[M3devel] thouhts on -Wall with C backend output

[Jay K]

drat, these are worse:

"../src/Macro.m3", line 949: warning: unreachable ELSE in TYPECASE


== package /Users/jay/dev2/cm3/m3-ui/formsvbt ==

 +++ /cm3/bin/cm3    -build -DROOT=/Users/jay/dev2/cm3 +++
--- building in AMD64_DARWIN ---

ignoring ../src/m3overrides

new source -> compiling Macro.m3
cc1plus: warnings being treated as errors
Macro.mc.c: In function ‘char* Macro__EvalLength(char*, char*)’:
Macro.mc.c:5271: warning: control reaches end of non-void function
Macro.mc.c: In function ‘char* Macro__EvalPlus(char*, char*)’:
Macro.mc.c:9004: warning: control reaches end of non-void function
Macro.mc.c: In function ‘char* Macro__EvalMinus(char*, char*)’:
Macro.mc.c:9468: warning: control reaches end of non-void function


If I put in the somewhat obvious:


    ELSE <* ASSERT FALSE *>


then:

new source -> compiling Macro.m3
"../src/Macro.m3", line 949: warning: unreachable ELSE in TYPECASE
1 warning encountered
cc1plus: warnings being treated as errors
Macro.mc.c: In function ‘char* Macro__EvalLength(char*, char*)’:
Macro.mc.c:5271: warning: control reaches end of non-void function
Macro.mc.c: In function ‘char* Macro__EvalPlus(char*, char*)’:
Macro.mc.c:9004: warning: control reaches end of non-void function



For stablegen, I am inclined to put in that ELSE <* ASSERT FALSE *>.


I might might might be able to put in C assert(false) in these places.

 - Jay


> To: hendrik at topoi.pooq.com
> Date: Sun, 16 Dec 2012 10:55:29 -0800
> From: mika at async.caltech.edu
> CC: m3devel at elegosoft.com
> Subject: Re: [M3devel] thouhts on -Wall with C backend output
> 
> Can you have an option to add an assertion in the output for these cases?
> 
> Here either
> 
> 1. gcc has found a bug in the C code generator and/or front end, in that
>    there's no default (abortion) case
> 
> or
> 
> 2. the front end has deduced there is no need for abortion because it can
>    see that the missing ELSE is never going to be exercised, based on the
>    already existing type information
> 
> What I'm proposing is two modes for the compiler:
> 
> -- ignore the errors
> 
> or
> 
> -- add proper assertions to the C code, e.g., 
> 
>     assert(false, "front-end deduced this cant happen by inspecting type information")
> 
>    which, when enabled, should make gcc shut up, and instead turn into
>    runtime checks on the compiler
> 
>       Mika
> 
> Hendrik Boom writes:
> >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
 		 	   		  
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