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Re: VTA merge - introduction

On Jun  5, 2009, Richard Guenther <> wrote:

> On Fri, Jun 5, 2009 at 9:34 PM, Alexandre Oliva<> wrote:

>>>> available in what sense? ÂIf this kept the variable available as in it
>>>> got a stack slot, this would have been flagged by -fcompare-debug, so
>>>> you must be speaking of something else. ÂI can't tell what it is.
>>> Available in the sense that it is still in the IL and the variable lists
>>> and thus consumes memory and compile-time during stmt walks.
>> Erhm... ÂIf it's removed from the stmt list without vta, I think it
>> should be removed from it with vta as well, otherwise we'd risk getting
>> different code.
>> It should remain only in the lexical blocks, so that we can generate
>> debug info, and where it doesn't cost much, considering we don't walk it
>> often and we need to keep the decl around to generate debug info anyway.
>> Does this not match what you see?

> No, I see it used in DEBUG stmts.

>  # DEBUG p <= &x;

But neither p's nor x's DECLs are available in the IL any more, right?
I understood, from what you wrote before, that they were.

A statement that p is modified at that point remains, for sure, as it
should.  Even if we were to drop the &x, we'd still have to note that
whatever value p held before that point is no longer applicable.

So it's not like retaining the &x makes a lot of difference, and it
enables us to say that p points to that if we end up assigning a memory
location to x anyway.

Is your objection that there's a mark saying that p is modified, and
that this would slow down walking over statements around that point?

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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