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Re: VTA merge?


I'm back!

On Jun 21, 2009, Richard Guenther <> wrote:

> So I just tested tramp3d for memory usage


> -g -fno-var-tracking -fno-var-tracking-assignments: 615305 kB +18.5%
> -g -fno-var-tracking -fvar-tracking-assignments: 647773 kB +5%

> So keeping the VTA notes for tramp3d is an overhead of 5%

> -g0 -fno-var-tracking -fno-var-tracking-assignments: 502361 kB
> -g0 -fno-var-tracking -fvar-tracking-assignments: 521869 kB +3.8%

> (no idea what that actually tests)

It tests the memory overhead of carrying the VTA notes in a compilation
without debug information.

> without a trunk build to compare I cannot state anything about
> overhead of the branch (var-tracking or -g may be more expensive
> due to changes on the branch).

Memory-wise, VTA shouldn't have significant changes compared with trunk,
at least when VTA isn't enabled.  When it is, the VTA pass itself will
tend to consume more memory (although sometimes it may use less, because
of the much-smaller data structure allocated for variables suitable for
gimple regs), and because of the notes carried throughout compilation.

> Can you specify how you built VTA?

Is complete enough?

> Your GCC testing may be representative for random C applications
> (can you check a kernel build to asses compile-time, memory-usage
> and debug-size differences?)

Sure.  It will take time away from implementing some improvements I'd
like to implement before the cut-off for 4.5, but...  I'll try.

> Are the number and positions of VTA notes the same at -g vs. -g0?

They ought to be, by construction, but I haven't devised a way to verify
this property.

> If so the difference to the extrapolated 6% must be a GC artifact...?

I guess...  I can't think of any other reason for it.

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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