#15573: Make bindings with multiple occurrences a join point instead of duplicating code during inlining. -------------------------------------+------------------------------------- Reporter: AndreasK | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: JoinPoints | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I have some intermediate core of the form: {{{ -- RHS size: {terms: 9, types: 2, coercions: 0, joins: 0/0} cseAlts_s1dD [Occ=Once!T[1]] :: T -> Int# [LclId, CallArity=1, Str=] cseAlts_s1dD = \ (lamVar_s1dw [Occ=Once!, Dmd=, OS=OneShot] :: T) -> case lamVar_s1dw of wild_Xc [Dmd=] { __DEFAULT -> 1#; B -> 2#; C -> 3# } -- RHS size: {terms: 14, types: 3, coercions: 0, joins: 0/0} $wfmerge_s1cZ [InlPrag=NOUSERINLINE[0]] :: T -> T -> Int# [LclId, Arity=2, CallArity=2, Str=] $wfmerge_s1cZ = \ (w_s1cU [Occ=Once!, Dmd=] :: T) (w_s1cV [Occ=Once*, Dmd=] :: T) -> case w_s1cU of wild_XA [Dmd=] { __DEFAULT -> -1#; A -> 2#; B -> cseAlts_s1dD w_s1cV; C -> cseAlts_s1dD w_s1cV } }}} Which after the simplifier ran got inlined into the branches to give us: {{{ fmerge = \ (w_s1cU :: T) (w_s1cV :: T) -> case w_s1cU of { __DEFAULT -> GHC.Types.I# -1#; A -> GHC.Types.I# 2#; B -> case w_s1cV of { __DEFAULT -> GHC.Types.I# 1#; B -> GHC.Types.I# 2#; C -> GHC.Types.I# 3# }; C -> case w_s1cV of { __DEFAULT -> GHC.Types.I# 1#; B -> GHC.Types.I# 2#; C -> GHC.Types.I# 3# } } }}} What I would really like GHC to do instead though is to make `cseAlts_s1dD` a join point when possible. This would eliminate both the call overhead AND the call duplication. The current behavior seems fine when we can't make it a join point. But when we can we should try to take advantage of that opportunity. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15573 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler