<s>
A	O
leaf	B-General_Concept
subroutine	I-General_Concept
is	O
a	O
subroutine	O
which	O
cannot	O
in	O
turn	O
call	O
another	O
subroutine	O
.	O
</s>
<s>
Some	O
compilers	O
can	O
apply	O
special	O
program	O
optimizations	O
to	O
leaf	B-General_Concept
subroutines	I-General_Concept
,	O
such	O
as	O
the	O
use	O
of	O
link	B-General_Concept
registers	I-General_Concept
to	O
avoid	O
having	O
to	O
push	O
the	O
return	O
address	O
on	O
the	O
stack	O
.	O
</s>
<s>
The	O
term	O
"	O
leaf	O
"	O
refers	O
to	O
their	O
position	O
as	O
leaf	B-Data_Structure
nodes	I-Data_Structure
in	O
the	O
call	B-Application
graph	I-Application
of	O
the	O
program	O
.	O
</s>
