[M3devel] thouhts on -Wall with C backend output

[Hendrik Boom]

On Sun, Dec 16, 2012 at 09:58:10AM +0000, Jay K wrote:
> 
> I've tried to generate "very good C".
> I've fixed some of what gcc -Wall complains about.
> For default gcc on my old MacBook -- old enough that it can still emulate PowerPC, gcc is 4.0.1.
> (at least one of what I deal with, I think anything newer won't complain..)
> 
> 
> 
> do-cm3-all with -Wall -Werror gets very far, to:
> 
> == package /Users/jay/dev2/cm3/m3-db/stablegen ==
> 
>  +++ /cm3/bin/cm3    -build -DROOT=/Users/jay/dev2/cm3 +++
> --- building in AMD64_DARWIN ---
> 
> ignoring ../src/m3overrides
> 
> w source -> compiling GenCode.m3
> cc1: warnings being treated as errors
> GenCode.mc.c: In function ‘GenCode__BuildMethods__Search’:
> GenCode.mc.c:3505: warning: control reaches end of non-void function
>   m3_backend => 1
> 
>   PROCEDURE Search (    type    : Type.Reference;
>                     VAR count   : INTEGER;
>                     VAR top     : CARDINAL;
>                         umethods: AtomList.T   ):
>     ImportList.MethodList RAISES {StablegenError.E} =
>     VAR methods: ImportList.MethodList;
>     BEGIN
>       IF (type = Type.root) OR (type = NIL) THEN (* base of
>                                                     recursion *)
>         RETURN NEW(ImportList.MethodList, ABS(count))
>       ELSE
>     TYPECASE type OF
>           Type.Object (ob) => 
>           IF count <= 0 THEN
>             count:= count - NUMBER(ob.methods^)
>           END;
>           methods := Search(ob.super, count, top, umethods);
>           FOR i := 0 TO LAST(ob.methods^) DO
>             IF umethods = NIL
>               OR AtomList.Member(
>                      umethods, ob.methods[i].name) THEN
>               IF AtomList.Member(reserved, ob.methods[i].name) THEN
>                 RAISE StablegenError.E(Atom.ToText(ob.methods[i].name)
>                 &" is a reserved method name in stable objects. "
>                 &"Must not be an update method.")
>               END;
>               methods[top].name := ob.methods[i].name;
>               methods[top].sig := ob.methods[i].sig;
>               INC(top)
>             END
>           END;
>           RETURN methods
>         | Type.Opaque (op) =>
>           RETURN Search(op.revealedSuperType, count, top, umethods)
>         | Type.Reference => <*ASSERT FALSE*>
>         END
>       END
>     END Search;
> 
> I think we can't expect gcc -Wall -Werror to pass.
> I really wanted it to, and I tried, and I fixed stuff.
> But I don't think it is viable.
> Ok?

Could  it be that the TYPECASE doesn't have an ELSE clause, possibly
translated to a switch withouy a default: label?  This would give the
C code an apparent path to the end of the function.  M3 may know that
the TYPECASE exhausts all the possibilities, but C will not.

-- hendrik