<s>
A	O
data	B-Operating_System
dependency	I-Operating_System
in	O
computer	B-General_Concept
science	I-General_Concept
is	O
a	O
situation	O
in	O
which	O
a	O
program	O
statement	O
(	O
instruction	O
)	O
refers	O
to	O
the	O
data	O
of	O
a	O
preceding	O
statement	O
.	O
</s>
<s>
In	O
compiler	O
theory	O
,	O
the	O
technique	O
used	O
to	O
discover	O
data	B-Operating_System
dependencies	I-Operating_System
among	O
statements	O
(	O
or	O
instructions	O
)	O
is	O
called	O
dependence	O
analysis	O
.	O
</s>
<s>
A	O
Flow	O
dependency	O
,	O
also	O
known	O
as	O
a	O
data	B-Operating_System
dependency	I-Operating_System
or	O
true	O
dependency	O
or	O
read-after-write	O
(	O
RAW	O
)	O
,	O
occurs	O
when	O
an	O
instruction	O
depends	O
on	O
the	O
result	O
of	O
a	O
previous	O
instruction	O
.	O
</s>
<s>
Instruction	B-Operating_System
level	I-Operating_System
parallelism	I-Operating_System
is	O
therefore	O
not	O
an	O
option	O
in	O
this	O
example	O
.	O
</s>
<s>
A	O
commonly	O
used	O
naming	O
convention	O
for	O
data	B-Operating_System
dependencies	I-Operating_System
is	O
the	O
following	O
:	O
Read-after-Write	O
or	O
RAW	O
(	O
flow	O
dependency	O
)	O
,	O
Write-After-Read	O
or	O
WAR	O
(	O
anti-dependency	O
)	O
,	O
or	O
Write-after-Write	O
or	O
WAW	O
(	O
output	O
dependency	O
)	O
.	O
</s>
<s>
Control	O
dependences	O
are	O
essentially	O
the	O
dominance	B-Application
frontier	I-Application
in	O
the	O
reverse	O
graph	O
of	O
the	O
control-flow	O
graph	O
(	O
CFG	O
)	O
.	O
</s>
<s>
for	O
each	O
X	O
in	O
a	O
bottom-up	O
traversal	O
of	O
the	O
post-dominator	O
tree	O
do	O
:	O
</s>
<s>
However	O
,	O
dependencies	O
among	O
statements	O
or	O
instructions	O
may	O
hinder	O
parallelism	O
—	O
parallel	O
execution	O
of	O
multiple	O
instructions	O
,	O
either	O
by	O
a	O
parallelizing	O
compiler	O
or	O
by	O
a	O
processor	O
exploiting	O
instruction-level	B-Operating_System
parallelism	I-Operating_System
.	O
</s>
<s>
Recklessly	O
executing	O
multiple	O
instructions	O
without	O
considering	O
related	O
dependences	O
may	O
cause	O
danger	O
of	O
getting	O
wrong	O
results	O
,	O
namely	O
hazards	B-General_Concept
.	O
</s>
