Make WordQuotRem2Op ok-for-speculation too

compiler/GHC/Builtin/PrimOps.hs

@@ -551,7 +551,6 @@ primOpIsCheap op = primOpOkForSpeculation op
 primOpIsDiv :: PrimOp -> Bool
 primOpIsDiv op = case op of
 
-  -- TODO: quotRemWord2
   IntQuotOp       -> True
   Int8QuotOp      -> True
   Int16QuotOp     -> True
@@ -588,6 +587,8 @@ primOpIsDiv op = case op of
   Word32QuotRemOp -> True
   -- Word64QuotRemOp doesn't exist (yet)
 
+  WordQuotRem2Op  -> True
+
   FloatDivOp      -> True
   DoubleDivOp     -> True
   _               -> False

compiler/GHC/Core/Utils.hs

@@ -1615,8 +1615,10 @@ app_ok fun_ok primop_ok fun args
 
       PrimOpId op _
         | primOpIsDiv op
-        , [arg1, Lit lit] <- args
-        -> not (isZeroLit lit) && expr_ok fun_ok primop_ok arg1
+        , Lit divisor <- last args
+            -- there can be 2 args (most div primops) or 3 args
+            -- (WordQuotRem2Op), hence the use of last/init
+        -> not (isZeroLit divisor) && all (expr_ok fun_ok primop_ok) (init args)
               -- Special case for dividing operations that fail
               -- In general they are NOT ok-for-speculation
               -- (which primop_ok will catch), but they ARE OK