#15832: fprintCCS_stderr (+RTS -xc) should be able to recurse into stacks that evaluated a given stack even if the latter does not come from a CAF -------------------------------------+------------------------------------- Reporter: infinity0 | Owner: (none) Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.6.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by infinity0): <bgamari> infinity0, have you considered simply using a more aggressive -fprof-* flag? <infinity0> bgamari: i'm already using "-fprof-auto -fprof-auto-calls -fprof-cafs" that seems to be the most aggressive available option <bgamari> ahh yes, so you are <bgamari> well then, that is indeed tricky <bgamari> can you describe where ideally you would like CCs to be inserted? <infinity0> i tried manually inserting CCs in the bad cases and couldn't get them working, so i don't really know <infinity0> but it seems to me that the logic that traverses different stacks to find subsequent "evaluated by" stacks, maybe can be expanded <infinity0> because it apparently only works when each stack except the last starts from a CAF <infinity0> i previously thought perhaps everything is supposed to start from a CAF but from what you're saying now it seems maybe not <infinity0> in which case, the "evaluated by" traversal logic ofc can't work for these latter cases * bgamari tries to work out what the stack looks like in the bad case <bgamari> infinity0, for what it's worth, I'm not sure this will just be a matter of expanding the existing stack printing logic <bgamari> infinity0, I suspect the information you need is actually not present at runtime <infinity0> oh :( <bgamari> afterall, in both cases we have tail-called <bgamari> so there is no stack frame to reconstruct execution from <bgamari> it just happens that in the good case we tail called into a CAF, which had a cost center <bgamari> I agree that this is an unfortunate behavior though <bgamari> I may be missing something but I think the right way to think about this may be from the perspective of finding a heuristic to use to insert the necessary CCs <bgamari> admittedly it's not immediately clear what that should look like, however <infinity0> yeah, going back to the original bad example, I tried changing it to {-# SCC test0 #-} ( {-# SCC test1 #-} \_ -> {-# SCC test2 #-} (print ... <infinity0> and this didn't fix the stack either <bgamari> I'll admit, that's a bit surprising <bgamari> oh, perhaps because it's non-updateable <bgamari> so you don't get an update frame -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15832#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler