Segfault in a CoreLinted program (and a GHC-generated Core question)

Simon Peyton Jones simonpj at
Mon Oct 26 17:43:09 UTC 2015

|  So my questions are: Am I right in assuming that CoreLint accepted programs
|  should not segfault?

Yes.  Modulo unsafeCoerce, and FFI calls.

| What about internal invariants? Should CoreLint check
|  for those? Is there any pass that checks for invariants and prints helpful
|  messages in case of a invariant invalidation?

Yes; they are documented in CoreSyn, which the data type, and Lint checks them.

|  As an attempt at debugging the code generated by my plugin, I wrote the
|  function that is supposed to be generated by my Core pass in Haskell and
|  compiled with GHC. Generated Core is mostly the same, except at one point it
|  has an extra lambda directly applied to a void#, something like ((\_ -> ...)
|  void#). Where can I learn more about why GHC is doing that?

Show me the code! 

Instead of generating

    x :: Int# = <some expression that might fail>

GHC sometimes generates

    x :: Void# -> Int# = \_ - <some expression that might fail>

and then calls (x void#), to make any div-zero failures happen at the right place.

I'm not sure if that is what you are seeing, but we can work it out when you give more detail.


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