[M3commit] CVS Update: cm3

[Jay K]

 > Your C compiler will be silent about this code unless you ask it to warn you.

 These days, most people know to ask for these warnings.
 The warnings are fairly accurate and more often find real bugs than complain about correct code.

 > > Do you want your C compiler to be silent about this code? No.
 > Why not.

The compiler, at least when optimizing (doing data/control flow analysis), can easily find bugs in code.
Asking it not to is just the wrong thing to do.

 - Jay

----------------------------------------
> From: hosking at cs.purdue.edu
> Date: Mon, 5 Jul 2010 18:42:20 -0400
> To: jay.krell at cornell.edu
> CC: m3commit at elegosoft.com
> Subject: Re: [M3commit] CVS Update: cm3
>
> Your C compiler will be silent about this code unless you ask it to warn you.
>
> On 5 Jul 2010, at 17:46, Jay K wrote:
>
> > Meeting the language spec is inadequate.
>
> What?
>
> > It is a "quality of implementation" thing.
> > Do you want your C compiler to be silent about this code? No.
>
> Why not?
>
> > Or do you want it to try a little harder and point out bugs in your code?
>
> Those are C bugs because C says nothing about variable initialisation.
>
> > Even where it meets the language spec? Yes.
> > Maybe meeting the language spec is more meaningful for Modula-3 than for C, but still inadequate.
> > Now, compiler can't in general be a "correct program proofer", but it can and does catch a few things and that is a good thing not to be avoided.
> >
> >
> > - Jay
> >
> > ----------------------------------------
> >> From: hosking at cs.purdue.edu
> >> Date: Mon, 5 Jul 2010 17:40:50 -0400
> >> To: jay.krell at cornell.edu
> >> CC: m3commit at elegosoft.com
> >> Subject: Re: [M3commit] CVS Update: cm3
> >>
> >> But the front-end should be OK with the first. It is "correct" because whatever value is in a when F1 is called is legal for a. Why should the backend give a warning? The semantics of Modula-3 allow any legal bit-value for a variable as its initial value. You will force an initialising assignment when none is required by the language spec.
> >>
> >> On 5 Jul 2010, at 17:36, Jay K wrote:
> >>
> >>>
> >>> unsigned F1()
> >>> {
> >>> unsigned a;
> >>> return a;
> >>> }
> >>>
> >>> should generate a warning.
> >>>
> >>> unsigned F1()
> >>>
> >>> {
> >>>
> >>> unsigned a = 0;
> >>>
> >>> return a;
> >>>
> >>> }
> >>>
> >>>
> >>> is much preferred.
> >>>
> >>> Just because the front end is ok with the first, doesn't make it correct.
> >>>
> >>> - Jay
> >>>
> >>> ----------------------------------------
> >>>> Subject: Re: [M3commit] CVS Update: cm3
> >>>> From: hosking at cs.purdue.edu
> >>>> Date: Mon, 5 Jul 2010 17:34:51 -0400
> >>>> CC: m3commit at elegosoft.com
> >>>> To: jay.krell at cornell.edu
> >>>>
> >>>> Huh?
> >>>>
> >>>> On 5 Jul 2010, at 17:15, Jay K wrote:
> >>>>
> >>>>>
> >>>>> At least some of these were Word.T. "valid" is still "random" and the code is unpredictable, at least by a quick read, even if type safe.
> >>>>> Type safe is just a minimum bar, one that should always be exceeded, even if the compiler is completely unable to validate it.
> >>>>>
> >>>>> That is, the compiler guarantees are from sufficient relative to correctness.
> >>>>>
> >>>>> - Jay
> >>>>>
> >>>>> ----------------------------------------
> >>>>>> From: hosking at cs.purdue.edu
> >>>>>> Date: Mon, 5 Jul 2010 16:50:00 -0400
> >>>>>> To: jay.krell at cornell.edu
> >>>>>> CC: m3commit at elegosoft.com
> >>>>>> Subject: Re: [M3commit] CVS Update: cm3
> >>>>>>
> >>>>>> But we've been this route before. Modula-3 ensures every variable is initialised with a valid value. I don't see how your adding an initialiser makes it more obviously correct.
> >>>>>>
> >>>>>> On 5 Jul 2010, at 16:45, Jay K wrote:
> >>>>>>
> >>>>>>>
> >>>>>>> I will maybe see about doing better here.
> >>>>>>> Initializing locals doesn't seem like such a bad change though.
> >>>>>>> I like the code to be "obviously correct" by a quick read by a human.
> >>>>>>>
> >>>>>>> - Jay
> >>>>>>>
> >>>>>>> ----------------------------------------
> >>>>>>>> From: hosking at cs.purdue.edu
> >>>>>>>> Date: Mon, 5 Jul 2010 14:31:01 -0400
> >>>>>>>> To: jkrell at elego.de
> >>>>>>>> CC: m3commit at elegosoft.com
> >>>>>>>> Subject: Re: [M3commit] CVS Update: cm3
> >>>>>>>>
> >>>>>>>> Jay, I am perplexed that we are adding things to Modula-3 source because of compiler backend brokenness just to avoid back-end warnings. Better to fix the backend so that RAISE is noreturn. This should not be difficult to do.
> >>>>>>>>
> >>>>>>>> On 5 Jul 2010, at 15:22, Jay Krell wrote:
> >>>>>>>>
> >>>>>>>>> CVSROOT: /usr/cvs
> >>>>>>>>> Changes by: jkrell at birch. 10/07/05 15:22:28
> >>>>>>>>>
> >>>>>>>>> Modified files:
> >>>>>>>>> cm3/m3-tools/cvsup/suplib/src/text_cm3/: SupMiscText.m3
> >>>>>>>>>
> >>>>>>>>> Log message:
> >>>>>>>>> ../src/text_cm3/SupMiscText.m3: In function 'SupMisc__DecodeWS':
> >>>>>>>>> ../src/text_cm3/SupMiscText.m3:211: warning: 'M3_Bkn9rd_ch' may be used uninitialized in this function
> >>>>>>>>> ../src/text_cm3/SupMiscText.m3:211: note: 'M3_Bkn9rd_ch' was declared here
> >>>>>>>>>
> >>>>>>>>> because raising an exception isn't currently "noreturn"
> >>>>>>>>> so initialize it to 0
> >>>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>
> >>>>
> >>>
> >>
> >
>