Reini Urban

In the first B::C debugging article we stepped into the B::C compiler with Od.
In the second B::C debugging article we stepped the c code with gdb.
We saw that the compiler is missing a sub in a seperate package, the most typical
problem with the current compiler. (since 1995)

We have a cool workaround for this, the -u option for "use".
-udummy forces all symbols in the package dummy to be dumped.

Remember, our testcase was:
'package dummy;sub meth{print "ok"};package main;dummy->meth' as ccode35.pl

$ perl -MO=C,-Do,-v,-udummy,-occode35.c ccode35.pl

Starting compile

Walking tree

walkoptree: 0. LISTOP (0x1471a20) leave

walkoptree: 1. OP (0x1471a48) enter

walkoptree: 1. COP (0x14719e0) nextstate

walkoptree: 1. UNOP (0x1471998) entersub

walkoptree: 2. OP (0x14719c0) pushmark

walkoptree: 2. SVOP (0x1472000) const

walkoptree: 2. SVOP (0x1471978) method_named

done main optree, walking symtable for extras

Prescan for unused subs

Saving unused subs

walkoptree: 0. UNOP (0x164a6c0) leavesub

walkoptree: 1. LISTOP (0x164a698) lineseq

walkoptree: 2. COP (0x1472a00) nextstate

walkoptree: 2. LISTOP (0x1472d48) print

walkoptree: 3. OP (0x1523598) pushmark

walkoptree: 3. SVOP (0x147fad8) const

save context:

curpad names:

curpad syms:

%INC and @INC:

amagic_generation = 1

Writing output

Total number of OPs processed: 13

NULLOP count: 0

Loaded Cwd

Loaded B

Loaded IO

Loaded Fcntl

Loaded B::C

ccode35.pl syntax OK

Here it is!
0. UNOP (0x164a6c0) leavesub
1. LISTOP (0x164a698) lineseq
2. COP (0x1472a00) nextstate
2. LISTOP (0x1472d48) print
3. OP (0x1523598) pushmark
3. SVOP (0x147fad8) const

is indeed our missing &dummy::meth

$ perl -MO=Concise,dummy::meth ccode35.pl

dummy::meth:

5  <1> leavesub[1 ref] K/REFC,1 ->(end)

-     <@> lineseq KP ->5

1        <;> nextstate(dummy 1 ccode35.pl:1) v ->2

4        <@> print sK ->5

2           <0> pushmark s ->3

3           <$> const(PV "ok") s ->4

Any sub argument to B::Concise dumps the optree for this sub,
not just main.

So we still have the compiler bug that dummy->meth is not detected as it says
Prescan for unused subs
Saving unused subs

We'll have to fix the scanner which tries to detect which symbols are used
and which not. Why not just dump all symbols?
We would then also dump the compiler package and all its dependencies.
This will work, but it is bloating the resulting code and reducing the speedup
which we get by not having to parse the perl code again, dumping the optree
and just executing the optree.

To be continued at part 4 - fixing method_named.