[Python-Dev] Nuking wstr [Re: How can we use 48bit pointer safely?]

[Antoine Pitrou]

On Fri, 30 Mar 2018 15:28:47 +0900
INADA Naoki <songofacandy at gmail.com> wrote:
> 
> # Possible optimizations by 48bit pointer
> 
> ## PyASCIIObject
> 
> [snip]
>         unsigned int ready:1;
>         /* Padding to ensure that PyUnicode_DATA() is always aligned to
>            4 bytes (see issue #19537 on m68k). */
>         unsigned int :24;
>     } state;
>     wchar_t *wstr;              /* wchar_t representation (null-terminated) */
> } PyASCIIObject;
> 
> Currently, state is 8bit + 24bit padding.  I think we can pack state and wstr
> in 64bit.

We could also simply nuke wstr.  I frankly don't think it's very
important.  It's only used when calling system functions taking a
wchar_t argument, as an « optimization ».  I'd be willing to
guess that modern workloads aren't bottlenecked by the cost overhead of
those system functions...

Of course, the question is whether all this matters.  Is it important
to save 8 bytes on each unicode object?  Only testing would tell.

Regards

Antoine.