[Haskell-cafe] [GHC 7.8.4] IO Monad leak space?

[Baojun Wang]

Appreciate for the prompt reply, sorry for that I assumed the allocations
was caused by space leak. I guess profiling with -auto-all really has huge
impact on allocations. without profiling, haskell version runs about 50%
slower than equivalent C version (both with -O2). Maybe that's  as much as
one could expect.

On Fri, Jul 3, 2015 at 2:41 PM Tom Ellis <
tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk> wrote:

> On Fri, Jul 03, 2015 at 06:00:48PM +0000, Baojun Wang wrote:
> > My concerns is ~80% alloc happens in f3, but both array is allocated by
> > newArray? Since I'm using unboxed array I'm not expecting this kind of
> > laziness.
>
> I see.  You seem to be asking why it is allocating *at all*.  That's not
> a phenomenon that normally falls under the terminology of "space leak",
> hence my confusion.
>
> I'm not an expert at reading Core, but I spent some time looking at it
> without seeing anywhere that would obviously allocate a lot.  Eventually I
> decided to supply the profiling options to ghc-core and lo and behold the
> output changed dramatically!
>
> Unless I am very much misunderstanding how cost centre annotations work,
> the
> amount of allocation without -auto-all is only 10% of the amount with it.
> Please check and let me know if you concur that it is the profiling itself
> that is the root cause of all the allocation!
>
> Tom
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