Re: g++.old-deja/g++.mike/p7325.C - suspected bogus test case

[Mark Mitchell <mark at codesourcery dot com>]

Michael Matz wrote:

> Hi Mark,
>
> On Mon, 12 Jul 2004, Mark Mitchell wrote:
>
>  
>
> > > The probability for this is quite small.  If such machine happens to exist
> > > the testcase can be XFAILed for it.  Equally unlikely are machines for
> > > which not merging stack slots produces faster code, be it for smaller
> > > stack frame, hence possibly shorter insn encoding, not to mention cache
> > > effects.  Why do you use such constructed examples?
> > >
> > >      
> > I'm uncomfortable with using this kind of black-box approach for testing
> > optimization capabilities.
> >    
>
> black-box in the sort of testing in a way for which no guarantee is given 
> by the language standard?  Well, then call it testing of implementation 
> defined behaviour (and we define it to reuse stack slots under well 
> defined circumstances; as first iteration circumstance == {compiled with 
> not -O0}).  This testcase is testing a specific behaviour of 
> the implementation, and I think it does so reliably (if it would work ;-) 
> ).  Namely that the this pointer doesn't change (by extension this means 
> that stack slots were reused for this class, i.e. what we wanted).
>  
If we all agree on a well-defined set of circumstances under which we 
want to do this optimization, and document that, then I certainly have 
no objection to having test cases that test for that functionality.

--
Mark Mitchell
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