[M3devel] thouhts on -Wall with C backend output
Jay K
jay.krell at cornell.edu
Wed Jan 9 07:46:00 CET 2013
I'm going with "gcc -Wno-return-type " for now. Alas.
I put in "default:assert(!"case_jump hit default") for case_jumps, but of coursethat doesn't help.
If/when I make the C backend even more sophisticated, I'll detectlabel:;} // end of non-void function
and change it to:label:assert(!"control reaches end of non-void function");} // end of non-void function
This level of sophistication is basically to run the last pass multiple times, suppressing some/most logic/code, esp. the prints on all but the last pass.
The other passes, so far, have been useful in that they run over a subset of operations, and leavefewer for the last pass to deal with.
Hm. I do have "op_index", so at end of function, I might be able to just look back one operation for the set_label.
But that wouldn't detect:label: a = b;} // end of function
maybe that never occurs.
I also can't likely just put the assert at the end of every non-void function. 1) it bloats the code a bit 2) it would be usually unreachable.
I'm not even sure gcc wouldn't complain here about reachability...except..I already omit unused labels, so I know this label is branched to... anyway..later...
- Jay
> To: jay.krell at cornell.edu
> Date: Sun, 16 Dec 2012 23:49:35 -0800
> From: mika at async.caltech.edu
> CC: m3devel at elegosoft.com
> Subject: Re: [M3devel] thouhts on -Wall with C backend output
>
> Yeah it sounds like the frontend knows something that it's not telling
> the backend about... if I am reading your emails right.
>
> Jay K writes:
> >--_ad389312-f922-410e-bb8f-e7106388428f_
> >Content-Type: text/plain; charset="Windows-1252"
> >Content-Transfer-Encoding: quoted-printable
> >
> >
> >drat=2C these are worse:
> >
> >"../src/Macro.m3"=2C line 949: warning: unreachable ELSE in TYPECASE
> >
> >
> >=3D=3D package /Users/jay/dev2/cm3/m3-ui/formsvbt =3D=3D
> >
> > +++ /cm3/bin/cm3 -build -DROOT=3D/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 =91char* Macro__EvalLength(char*=2C char*)=92:
> >Macro.mc.c:5271: warning: control reaches end of non-void function
> >Macro.mc.c: In function =91char* Macro__EvalPlus(char*=2C char*)=92:
> >Macro.mc.c:9004: warning: control reaches end of non-void function
> >Macro.mc.c: In function =91char* Macro__EvalMinus(char*=2C char*)=92:
> >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"=2C line 949: warning: unreachable ELSE in TYPECASE
> >1 warning encountered
> >cc1plus: warnings being treated as errors
> >Macro.mc.c: In function =91char* Macro__EvalLength(char*=2C char*)=92:
> >Macro.mc.c:5271: warning: control reaches end of non-void function
> >Macro.mc.c: In function =91char* Macro__EvalPlus(char*=2C char*)=92:
> >Macro.mc.c:9004: warning: control reaches end of non-void function
> >
> >
> >
> >For stablegen=2C 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=2C 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
> >>=20
> >> Can you have an option to add an assertion in the output for these cases?
> >>=20
> >> Here either
> >>=20
> >> 1. gcc has found a bug in the C code generator and/or front end=2C in tha=
> >t
> >> there's no default (abortion) case
> >>=20
> >> or
> >>=20
> >> 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=2C based on t=
> >he
> >> already existing type information
> >>=20
> >> What I'm proposing is two modes for the compiler:
> >>=20
> >> -- ignore the errors
> >>=20
> >> or
> >>=20
> >> -- add proper assertions to the C code=2C e.g.=2C=20
> >>=20
> >> assert(false=2C "front-end deduced this cant happen by inspecting typ=
> >e information")
> >>=20
> >> which=2C when enabled=2C should make gcc shut up=2C and instead turn i=
> >nto
> >> runtime checks on the compiler
> >>=20
> >> Mika
> >>=20
> >> Hendrik Boom writes:
> >> >On Sun=2C Dec 16=2C 2012 at 09:58:10AM +0000=2C Jay K wrote:
> >> >>=20
> >> >> 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 emul=
> >ate PowerPC=2C gcc is 4.0.1.
> >> >> (at least one of what I deal with=2C I think anything newer won't comp=
> >lain..)
> >> >>=20
> >> >>=20
> >> >>=20
> >> >> do-cm3-all with -Wall -Werror gets very far=2C to:
> >> >>=20
> >> >> =3D=3D package /Users/jay/dev2/cm3/m3-db/stablegen =3D=3D
> >> >>=20
> >> >> +++ /cm3/bin/cm3 -build -DROOT=3D/Users/jay/dev2/cm3 +++
> >> >> --- building in AMD64_DARWIN ---
> >> >>=20
> >> >> ignoring ../src/m3overrides
> >> >>=20
> >> >> w source -> compiling GenCode.m3
> >> >> cc1: warnings being treated as errors
> >> >> GenCode.mc.c: In function =91GenCode__BuildMethods__Search=92:
> >> >> GenCode.mc.c:3505: warning: control reaches end of non-void function
> >> >> m3_backend =3D> 1
> >> >>=20
> >> >> PROCEDURE Search ( type : Type.Reference=3B
> >> >> VAR count : INTEGER=3B
> >> >> VAR top : CARDINAL=3B
> >> >> umethods: AtomList.T ):
> >> >> ImportList.MethodList RAISES {StablegenError.E} =3D
> >> >> VAR methods: ImportList.MethodList=3B
> >> >> BEGIN
> >> >> IF (type =3D Type.root) OR (type =3D NIL) THEN (* base of
> >> >> recursion *)
> >> >> RETURN NEW(ImportList.MethodList=2C ABS(count))
> >> >> ELSE
> >> >> TYPECASE type OF
> >> >> Type.Object (ob) =3D>=20
> >> >> IF count <=3D 0 THEN
> >> >> count:=3D count - NUMBER(ob.methods^)
> >> >> END=3B
> >> >> methods :=3D Search(ob.super=2C count=2C top=2C umethods)=3B
> >> >> FOR i :=3D 0 TO LAST(ob.methods^) DO
> >> >> IF umethods =3D NIL
> >> >> OR AtomList.Member(
> >> >> umethods=2C ob.methods[i].name) THEN
> >> >> IF AtomList.Member(reserved=2C 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=3B
> >> >> methods[top].name :=3D ob.methods[i].name=3B
> >> >> methods[top].sig :=3D ob.methods[i].sig=3B
> >> >> INC(top)
> >> >> END
> >> >> END=3B
> >> >> RETURN methods
> >> >> | Type.Opaque (op) =3D>
> >> >> RETURN Search(op.revealedSuperType=2C count=2C top=2C umetho=
> >ds)
> >> >> | Type.Reference =3D> <*ASSERT FALSE*>
> >> >> END
> >> >> END
> >> >> END Search=3B
> >> >>=20
> >> >> I think we can't expect gcc -Wall -Werror to pass.
> >> >> I really wanted it to=2C and I tried=2C 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=2C 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=2C but C will not.
> >> >
> >> >-- hendrik
> > =
> >
> >--_ad389312-f922-410e-bb8f-e7106388428f_
> >Content-Type: text/html; charset="Windows-1252"
> >Content-Transfer-Encoding: quoted-printable
> >
> ><html>
> ><head>
> ><style><!--
> >.hmmessage P
> >{
> >margin:0px=3B
> >padding:0px
> >}
> >body.hmmessage
> >{
> >font-size: 10pt=3B
> >font-family:Tahoma
> >}
> >--></style></head>
> ><body class=3D'hmmessage'><div dir=3D'ltr'>
> >drat=2C these are worse:<br><br>"../src/Macro.m3"=2C line 949: warning: unr=
> >eachable ELSE in TYPECASE<br><br><br>=3D=3D package /Users/jay/dev2/cm3/m3-=
> >ui/formsvbt =3D=3D<br><br> =3B+++ /cm3/bin/cm3 =3B =3B =3B =
> >-build -DROOT=3D/Users/jay/dev2/cm3 +++<br>--- building in AMD64_DARWIN ---=
> ><br><br>ignoring ../src/m3overrides<br><br>new source ->=3B compiling Mac=
> >ro.m3<br>cc1plus: warnings being treated as errors<br>Macro.mc.c: In functi=
> >on =91char* Macro__EvalLength(char*=2C char*)=92:<br>Macro.mc.c:5271: warni=
> >ng: control reaches end of non-void function<br>Macro.mc.c: In function =91=
> >char* Macro__EvalPlus(char*=2C char*)=92:<br>Macro.mc.c:9004: warning: cont=
> >rol reaches end of non-void function<br>Macro.mc.c: In function =91char* Ma=
> >cro__EvalMinus(char*=2C char*)=92:<br>Macro.mc.c:9468: warning: control rea=
> >ches end of non-void function<br><br><br>If I put in the somewhat obvious:<=
> >br><br><br> =3B =3B =3B ELSE <=3B* ASSERT FALSE *>=3B<br><b=
> >r><br>then:<br><br>new source ->=3B compiling Macro.m3<br>"../src/Macro.m=
> >3"=2C line 949: warning: unreachable ELSE in TYPECASE<br>1 warning encounte=
> >red<br>cc1plus: warnings being treated as errors<br>Macro.mc.c: In function=
> > =91char* Macro__EvalLength(char*=2C char*)=92:<br>Macro.mc.c:5271: warning=
> >: control reaches end of non-void function<br>Macro.mc.c: In function =91ch=
> >ar* Macro__EvalPlus(char*=2C char*)=92:<br>Macro.mc.c:9004: warning: contro=
> >l reaches end of non-void function<br><br><br><br>For stablegen=2C I am inc=
> >lined to put in that ELSE <=3B* ASSERT FALSE *>=3B.<br><br><br>I might =
> >might might be able to put in C assert(false) in these places.<br><br> =
> >=3B- Jay<br><br><br><div><div id=3D"SkyDrivePlaceholder"></div>>=3B To: h=
> >endrik at topoi.pooq.com<br>>=3B Date: Sun=2C 16 Dec 2012 10:55:29 -0800<br>=
> >>=3B From: mika at async.caltech.edu<br>>=3B CC: m3devel at elegosoft.com<br>=
> >>=3B Subject: Re: [M3devel] thouhts on -Wall with C backend output<br>>=
> >=3B <br>>=3B Can you have an option to add an assertion in the output for=
> > these cases?<br>>=3B <br>>=3B Here either<br>>=3B <br>>=3B 1. gcc =
> >has found a bug in the C code generator and/or front end=2C in that<br>>=
> >=3B there's no default (abortion) case<br>>=3B <br>>=3B or<br>>=3B=
> > <br>>=3B 2. the front end has deduced there is no need for abortion beca=
> >use it can<br>>=3B see that the missing ELSE is never going to be exer=
> >cised=2C based on the<br>>=3B already existing type information<br>>=
> >=3B <br>>=3B What I'm proposing is two modes for the compiler:<br>>=3B =
> ><br>>=3B -- ignore the errors<br>>=3B <br>>=3B or<br>>=3B <br>>=
> >=3B -- add proper assertions to the C code=2C e.g.=2C <br>>=3B <br>>=3B=
> > assert(false=2C "front-end deduced this cant happen by inspecting type=
> > information")<br>>=3B <br>>=3B which=2C when enabled=2C should make=
> > gcc shut up=2C and instead turn into<br>>=3B runtime checks on the co=
> >mpiler<br>>=3B <br>>=3B Mika<br>>=3B <br>>=3B Hendrik Boom wr=
> >ites:<br>>=3B >=3BOn Sun=2C Dec 16=2C 2012 at 09:58:10AM +0000=2C Jay K=
> > wrote:<br>>=3B >=3B>=3B <br>>=3B >=3B>=3B I've tried to genera=
> >te "very good C".<br>>=3B >=3B>=3B I've fixed some of what gcc -Wall =
> >complains about.<br>>=3B >=3B>=3B For default gcc on my old MacBook -=
> >- old enough that it can still emulate PowerPC=2C gcc is 4.0.1.<br>>=3B &=
> >gt=3B>=3B (at least one of what I deal with=2C I think anything newer won=
> >'t complain..)<br>>=3B >=3B>=3B <br>>=3B >=3B>=3B <br>>=3B &g=
> >t=3B>=3B <br>>=3B >=3B>=3B do-cm3-all with -Wall -Werror gets very =
> >far=2C to:<br>>=3B >=3B>=3B <br>>=3B >=3B>=3B =3D=3D package /U=
> >sers/jay/dev2/cm3/m3-db/stablegen =3D=3D<br>>=3B >=3B>=3B <br>>=3B =
> >>=3B>=3B +++ /cm3/bin/cm3 -build -DROOT=3D/Users/jay/dev2/cm3 +++<b=
> >r>>=3B >=3B>=3B --- building in AMD64_DARWIN ---<br>>=3B >=3B>=
> >=3B <br>>=3B >=3B>=3B ignoring ../src/m3overrides<br>>=3B >=3B>=
> >=3B <br>>=3B >=3B>=3B w source ->=3B compiling GenCode.m3<br>>=3B=
> > >=3B>=3B cc1: warnings being treated as errors<br>>=3B >=3B>=3B =
> >GenCode.mc.c: In function =91GenCode__BuildMethods__Search=92:<br>>=3B &g=
> >t=3B>=3B GenCode.mc.c:3505: warning: control reaches end of non-void func=
> >tion<br>>=3B >=3B>=3B m3_backend =3D>=3B 1<br>>=3B >=3B>=3B=
> > <br>>=3B >=3B>=3B PROCEDURE Search ( type : Type.Reference=
> >=3B<br>>=3B >=3B>=3B VAR count : INTEGER=3B<br>=
> >>=3B >=3B>=3B VAR top : CARDINAL=3B<br>>=3B=
> > >=3B>=3B umethods: AtomList.T ):<br>>=3B &=
> >gt=3B>=3B ImportList.MethodList RAISES {StablegenError.E} =3D<br>>=
> >=3B >=3B>=3B VAR methods: ImportList.MethodList=3B<br>>=3B >=3B=
> >>=3B BEGIN<br>>=3B >=3B>=3B IF (type =3D Type.root) OR (t=
> >ype =3D NIL) THEN (* base of<br>>=3B >=3B>=3B =
> > recursion *)<br>>=3B >=3B>=3B RE=
> >TURN NEW(ImportList.MethodList=2C ABS(count))<br>>=3B >=3B>=3B =
> >ELSE<br>>=3B >=3B>=3B TYPECASE type OF<br>>=3B >=3B>=3B =
> > Type.Object (ob) =3D>=3B <br>>=3B >=3B>=3B IF coun=
> >t <=3B=3D 0 THEN<br>>=3B >=3B>=3B count:=3D count - NUM=
> >BER(ob.methods^)<br>>=3B >=3B>=3B END=3B<br>>=3B >=3B&g=
> >t=3B methods :=3D Search(ob.super=2C count=2C top=2C umethods)=3B=
> ><br>>=3B >=3B>=3B FOR i :=3D 0 TO LAST(ob.methods^) DO<br>&=
> >gt=3B >=3B>=3B IF umethods =3D NIL<br>>=3B >=3B>=3B =
> > OR AtomList.Member(<br>>=3B >=3B>=3B =
> > umethods=2C ob.methods[i].name) THEN<br>>=3B >=3B>=3B =
> > IF AtomList.Member(reserved=2C ob.methods[i].name) THEN<br>>=3B >=3B&g=
> >t=3B RAISE StablegenError.E(Atom.ToText(ob.methods[i].name)=
> ><br>>=3B >=3B>=3B &=3B" is a reserved method name =
> >in stable objects. "<br>>=3B >=3B>=3B &=3B"Must no=
> >t be an update method.")<br>>=3B >=3B>=3B END=3B<br>>=
> >=3B >=3B>=3B methods[top].name :=3D ob.methods[i].name=3B=
> ><br>>=3B >=3B>=3B methods[top].sig :=3D ob.methods[i].s=
> >ig=3B<br>>=3B >=3B>=3B INC(top)<br>>=3B >=3B>=3B =
> > END<br>>=3B >=3B>=3B END=3B<br>>=3B >=3B>=
> >=3B RETURN methods<br>>=3B >=3B>=3B | Type.Opaque (=
> >op) =3D>=3B<br>>=3B >=3B>=3B RETURN Search(op.revealedSup=
> >erType=2C count=2C top=2C umethods)<br>>=3B >=3B>=3B | Type.R=
> >eference =3D>=3B <=3B*ASSERT FALSE*>=3B<br>>=3B >=3B>=3B =
> > END<br>>=3B >=3B>=3B END<br>>=3B >=3B>=3B END Searc=
> >h=3B<br>>=3B >=3B>=3B <br>>=3B >=3B>=3B I think we can't expect=
> > gcc -Wall -Werror to pass.<br>>=3B >=3B>=3B I really wanted it to=2C=
> > and I tried=2C and I fixed stuff.<br>>=3B >=3B>=3B But I don't think=
> > it is viable.<br>>=3B >=3B>=3B Ok?<br>>=3B >=3B<br>>=3B >=3B=
> >Could it be that the TYPECASE doesn't have an ELSE clause=2C possibly<br>&=
> >gt=3B >=3Btranslated to a switch withouy a default: label? This would gi=
> >ve the<br>>=3B >=3BC code an apparent path to the end of the function. =
> > M3 may know that<br>>=3B >=3Bthe TYPECASE exhausts all the possibiliti=
> >es=2C but C will not.<br>>=3B >=3B<br>>=3B >=3B-- hendrik<br></div>=
> > </div></body>
> ></html>=
> >
> >--_ad389312-f922-410e-bb8f-e7106388428f_--
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