why basic block 0 and 1 not in output graph

[tys lefering <twlevo@xxxxxxxxx>]

using gcc-4.3.2 and tested gcc-4.5 development snapshot noticed that using
'gcc -da -dv test.c' to generate vcg graph output files these files do not have
"basic block 0" and "basic block 1" in the vcg graph output.

is this intended and what exactly represent block 0 and block 1 ?

for example current output is: (it starts with block 2)

graph: {
port_sharing: no
graph: { title: "gcd"
folding: 1
hidden: 2
node: { title: "gcd.0" }
graph: {
title: "gcd.BB2"
folding: 1
color: lightblue
label: "basic block 2"

node: {
  title: "gcd.3"
  color: lightgrey
  label: "note 3
 NOTE_INSN_BASIC_BLOCK"
}
...

but older gcc versions generated output with a basic block 0 and 1 like this:

graph: {
port_sharing: no
graph: { title: "create_alloc_pool"
folding: 1
hidden: 2
node: { title: "create_alloc_pool.0" }
graph: {
title: "create_alloc_pool.BB0"
folding: 1
color: lightblue
label: "basic block 0"
...
and looked at the place where start_bb() is called in gcc/graph.c