Add SS_ADD_* macros and replace most SSPUSH* uses
The current idiom for adding an entry to the savestack is
SSCHECK(3);
SSPUSHINT(...);
SSPUSHPTR(...);
SSPUSHUV(SAVEt_...);
Replace this with a new idiom:
{
dSS_ADD;
SS_ADD_INT(...);
SS_ADD_PTR(...);
SS_ADD_UV(SAVEt_...);
SS_ADD_END(3);
}
This is designed to be more efficient.
First, it defines some local vars, and defers updating PL_savestack_ix
to the end.
Second, it performs the 'is there space on the stack' check *after*
pushing. Doing the check last means that values in registers will have
been pushed and no longer needed, so don't need saving around the call to
grow. Also, tail-call elimination of the grow() can be done. These changes
reduce the code of something like save_pushptrptr() to half its former
size.
Of course, doing the size check *after* pushing means we must always
ensure there are SS_MAXPUSH free slots on the savestack */