#14626: No need to enter a scrutinised value -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: heisenbug Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: performance Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #13861 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj):
So something is definitely fishy here.
I think that there's something different about '''top-level''' binders. Consider {{{ data T = MkT !Bool top_x = True f True (MkT local_y) = local_y f False _ = top_x }}} Here I think that `local_y` gets bound to a correctly-tagged pointer, fetched out of the `MkT` constructor. But, in contrast, I think that `top_x` is bound to the label for the top- level closure for `top_x`, which is 8-byte aligned. So the label isn't tagged; instead, the code generator has to tag it. Is that happening in your "return it instead of eantering it" path? Other than that I have no idea why it crashes. Things you might try: * Switch off the new optimisation when building stage2 and the libraries. Use it only for the test suite: these are small programs and easier to debug. * Maybe add an assertion in the Cmm: the claim is that on the "return it" path, the thing beign returned is a correctly-tagged pointer. So, the assertion can follow the pointer and check that the thing pointed to is a value, with the right tag, etc. There must be some code in the RTS (or somewhere) that checks that. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14626#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler