share stored predicates

while most of the duplication in predicates was caused by stubs,
this is still a 5% win on libcore.

567924 liballoc-bb943c5a.rlib
1425564 liballoc_jemalloc-bb943c5a.rlib
10520 liballoc_system-bb943c5a.rlib
154842 libarena-bb943c5a.rlib
4113790 libcollections-bb943c5a.rlib
18513674 libcore-bb943c5a.rlib
199466 libflate-bb943c5a.rlib
249548 libfmt_macros-bb943c5a.rlib
560488 libgetopts-bb943c5a.rlib
226772 libgraphviz-bb943c5a.rlib
442966 liblibc-bb943c5a.rlib
189884 liblog-bb943c5a.rlib
736764 librand-bb943c5a.rlib
609874 librbml-bb943c5a.rlib
1411678 librustc_back-bb943c5a.rlib
38770354 librustc-bb943c5a.rlib
12868 librustc_bitflags-bb943c5a.rlib
2327196 librustc_borrowck-bb943c5a.rlib
582178 librustc_data_structures-bb943c5a.rlib
9379344 librustc_driver-bb943c5a.rlib
9540324 librustc_front-bb943c5a.rlib
1614996 librustc_lint-bb943c5a.rlib
79217876 librustc_llvm-bb943c5a.rlib
4833518 librustc_mir-bb943c5a.rlib
3535794 librustc_platform_intrinsics-bb943c5a.rlib
603190 librustc_privacy-bb943c5a.rlib
3158032 librustc_resolve-bb943c5a.rlib
14300126 librustc_trans-bb943c5a.rlib
12024054 librustc_typeck-bb943c5a.rlib
1834852 librustc_unicode-bb943c5a.rlib
15611582 librustdoc-bb943c5a.rlib
2926594 libserialize-bb943c5a.rlib
8780060 libstd-bb943c5a.rlib
30772000 libsyntax-bb943c5a.rlib
917984 libterm-bb943c5a.rlib
1369754 libtest-bb943c5a.rlib

src/librustc/metadata/common.rs

@@ -222,9 +222,9 @@ pub const tag_type_param_def: usize = 0x94;
 pub const tag_item_generics: usize = 0x95;
 pub const tag_method_ty_generics: usize = 0x96;
 
-pub const tag_predicate: usize = 0x97;
-pub const tag_predicate_space: usize = 0x98;
-pub const tag_predicate_data: usize = 0x99;
+pub const tag_type_predicate: usize = 0x97;
+pub const tag_self_predicate: usize = 0x98;
+pub const tag_fn_predicate: usize = 0x99;
 
 pub const tag_unsafety: usize = 0x9a;
 

src/librustc/metadata/decoder.rs

@@ -1473,6 +1473,19 @@ fn doc_generics<'tcx>(base_doc: rbml::Doc,
     ty::Generics { types: types, regions: regions }
 }
 
+fn doc_predicate<'tcx>(cdata: Cmd,
+                       doc: rbml::Doc,
+                       tcx: &ty::ctxt<'tcx>)
+                       -> ty::Predicate<'tcx>
+{
+    let predicate_pos = cdata.xref_index.lookup(
+        cdata.data(), reader::doc_as_u32(doc)).unwrap() as usize;
+    TyDecoder::new(
+        cdata.data(), cdata.cnum, predicate_pos, tcx,
+        &mut |_, did| translate_def_id(cdata, did)
+    ).parse_predicate()
+}
+
 fn doc_predicates<'tcx>(base_doc: rbml::Doc,
                         tcx: &ty::ctxt<'tcx>,
                         cdata: Cmd,
@@ -1482,17 +1495,17 @@ fn doc_predicates<'tcx>(base_doc: rbml::Doc,
     let doc = reader::get_doc(base_doc, tag);
 
     let mut predicates = subst::VecPerParamSpace::empty();
-    for predicate_doc in reader::tagged_docs(doc, tag_predicate) {
-        let space_doc = reader::get_doc(predicate_doc, tag_predicate_space);
-        let space = subst::ParamSpace::from_uint(reader::doc_as_u8(space_doc) as usize);
-
-        let data_doc = reader::get_doc(predicate_doc, tag_predicate_data);
-        let data =
-            TyDecoder::with_doc(tcx, cdata.cnum, data_doc,
-                                &mut |_, did| translate_def_id(cdata, did))
-            .parse_predicate();
-
-        predicates.push(space, data);
+    for predicate_doc in reader::tagged_docs(doc, tag_type_predicate) {
+        predicates.push(subst::TypeSpace,
+                        doc_predicate(cdata, predicate_doc, tcx));
+    }
+    for predicate_doc in reader::tagged_docs(doc, tag_self_predicate) {
+        predicates.push(subst::SelfSpace,
+                        doc_predicate(cdata, predicate_doc, tcx));
+    }
+    for predicate_doc in reader::tagged_docs(doc, tag_fn_predicate) {
+        predicates.push(subst::FnSpace,
+                        doc_predicate(cdata, predicate_doc, tcx));
     }
 
     ty::GenericPredicates { predicates: predicates }