#9370: unfolding info as seen when building a module depends on flags in a previously-compiled module -------------------------------------+------------------------------------- Reporter: carter | Owner: richardfung Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 7.8.3 Resolution: | Keywords: newcomer, | Inlining Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #8635 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by richardfung): Ah yes sorry I shall try to keep my comments more self contained. The ticket addresses the issue that the unfolding info seen depends on previously compiled modules with --make. As I understand it, this can either cause ghc to inline when it shouldn't (in -O0) or to be unable to inline when it should. For example, if we have modules A and B, both which import module C, and we assume A is built first, then whether B sees the interface pragmas of C is dependent on whether they were read in when compiling A. If A is built with -O0, then even if B is built with -O it can not inline things from C because it doesn't have the unfolding info. Alternatively, if A is built with -O and B is built with -O0, B will still see the unfolding info and use it. The suggested fix is to disable -fignore-interface-pragmas being implied by -O0 and to make sm_inline = False when -O0. I do believe this solves both of the scenarios described above, but I'm concerned that if A is built with -fignore-interface-pragmas, and B is built with -O, B will still not have the unfolding info from C when compiling. This would be identical to what's currently happening when A is built with -O0 and B with -O. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9370#comment:38 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler