Revert "save the subobligations as well"

This reverts commit 309ab47.

Author: arielb1

src/librustc/traits/project.rs

@@ -462,19 +462,13 @@ fn opt_normalize_projection_type<'a, 'b, 'gcx, 'tcx>(
             selcx.infcx().report_overflow_error(&obligation, false);
         }
         Err(ProjectionCacheEntry::NormalizedTy(ty)) => {
-            // If we find the value in the cache, then return it along
-            // with the obligations that went along with it. Note
-            // that, when using a fulfillment context, these
-            // obligations could in principle be ignored: they have
-            // already been registered when the cache entry was
-            // created (and hence the new ones will quickly be
-            // discarded as duplicated). But when doing trait
-            // evaluation this is not the case, and dropping the trait
-            // evaluations can causes ICEs (e.g. #43132).
+            // If we find the value in the cache, then the obligations
+            // have already been returned from the previous entry (and
+            // should therefore have been honored).
             debug!("opt_normalize_projection_type: \
                     found normalized ty `{:?}`",
                    ty);
-            return Some(ty);
+            return Some(NormalizedTy { value: ty, obligations: vec![] });
         }
         Err(ProjectionCacheEntry::Error) => {
             debug!("opt_normalize_projection_type: \
@@ -1342,7 +1336,7 @@ enum ProjectionCacheEntry<'tcx> {
     InProgress,
     Ambiguous,
     Error,
-    NormalizedTy(NormalizedTy<'tcx>),
+    NormalizedTy(Ty<'tcx>),
 }
 
 // NB: intentionally not Clone
@@ -1395,7 +1389,7 @@ impl<'tcx> ProjectionCache<'tcx> {
         let fresh_key = if cacheable {
             debug!("ProjectionCacheEntry::complete: adding cache entry: key={:?}, value={:?}",
                    key, value);
-            self.map.insert(key, ProjectionCacheEntry::NormalizedTy(value.clone()))
+            self.map.insert(key, ProjectionCacheEntry::NormalizedTy(value.value))
         } else {
             debug!("ProjectionCacheEntry::complete: cannot cache: key={:?}, value={:?}",
                    key, value);