I'm trying to understand lvalue subs on the opcode level and would appreciate some help. For the motivation please read Another approach to extend lvalues ?

here the perlcode I want to analyze

my $scalar;
test();

sub normal :lvalue {
    proxy();
}
sub proxy :lvalue  {
    $scalar;
}

sub nlv {
    my $x="not lvalue"
}

sub test {
    nlv();
    normal=42;
    print $scalar;
}
[download]

perl -MO=Concise,-exec,test,normal,proxy,nlv lvalue.pl
main::test:
1  <;> nextstate(main 6 concise.pl:16) v   #    nlv();
2  <0> pushmark s
3  <#> gv[*nlv] s
4  <1> entersub[t2] vKS/TARG,1
5  <;> nextstate(main 6 concise.pl:17) v   #    normal=42;
6  <$> const[IV 42] s
7  <0> pushmark s
8  <#> gv[*normal] s
9  <1> entersub[t4] sKRMS*/NO(),TARG,1
a  <2> sassign vKS/2
b  <;> nextstate(main 6 concise.pl:18) v   #    print $scalar;
c  <0> pushmark s
d  <0> padsv[$scalar:FAKE] l
e  <@> print sK
f  <1> leavesub[1 ref] K/REFC,1
main::normal:
g  <;> nextstate(main 2 concise.pl:5) v    #    proxy();
h  <0> pushmark s
i  <#> gv[*proxy] s/EARLYCV   
j  <1> rv2cv sK/NO(),1
k  <1> entersub[t2] KS/NO(),TARG,1
l  <1> leavesublv[1 ref] K/REFC,1
main::proxy:
m  <;> nextstate(main 3 concise.pl:8) v    #    $scalar;
n  <0> padsv[$scalar:FAKE] 
o  <1> leavesublv[1 ref] K/REFC,1
main::nlv:
p  <;> nextstate(main 4 concise.pl:12) v   #    my $x="not lvalue"
q  <$> const[PV "not lvalue"] s
r  <0> padsv[$x:4,5] sRM*/LVINTRO
s  <2> sassign sKS/2
t  <1> leavesub[1 ref] K/REFC,1
[download]

Well I'm still struggling to understand the opcodes, but please look at the lines 6-a and k.

my interpretation is that by assigning a value to a lvalue-sub the steps are:

1. cache the value
2. call the lvalue-sub, which returns a var by refrence
3. assign the cached value to this var

so even on the level of the opcodes the lvaluesub has no chance to know which value will be assigned to the variable he returns ... Correct?

I'm a little bit confused about line j, what means "rv2cv" (it's the first time this happens right before a sub call)?

I googled through perlguts op.c and concise.pod but can't get a sufficient answer...

Thanx Rolf

* I know with 5.10 I wouldn't need to do it manually but I'm sticking on 5.8.8. I have to figure out how to safely install two different perl-versions on the same system, so that I can maintain both with aptitude.