optimise save/restore of PL_delaymagic.

A few places (pp_push, pp_unshift, pp_aassign) have to
set PL_delaymagic on entry, and restore it on exit. These are hot
pieces of code. Rather than using  ENTER/SAVEI16(PL_delaymagic)/LEAVE,
add an extra field to the jumpenv struct, and make the JUMPENV_PUSH / POP
macros automatically save and restore this var.

This means that pp_push etc only need to do a local save:

    U16 old_delaymagic = PL_delaymagic;
    PL_delaymagic = DM_DELAY;
    ....
    PL_delaymagic = old_delaymagic;

and in case of an exception being raised, PL_delaymagic still gets
restored.

This transfers the cost of saving PL_delaymagic from each call to
pp_aassign etc to each time a new run level is invoked. The latter should
be much less frequent.

Note that prior to this commit, pp_aassign wasn't actually saving and
restoring PL_delaymagic; it was just setting it to 0 at the end. So this
commit also makes pp_aassign safe against PL_delaymagic re-entrancy like
pp_push and pp_unshift already were.

1 files changed, 10 insertions, 6 deletions

diff --git a/pp.c b/pp.c
index b84747a6cc..6e9995af2a 100644
--- a/pp.c
+++ b/pp.c
@@ -5443,9 +5443,11 @@ PP(pp_push)
 	/* SPAGAIN; not needed: SP is assigned to immediately below */
     }
     else {
+        /* PL_delaymagic is restored by JUMPENV_POP on dieing, so we
+         * only need to save locally, not on the save stack */
+        U16 old_delaymagic = PL_delaymagic;
+
 	if (SvREADONLY(ary) && MARK < SP) Perl_croak_no_modify();
-        ENTER;
-        SAVEI16(PL_delaymagic);
 	PL_delaymagic = DM_DELAY;
 	for (++MARK; MARK <= SP; MARK++) {
 	    SV *sv;
@@ -5457,7 +5459,7 @@ PP(pp_push)
 	}
 	if (PL_delaymagic & DM_ARRAY_ISA)
 	    mg_set(MUTABLE_SV(ary));
-        LEAVE;
+        PL_delaymagic = old_delaymagic;
     }
     SP = ORIGMARK;
     if (OP_GIMME(PL_op, 0) != G_VOID) {
@@ -5497,10 +5499,12 @@ PP(pp_unshift)
 	/* SPAGAIN; not needed: SP is assigned to immediately below */
     }
     else {
+        /* PL_delaymagic is restored by JUMPENV_POP on dieing, so we
+         * only need to save locally, not on the save stack */
+        U16 old_delaymagic = PL_delaymagic;
 	SSize_t i = 0;
+
 	av_unshift(ary, SP - MARK);
-        ENTER;
-        SAVEI16(PL_delaymagic);
         PL_delaymagic = DM_DELAY;
 	while (MARK < SP) {
 	    SV * const sv = newSVsv(*++MARK);
@@ -5508,7 +5512,7 @@ PP(pp_unshift)
 	}
         if (PL_delaymagic & DM_ARRAY_ISA)
             mg_set(MUTABLE_SV(ary));
-        LEAVE;
+        PL_delaymagic = old_delaymagic;
     }
     SP = ORIGMARK;
     if (OP_GIMME(PL_op, 0) != G_VOID) {