<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
compile	B-Application
time	I-Application
(	O
or	O
compile-time	B-Application
)	O
describes	O
the	O
time	O
window	O
during	O
which	O
a	O
language	O
's	O
statements	O
are	O
converted	O
into	O
0s	O
and	O
1s	O
for	O
the	O
computer	O
to	O
understand	O
.	O
</s>
<s>
The	O
term	O
is	O
used	O
as	O
an	O
adjective	O
to	O
describe	O
concepts	O
related	O
to	O
the	O
context	O
of	O
program	B-Language
compilation	I-Language
,	O
as	O
opposed	O
to	O
concepts	O
related	O
to	O
the	O
context	O
of	O
program	B-Application
execution	O
(	O
runtime	B-Library
)	O
.	O
</s>
<s>
For	O
example	O
,	O
compile-time	B-Application
requirements	O
are	O
programming	O
language	O
requirements	O
that	O
must	O
be	O
met	O
by	O
source	O
code	O
before	O
compilation	B-Language
and	O
compile-time	B-Application
properties	O
are	O
properties	O
of	O
the	O
program	B-Application
that	O
can	O
be	O
reasoned	O
about	O
during	O
compilation	B-Language
.	O
</s>
<s>
The	O
actual	O
length	O
of	O
time	O
it	O
takes	O
to	O
compile	B-Language
a	O
program	B-Application
is	O
usually	O
referred	O
to	O
as	O
compilation	B-Language
time	O
.	O
</s>
<s>
The	O
determination	O
of	O
execution	O
model	O
have	O
been	O
set	O
during	O
the	O
compile	B-Application
time	I-Application
stage	O
.	O
</s>
<s>
Run	B-Library
time	I-Library
-	O
the	O
method	O
of	O
execution	O
and	O
allocation	O
-	O
have	O
been	O
set	O
during	O
the	O
run	B-Library
time	I-Library
and	O
are	O
based	O
on	O
the	O
run	B-Library
time	I-Library
dynamicity	O
.	O
</s>
<s>
Most	O
compilers	B-Language
have	O
at	O
least	O
the	O
following	O
compiler	B-Language
phases	O
(	O
which	O
therefore	O
occur	O
at	O
compile-time	B-Application
)	O
:	O
syntax	B-Language
analysis	I-Language
,	O
semantic	O
analysis	O
,	O
and	O
code	B-Application
generation	I-Application
.	O
</s>
<s>
During	O
optimization	O
phases	O
,	O
constant	O
expressions	O
in	O
the	O
source	O
code	O
can	O
also	O
be	O
evaluated	O
at	O
compile-time	B-Application
using	O
compile-time	B-Application
execution	O
,	O
which	O
reduces	O
the	O
constant	O
expressions	O
to	O
a	O
single	O
value	O
.	O
</s>
<s>
This	O
is	O
not	O
necessary	O
for	O
correctness	O
,	O
but	O
improves	O
program	B-Application
performance	O
during	O
runtime	B-Library
.	O
</s>
<s>
Programming	O
language	O
definitions	O
usually	O
specify	O
compile	B-Application
time	I-Application
requirements	O
that	O
source	O
code	O
must	O
meet	O
to	O
be	O
successfully	O
compiled	B-Language
.	O
</s>
<s>
Properties	O
of	O
a	O
program	B-Application
that	O
can	O
be	O
reasoned	O
about	O
at	O
compile	B-Application
time	I-Application
include	O
range-checks	O
(	O
e.g.	O
,	O
proving	O
that	O
an	O
array	O
index	O
will	O
not	O
exceed	O
the	O
array	O
bounds	O
)	O
,	O
deadlock	B-Operating_System
freedom	O
in	O
concurrent	B-Operating_System
languages	I-Operating_System
,	O
or	O
timings	O
(	O
e.g.	O
,	O
proving	O
that	O
a	O
sequence	O
of	O
code	O
takes	O
no	O
more	O
than	O
an	O
allocated	O
amount	O
of	O
time	O
)	O
.	O
</s>
<s>
Compile-time	B-Application
occurs	O
before	O
link	B-Application
time	I-Application
(	O
when	O
the	O
output	O
of	O
one	O
or	O
more	O
compiled	B-Language
files	O
are	O
joined	O
together	O
)	O
and	O
runtime	B-Library
(	O
when	O
a	O
program	B-Application
is	O
executed	B-General_Concept
)	O
.	O
</s>
<s>
Although	O
in	O
the	O
case	O
of	O
dynamic	B-Application
compilation	I-Application
,	O
the	O
final	O
transformations	O
into	O
machine	B-Language
language	I-Language
happen	O
at	B-Library
runtime	I-Library
.	O
</s>
<s>
There	O
is	O
a	O
trade-off	O
between	O
compile-time	B-Application
and	O
link-time	O
in	O
that	O
many	O
compile	B-Application
time	I-Application
operations	O
can	O
be	O
deferred	O
to	O
link-time	O
without	O
incurring	O
run-time	O
cost	O
.	O
</s>
