import FastString
import StaticFlags ( opt_SimplExcessPrecision )
-import DATA_BITS ( Bits(..) )
+import Data.Bits ( Bits(..) )
#if __GLASGOW_HASKELL__ >= 500
-import DATA_WORD ( Word )
+import Data.Word ( Word )
#else
-import DATA_WORD ( Word64 )
+import Data.Word ( Word64 )
#endif
\end{code}
+Note [Constant folding]
+~~~~~~~~~~~~~~~~~~~~~~~
+primOpRules generates the rewrite rules for each primop
+These rules do what is often called "constant folding"
+E.g. the rules for +# might say
+ 4 +# 5 = 9
+Well, of course you'd need a lot of rules if you did it
+like that, so we use a BuiltinRule instead, so that we
+can match in any two literal values. So the rule is really
+more like
+ (Lit 4) +# (Lit y) = Lit (x+#y)
+where the (+#) on the rhs is done at compile time
+
+That is why these rules are built in here. Other rules
+which don't need to be built in are in GHC.Base. For
+example:
+ x +# 0 = x
+
+
\begin{code}
primOpRules :: PrimOp -> Name -> [CoreRule]
primOpRules op op_name = primop_rule op