Branch: refs/heads/blead
Home: https://github.com/Perl/perl5
Commit: d002fa41bf2faf250192ebc6fa26bce91c322359
https://github.com/Perl/perl5/commit/d002fa41bf2faf250192ebc6fa26bce91c322359
Author: Richard Leach <[email protected]>
Date: 2025-03-12 (Wed, 12 Mar 2025)
Changed paths:
M embed.fnc
M embed.h
M proto.h
M sv.c
Log Message:
-----------
Perl_sv_can_can_swipe_pv_buf - extracts swipe test from Perl_sv_setsv_flags
Perl_sv_setsv_flags contains the canonical logic for determining the best
method for assigning the string value from a source SV to a destination SV:
* "Swipe" the string buffer from the source SV
* COW the source SV's string buffer
* Do a full copy
This commit extracts the "can the swipe the buffer" tests out into a new
macro (`S_SvPV_can_swipe_buf`) within sv.c. It has two users:
* Perl_sv_setsv_flags - so that the logic remains inline in this hot code
* Perl_sv_can_can_swipe_pv_buf - a new function
`pp_reverse` will shortly make use of the new function to avoid unnecessary
string copies when doing a reversal in scalar context.
Commit: 84fa6b0d2566bd50a283a95cb482ef9317647d25
https://github.com/Perl/perl5/commit/84fa6b0d2566bd50a283a95cb482ef9317647d25
Author: Richard Leach <[email protected]>
Date: 2025-03-12 (Wed, 12 Mar 2025)
Changed paths:
M t/op/reverse.t
Log Message:
-----------
t/op/reverse.t: add a test for single character reversal
This could help detect implementation bugs in algorithms for reverse
copying from a source buffer to a different destination buffer.
Commit: d0b93b3f420aff04038a79c537e62d91eb9f1cdf
https://github.com/Perl/perl5/commit/d0b93b3f420aff04038a79c537e62d91eb9f1cdf
Author: Richard Leach <[email protected]>
Date: 2025-03-12 (Wed, 12 Mar 2025)
Changed paths:
M pp.c
Log Message:
-----------
Faster string reversal when source/dest buffers are distinct
`pp_reverse()` has traditionally operated on a single string buffer,
reversing it in place.
When `pp_reverse()` takes a single SV argument, whose buffer cannot be
swiped by `sv_setsv_flags()`, a straight copy of the buffer is taken
and then that is reversed. In such cases, two complete passes over the
entire string are needed to reverse a non-UTF8 string, and reversing a
UTF8 string takes three complete passes.
This commit enables `pp_reverse()` to apply the "swipe" test itself
and, for straightforward copy cases, to avoid calling `sv_setsv_flags()`.
Instead, it does the work of preparing the `TARG` SV and reverse copies
the string (UTF8 or otherwise) in a single pass.
The performance improvement will vary by compiler and CPU. With gcc 12.2.0
on Linux running on "znver3" hardware, performance for both UTF8 and
non-UTF8 strings approximately doubled. Using clang-11 instead on the same
machine gave a fivefold improvement for the non-UTF8 case.
Commit: e792078d06516df587796501dcbe7d26e396faf1
https://github.com/Perl/perl5/commit/e792078d06516df587796501dcbe7d26e396faf1
Author: Richard Leach <[email protected]>
Date: 2025-03-12 (Wed, 12 Mar 2025)
Changed paths:
M pod/perldelta.pod
Log Message:
-----------
Perldelta for reverse string copies in one pass
Compare: https://github.com/Perl/perl5/compare/9c5f1c44fd7a...e792078d0651
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