make PL_reg_curpm global

Currently PL_reg_curpm is actually #deffed to a field within PL_reg_state;
promote it into a fully autonomous perl-interpreter variable.

PL_reg_curpm points to a fake PMOP that's used to temporarily point
PL_curpm to, that we can hang the current regex off, so that this works:

    "a" =~ /^(.)(?{ print $1 })/ # prints 'a'

It turns out that it doesn't need to be saved and restored when we
recursively enter the regex engine; that is already handled by saving and
restoring which regex is currently attached to PL_reg_curpm.
So we just need a single global (per interpreter) placeholder.

Since we're shortly going to get rid of PL_reg_state, we need to move it
out of that struct.

1 files changed, 4 insertions, 0 deletions

diff --git a/regexec.c b/regexec.c
index a144138dd3..13dce3fb8e 100644
--- a/regexec.c
+++ b/regexec.c
@@ -7576,6 +7576,10 @@ S_setup_eval_state(pTHX_ regmatch_info *const reginfo)
         eval_state->pos_magic = NULL;
 
     if (!PL_reg_curpm) {
+        /* PL_reg_curpm is a fake PMOP that we can attach the current
+         * regex to and point PL_curpm at, so that $1 et al are visible
+         * within a /(?{})/. It's just allocated once per interpreter the
+         * first time its needed */
         Newxz(PL_reg_curpm, 1, PMOP);
 #ifdef USE_ITHREADS
         {