"Failed to find interface decl for `Offside.a1'" with -O2

[Ian Lynagh]

Hi guys,

I'm afraid I haven't got a simple test case for this one.

ghc is giving me the error
    Failed to find interface decl for `Offside.a1'
in a rather large program. I have shown how to reproduce the problem
below (indenting the output). The code, compiled as shown below, is at
http://c93.keble.ox.ac.uk/~ian/igl-0.0.8-b1.tar.gz

$ hmake -ghc Project -package lang -O2
    ghc  -package lang -O2   -c -o Tokens.o Tokens.lhs
    ghc  -package lang -O2   -c -o Tree.o Tree.lhs
    ghc  -package lang -O2   -c -o Subject.o Subject.lhs
    ghc  -package lang -O2   -c -o PPTeX.o PPTeX.lhs
    ghc  -package lang -O2   -c -o Position.o Position.lhs
    ghc  -package lang -O2   -c -o Either.o Either.lhs
    ghc  -package lang -O2   -c -o PCbase.o PCbase.lhs
    ghc  -package lang -O2   -c -o PC.o PC.lhs
    ghc  -package lang -O2   -c -o Parser.o Parser.lhs
    ghc  -package lang -O2   -c -o Mangle.o Mangle.lhs
    ghc  -package lang -O2   -c -o Sort.o Sort.lhs
    ghc  -package lang -O2   -c -o FiniteMap.o FiniteMap.lhs
    ghc  -package lang -O2   -c -o IA.o IA.lhs
    ghc  -package lang -O2   -c -o Offside.o Offside.lhs

    Offside.lhs:116: Warning: Pattern match(es) are overlapped
        In the definition of `step': step _ pos [] _ = ...
    ghc  -package lang -O2   -c -o Scanner.o Scanner.lhs
    ghc  -package lang -O2   -c -o Args.o Args.lhs
    ghc  -package lang -O2   -c -o Project.o Project.lhs

    Project.lhs:4:
        Failed to find interface decl for `Offside.a1'
        from module `Offside'

    Project.lhs:4:
        Failed to find interface decl for `Offside.a3'
        from module `Offside'
$ ghc  -package lang -O   -c -o Project.o Project.lhs

    Project.lhs:4:
        Failed to find interface decl for `Offside.a1'
        from module `Offside'

    Project.lhs:4:
        Failed to find interface decl for `Offside.a3'
        from module `Offside'
$ ghc  -package lang   -c -o Project.o Project.lhs
$ 


Thanks
Ian