn raw_pat(p: Gc<Pat>) -> Gc<Pat> {
-    match p.node {
-        PatIdent(_, _, Some(s)) => { raw_pat(s) }
-        _ => { p }
-    }
-}
-
 fn check_exhaustive(cx: &MatchCheckCtxt, sp: Span, matrix: &Matrix) {
     match is_useful(cx, matrix, [wild()], ConstructWitness) {
         UsefulWithWitness(pats) => {
@@ -821,6 +815,14 @@ pub fn specialize(cx: &MatchCheckCtxt, r: &[Gc<Pat>],
                     pats.push_all(after.as_slice());
                     Some(pats)
                 },
+                SliceWithSubslice(prefix, suffix)
+                    if before.len() == prefix
+                        && after.len() == suffix
+                        && slice.is_some() => {
+                    let mut pats = before.clone();
+                    pats.push_all(after.as_slice());
+                    Some(pats)
+                }
                 _ => None
             }
         }

src/librustc/middle/pat_util.rs

@@ -119,6 +119,13 @@ pub fn wild() -> Gc<Pat> {
     box (GC) Pat { id: 0, node: PatWild(PatWildSingle), span: DUMMY_SP }
 }
 
+pub fn raw_pat(p: Gc<Pat>) -> Gc<Pat> {
+    match p.node {
+        PatIdent(_, _, Some(s)) => { raw_pat(s) }
+        _ => { p }
+    }
+}
+
 pub fn def_to_path(tcx: &ty::ctxt, id: DefId) -> Path {
     ty::with_path(tcx, id, |mut path| Path {
         global: false,