+
+-- Comparison of literal with widened operand: perform the comparison
+-- at the smaller width, as long as the literal is within range.
+
+-- We can't do the reverse trick, when the operand is narrowed:
+-- narrowing throws away bits from the operand, there's no way to do
+-- the same comparison at the larger size.
+
+#if i386_TARGET_ARCH || x86_64_TARGET_ARCH
+-- powerPC NCG has a TODO for I8/I16 comparisons, so don't try
+
+cmmMachOpFold cmp [CmmMachOp conv [x], CmmLit (CmmInt i _)]
+ | -- if the operand is widened:
+ Just (rep, signed, narrow_fn) <- maybe_conversion conv,
+ -- and this is a comparison operation:
+ Just narrow_cmp <- maybe_comparison cmp rep signed,
+ -- and the literal fits in the smaller size:
+ i == narrow_fn rep i
+ -- then we can do the comparison at the smaller size
+ = cmmMachOpFold narrow_cmp [x, CmmLit (CmmInt i rep)]
+ where
+ maybe_conversion (MO_U_Conv from to)
+ | to > from
+ = Just (from, False, narrowU)
+ maybe_conversion (MO_S_Conv from to)
+ | to > from, not (isFloatingRep from)
+ = Just (from, True, narrowS)
+ -- don't attempt to apply this optimisation when the source
+ -- is a float; see #1916
+ maybe_conversion _ = Nothing
+
+ -- careful (#2080): if the original comparison was signed, but
+ -- we were doing an unsigned widen, then we must do an
+ -- unsigned comparison at the smaller size.
+ maybe_comparison (MO_U_Gt _) rep _ = Just (MO_U_Gt rep)
+ maybe_comparison (MO_U_Ge _) rep _ = Just (MO_U_Ge rep)
+ maybe_comparison (MO_U_Lt _) rep _ = Just (MO_U_Lt rep)
+ maybe_comparison (MO_U_Le _) rep _ = Just (MO_U_Le rep)
+ maybe_comparison (MO_Eq _) rep _ = Just (MO_Eq rep)
+ maybe_comparison (MO_S_Gt _) rep True = Just (MO_S_Gt rep)
+ maybe_comparison (MO_S_Ge _) rep True = Just (MO_S_Ge rep)
+ maybe_comparison (MO_S_Lt _) rep True = Just (MO_S_Lt rep)
+ maybe_comparison (MO_S_Le _) rep True = Just (MO_S_Le rep)
+ maybe_comparison (MO_S_Gt _) rep False = Just (MO_U_Gt rep)
+ maybe_comparison (MO_S_Ge _) rep False = Just (MO_U_Ge rep)
+ maybe_comparison (MO_S_Lt _) rep False = Just (MO_U_Lt rep)
+ maybe_comparison (MO_S_Le _) rep False = Just (MO_U_Le rep)
+ maybe_comparison _ _ _ = Nothing
+
+#endif
+