| coreToStgExpr (Case scrut bndr ty [])
| = coreToStgExpr (Case scrut bndr ty [(DEFAULT, [], mkImpossibleExpr
| ty)])
Yes that should be fine.
I'm afraid I have no idea why you are getting
| Oops! Entered absent arg w_sc1l FilePath
or seg-faults.
Simon
|
| But that may be because of some libraries I need to recompile, although I'm
| not
| sure why this would be the case.
|
| The problem I'm trying to solve is my lint-safe (after the smarter lint check
| about bottoming expressions) programs are failing with segfaults. Of course
| that may be because I'm doing something wrong in STG level, but I'm trying to
| make sure everything above STG is correct and bug-free. It'd be really great
| if
| I could somehow generate an erroring expression in some places that are
| supposed to be unreachable, just to make sure my segfaults are not related
| with
| those.
|
| 2016-02-29 6:32 GMT-05:00 Simon Peyton Jones :
| > | I wanted to ask: Is there a restriction on what kind empty case
| > | expressions are supported by the code generator or can I just improve
| > | the lint check and assume that the code will be handled by the code
| > | generator correctly?
| >
| > I believe the latter. See CoreToStg line 364.
| >
| > So feel free to make Lint cleverer; make sure you add a Note. But if it
| /needs/ to be cleverer, that suggests that the simplifier should be cleverer
| instead, and should simplify the code so that even a dumb Core Lint has no
| trouble.
| >
| > In your example why didn't the simplifier do case-of-case?
| >
| > I suppose that this might be after some pass and before a simplifier run.
| >
| > Simon
| >
| > | -----Original Message-----
| > | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Ömer
| > | Sinan Agacan
| > | Sent: 29 February 2016 03:16
| > | To: ghc-devs
| > | Subject: CoreLint check for case with no alts
| > |
| > | Hi all,
| > |
| > | CoreLint has a check that, when seeing a case expression with empty
| > | list of alternatives, checks whether the scrutinee is bottom. This
| > | "bottom-ness" check is, however, very simple and returning many false
| > | negatives. For example, when it sees a case expression, all it does is:
| > |
| > | go _ (Case _ _ _ alts) = null alts
| > |
| > | Which is just too simple for some cases. (it could check if all the
| > | RHSs are bottom, or if the scrutinee is bottom etc.)
| > |
| > | I guess this makes sense, since it's OK to generate unreachable code,
| > | but it's not OK to not generate a code in a reachable path.
| > |
| > | But in my case this is becoming problem as it's rejecting my seemingly
| > | valid program. One of the relevant parts in my code is this:
| > |
| > | case ww_s4C3 of ww_X4Fb {
| > | (#_||#) ww_s4Ce ->
| > | case case ww_s4Ce of ww_s4F1 { (# ww_s4F2, ww_s4F3 #) ->
| > | lvl_s4F4 ww_s4F3 ww_s4F2
| > | }
| > | of wild_00 {
| > | -- empty
| > | };
| > |
| > | lvl_s4F4 :: Int# -> String -> Var
| > | [LclId, Arity=2, Str=DmdType (args: ) (res: x)]
| > | lvl_s4F4 =
| > | \ (ww_s4F3 :: Int#) (ww_s4F2 :: String) ->
| > | lvl_s3V4 (TyVar ww_s4F2 ww_s4F3)
| > |
| > | lvl_s3V4 :: Var -> Var
| > | [LclId, Arity=1, CallArity=1, Str=DmdType (args: ) (res: x)]
| > | lvl_s3V4 = \ (i_a1vO :: Var) -> lvl_s4EZ i_a1vO
| > |
| > | lvl_s4EZ :: Var -> Var
| > | [LclId, Arity=1, Str=DmdType (args: ) (res: x)]
| > | lvl_s4EZ = \ (i_a1vO :: Var) -> error ...
| > |
| > | The scrutinee part of the case expression in the alternative is clearly
| > | bottom, but this expression is rejected by the linter.
| > |
| > | One easy solution is to implement a more precise test and use it in
| > | linter. But I thought maybe the current implementation is deliberately
| > | so. Maybe the code generator doesn't support that type of code etc. so
| > | I wanted to ask: Is there a restriction on what kind empty case
| > | expressions are supported by the code generator or can I just improve
| > | the lint check and assume that the code will be handled by the code
| > | generator correctly?
| > |
| > | Thanks.
| > | _______________________________________________
| > | ghc-devs mailing list
| > | ghc-devs@haskell.org
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| > | skell.org%2fcgi-bin%2fmailman%2flistinfo%2fghc-
| > | devs&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7ce621b9bcb2774ff8
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