Disable PL_sawampersand

PL_sawampersand actually causes bugs (e.g., perl #4289), because the
behaviour changes.  eval '$&' after a match will produce different
results depending on whether $& was seen before the match.

Using copy-on-write for the pre-match copy (preceding patches do that)
alleviates the slowdown caused by mentioning $&.  The copy doesn’t
happen unless the string is modified after the match.  It’s now a
post- match copy.  So we no longer need to do things differently
depending on whether $& has been seen.

PL_sawampersand is now #defined to be equal to what it would be if
every program began with $',$&,$`.

I left the PL_sawampersand code in place, in case this commit proves
immature.  Running Configure with -Accflags=PERL_SAWAMPERSAND will
reënable the PL_sawampersand mechanism.

1 files changed, 2 insertions, 0 deletions

diff --git a/sv.c b/sv.c
index 6a700e6ff8..d8d0ff8add 100644
--- a/sv.c
+++ b/sv.c
@@ -13057,7 +13057,9 @@ perl_clone_using(PerlInterpreter *proto_perl, UV flags,
     PL_minus_F		= proto_perl->Iminus_F;
     PL_doswitches	= proto_perl->Idoswitches;
     PL_dowarn		= proto_perl->Idowarn;
+#ifdef PERL_SAWAMPERSAND
     PL_sawampersand	= proto_perl->Isawampersand;
+#endif
     PL_unsafe		= proto_perl->Iunsafe;
     PL_perldb		= proto_perl->Iperldb;
     PL_perl_destruct_level = proto_perl->Iperl_destruct_level;