par# and spark# call newSpark differently, confuses LLVM backend

If par# and spark# are being used in the same compilation unit, say like

  case spark# (work 2) realWorld# of
    (# _, _ #) -> case par# (work 1) of
        _ -> return ()

The LLVM backend generates code like follows:

    call ccc void (i8*,i8*)* @newSpark( i8* %lnnX, i8* %lnnZ ) nounwind
[...]
    %lno7 = call ccc void (i8*,i8*)* @newSpark( i8* %lno4, i8* %lno6 ) nounwind

So both call newSpark under the hood - but inconsistently. The first call expects no returned value, while the second does. As the first seen call doesn't have a returned value, the backend concludes that the function's type must be void (i8*,i8*) *, which make opt choke on the second usage:

opt: /tmp/ghc23150_0/ghc23150_0.ll:845:1: error: instructions returning void cannot have a name
%lno7 = call ccc void (i8*,i8*)* @newSpark( i8* %lno4, i8* %lno6 ) nounwind
^

The underlying reason is in code generation: It doesn't always ask for the return value of newSpark. So one way to fix this is to just always get the return value - but simply discard it if it's not needed. Patch attached.

Trac metadata

Trac field	Value
Version	7.2.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (LLVM)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture