don't mark_stable_position needlessly in tyencode

another 1% improvement in libcore size - also 1% in librustc

550076 liballoc-bb943c5a.rlib
1425150 liballoc_jemalloc-bb943c5a.rlib
10100 liballoc_system-bb943c5a.rlib
149372 libarena-bb943c5a.rlib
3964144 libcollections-bb943c5a.rlib
17744342 libcore-bb943c5a.rlib
197420 libflate-bb943c5a.rlib
241582 libfmt_macros-bb943c5a.rlib
550560 libgetopts-bb943c5a.rlib
219444 libgraphviz-bb943c5a.rlib
402668 liblibc-bb943c5a.rlib
187158 liblog-bb943c5a.rlib
704588 librand-bb943c5a.rlib
594522 librbml-bb943c5a.rlib
1392516 librustc_back-bb943c5a.rlib
38196500 librustc-bb943c5a.rlib
12826 librustc_bitflags-bb943c5a.rlib
2286918 librustc_borrowck-bb943c5a.rlib
561714 librustc_data_structures-bb943c5a.rlib
9356400 librustc_driver-bb943c5a.rlib
9378650 librustc_front-bb943c5a.rlib
1603680 librustc_lint-bb943c5a.rlib
79184908 librustc_llvm-bb943c5a.rlib
4746824 librustc_mir-bb943c5a.rlib
3532474 librustc_platform_intrinsics-bb943c5a.rlib
592664 librustc_privacy-bb943c5a.rlib
3114986 librustc_resolve-bb943c5a.rlib
14153174 librustc_trans-bb943c5a.rlib
11918356 librustc_typeck-bb943c5a.rlib
1669986 librustc_unicode-bb943c5a.rlib
15611582 librustdoc-bb943c5a.rlib
2836912 libserialize-bb943c5a.rlib
8549994 libstd-bb943c5a.rlib
30399156 libsyntax-bb943c5a.rlib
907058 libterm-bb943c5a.rlib

Author: Ariel Ben-Yehuda

src/librustc/metadata/tyencode.rs

@@ -14,6 +14,7 @@
 #![allow(non_camel_case_types)]
 
 use std::cell::RefCell;
+use std::str;
 use std::io::prelude::*;
 
 use middle::def_id::DefId;
@@ -173,12 +174,18 @@ pub fn enc_ty<'a, 'tcx>(w: &mut Encoder, cx: &ctxt<'a, 'tcx>, t: Ty<'tcx>) {
         return len;
     }
     let abbrev_len = 3 + estimate_sz(pos) + estimate_sz(len);
-    if abbrev_len < len {
-        // I.e. it's actually an abbreviation.
-        cx.abbrevs.borrow_mut().insert(t, ty_abbrev {
-            s: format!("#{:x}:{:x}#", pos, len)
-        });
-    }
+    cx.abbrevs.borrow_mut().insert(t, ty_abbrev {
+        s: if abbrev_len < len {
+            format!("#{:x}:{:x}#", pos, len)
+        } else {
+            // if the abbreviation is longer than the real type,
+            // don't use #-notation. However, insert it here so
+            // other won't have to `mark_stable_position`
+            str::from_utf8(
+                &w.writer.get_ref()[pos as usize..end as usize]
+            ).unwrap().to_owned()
+        }
+    });
 }
 
 fn enc_mutability(w: &mut Encoder, mt: hir::Mutability) {