debugging memory allocations

[Simon Marlow]

On 02 February 2005 13:38, Duncan Coutts wrote:

> I'm looking for advice on how to figure out why some piece of code is
> allocating memory when I think it ought to be able to work in constant
> space.
> 
> In these cases we cannot turn on traditional profiling since that
> would 
> interfere with the optimisations we are relying on to eliminate most
> of 
> the other memory allocations.
> 
> Would looking at the core files help? What would I be looking for?
> 
> Here's a simple version that I would expect to run in constance space.
> 
> pixbufSetGreen :: Pixbuf -> IO ()
> pixbufSetGreen pixbuf = do
>   ptr <- pixbufGetPixels pixbuf
>   sequence_
>     [ do pokeByteOff ptr (y*384+3*x)   (0  ::Word8)
>          pokeByteOff ptr (y*384+3*x+1) (128::Word8)
>          pokeByteOff ptr (y*384+3*x+2) (96 ::Word8)
>     | y <- [0..127]
>     , x <- [0..127] ]
> 
> (Don't worry about all those random constants, it's just test code!)

Yes, let's see the core.  Since you're interested in allocation, you
might be better off with -ddump-prep rather than -ddump-simpl: the
former has all the allocation made into explicit 'let' expressions ready
for code generation.

Cheers,
	Simon