4 files changed, 51 insertions, 31 deletions
diff --git a/src/librustc/middle/trans/expr.rs b/src/librustc/middle/trans/expr.rs
index 0a557869758..01702e749a3 100644
--- a/src/librustc/middle/trans/expr.rs
+++ b/src/librustc/middle/trans/expr.rs
@@ -313,6 +313,36 @@ pub fn trans_to_datum(bcx: @mut Block, expr: @ast::Expr) -> DatumBlock {
         let target_obj_ty = expr_ty_adjusted(bcx, expr);
         debug!("auto_borrow_obj(target=%s)",
                target_obj_ty.repr(tcx));
+
+        // Extract source store information
+        let (source_store, source_mutbl) = match ty::get(source_datum.ty).sty {
+            ty::ty_trait(_, _, s, m, _) => (s, m),
+            _ => {
+                bcx.sess().span_bug(
+                    expr.span,
+                    fmt!("auto_borrow_trait_obj expected a trait, found %s",
+                         source_datum.ty.repr(bcx.tcx())));
+            }
+        };
+
+        // check if any borrowing is really needed or we could reuse the source_datum instead
+        match ty::get(target_obj_ty).sty {
+            ty::ty_trait(_, _, ty::RegionTraitStore(target_scope), target_mutbl, _) => {
+                if target_mutbl == ast::MutImmutable && target_mutbl == source_mutbl {
+                    match source_store {
+                        ty::RegionTraitStore(source_scope) => {
+                            if tcx.region_maps.is_subregion_of(target_scope, source_scope) {
+                                return DatumBlock { bcx: bcx, datum: source_datum };
+                            }
+                        },
+                        _ => {}
+
+                    };
+                }
+            },
+            _ => {}
+        }
+
         let scratch = scratch_datum(bcx, target_obj_ty,
                                     "__auto_borrow_obj", false);
 
@@ -331,15 +361,6 @@ pub fn trans_to_datum(bcx: @mut Block, expr: @ast::Expr) -> DatumBlock {
         // ~T, or &T, depending on source_obj_ty.
         let source_data_ptr = GEPi(bcx, source_llval, [0u, abi::trt_field_box]);
         let source_data = Load(bcx, source_data_ptr); // always a ptr
-        let (source_store, source_mutbl) = match ty::get(source_datum.ty).sty {
-            ty::ty_trait(_, _, s, m, _) => (s, m),
-            _ => {
-                bcx.sess().span_bug(
-                    expr.span,
-                    fmt!("auto_borrow_trait_obj expected a trait, found %s",
-                         source_datum.ty.repr(bcx.tcx())));
-            }
-        };
         let target_data = match source_store {
             ty::BoxTraitStore(*) => {
                 // For deref of @T or @mut T, create a dummy datum and
diff --git a/src/librustc/middle/trans/meth.rs b/src/librustc/middle/trans/meth.rs
index 06d88f66323..934dfabbb4d 100644
--- a/src/librustc/middle/trans/meth.rs
+++ b/src/librustc/middle/trans/meth.rs
@@ -434,13 +434,22 @@ pub fn trans_trait_callee(bcx: @mut Block,
     let _icx = push_ctxt("impl::trans_trait_callee");
     let mut bcx = bcx;
 
+    // make a local copy for trait if needed
     let self_ty = expr_ty_adjusted(bcx, self_expr);
-    let self_scratch = scratch_datum(bcx, self_ty, "__trait_callee", false);
-    bcx = expr::trans_into(bcx, self_expr, expr::SaveIn(self_scratch.val));
+    let self_scratch = match ty::get(self_ty).sty {
+        ty::ty_trait(_, _, ty::RegionTraitStore(*), _, _) => {
+            unpack_datum!(bcx, expr::trans_to_datum(bcx, self_expr))
+        }
+        _ => {
+            let d = scratch_datum(bcx, self_ty, "__trait_callee", false);
+            bcx = expr::trans_into(bcx, self_expr, expr::SaveIn(d.val));
+            // Arrange a temporary cleanup for the object in case something
+            // should go wrong before the method is actually *invoked*.
+            d.add_clean(bcx);
+            d
+        }
+    };
 
-    // Arrange a temporary cleanup for the object in case something
-    // should go wrong before the method is actually *invoked*.
-    self_scratch.add_clean(bcx);
 
     let callee_ty = node_id_type(bcx, callee_id);
     trans_trait_callee_from_llval(bcx,
diff --git a/src/librustc/middle/trans/type_.rs b/src/librustc/middle/trans/type_.rs
index 8b221a89c36..0954302ba81 100644
--- a/src/librustc/middle/trans/type_.rs
+++ b/src/librustc/middle/trans/type_.rs
@@ -278,23 +278,12 @@ impl Type {
 
     pub fn opaque_trait(ctx: &CrateContext, store: ty::TraitStore) -> Type {
         let tydesc_ptr = ctx.tydesc_type.ptr_to();
-        match store {
-            ty::BoxTraitStore => {
-                Type::struct_(
-                    [ tydesc_ptr, Type::opaque_box(ctx).ptr_to() ],
-                false)
-            }
-            ty::UniqTraitStore => {
-                Type::struct_(
-                    [ tydesc_ptr, Type::unique(ctx, &Type::i8()).ptr_to()],
-                false)
-            }
-            ty::RegionTraitStore(*) => {
-                Type::struct_(
-                    [ tydesc_ptr, Type::i8().ptr_to() ],
-                false)
-            }
-        }
+        let box_ty = match store {
+            ty::BoxTraitStore => Type::opaque_box(ctx),
+            ty::UniqTraitStore => Type::unique(ctx, &Type::i8()),
+            ty::RegionTraitStore(*) => Type::i8()
+        };
+        Type::struct_([tydesc_ptr, box_ty.ptr_to()], false)
     }
 
     pub fn kind(&self) -> TypeKind {
diff --git a/src/test/run-pass/core-run-destroy.rs b/src/test/run-pass/core-run-destroy.rs
index 1c3e83f3cab..789295edaaa 100644
--- a/src/test/run-pass/core-run-destroy.rs
+++ b/src/test/run-pass/core-run-destroy.rs
@@ -55,6 +55,7 @@ fn test_destroy_actually_kills(force: bool) {
 
     #[cfg(windows)]
     fn process_exists(pid: libc::pid_t) -> bool {
+        #[fixed_stack_segment];
 
         use std::libc::types::os::arch::extra::DWORD;
         use std::libc::funcs::extra::kernel32::{CloseHandle, GetExitCodeProcess, OpenProcess};