stop $foo =~ /(bar)/g skipping copy

Normally in the presence of captures, a successful regex execution
makes a copy of the matched string, so that $1 et al give the right
value even if the original string is changed; i.e.

    $foo =~ /(123)/g;
    $foo = "bar";
    is("$1", "123");

Until now that test would fail, because perl used to skip the copy for
the scalar /(...)/g case (but not the C<$&; //g> case). This was to
avoid a huge slowdown in code like the following:

    $x = 'x' x 1_000_000;
    1 while $x =~ /(.)/g;

which would otherwise end up copying a 1Mb string a million times.

Now that (with the last commit but one) we copy only the required
substring of the original string (a 1-byte substring in the above
example), we can remove this fast-but-incorrect hack.

1 files changed, 1 insertions, 6 deletions

diff --git a/pp_hot.c b/pp_hot.c
index 91958ac441..6530ae5b4d 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -1319,12 +1319,7 @@ PP(pp_match)
 	    }
 	}
     }
-    /* XXX: comment out !global get safe $1 vars after a
-       match, BUT be aware that this leads to dramatic slowdowns on
-       /g matches against large strings.  So far a solution to this problem
-       appears to be quite tricky.
-       Test for the unsafe vars are TODO for now. */
-    if (       (!global && RX_NPARENS(rx))
+    if (       RX_NPARENS(rx)
             || PL_sawampersand
             || SvTEMP(TARG)
             || SvAMAGIC(TARG)