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S_invlist_trim - don't SvPV_renew if SvLEN(invlist) is < PTRSIZE larger #23111

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S_invlist_trim - don't SvPV_renew if SvLEN(invlist) is < PTRSIZE larger #23111

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richardleach
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Currently, S_invlist_trim always calls SvPV_renew(invlist, <size>),
which is a macro wrapping a call to safesysrealloc().

However, SvLEN(invlist) is often already exactly the desired size,
or it is larger by less than the size of a pointer. With this commit,
such cases just return without calling SvPV_renew().

  • This set of changes does not require a perldelta entry.

@richardleach
S_invlist_trim - don't SvPV_renew if SvLEN(invlist) is < PTRSIZE larger
bd9b4e9 
Currently, `S_invlist_trim` always calls `SvPV_renew(invlist, <size>)`,
which is a macro wrapping a call to `safesysrealloc()`.

However, `SvLEN(invlist)` is often already exactly the desired size, or
it is larger by less than the size of a pointer. With this commit, such
cases just return without calling `SvPV_renew()`.
@richardleach
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Tow comments:

  • It will still be common to try to resize SvLEN == 34 down to 25 bytes. Given that it's common for malloc implementations to increase chunk sizes by 2 x PTRLEN, should that be the check here too?
  • Allocated chunks will be pointer-aligned. 34 is not a multiple of 8! Maybe we should round up allocation sizes to a multiple of the pointer size generally?

@richardleach richardleach linked an issue Mar 17, 2025 that may be closed by this pull request
S_invlist_trim maybe doesn't need to SvPV_renew every time? #23103
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S_invlist_trim maybe doesn't need to SvPV_renew every time?
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@richardleach