#9370: unfolding info as seen when building a module depends on flags in a previously-compiled module -------------------------------------+------------------------------------- Reporter: carter | Owner: Type: bug | Status: new Priority: high | Milestone: 7.10.1 Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: Compile- | Blocked By: time performance bug | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by simonpj): Hmm. Is this with `ghc --make`? Then yes, that sounds plausible. * When compiling a module M with -O, and then reading an interface file to support that compilation, GHC makes the unfolding of Ids in that interface file. * With `ghc --make` when GHC goes on to compile a new module L, it doesn't re-read interface files it has already read (that is part of why `--make` is faster). So the already-read Ids still have those unfoldings in them. * As a result, if L is compiled with -O0, it will still see the unfoldings. I can see that is perplexing. If it's important, the solution would be to disable inlining for imported functions when -O0 is on. (Actually, more precisely, it's controlled by `-fignore-interface-pragmas`.) I don't think it would be terribly hard to do that, although it would be an extra test on every inlining for an imported function. I still wish someone could explain why it's so crucial for this module to be compiled with -O0. That must be a bug, either in the RULES for some package, or in GHC. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9370#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler