mPUSHn()/mPUSHi()/mPUSHu() convert from slow sv_set() to newSV()+2mortal()

commit d82b684 - Apr 30 2004 - Steve Hay
Document limitations in PUSHi et al macros and add new mPUSHi et al macros

which is day 1 of these macros, introduced this not ideal pattern doing
"sv_setiv(PUSHmortal,)". sv_set*() funcs are much more complex/more work
at runtime, since they must undo *everything* prior in the SV* and
maybe upgrade the body and copy over fields from the prev "body[less]".
newSV*() funcs dont have to do that. sv_2mortal() is very small and
light weight internally, so rmving sv_newmortal() then adding sv_2mortal()
isn't a problem, but for full disclosure, this commit makes better macros
mPUSHn()/mPUSHi()/mPUSHu() than before, but this commit isn't perfect.
sv_2mortal() is public api, and while it has exactly 1 conditional fn
call in it (stack grower), it is a little bit heavier and does more work
than a perfection hand written solution (see PUSH_EXTEND_MORTAL__SV_C).
sv_2mortal() contains 4 branches, PUSH_EXTEND_MORTAL__SV_C has 1 branch.

Another benefit of this commit is XS code that looks like
if(r=c_syscall()) PUSHs(sv_2mortal(newSViv(r)));
is better than
if(r=c_syscall()) sv = newSV(); PUSHs(sv); sv_setiv(r);
b/c var r, will effortlessly flow from the volatile retval register to a
volatile outgoing "C stk" register (xfering control to newSViv()) and
doesn't need to be save/restored from a non-vol storage location to
preserve var r around a extern linked C fn.

The 2004 commit above also has a same title medium sized P5P thread.
This 2004 patch doesn't have a spotless history as a patch, and it went
through multiple revisions b/c of typos and mistakes at the time, until it
was decided to publish it. That commit probably did the
"sv_setiv(PUSHmortal,)" pattern b/c of copy pasting from the existing
TARG macros. And the commit is an improvement/fix for flaws or
unfriendlyness that TARG macros had.

Author: bulk88

pp.h

@@ -568,9 +568,9 @@ Does not use C<TARG>.  See also C<L</XPUSHu>>, C<L</mPUSHu>> and C<L</PUSHu>>.
 #define PUSHmortal	PUSHs(sv_newmortal())
 #define mPUSHp(p,l)	PUSHs(newSVpvn_flags((p), (l), SVs_TEMP))
 #define mPUSHpvs(s)     mPUSHp("" s "", sizeof(s)-1)
-#define mPUSHn(n)	sv_setnv(PUSHmortal, (NV)(n))
-#define mPUSHi(i)	sv_setiv(PUSHmortal, (IV)(i))
-#define mPUSHu(u)	sv_setuv(PUSHmortal, (UV)(u))
+#define mPUSHn(n)	mPUSHs(newSVnv((NV)(n)))
+#define mPUSHi(i)	mPUSHs(newSViv((IV)(i)))
+#define mPUSHu(u)	mPUSHs(newSVuv((UV)(u)))
 
 #define mXPUSHs(s)	XPUSHs(sv_2mortal(s))
 #define XPUSHmortal	XPUSHs(sv_newmortal())