#9509: No automatic specialization of inlinable imports in 7.8 -------------------------------------+------------------------------------- Reporter: dolio | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by nfrisby): With no pragma, {{{foo}}} has the following unfolding and gets inlined. {{{ 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) }}} With the {{{INLINABLE}}} pragma, {{{foo}}} has the following unfolding and does not get inlined. {{{ Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 210 60 }}} In both cases, its RHS is just a cast. I think the inferred {{{IF_ARGS}}} guidance is the cause of this unexpected behavior, because it violates the {{{"Mind you, then 'choose' will be inlined (since RHS is trivial)"}}} assumption in {{{Note [Specialisation shape]}}}, which otherwise anticipated this consequence of the ({{{IO}}}) newtype. https://github.com/ghc/ghc/blob/c36904d66f30d4386a231ce365a056962a881767/com... I did not investigate where the {{{IF_ARGS}}} guidance is coming from for such a trivial declaration. Seems like a leftover from the "actual" RHS (at the newtype's representative type), in this specific example and context. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9509#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler