save old PL_comppad in CXt_SUB/FORMAT block

Currently when we call a sub, the old value of PL_comppad is
saved on the save stack using SAVECOMPPAD(). Instead, save it in
a new field in the context struct, called prevcomppad. This is simpler
and more efficient.

Note that there is already a confusingly-named field in the CXt_SUB
context struct called oldcomppad, which holds the value of PL_comppad for
the *current* sub, not for its caller. So the new field had to be called
something else.

One side effect of this is that an existing bug  - which causes too much
to be popped off the savestack when dieing while leaving a sub scope - is
now more noticeable, since PL_curpad and SAVEt_CLEARSV are now out of
sync: formerly, the unwinding of the save stack restored PL_curpad in
lockstep. The fix for this will come later in this branch, when the whole
issue of context stack popping order and reentrancy is addressed; for
now, a TODO test has been added.

1 files changed, 0 insertions, 1 deletions

diff --git a/pp_sys.c b/pp_sys.c
index 15b4d8bb75..83cf32ba36 100644
--- a/pp_sys.c
+++ b/pp_sys.c
@@ -1395,7 +1395,6 @@ S_doform(pTHX_ CV *cv, GV *gv, OP *retop)
 	PERL_STACK_OVERFLOW_CHECK();
 	pad_push(CvPADLIST(cv), CvDEPTH(cv));
     }
-    SAVECOMPPAD();
     PAD_SET_CUR_NOSAVE(CvPADLIST(cv), CvDEPTH(cv));
 
     setdefout(gv);	    /* locally select filehandle so $% et al work */