Enforce evaluation order in IRC.add_interf and IRC.add_pref

As written previously, OCaml can evaluate `nodeOfVar g v1` and
`nodeOfVar g v2` in any order.  Consequently, `v1` and `v2` can be
entered in the `varTable` hash table in different order.  This can
result in different (but equally valid) register allocations.

It's better to enforce one evaluation order for the sake of
reproducible compilations when the OCaml version changes.

1 files changed, 2 insertions, 2 deletions

diff --git a/backend/IRC.ml b/backend/IRC.ml
index 6f4bbe29..1246a2d0 100644
--- a/backend/IRC.ml
+++ b/backend/IRC.ml
@@ -911,10 +911,10 @@ let location_of_var g v =
 (* The exported interface *)
 
 let add_interf g v1 v2 =
-  addEdge g (nodeOfVar g v1) (nodeOfVar g v2)
+  let n1 = nodeOfVar g v1 in let n2 = nodeOfVar g v2 in addEdge g n1 n2
 
 let add_pref g v1 v2 =
-  addMovePref g (nodeOfVar g v1) (nodeOfVar g v2)
+  let n1 = nodeOfVar g v1 in let n2 = nodeOfVar g v2 in addMovePref g n1 n2
 
 let coloring g =
   initialNodePartition g;