Cast more aggressively to the callee type when calling generic functions. Add a test-case for this, and XFAIL it in rustboot.

src/Makefile

@@ -416,6 +416,7 @@ TEST_XFAILS_BOOT :=  $(TASK_XFAILS) \
                     test/run-pass/obj-as.rs \
                     test/run-pass/vec-slice.rs \
                     test/run-pass/fn-lval.rs \
+                    test/run-pass/generic-fn-box.rs \
                     test/run-pass/generic-recursive-tag.rs \
                     test/run-pass/generic-tup.rs \
                     test/run-pass/iter-ret.rs \

src/comp/middle/trans.rs

@@ -3132,9 +3132,9 @@ fn trans_args(@block_ctxt cx,
             bcx = re.bcx;
         }
 
-        if (ty.type_has_dynamic_size(args.(i).ty)) {
-            val = bcx.build.PointerCast(val,
-                                        T_typaram_ptr(cx.fcx.ccx.tn));
+        if (ty.count_ty_params(args.(i).ty) > 0u) {
+            auto lldestty = type_of(cx.fcx.ccx, args.(i).ty);
+            val = bcx.build.PointerCast(val, lldestty);
         }
 
         llargs += val;

src/test/run-pass/generic-fn-box.rs

@@ -0,0 +1,9 @@
+fn f[T](@T x) -> @T {
+    ret x;
+}
+
+fn main() {
+    auto x = f(@3);
+    log *x;
+}
+