Make non-natural alignment a validation error in spec interpreter / test (#242)

Followup to #243. Prior to #243, a non-natural alignment for an atomic instruction was *not* a parse, validation or runtime failure in the spec interpreter / tests, although the spec specified that it would be a parse error (and would be a validation error after #243). Change the reference interpreter and spec test to make a non-natural alignment into a validation error. 8-bit instructions aren't tested for the validation failure since there's no way to have a non-natural alignment for those cases (only a greater one which results in a different validation failure).

Also removed some extra spaces in cmpxchg tests.

Tested with `make test` locally.

Author: stevenfontanella

interpreter/valid/valid.ml

@@ -189,7 +189,9 @@ let check_vec_binop binop at =
       error at "invalid lane index"
   | _ -> ()
 
-let check_memop (c : context) (memop : ('t, 's) memop) ty_size get_sz at =
+type mem_mode = NonAtomic | Atomic
+
+let check_memop (mode : mem_mode) (c : context) (memop : ('t, 's) memop) ty_size get_sz at =
   let _mt = memory c (0l @@ at) in
   let size =
     match get_sz memop.pack with
@@ -198,8 +200,13 @@ let check_memop (c : context) (memop : ('t, 's) memop) ty_size get_sz at =
       check_pack sz (ty_size memop.ty) at;
       packed_size sz
   in
-  require (1 lsl memop.align <= size) at
-    "alignment must not be larger than natural"
+  match mode with
+  | NonAtomic ->
+    require (1 lsl memop.align <= size) at
+      "alignment must not be larger than natural";
+  | Atomic ->
+    require (1 lsl memop.align = size) at
+      "atomic alignment must be natural"
 
 
 (*
@@ -354,29 +361,29 @@ let rec check_instr (c : context) (e : instr) (s : infer_result_type) : op_type
     [] --> []
 
   | Load memop ->
-    check_memop c memop num_size (Lib.Option.map fst) e.at;
+    check_memop NonAtomic c memop num_size (Lib.Option.map fst) e.at;
     [NumType I32Type] --> [NumType memop.ty]
 
   | Store memop ->
-    check_memop c memop num_size (fun sz -> sz) e.at;
+    check_memop NonAtomic c memop num_size (fun sz -> sz) e.at;
     [NumType I32Type; NumType memop.ty] --> []
 
   | VecLoad memop ->
-    check_memop c memop vec_size (Lib.Option.map fst) e.at;
+    check_memop NonAtomic c memop vec_size (Lib.Option.map fst) e.at;
     [NumType I32Type] --> [VecType memop.ty]
 
   | VecStore memop ->
-    check_memop c memop vec_size (fun _ -> None) e.at;
+    check_memop NonAtomic c memop vec_size (fun _ -> None) e.at;
     [NumType I32Type; VecType memop.ty] --> []
 
   | VecLoadLane (memop, i) ->
-    check_memop c memop vec_size (fun sz -> Some sz) e.at;
+    check_memop NonAtomic c memop vec_size (fun sz -> Some sz) e.at;
     require (i < vec_size memop.ty / packed_size memop.pack) e.at
       "invalid lane index";
     [NumType I32Type; VecType memop.ty] -->  [VecType memop.ty]
 
   | VecStoreLane (memop, i) ->
-    check_memop c memop vec_size (fun sz -> Some sz) e.at;
+    check_memop NonAtomic c memop vec_size (fun sz -> Some sz) e.at;
     require (i < vec_size memop.ty / packed_size memop.pack) e.at
       "invalid lane index";
     [NumType I32Type; VecType memop.ty] -->  []
@@ -514,23 +521,23 @@ let rec check_instr (c : context) (e : instr) (s : infer_result_type) : op_type
       "invalid lane index";
     [t; NumType t2] --> [t]
   | MemoryAtomicWait atomicop -> 
-    check_memop c atomicop num_size (fun sz -> sz) e.at;
+    check_memop Atomic c atomicop num_size (fun sz -> sz) e.at;
     [NumType I32Type; NumType atomicop.ty; NumType I64Type] --> [NumType I32Type]
   | MemoryAtomicNotify atomicop ->
-    check_memop c atomicop num_size (fun sz -> sz) e.at;
+    check_memop Atomic c atomicop num_size (fun sz -> sz) e.at;
     [NumType I32Type; NumType I32Type] --> [NumType I32Type]
   | AtomicFence -> [] --> []
   | AtomicLoad atomicop -> 
-    check_memop c atomicop num_size (fun sz -> sz) e.at;
+    check_memop Atomic c atomicop num_size (fun sz -> sz) e.at;
     [NumType I32Type] --> [NumType atomicop.ty]
   | AtomicStore atomicop ->
-    check_memop c atomicop num_size (fun sz -> sz) e.at;
+    check_memop Atomic c atomicop num_size (fun sz -> sz) e.at;
     [NumType I32Type; NumType atomicop.ty] --> []
   | AtomicRmw (rmwop, atomicop) -> 
-    check_memop c atomicop num_size (fun sz -> sz) e.at;
+    check_memop Atomic c atomicop num_size (fun sz -> sz) e.at;
     [NumType I32Type; NumType atomicop.ty] --> [NumType atomicop.ty]
   | AtomicRmwCmpXchg atomicop ->
-    check_memop c atomicop num_size (fun sz -> sz) e.at;
+    check_memop Atomic c atomicop num_size (fun sz -> sz) e.at;
     [NumType I32Type; NumType atomicop.ty; NumType atomicop.ty] --> [NumType atomicop.ty]
 
 and check_seq (c : context) (s : infer_result_type) (es : instr list)