llvm dev - Aug 2010 - [LLVMdev] NumLoads/NumStores for linearscan?

Hi,

Is there a way for me to collect statistics about the number of loads/stores
added by the "linearscan" register allocator (just like can be done
with the
"local" allocator)?  I still haven't grokked very well the
interaction
between RALinScan and Spiller... Should I add those two statistics to the
spiller's class?

Thanks,
-- Silvio Ricardo Cordeiro
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On Aug 15, 2010, at 5:12 PM, Silvio Ricardo Cordeiro wrote:
> Is there a way for me to collect statistics about the number of
loads/stores added by the "linearscan" register allocator (just like
can be done with the "local" allocator)?  I still haven't grokked
very well the interaction between RALinScan and Spiller... Should I add those
two statistics to the spiller's class?
RALinearScan asks the Spiller to spill a virtual register. The StandardSpiller
passes the request to LiveIntervals::addIntervalsForSpills. Here, the spill and
restore points are added to the VirtRegMap. No spill code has been inserted yet.
After register allocation completes, VirtRegRewriter inserts the store and load
instructions specified in VirtRegMap.

The counters you are looking for are in VirtRegRewriter.cpp.

We are working on simplifying this for obvious reasons. If you specify
-spiller=inline, the InlineSpiller will insert loads and stores immediately.
There are currently no statistics counters in InlineSpiller.cpp. Feel free to
add some.

/jakob

On Sun, Aug 15, 2010 at 10:04 PM, Jakob Stoklund Olesen <stoklund at
2pi.dk>wrote:
>
> On Aug 15, 2010, at 5:12 PM, Silvio Ricardo Cordeiro wrote:
>
> > Is there a way for me to collect statistics about the number of
> loads/stores added by the "linearscan" register allocator (just
like can be
> done with the "local" allocator)?  I still haven't grokked
very well the
> interaction between RALinScan and Spiller... Should I add those two
> statistics to the spiller's class?
>
> RALinearScan asks the Spiller to spill a virtual register. The
> StandardSpiller passes the request to LiveIntervals::addIntervalsForSpills.
> Here, the spill and restore points are added to the VirtRegMap. No spill
> code has been inserted yet. After register allocation completes,
> VirtRegRewriter inserts the store and load instructions specified in
> VirtRegMap.
>
> The counters you are looking for are in VirtRegRewriter.cpp.
>
I compiled "sort.c" from coreutils8.5 using both *local* and
*linearscan* allocators
(I'm using LLVM 2.7). For *local*, I get a Load/Store count of 314/367. But
when I use *linearscan*, the counters at VirtRegRewriter.cpp end up being
0/0. I've also tried to compile a couple other source files, and
VirtRegRewriter.cpp
always has NumLoads=0 and NumStores=0 in the end.

I can't believe linearscan is *that *good! I've tried to add other
variables
to the source code, but it seems to be spiling them without updating
NumLoads/NumStores...

Is there a source file that's commonly used to test this kind of thing?


We are working on simplifying this for obvious reasons. If you
specify
> -spiller=inline, the InlineSpiller will insert loads and stores
immediately.
> There are currently no statistics counters in InlineSpiller.cpp. Feel free
> to add some.
>
Hmmm yeah, but that's not available for LLVM 2.7, so no luck (although I may
try to "adapt" it for 2.7 if I need to).


>  /jakob
>
>
-- 
Silvio Ricardo Cordeiro
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