Re: Where does the time go?

[Xinliang David Li <davidxl@google.com>]

On Fri, May 21, 2010 at 2:24 AM, Richard Guenther
<richard.guenther@gmail.com> wrote:
> On Thu, May 20, 2010 at 11:21 PM, Xinliang David Li <davidxl@google.com> wrote:
>> On Thu, May 20, 2010 at 2:18 PM, Steven Bosscher <stevenb.gcc@gmail.com> wrote:
>>> On Thu, May 20, 2010 at 11:14 PM, Xinliang David Li <davidxl@google.com> wrote:
>>>> stack variable overlay and stack slot assignments is here too.
>>>
>>> Yes, and for these I would like to add a separate timevar. Agree?
>>
>> Yes.  (By the way, we are rewriting this pass to eliminate the code
>> motion/aliasing problem -- but that is a different topic).
>


> Btw, we want to address the same problem by representing the
> points where (big) variables go out-of scope in the IL, also to
> help DSE.  The original idea was to simply drop in an aggregate
> assignment from an undefined value at the end of the scope
> during lowering, like
>
>  var = {undefined};
>
> which we'd expand to nothing.  Of course shifting the problem to
> the RTL optimizers, so better expand to a similar RTL construct.
> But then are you addressing the similar problem on the RTL side?

We are probably talking about different problems -- the one I
mentioned is that code motion leading to overlapping live range for
variables in different scopes which invalidates the scope based stack
variable overlay. What is the problem you referred? Any PR? I wonder
why a dummy assignment is needed.

Thanks,

David


>
> Richard.
>