Small optimisation: always sink/inline reg1 = reg2 assignments

compiler/cmm/CmmSink.hs

@@ -178,7 +178,7 @@ cmmSink dflags graph = ofBlockList (g_entry graph) $ sink mapEmpty $ blocks
       drop_if a@(r,rhs,_) live_sets = (should_drop, live_sets')
           where
             should_drop =  conflicts dflags a final_last
-                        || {- not (isSmall rhs) && -} live_in_multi live_sets r
+                        || not (isTrivial rhs) && live_in_multi live_sets r
                         || r `Set.member` live_in_joins
 
             live_sets' | should_drop = live_sets
@@ -205,12 +205,12 @@ isSmall (CmmLit _) = True
 isSmall (CmmMachOp (MO_Add _) [x,y]) = isTrivial x && isTrivial y
 isSmall (CmmRegOff (CmmLocal _) _) = True
 isSmall _ = False
+-}
 
 isTrivial :: CmmExpr -> Bool
 isTrivial (CmmReg (CmmLocal _)) = True
-isTrivial (CmmLit _) = True
+-- isTrivial (CmmLit _) = True
 isTrivial _ = False
--}
 
 --
 -- annotate each node with the set of registers live *after* the node
@@ -365,9 +365,8 @@ tryToInline dflags live node assigs = go usages node [] assigs
   go _usages node _skipped [] = (node, [])
 
   go usages node skipped (a@(l,rhs,_) : rest)
-   | can_inline              = inline_and_discard
-   | False {- isTiny rhs -}  = inline_and_keep
-     --  ^^ seems to make things slightly worse
+   | can_inline     = inline_and_discard
+   | isTrivial rhs  = inline_and_keep
    where
         inline_and_discard = go usages' node' skipped rest