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S_fold_constants: remove early SvREADONLY(sv) to allow SvIsCOW(sv) #20595

Merged
merged 1 commit into from
Jun 11, 2024
Merged

S_fold_constants: remove early SvREADONLY(sv) to allow SvIsCOW(sv) #20595

merged 1 commit into from
Jun 11, 2024

Commits on Jun 10, 2024

  1. S_fold_constants: remove early SvREADONLY(sv) to allow SvIsCOW(sv) 

    Standard CONST PVs have the IsCOW flag set, meaning that COW can
be used when assigning the CONST to a variable, rather than making
a copy of the buffer. CONST PVs arising from constant folding have
been lacking this flag, leading to unnecessary copying of PV buffers.

This seems to have occurred because a common branch in S_fold_constants
marks SVs as READONLY before the new CONST OP is created. When the OP
is created, the Perl_ck_svconst() check function is called - this is
the same as when a standard CONST OP is created. If the SV is not
already marked as READONLY, the check function will try to set IsCOW
if it is safe to do so, then in either case will make sure that the
READONLY flag is set.

This commit therefore removes the SvREADONLY(sv) statement from
S_fold_constants(), allowing Perl_ck_svconst() to set the IsCOW
and READONLY flags itself. Minor test updates are also included.
    @richardleach
    richardleach committed Jun 10, 2024
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