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Re: [perl #18127] [PATCH] Implicit stack direction probe

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Leopold Toetsch
October 29, 2002 07:05
Re: [perl #18127] [PATCH] Implicit stack direction probe
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Jason Gloudon wrote:

> On Tue, Oct 29, 2002 at 02:40:14PM +0100, Leopold Toetsch wrote:
>>>+        cur_var_ptr = (size_t)((ptrdiff_t)cur_var_ptr + 
>>When PARROT_PTR_ALIGNMENT is not 1, that much pointers -1 are skipped 
>>during stack scanning by incrementing cur_var_ptr by sizeof(size_t) * 
> ptrdiff_t is not a pointer type, so cur_var_ptr + PARROT_PTR_ALIGNMENT skips
> exactly PARROT_PTR_ALIGNMENT bytes. You may not be matching ( )'s quite right.

Brr, yes. I checked with gdb. cur_var_ptr is incremented by 
PARROT_PTR_ALIGNMENT _bytes_ i.e. by 1 byte on i386. Can we really have 
e.g. odd aligned PMCs on stack? I don't think so. Or am I still missing 

>>As a side note: applying your patch slows down e.g. life.pasm by ~2%.
>>(I really don't see why).

> Are you compiling with optimization enabled ? Is the difference consistent ?

W/o optimization, but consistent.

> If the answer to both questions is yes, it is probably a cache effect related
> to the new variable on the function stack. I doubt the slowdown is universal.
> I will try to check on SPARC sometime today.


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