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Re: [trunk<-vta] Re: [vtab] Permit coalescing of user variables

On Wed, Jun 3, 2009 at 7:43 PM, Alexandre Oliva <> wrote:
> On Jun ?3, 2009, Richard Guenther <> wrote:
>> On Wed, Jun 3, 2009 at 3:13 AM, Andrew MacLeod <> wrote:
>>> I think we are simply proposing that when VTA code is added and enabled, the
>>> default behaviour is then changed such that we do this coalescing. ?Until
>>> then it stays with the current tradeoffs. no options required...
>> Right, this is what I would suggest as well.
> Hmm... ?That's a “wilder” path than the incremental one I had in mind.
> I wasn't thinking VTA would have been enabled by default right away.
> Even if it was, I think it would be important to retain a possibility to
> turn it off, at least until it's proven on more ports than the testing
> it got so far.
> And then, if VTA can be turned on or off, other trade-offs (like this
> one), that work better with VTA but worse without it, should be
> controllable too.
> And then, there's the factor of being able to measure the impact of the
> changes. ?If we support the options, we can simply compare one with the
> other, using the very same compiler. ?If we don't, at the very least
> we'd have to maintain patches that revert to past behavior, or that
> advance to future behavior, build more toolchains and compare compiler
> output like that.
> This was my reasoning to implement the proposed options. ?They're useful
> on their own right now, regardless of VTA. ?One of them can bring about
> significant compile-time and run-time improvements, whereas the other
> can bring about slightly better debug information. ?With or without VTA.
> Sure enough, if VTA goes in and becomes default and can't be disabled,
> the options cease to make much sense. ?We can remove them then, when and
> if it happens. ?But since so far there's no indication that VTA is
> actually going in, rejecting this patch on the grounds of an unwarranted
> assumption comes off as very odd to me.

Btw, _is_ there really a such big effect with enabling the extra coalescing?


> --
> Alexandre Oliva, freedom fighter ? ?
> You must be the change you wish to see in the world. -- Gandhi
> Be Free! -- ? FSF Latin America board member
> Free Software Evangelist ? ? ?Red Hat Brazil Compiler Engineer

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