#10844: CallStack should not be inlined -------------------------------------+------------------------------------- Reporter: nomeata | Owner: gridaphobe Type: task | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1259 Wiki Page: | -------------------------------------+------------------------------------- Comment (by gridaphobe): The work in #8472 to float primitive string literals to the top did fix the issue I described in https://phabricator.haskell.org/D1259#72921, but it turns out there's another issue leading to increased allocations elsewhere in nofib. I've minimized the `parstof` benchmark to {{{ module Foo where c_the_program=(++) "main ip =\n" ((++) " i2str (optim (myMain deciem))\n" ((++) ";\n" ((++) "\n" ((++) "TYPE tJobdef = [ JOBDEF, int, int, int, tJobdef, tJobdef ] ;\n" ((++) "TYPE tJobstat = [ JOBSTAT, int, int, int, int, tJobdef ] ;\n" ((++) "TYPE tTree = [ LEAF, int |\n" ((++) " TREE, tTree, tTree ] ;\n" ((++) "TYPE tProc = [ PROC, int, tJobstat ] ;\n" ((++) "\n" ((++) "\n" ((++) "\n" ((++) "emptyjobdef = [JOBDEF, 0 , 0 , 0, emptyjobdef, emptyjobdef] ;\n" "")))))))))))) }}} which is just a chain of appends (though the number of `(++)` seems to matter!). GHC HEAD optimizes this into a single string literal, whereas my patch gives {{{ -- RHS size: {terms: 1, types: 0, coercions: 0} Foo.c_the_program11 :: GHC.Prim.Addr# [GblId, Caf=NoCafRefs, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 120 0}] Foo.c_the_program11 = "main ip =\n\ \ i2str (optim (myMain deciem))\n\ \;\n"# -- RHS size: {terms: 1, types: 0, coercions: 0} Foo.c_the_program10 :: GHC.Prim.Addr# [GblId, Caf=NoCafRefs, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 620 0}] Foo.c_the_program10 = "TYPE tJobdef = [ JOBDEF, int, int, int, tJobdef, tJobdef ] ;\n\ \TYPE tJobstat = [ JOBSTAT, int, int, int, int, tJobdef ] ;\n\ \TYPE tTree = [ LEAF, int |\n\ \ TREE, tTree, tTree ] ;\n\ \TYPE tProc = [ PROC, int, tJobstat ] ;\n"# -- RHS size: {terms: 1, types: 0, coercions: 0} Foo.c_the_program7 :: GHC.Prim.Addr# [GblId, Caf=NoCafRefs, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 190 0}] Foo.c_the_program7 = "emptyjobdef = [JOBDEF, 0 , 0 , 0, emptyjobdef, emptyjobdef] ;\n"# -- RHS size: {terms: 2, types: 0, coercions: 0} Foo.c_the_program6 :: [Char] [GblId, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=False, ConLike=True, WorkFree=False, Expandable=True, Guidance=IF_ARGS [] 20 0}] Foo.c_the_program6 = GHC.CString.unpackCString# Foo.c_the_program7 -- RHS size: {terms: 3, types: 1, coercions: 0} Foo.c_the_program5 :: [Char] [GblId, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=False, ConLike=False, WorkFree=False, Expandable=False, Guidance=IF_ARGS [] 30 0}] Foo.c_the_program5 = ++ @ Char Foo.c_the_program8 Foo.c_the_program6 ... }}} It's able to eliminate some of the `(++)` calls, but not all. I'm not yet sure why this is happening, but I imagine it involves a `(++)` term being floated out before we eliminate it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10844#comment:20 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler