Re: [Tinycc-devel] [PATCH] deprecating VT_REF

[Thomas Preud'homme]

Le dimanche 22 février 2015, 00:16:20 Michael Matz a écrit :
> Hi,
> 
> On Sat, 21 Feb 2015, Edmund Grimley Evans wrote:
> > 
> > I agree, but inserting those #ifdefs is merely making the
> > architecture-specificity explicit, thereby perhaps encouraging someone
> > to do something about it. Without the #ifdefs, but with VT_REF only
> > used by the x86_64 back end, you have hidden target-specificity, which
> > is more dangerous.
> 
> I disagree about dangerous; it's only a problem for those targets, and
> presumably for them the generic handling of VT_REF is correct.  If you
> mean dangerous as in "others might be tempted to use it in their target,
> even though the generic handling isn't correct for them", then, well, life
> is tough; it's not enough reason IMHO to uglify common code.  Neither is
> trying to make others interested in removing the thing.

FWIW, I fully agree.

> 
> But apart from that philosophical argument, I claim that the concept of
> VT_REF is not target specific at all.  It does have things in common with
> VT_LLOCAL, but is not _quite_ the same currently, as we now found out in
> the other mails.  This not-quite-equality might indeed be bugs in how
> VT_LLOCAL is handled, e.g. VT_LLOCAL might be understood as an
> optimization to VT_REF (even though the latter was introduced later), the
> optimization being that lvalueness/referenceness can be changed by a
> simple bitflip, instead of generating code.
> 
> So, yes, ideally VT_LLOCAL and VT_REF should be merged.  Though the
> question still is into which one.  VT_LLOCAL is tricky, as the docu said
> 
> :)  And it currently contains bugs, when used for some things.
> 
> _If_ the issues with VT_LLOCAL can be fixed, then I'd be in favor of
> removing VT_REF.  After such fixing goes in.

No matter which one is used, it would be nice to use the name VT_REF as the 
name encompasse better what it is about: a value for a memory reference that 
contains the address of another value. The name VT_LLOCAL refers to much to 
the purpose of VT_LVAL on stack. 

Best regards,

Thomas

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