---

yaml
---
r: 156419
b: refs/heads/snap-stage3
c: e74e059
h: refs/heads/master
i:
  156417: f113a5d
  156415: bc185d2
v: v3

Author: arielb1

[refs]

@@ -1,7 +1,7 @@
 ---
 refs/heads/master: c29a7520e7fb4a5b4d4eccfc594e05793ef6688d
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
-refs/heads/snap-stage3: 5bcd0a0b5030487613bee37ed38945e42c4e6b85
+refs/heads/snap-stage3: e74e059bd428332216d1b780e608cb824bc8c150
 refs/heads/try: 6601b0501e31d08d3892a2d5a7d8a57ab120bf75
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b

branches/snap-stage3/src/librustc/middle/trans/adt.rs

@@ -471,14 +471,16 @@ fn ensure_struct_fits_in_address_space(ccx: &CrateContext,
                                        scapegoat: ty::t) {
     let mut offset = 0;
     for &llty in fields.iter() {
+        // Invariant: offset < ccx.max_obj_size() <= 1<<61
         if !packed {
             let type_align = machine::llalign_of_min(ccx, llty);
             offset = roundup(offset, type_align);
         }
+        // type_align is a power-of-2, so still offset < ccx.max_obj_size()
+        // llsize_of_alloc(ccx, llty) is also less than ccx.max_obj_size()
+        // so the sum is less than 1<<62 (and therefore can't overflow).
         offset += machine::llsize_of_alloc(ccx, llty);
 
-        // We can get away with checking for overflow once per iteration,
-        // because field sizes are less than 1<<61.
         if offset >= ccx.max_obj_size() {
             ccx.report_overbig_object(scapegoat);
         }
@@ -498,7 +500,8 @@ fn ensure_enum_fits_in_address_space(ccx: &CrateContext,
     let discr_size = machine::llsize_of_alloc(ccx, ll_inttype(ccx, discr));
     let (field_size, field_align) = union_size_and_align(fields);
 
-    // This can't overflow because field_size, discr_size, field_align < 1<<61
+    // field_align < 1<<32, discr_size <= 8, field_size < MAX_OBJ_SIZE <= 1<<61
+    // so the sum is less than 1<<62 (and can't overflow).
     let total_size = roundup(discr_size, field_align) + field_size;
 
     if total_size >= ccx.max_obj_size() {