#16402: GHC doesnt' notice that (narrowWordFOO (x .&. FOO)) is just `x`. -------------------------------------+------------------------------------- Reporter: Fuuzetsu | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs {-# OPTIONS_GHC -ddump-simpl -ddump-to-file -dhex-word-literals -O2 #-} {-# LANGUAGE TypeApplications #-} module NarrowWord where import Data.Word import Data.Bits smallWord_foo :: Word64 -> Word64 smallWord_foo x = fromIntegral @Word16 $ fromIntegral (x .&. 0xFFFF) smallWord_bar :: Word64 -> Word64 smallWord_bar x = fromIntegral @Word16 $ fromIntegral x test :: Bool test = let w = 72430412501 in smallWord_foo w == smallWord_bar w }}} {{{#!hs -- RHS size: {terms: 7, types: 3, coercions: 0, joins: 0/0} smallWord_bar :: Word64 -> Word64 [GblId, Arity=1, Caf=NoCafRefs, Str=<S(S),1*U(U)>m, Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=ALWAYS_IF(arity=1,unsat_ok=True,boring_ok=False) Tmpl= \ (x_a1so [Occ=Once!] :: Word64) -> case x_a1so of { GHC.Word.W64# x#_a2Mw [Occ=Once] -> GHC.Word.W64# (GHC.Prim.narrow16Word# x#_a2Mw) }}] smallWord_bar = \ (x_a1so :: Word64) -> case x_a1so of { GHC.Word.W64# x#_a2Mw -> GHC.Word.W64# (GHC.Prim.narrow16Word# x#_a2Mw) } -- RHS size: {terms: 9, types: 3, coercions: 0, joins: 0/0} smallWord_foo :: Word64 -> Word64 [GblId, Arity=1, Caf=NoCafRefs, Str=<S(S),1*U(U)>m, Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=ALWAYS_IF(arity=1,unsat_ok=True,boring_ok=False) Tmpl= \ (x_a1hU [Occ=Once!] :: Word64) -> case x_a1hU of { GHC.Word.W64# x#_a30a [Occ=Once] -> GHC.Word.W64# (GHC.Prim.narrow16Word# (GHC.Prim.and# x#_a30a 0xffff##)) }}] smallWord_foo = \ (x_a1hU :: Word64) -> case x_a1hU of { GHC.Word.W64# x#_a30a -> GHC.Word.W64# (GHC.Prim.narrow16Word# (GHC.Prim.and# x#_a30a 0xffff##)) } -- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0} test :: Bool [GblId, Caf=NoCafRefs, Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=ALWAYS_IF(arity=0,unsat_ok=True,boring_ok=True) Tmpl= GHC.Types.True}] test = GHC.Types.True }}} For Word8, Word16, Word32, Word64 and Int8, Int16, Int32, Int64, I would expect GHC to never produce the {{{and}}}. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16402> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler