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, 4 insertions, 1 deletions

diff --git a/pp_hot.c b/pp_hot.c
index 9ac606665f..e866841ec4 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -1174,6 +1174,9 @@ PP(pp_aassign)
     SSize_t i;
     int magic;
     U32 lval;
+    /* 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;
 #ifdef DEBUGGING
     bool fake = 0;
 #endif
@@ -1545,7 +1548,7 @@ PP(pp_aassign)
         PERL_UNUSED_VAR(tmp_egid);
 #endif
     }
-    PL_delaymagic = 0;
+    PL_delaymagic = old_delaymagic;
 
     if (gimme == G_VOID)
 	SP = firstrelem - 1;