<s>
The	O
GNU	B-Application
Compiler	I-Application
Collection	I-Application
(	O
GCC	B-Application
)	O
is	O
an	O
optimizing	B-Application
compiler	I-Application
produced	O
by	O
the	B-Application
GNU	I-Application
Project	I-Application
supporting	O
various	O
programming	B-General_Concept
languages	O
,	O
hardware	B-General_Concept
architectures	I-General_Concept
and	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
The	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
(	O
FSF	O
)	O
distributes	O
GCC	B-Application
as	O
free	B-Application
software	I-Application
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
(	O
GNU	B-License
GPL	I-License
)	O
.	O
</s>
<s>
GCC	B-Application
is	O
a	O
key	O
component	O
of	O
the	O
GNU	B-Application
toolchain	I-Application
and	O
the	O
standard	O
compiler	B-Language
for	O
most	O
projects	O
related	O
to	O
GNU	B-Operating_System
and	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
.	O
</s>
<s>
With	O
roughly	O
15	O
million	O
lines	O
of	O
code	O
in	O
2019	O
,	O
GCC	B-Application
is	O
one	O
of	O
the	O
biggest	O
free	O
programs	O
in	O
existence	O
.	O
</s>
<s>
It	O
has	O
played	O
an	O
important	O
role	O
in	O
the	O
growth	O
of	O
free	B-Application
software	I-Application
,	O
as	O
both	O
a	O
tool	O
and	O
an	O
example	O
.	O
</s>
<s>
When	O
it	O
was	O
first	O
released	O
in	O
1987	O
by	O
Richard	O
Stallman	O
,	O
GCC	B-Application
1.0	O
was	O
named	O
the	O
GNU	B-Application
C	I-Application
Compiler	I-Application
since	O
it	O
only	O
handled	O
the	O
C	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
It	O
was	O
extended	O
to	O
compile	B-Language
C++	B-Language
in	O
December	O
of	O
that	O
year	O
.	O
</s>
<s>
Front	O
ends	O
were	O
later	O
developed	O
for	O
Objective-C	B-Language
,	O
Objective-C	B-Language
++	O
,	O
Fortran	B-Application
,	O
Ada	B-Language
,	O
D	B-Application
and	O
Go	B-Application
,	O
among	O
others	O
.	O
</s>
<s>
The	O
OpenMP	B-Application
and	O
OpenACC	B-Operating_System
specifications	O
are	O
also	O
supported	O
in	O
the	O
C	B-Language
and	O
C++	B-Language
compilers	B-Language
.	O
</s>
<s>
GCC	B-Application
has	O
been	O
ported	O
to	O
more	O
platforms	O
and	O
instruction	B-General_Concept
set	I-General_Concept
architectures	I-General_Concept
than	O
any	O
other	O
compiler	B-Language
,	O
and	O
is	O
widely	O
deployed	O
as	O
a	O
tool	O
in	O
the	O
development	O
of	O
both	O
free	O
and	O
proprietary	B-Application
software	I-Application
.	O
</s>
<s>
GCC	B-Application
is	O
also	O
available	O
for	O
many	O
embedded	B-Architecture
systems	I-Architecture
,	O
including	O
ARM-based	O
and	O
Power	O
ISA-based	O
chips	O
.	O
</s>
<s>
As	O
well	O
as	O
being	O
the	O
official	O
compiler	B-Language
of	O
the	B-Operating_System
GNU	I-Operating_System
operating	I-Operating_System
system	I-Operating_System
,	O
GCC	B-Application
has	O
been	O
adopted	O
as	O
the	O
standard	O
compiler	B-Language
by	O
many	O
other	O
modern	O
Unix-like	B-Operating_System
computer	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
,	O
including	O
most	O
Linux	B-Application
distributions	O
.	O
</s>
<s>
Most	O
BSD	B-Operating_System
family	O
operating	B-General_Concept
systems	I-General_Concept
also	O
switched	O
to	O
GCC	B-Application
shortly	O
after	O
its	O
release	O
,	O
although	O
since	O
then	O
,	O
FreeBSD	B-Operating_System
,	O
OpenBSD	B-Operating_System
and	O
Apple	B-Application
macOS	I-Application
have	O
moved	O
to	O
the	O
Clang	B-Application
compiler	B-Language
,	O
largely	O
due	O
to	O
licensing	O
reasons	O
.	O
</s>
<s>
GCC	B-Application
can	O
also	O
compile	B-Language
code	O
for	O
Windows	B-Application
,	O
Android	B-Application
,	O
iOS	B-Application
,	O
Solaris	B-Application
,	O
HP-UX	B-Application
,	O
AIX	B-Application
and	O
DOS	B-Device
.	O
</s>
<s>
In	O
late	O
1983	O
,	O
in	O
an	O
effort	O
to	O
bootstrap	B-Application
the	B-Operating_System
GNU	I-Operating_System
operating	I-Operating_System
system	I-Operating_System
,	O
Richard	O
Stallman	O
asked	O
Andrew	O
S	O
.	O
Tanenbaum	O
,	O
the	O
author	O
of	O
the	B-Device
Amsterdam	I-Device
Compiler	I-Device
Kit	I-Device
(	O
also	O
known	O
as	O
the	O
Free	O
University	O
Compiler	B-Language
Kit	O
)	O
for	O
permission	O
to	O
use	O
that	O
software	O
for	O
GNU	B-Operating_System
.	O
</s>
<s>
When	O
Tanenbaum	O
advised	O
him	O
that	O
the	O
compiler	B-Language
was	O
not	O
free	O
,	O
and	O
that	O
only	O
the	O
university	O
was	O
free	O
,	O
Stallman	O
decided	O
to	O
work	O
on	O
a	O
different	O
compiler	B-Language
.	O
</s>
<s>
His	O
initial	O
plan	O
was	O
to	O
rewrite	O
an	O
existing	O
compiler	B-Language
from	O
Lawrence	O
Livermore	O
National	O
Laboratory	O
from	O
Pastel	B-Application
to	O
C	B-Language
with	O
some	O
help	O
from	O
Len	O
Tower	O
and	O
others	O
.	O
</s>
<s>
Stallman	O
wrote	O
a	O
new	O
C	B-Language
front	O
end	O
for	O
the	O
Livermore	O
compiler	B-Language
,	O
but	O
then	O
realized	O
that	O
it	O
required	O
megabytes	O
of	O
stack	O
space	O
,	O
an	O
impossibility	O
on	O
a	O
68000	B-Device
Unix	B-Application
system	I-Application
with	O
only	O
64KB	O
,	O
and	O
concluded	O
he	O
would	O
have	O
to	O
write	O
a	O
new	O
compiler	B-Language
from	O
scratch	O
.	O
</s>
<s>
None	O
of	O
the	O
Pastel	B-Application
compiler	B-Language
code	O
ended	O
up	O
in	O
GCC	B-Application
,	O
though	O
Stallman	O
did	O
use	O
the	O
C	B-Language
front	O
end	O
he	O
had	O
written	O
.	O
</s>
<s>
GCC	B-Application
was	O
first	O
released	O
March	O
22	O
,	O
1987	O
,	O
available	O
by	O
FTP	B-Protocol
from	O
MIT	O
.	O
</s>
<s>
Stallman	O
was	O
listed	O
as	O
the	O
author	O
but	O
cited	O
others	O
for	O
their	O
contributions	O
,	O
including	O
Tower	O
for	O
"	O
parts	O
of	O
the	O
parser	O
,	O
RTL	B-Application
generator	O
,	O
RTL	B-Application
definitions	O
,	O
and	O
of	O
the	O
Vax	B-Device
machine	O
description	O
"	O
,	O
Jack	O
Davidson	O
and	O
Christopher	B-Language
W	I-Language
.	I-Language
Fraser	I-Language
for	O
the	O
idea	O
of	O
using	O
RTL	B-Application
as	O
an	O
intermediate	O
language	O
,	O
and	O
Paul	O
Rubin	O
for	O
writing	O
most	O
of	O
the	O
preprocessor	B-General_Concept
.	O
</s>
<s>
Described	O
as	O
the	O
"	O
first	O
free	B-Application
software	I-Application
hit	O
"	O
by	O
Peter	O
H	O
.	O
Salus	O
,	O
the	O
GNU	B-Application
compiler	I-Application
arrived	O
just	O
at	O
the	O
time	O
when	O
Sun	O
Microsystems	O
was	O
unbundling	O
its	O
development	O
tools	O
from	O
its	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
,	O
selling	O
them	O
separately	O
at	O
a	O
higher	O
combined	O
price	O
than	O
the	O
previous	O
bundle	O
,	O
which	O
led	O
many	O
of	O
Sun	O
's	O
users	O
to	O
buy	O
or	O
download	O
GCC	B-Application
instead	O
of	O
the	O
vendor	O
's	O
tools	O
.	O
</s>
<s>
While	O
Stallman	O
considered	O
GNU	B-Application
Emacs	I-Application
as	O
his	O
main	O
project	O
,	O
by	O
1990	O
,	O
GCC	B-Application
supported	O
thirteen	O
computer	B-General_Concept
architectures	I-General_Concept
,	O
was	O
outperforming	O
several	O
vendor	O
compilers	B-Language
,	O
and	O
was	O
used	O
commercially	O
by	O
several	O
companies	O
.	O
</s>
<s>
As	O
GCC	B-Application
was	O
licensed	O
under	O
the	O
GPL	B-License
,	O
programmers	O
wanting	O
to	O
work	O
in	O
other	O
directions	O
—	O
particularly	O
those	O
writing	O
interfaces	O
for	O
languages	O
other	O
than	O
C	B-Language
—	O
were	O
free	O
to	O
develop	O
their	O
own	O
fork	B-Application
of	O
the	O
compiler	B-Language
,	O
provided	O
they	O
meet	O
the	O
GPL	B-License
's	O
terms	O
,	O
including	O
its	O
requirements	O
to	O
distribute	O
source	O
code	O
.	O
</s>
<s>
Multiple	O
forks	B-Application
proved	O
inefficient	O
and	O
unwieldy	O
,	O
however	O
,	O
and	O
the	O
difficulty	O
in	O
getting	O
work	O
accepted	O
by	O
the	O
official	O
GCC	B-Application
project	O
was	O
greatly	O
frustrating	O
for	O
many	O
,	O
as	O
the	O
project	O
favored	O
stability	O
over	O
new	O
features	O
.	O
</s>
<s>
The	O
FSF	O
kept	O
such	O
close	O
control	O
on	O
what	O
was	O
added	O
to	O
the	O
official	O
version	O
of	O
GCC	B-Application
2.x	O
(	O
developed	O
since	O
1992	O
)	O
that	O
GCC	B-Application
was	O
used	O
as	O
one	O
example	O
of	O
the	O
"	O
cathedral	O
"	O
development	O
model	O
in	O
Eric	O
S	O
.	O
Raymond	O
's	O
essay	O
The	O
Cathedral	O
and	O
the	O
Bazaar	O
.	O
</s>
<s>
In	O
1997	O
,	O
a	O
group	O
of	O
developers	O
formed	O
the	O
Experimental/Enhanced	O
GNU	B-Application
Compiler	I-Application
System	O
(	O
EGCS	O
)	O
to	O
merge	O
several	O
experimental	O
forks	B-Application
into	O
a	O
single	O
project	O
.	O
</s>
<s>
The	O
basis	O
of	O
the	O
merger	O
was	O
a	O
development	O
snapshot	O
of	O
GCC	B-Application
(	O
taken	O
around	O
the	O
2.7.2	O
and	O
later	O
followed	O
up	O
to	O
2.8.1	O
release	O
)	O
.	O
</s>
<s>
Mergers	O
included	O
g77	O
(	O
Fortran	B-Application
)	O
,	O
PGCC	O
(	O
P5	B-General_Concept
Pentium-optimized	O
GCC	B-Application
)	O
,	O
many	O
C++	B-Language
improvements	O
,	O
and	O
many	O
new	O
architectures	O
and	O
operating	B-General_Concept
system	I-General_Concept
variants	O
.	O
</s>
<s>
While	O
both	O
projects	O
followed	O
each	O
other	O
's	O
changes	O
closely	O
,	O
EGCS	O
development	O
proved	O
considerably	O
more	O
vigorous	O
,	O
so	O
much	O
so	O
that	O
the	O
FSF	O
officially	O
halted	O
development	O
on	O
their	O
GCC	B-Application
2.x	O
compiler	B-Language
,	O
blessed	O
EGCS	O
as	O
the	O
official	O
version	O
of	O
GCC	B-Application
,	O
and	O
appointed	O
the	O
EGCS	O
project	O
as	O
the	O
GCC	B-Application
maintainers	O
in	O
April	O
1999	O
.	O
</s>
<s>
With	O
the	O
release	O
of	O
GCC	B-Application
2.95	O
in	O
July	O
1999	O
the	O
two	O
projects	O
were	O
once	O
again	O
united	O
.	O
</s>
<s>
GCC	B-Application
has	O
since	O
been	O
maintained	O
by	O
a	O
varied	O
group	O
of	O
programmers	O
from	O
around	O
the	O
world	O
under	O
the	O
direction	O
of	O
a	O
steering	O
committee	O
.	O
</s>
<s>
GCC	B-Application
3	O
(	O
2002	O
)	O
removed	O
a	O
front-end	O
for	O
CHILL	B-Language
due	O
to	O
a	O
lack	O
of	O
maintenance	O
.	O
</s>
<s>
Before	O
version	O
4.0	O
the	O
Fortran	B-Application
front	O
end	O
was	O
g77	O
,	O
which	O
only	O
supported	O
FORTRAN	B-Application
77	O
,	O
but	O
later	O
was	O
dropped	O
in	O
favor	O
of	O
the	O
new	O
GNU	B-Application
Fortran	I-Application
front	O
end	O
that	O
supports	O
Fortran	B-Application
95	O
and	O
large	O
parts	O
of	O
Fortran	B-Application
2003	O
and	O
Fortran	B-Application
2008	O
as	O
well	O
.	O
</s>
<s>
As	O
of	O
version	O
4.8	O
,	O
GCC	B-Application
is	O
implemented	O
in	O
C++	B-Language
.	O
</s>
<s>
Support	O
for	O
Cilk	O
Plus	O
existed	O
from	O
GCC	B-Application
5	O
to	O
GCC	B-Application
7	O
.	O
</s>
<s>
GCC	B-Application
has	O
been	O
ported	O
to	O
a	O
wide	O
variety	O
of	O
instruction	B-General_Concept
set	I-General_Concept
architectures	I-General_Concept
,	O
and	O
is	O
widely	O
deployed	O
as	O
a	O
tool	O
in	O
the	O
development	O
of	O
both	O
free	O
and	O
proprietary	B-Application
software	I-Application
.	O
</s>
<s>
GCC	B-Application
is	O
also	O
available	O
for	O
many	O
embedded	B-Architecture
systems	I-Architecture
,	O
including	O
Symbian	B-Operating_System
(	O
called	O
gcce	O
)	O
,	O
ARM-based	O
,	O
and	O
Power	O
ISA-based	O
chips	O
.	O
</s>
<s>
The	O
compiler	B-Language
can	O
target	O
a	O
wide	O
variety	O
of	O
platforms	O
,	O
including	O
video	B-Device
game	I-Device
consoles	I-Device
such	O
as	O
the	O
PlayStation	B-Device
2	I-Device
,	O
Cell	O
SPE	O
of	O
PlayStation	O
3	O
,	O
and	O
Dreamcast	B-Operating_System
.	O
</s>
<s>
It	O
has	O
been	O
ported	O
to	O
more	O
kinds	O
of	O
processors	B-General_Concept
and	O
operating	B-General_Concept
systems	I-General_Concept
than	O
any	O
other	O
compiler	B-Language
.	O
</s>
<s>
,	O
the	O
recent	O
11.1	O
release	O
of	O
GCC	B-Application
includes	O
front	O
ends	O
for	O
C	B-Language
(	O
gcc	B-Application
)	O
,	O
C++	B-Language
(	O
g++	B-Application
)	O
,	O
Objective-C	B-Language
,	O
Fortran	B-Application
(	O
gfortran	B-Application
)	O
,	O
Ada	B-Language
(	O
GNAT	B-Language
)	O
,	O
Go	B-Application
(	O
gccgo	B-Application
)	O
and	O
D	B-Application
(	O
gdc	O
,	O
since	O
9.1	O
)	O
programming	B-General_Concept
languages	O
,	O
with	O
the	O
OpenMP	B-Application
and	O
OpenACC	B-Operating_System
parallel	O
language	O
extensions	O
being	O
supported	O
since	O
GCC	B-Application
5.1	O
.	O
</s>
<s>
Versions	O
prior	O
to	O
GCC	B-Application
7	O
also	O
supported	O
Java	B-Language
(	O
gcj	B-Language
)	O
,	O
allowing	O
compilation	B-Language
of	O
Java	B-Language
to	O
native	O
machine	B-Language
code	I-Language
.	O
</s>
<s>
Modula-2	B-Language
support	O
,	O
previously	O
offered	O
by	O
third	O
parties	O
,	O
will	O
be	O
merged	O
into	O
GCC	B-Application
13	O
.	O
</s>
<s>
Regarding	O
language	O
version	O
support	O
for	O
C++	B-Language
and	O
C	B-Language
,	O
since	O
GCC	B-Application
11.1	O
the	O
default	O
target	O
is	O
gnu++17	O
,	O
a	O
superset	O
of	O
C++17	B-Language
,	O
and	O
gnu11	O
,	O
a	O
superset	O
of	O
C11	O
,	O
with	O
strict	O
standard	O
support	O
also	O
available	O
.	O
</s>
<s>
GCC	B-Application
also	O
provides	O
experimental	O
support	O
for	O
C++20	B-Language
and	O
upcoming	O
C++23	B-Language
.	O
</s>
<s>
Third-party	O
front	O
ends	O
exist	O
for	O
many	O
languages	O
,	O
such	O
as	O
Pascal	B-Application
(	O
gpc	B-Language
)	O
,	O
Modula-3	B-Language
,	O
and	O
VHDL	B-Language
(	O
GHDL	O
)	O
.	O
</s>
<s>
A	O
few	O
experimental	O
branches	O
exist	O
to	O
support	O
additional	O
languages	O
,	O
such	O
as	O
the	O
GCC	B-Application
UPC	B-Operating_System
compiler	B-Language
for	O
Unified	B-Operating_System
Parallel	I-Operating_System
C	I-Operating_System
or	O
Rust	B-Application
.	O
</s>
<s>
GCC	B-Application
's	O
external	O
interface	O
follows	O
Unix	B-Application
conventions	O
.	O
</s>
<s>
Users	O
invoke	O
a	O
language-specific	O
driver	O
program	O
(	O
gcc	B-Application
for	O
C	B-Language
,	O
g++	B-Application
for	O
C++	B-Language
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
which	O
interprets	O
command	O
arguments	O
,	O
calls	O
the	O
actual	O
compiler	B-Language
,	O
runs	O
the	O
assembler	B-Language
on	O
the	O
output	O
,	O
and	O
then	O
optionally	O
runs	O
the	O
linker	B-Application
to	O
produce	O
a	O
complete	O
executable	B-Application
binary	I-Application
.	O
</s>
<s>
Each	O
of	O
the	O
language	B-Language
compilers	I-Language
is	O
a	O
separate	O
program	O
that	O
reads	O
source	O
code	O
and	O
outputs	O
machine	B-Language
code	I-Language
.	O
</s>
<s>
A	O
per-language	O
front	O
end	O
parses	B-Language
the	O
source	O
code	O
in	O
that	O
language	O
and	O
produces	O
an	O
abstract	B-Data_Structure
syntax	I-Data_Structure
tree	I-Data_Structure
(	O
"	O
tree	O
"	O
for	O
short	O
)	O
.	O
</s>
<s>
Compiler	B-Application
optimizations	I-Application
and	O
static	O
code	O
analysis	O
techniques	O
(	O
such	O
as	O
FORTIFY_SOURCE	O
,	O
a	O
compiler	B-Language
directive	O
that	O
attempts	O
to	O
discover	O
some	O
buffer	B-General_Concept
overflows	I-General_Concept
)	O
are	O
applied	O
to	O
the	O
code	O
.	O
</s>
<s>
These	O
work	O
on	O
multiple	O
representations	O
,	O
mostly	O
the	O
architecture-independent	O
GIMPLE	O
representation	O
and	O
the	O
architecture-dependent	O
RTL	B-Application
representation	O
.	O
</s>
<s>
Finally	O
,	O
machine	B-Language
code	I-Language
is	O
produced	O
using	O
architecture-specific	O
pattern	B-Language
matching	I-Language
originally	O
based	O
on	O
an	O
algorithm	O
of	O
Jack	O
Davidson	O
and	O
Chris	O
Fraser	O
.	O
</s>
<s>
GCC	B-Application
was	O
written	O
primarily	O
in	O
C	B-Language
except	O
for	O
parts	O
of	O
the	O
Ada	B-Language
front	O
end	O
.	O
</s>
<s>
The	O
distribution	O
includes	O
the	O
standard	O
libraries	O
for	O
Ada	B-Language
and	O
C++	B-Language
whose	O
code	O
is	O
mostly	O
written	O
in	O
those	O
languages	O
.	O
</s>
<s>
On	O
some	O
platforms	O
,	O
the	O
distribution	O
also	O
includes	O
a	O
low-level	O
runtime	O
library	O
,	O
libgcc	B-Application
,	O
written	O
in	O
a	O
combination	O
of	O
machine-independent	B-Operating_System
C	B-Language
and	O
processor-specific	O
machine	B-Language
code	I-Language
,	O
designed	O
primarily	O
to	O
handle	O
arithmetic	O
operations	O
that	O
the	O
target	O
processor	O
cannot	O
perform	O
directly	O
.	O
</s>
<s>
GCC	B-Application
uses	O
many	O
additional	O
tools	O
in	O
its	O
build	O
,	O
many	O
of	O
which	O
are	O
installed	O
by	O
default	O
by	O
many	O
Unix	B-Application
and	O
Linux	B-Application
distributions	O
(	O
but	O
which	O
,	O
normally	O
,	O
are	O
n't	O
present	O
in	O
Windows	B-Application
installations	O
)	O
,	O
including	O
Perl	B-Language
,	O
Flex	B-General_Concept
,	O
Bison	B-Application
,	O
and	O
other	O
common	O
tools	O
.	O
</s>
<s>
In	O
addition	O
,	O
it	O
currently	O
requires	O
three	O
additional	O
libraries	O
to	O
be	O
present	O
in	O
order	O
to	O
build	O
:	O
GMP	B-Application
,	O
MPC	O
,	O
and	O
MPFR	B-Application
.	O
</s>
<s>
In	O
May	O
2010	O
,	O
the	O
GCC	B-Application
steering	O
committee	O
decided	O
to	O
allow	O
use	O
of	O
a	O
C++	B-Language
compiler	B-Language
to	O
compile	B-Language
GCC	B-Application
.	O
</s>
<s>
The	O
compiler	B-Language
was	O
intended	O
to	O
be	O
written	O
mostly	O
in	O
C	B-Language
plus	O
a	O
subset	O
of	O
features	O
from	O
C++	B-Language
.	O
</s>
<s>
In	O
particular	O
,	O
this	O
was	O
decided	O
so	O
that	O
GCC	B-Application
's	O
developers	O
could	O
use	O
the	O
destructors	B-Language
and	O
generics	B-Language
features	O
of	O
C++	B-Language
.	O
</s>
<s>
In	O
August	O
2012	O
,	O
the	O
GCC	B-Application
steering	O
committee	O
announced	O
that	O
GCC	B-Application
now	O
uses	O
C++	B-Language
as	O
its	O
implementation	O
language	O
.	O
</s>
<s>
This	O
means	O
that	O
to	O
build	O
GCC	B-Application
from	O
sources	O
,	O
a	O
C++	B-Language
compiler	B-Language
is	O
required	O
that	O
understands	O
ISO/IEC	B-Language
C++03	I-Language
standard	O
.	O
</s>
<s>
On	O
May	O
18	O
,	O
2020	O
,	O
GCC	B-Application
moved	O
away	O
from	O
ISO/IEC	B-Language
C++03	I-Language
standard	O
to	O
ISO/IEC	B-Language
C++11	I-Language
standard	O
(	O
i.e.	O
</s>
<s>
needed	O
to	O
compile	B-Language
,	O
bootstrap	B-Application
,	O
the	O
compiler	B-Language
itself	O
;	O
by	O
default	O
it	O
however	O
compiles	B-Language
later	O
versions	O
of	O
C++	B-Language
)	O
.	O
</s>
<s>
Each	O
front	O
end	O
uses	O
a	O
parser	O
to	O
produce	O
the	O
abstract	B-Data_Structure
syntax	I-Data_Structure
tree	I-Data_Structure
of	O
a	O
given	O
source	O
file	O
.	O
</s>
<s>
GCC	B-Application
started	O
out	O
using	O
LALR	B-Application
parsers	I-Application
generated	O
with	O
Bison	B-Application
,	O
but	O
gradually	O
switched	O
to	O
hand-written	O
recursive-descent	B-Application
parsers	I-Application
for	O
C++	B-Language
in	O
2004	O
,	O
and	O
for	O
C	B-Language
and	O
Objective-C	B-Language
in	O
2006	O
.	O
</s>
<s>
As	O
of	O
2021	O
all	O
front	O
ends	O
use	O
hand-written	O
recursive-descent	B-Application
parsers	I-Application
.	O
</s>
<s>
Until	O
GCC	B-Application
4.0	O
the	O
tree	O
representation	O
of	O
the	O
program	O
was	O
not	O
fully	O
independent	O
of	O
the	O
processor	O
being	O
targeted	O
.	O
</s>
<s>
This	O
was	O
simplified	O
with	O
the	O
introduction	O
of	O
GENERIC	O
and	O
GIMPLE	O
,	O
two	O
new	O
forms	O
of	O
language-independent	O
trees	O
that	O
were	O
introduced	O
with	O
the	O
advent	O
of	O
GCC	B-Application
4.0	O
.	O
</s>
<s>
GENERIC	O
is	O
more	O
complex	O
,	O
based	O
on	O
the	O
GCC	B-Application
3.x	O
Java	B-Language
front	O
end	O
's	O
intermediate	B-Application
representation	I-Application
.	O
</s>
<s>
The	O
C	B-Language
,	O
C++	B-Language
,	O
and	O
Java	B-Language
front	O
ends	O
produce	O
GENERIC	O
directly	O
in	O
the	O
front	O
end	O
.	O
</s>
<s>
Other	O
front	O
ends	O
instead	O
have	O
different	O
intermediate	B-Application
representations	I-Application
after	O
parsing	B-Language
and	O
convert	O
these	O
to	O
GENERIC	O
.	O
</s>
<s>
GENERIC	O
is	O
an	O
intermediate	B-Application
representation	I-Application
language	O
used	O
as	O
a	O
"	O
middle	O
end	O
"	O
while	O
compiling	B-Language
source	O
code	O
into	O
executable	B-Application
binaries	I-Application
.	O
</s>
<s>
A	O
subset	O
,	O
called	O
GIMPLE	O
,	O
is	O
targeted	O
by	O
all	O
the	O
front	O
ends	O
of	O
GCC	B-Application
.	O
</s>
<s>
The	O
middle	O
stage	O
of	O
GCC	B-Application
does	O
all	O
of	O
the	O
code	O
analysis	O
and	O
optimization	B-Application
,	O
working	O
independently	O
of	O
both	O
the	O
compiled	B-Language
language	O
and	O
the	O
target	O
architecture	O
,	O
starting	O
from	O
the	O
GENERIC	O
representation	O
and	O
expanding	O
it	O
to	O
register	B-Application
transfer	I-Application
language	I-Application
(	O
RTL	B-Application
)	O
.	O
</s>
<s>
The	O
GENERIC	O
representation	O
contains	O
only	O
the	O
subset	O
of	O
the	O
imperative	B-Application
programming	I-Application
constructs	O
optimized	O
by	O
the	O
middle	O
end	O
.	O
</s>
<s>
In	O
transforming	O
the	O
source	O
code	O
to	O
GIMPLE	O
,	O
complex	O
expressions	O
are	O
split	O
into	O
a	O
three-address	B-Application
code	I-Application
using	O
temporary	O
variables	O
.	O
</s>
<s>
This	O
representation	O
was	O
inspired	O
by	O
the	O
SIMPLE	O
representation	O
proposed	O
in	O
the	O
McCAT	O
compiler	B-Language
by	O
Laurie	O
J	O
.	O
Hendren	O
for	O
simplifying	O
the	O
analysis	O
and	O
optimization	B-Application
of	O
imperative	B-Application
programs	I-Application
.	O
</s>
<s>
Optimization	B-Application
can	O
occur	O
during	O
any	O
phase	O
of	O
compilation	B-Language
;	O
however	O
,	O
the	O
bulk	O
of	O
optimizations	O
are	O
performed	O
after	O
the	O
syntax	O
and	O
semantic	O
analysis	O
of	O
the	O
front	O
end	O
and	O
before	O
the	O
code	B-Application
generation	I-Application
of	O
the	O
back	O
end	O
;	O
thus	O
a	O
common	O
,	O
though	O
somewhat	O
self-contradictory	O
,	O
name	O
for	O
this	O
part	O
of	O
the	O
compiler	B-Language
is	O
the	O
"	O
middle	O
end.	O
"	O
</s>
<s>
The	O
exact	O
set	O
of	O
GCC	B-Application
optimizations	O
varies	O
from	O
release	O
to	O
release	O
as	O
it	O
develops	O
,	O
but	O
includes	O
the	O
standard	O
algorithms	O
,	O
such	O
as	O
loop	O
optimization	B-Application
,	O
jump	O
threading	O
,	O
common	O
subexpression	O
elimination	O
,	O
instruction	O
scheduling	O
,	O
and	O
so	O
forth	O
.	O
</s>
<s>
The	O
RTL	B-Application
optimizations	O
are	O
of	O
less	O
importance	O
with	O
the	O
addition	O
of	O
global	O
SSA-based	O
optimizations	O
on	O
GIMPLE	O
trees	O
,	O
as	O
RTL	B-Application
optimizations	O
have	O
a	O
much	O
more	O
limited	O
scope	O
,	O
and	O
have	O
less	O
high-level	O
information	O
.	O
</s>
<s>
Array	O
dependence	O
based	O
optimizations	O
such	O
as	O
automatic	B-General_Concept
vectorization	I-General_Concept
and	O
automatic	O
parallelization	O
are	O
also	O
performed	O
.	O
</s>
<s>
Profile-guided	O
optimization	B-Application
is	O
also	O
possible	O
.	O
</s>
<s>
The	O
GCC	B-Application
's	O
back	O
end	O
is	O
partly	O
specified	O
by	O
preprocessor	B-Language
macros	I-Language
and	O
functions	O
specific	O
to	O
a	O
target	O
architecture	O
,	O
for	O
instance	O
to	O
define	O
its	O
endianness	O
,	O
word	O
size	O
,	O
and	O
calling	O
conventions	O
.	O
</s>
<s>
The	O
front	O
part	O
of	O
the	O
back	O
end	O
uses	O
these	O
to	O
help	O
decide	O
RTL	B-Application
generation	O
,	O
so	O
although	O
GCC	B-Application
's	O
RTL	B-Application
is	O
nominally	O
processor-independent	O
,	O
the	O
initial	O
sequence	O
of	O
abstract	O
instructions	O
is	O
already	O
adapted	O
to	O
the	O
target	O
.	O
</s>
<s>
At	O
any	O
moment	O
,	O
the	O
actual	O
RTL	B-Application
instructions	O
forming	O
the	O
program	O
representation	O
have	O
to	O
comply	O
with	O
the	O
machine	O
description	O
of	O
the	O
target	O
architecture	O
.	O
</s>
<s>
The	O
machine	O
description	O
file	O
contains	O
RTL	B-Application
patterns	O
,	O
along	O
with	O
operand	O
constraints	O
,	O
and	O
code	O
snippets	O
to	O
output	O
the	O
final	O
assembly	O
.	O
</s>
<s>
The	O
constraints	O
indicate	O
that	O
a	O
particular	O
RTL	B-Application
pattern	O
might	O
only	O
apply	O
(	O
for	O
example	O
)	O
to	O
certain	O
hardware	O
registers	O
,	O
or	O
(	O
for	O
example	O
)	O
allow	O
immediate	O
operand	O
offsets	O
of	O
only	O
a	O
limited	O
size	O
(	O
e.g.	O
</s>
<s>
During	O
RTL	B-Application
generation	O
,	O
the	O
constraints	O
for	O
the	O
given	O
target	O
architecture	O
are	O
checked	O
.	O
</s>
<s>
In	O
order	O
to	O
issue	O
a	O
given	O
snippet	O
of	O
RTL	B-Application
,	O
it	O
must	O
match	O
one	O
(	O
or	O
more	O
)	O
of	O
the	O
RTL	B-Application
patterns	O
in	O
the	O
machine	O
description	O
file	O
,	O
and	O
satisfy	O
the	O
constraints	O
for	O
that	O
pattern	O
;	O
otherwise	O
,	O
it	O
would	O
be	O
impossible	O
to	O
convert	O
the	O
final	O
RTL	B-Application
into	O
machine	B-Language
code	I-Language
.	O
</s>
<s>
Towards	O
the	O
end	O
of	O
compilation	B-Language
,	O
valid	O
RTL	B-Application
is	O
reduced	O
to	O
a	O
strict	O
form	O
in	O
which	O
each	O
instruction	O
refers	O
to	O
real	O
machine	O
registers	O
and	O
a	O
pattern	O
from	O
the	O
target	O
's	O
machine	O
description	O
file	O
.	O
</s>
<s>
Forming	O
strict	O
RTL	B-Application
is	O
a	O
complicated	O
task	O
;	O
an	O
important	O
step	O
is	O
register	O
allocation	O
,	O
where	O
real	O
hardware	O
registers	O
are	O
chosen	O
to	O
replace	O
the	O
initially	O
assigned	O
pseudo-registers	O
.	O
</s>
<s>
This	O
is	O
followed	O
by	O
a	O
"	O
reloading	O
"	O
phase	O
;	O
any	O
pseudo-registers	O
that	O
were	O
not	O
assigned	O
a	O
real	O
hardware	O
register	O
are	O
'	O
spilled	O
 '	O
to	O
the	O
stack	O
,	O
and	O
RTL	B-Application
to	O
perform	O
this	O
spilling	O
is	O
generated	O
.	O
</s>
<s>
Likewise	O
,	O
offsets	O
that	O
are	O
too	O
large	O
to	O
fit	O
into	O
an	O
actual	O
instruction	O
must	O
be	O
broken	O
up	O
and	O
replaced	O
by	O
RTL	B-Application
sequences	O
that	O
will	O
obey	O
the	O
offset	O
constraints	O
.	O
</s>
<s>
In	O
the	O
final	O
phase	O
,	O
the	O
machine	B-Language
code	I-Language
is	O
built	O
by	O
calling	O
a	O
small	O
snippet	O
of	O
code	O
,	O
associated	O
with	O
each	O
pattern	O
,	O
to	O
generate	O
the	O
real	O
instructions	O
from	O
the	O
target	O
's	O
instruction	B-General_Concept
set	I-General_Concept
,	O
using	O
the	O
final	O
registers	O
,	O
offsets	O
,	O
and	O
addresses	O
chosen	O
during	O
the	O
reload	O
phase	O
.	O
</s>
<s>
The	O
assembly-generation	O
snippet	O
may	O
also	O
be	O
a	O
short	O
block	O
of	O
C	B-Language
code	O
,	O
performing	O
some	O
additional	O
work	O
,	O
but	O
ultimately	O
returning	O
a	O
string	O
containing	O
the	O
valid	O
assembly	B-Language
code	I-Language
.	O
</s>
<s>
The	O
GCC	B-Application
project	O
includes	O
an	O
implementation	O
of	O
the	O
C++	B-Language
Standard	I-Language
Library	I-Language
called	O
libstdc++	B-Language
,	O
licensed	O
under	O
the	O
GPLv3	O
License	O
with	O
an	O
exception	O
to	O
link	O
closed	B-Application
source	I-Application
application	O
when	O
sources	O
are	O
built	O
with	O
GCC	B-Application
.	O
</s>
<s>
Some	O
features	O
of	O
GCC	B-Application
include	O
:	O
</s>
<s>
Link-time	B-Application
optimization	B-Application
optimizes	O
across	O
object	O
file	O
boundaries	O
to	O
directly	O
improve	O
the	O
linked	O
binary	O
.	O
</s>
<s>
Link-time	B-Application
optimization	B-Application
relies	O
on	O
an	O
intermediate	O
file	O
containing	O
the	O
serialization	O
of	O
some	O
Gimple	O
representation	O
included	O
in	O
the	O
object	O
file	O
.	O
</s>
<s>
The	O
file	O
is	O
generated	O
alongside	O
the	O
object	O
file	O
during	O
source	O
compilation	B-Language
.	O
</s>
<s>
Each	O
source	O
compilation	B-Language
generates	O
a	O
separate	O
object	O
file	O
and	O
link-time	B-Application
helper	O
file	O
.	O
</s>
<s>
When	O
the	O
object	O
files	O
are	O
linked	O
,	O
the	O
compiler	B-Language
is	O
executed	O
again	O
and	O
uses	O
the	O
helper	O
files	O
to	O
optimize	O
code	O
across	O
the	O
separately	O
compiled	B-Language
object	O
files	O
.	O
</s>
<s>
Plugins	B-Application
extend	O
the	O
GCC	B-Application
compiler	I-Application
directly	O
.	O
</s>
<s>
Plugins	B-Application
allow	O
a	O
stock	O
compiler	B-Language
to	O
be	O
tailored	O
to	O
specific	O
needs	O
by	O
external	O
code	O
loaded	O
as	O
plugins	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
plugins	B-Application
can	O
add	O
,	O
replace	O
,	O
or	O
even	O
remove	O
middle-end	O
passes	O
operating	O
on	O
Gimple	O
representations	O
.	O
</s>
<s>
Several	O
GCC	B-Application
plugins	B-Application
have	O
already	O
been	O
published	O
,	O
notably	O
:	O
</s>
<s>
The	O
Python	O
plugin	B-Application
,	O
which	O
links	O
against	O
libpython	O
,	O
and	O
allows	O
one	O
to	O
invoke	O
arbitrary	O
Python	O
scripts	O
from	O
inside	O
the	O
compiler	B-Language
.	O
</s>
<s>
The	O
aim	O
is	O
to	O
allow	O
GCC	B-Application
plugins	B-Application
to	O
be	O
written	O
in	O
Python	O
.	O
</s>
<s>
The	O
MELT	O
plugin	B-Application
provides	O
a	O
high-level	O
Lisp-like	O
language	O
to	O
extend	O
GCC	B-Application
.	O
</s>
<s>
The	O
support	O
of	O
plugins	B-Application
was	O
once	O
a	O
contentious	O
issue	O
in	O
2007	O
.	O
</s>
<s>
The	O
C++	B-Language
language	I-Language
has	O
an	O
active	O
proposal	O
for	O
transactional	B-Operating_System
memory	I-Operating_System
.	O
</s>
<s>
It	O
can	O
be	O
enabled	O
in	O
GCC	B-Application
6	O
and	O
newer	O
when	O
compiling	B-Language
with	O
-fgnu-tm	O
.	O
</s>
<s>
Although	O
the	O
C++	B-Language
language	I-Language
requires	O
support	O
for	O
non-ASCII	O
Unicode	O
characters	O
in	O
identifiers	O
,	O
the	O
feature	O
has	O
only	O
been	O
supported	O
since	O
GCC	B-Application
10	O
.	O
</s>
<s>
The	O
feature	O
is	O
optional	O
in	O
C	B-Language
,	O
but	O
has	O
been	O
made	O
available	O
too	O
since	O
this	O
change	O
.	O
</s>
<s>
GNU	B-Application
C	I-Application
extends	O
the	O
C	B-Language
programming	I-Language
language	I-Language
with	O
several	O
non-standard-features	O
,	O
including	O
nested	O
functions	O
and	O
typeof	O
expressions	O
.	O
</s>
<s>
The	O
primary	O
supported	O
(	O
and	O
best	O
tested	O
)	O
processor	O
families	O
are	O
64	O
-	O
and	O
32-bit	O
ARM	B-Architecture
,	O
64	O
-	O
and	O
32-bit	O
x86_64	O
and	O
x86	B-Operating_System
and	O
64-bit	O
PowerPC	B-Architecture
and	O
SPARC	B-Architecture
.	O
</s>
<s>
GCC	B-Application
target	O
processor	O
families	O
as	O
of	O
version	O
11.1	O
include	O
:	O
</s>
<s>
Lesser-known	O
target	O
processors	B-General_Concept
supported	O
in	O
the	O
standard	O
release	O
have	O
included	O
:	O
</s>
<s>
Additional	O
processors	B-General_Concept
have	O
been	O
supported	O
by	O
GCC	B-Application
versions	O
maintained	O
separately	O
from	O
the	O
FSF	O
version	O
:	O
</s>
<s>
The	O
GCJ	B-Language
Java	B-Language
compiler	B-Language
can	O
target	O
either	O
a	O
native	O
machine	B-Language
language	I-Language
architecture	O
or	O
the	O
Java	B-Language
virtual	I-Language
machine	I-Language
's	O
Java	B-Language
bytecode	I-Language
.	O
</s>
<s>
When	O
retargeting	B-Application
GCC	B-Application
to	O
a	O
new	O
platform	O
,	O
bootstrapping	B-Application
is	O
often	O
used	O
.	O
</s>
<s>
Motorola	B-Device
68000	I-Device
,	O
Zilog	O
Z80	O
,	O
and	O
other	O
processors	B-General_Concept
are	O
also	O
targeted	O
in	O
the	O
GCC	B-Application
versions	O
developed	O
for	O
various	O
Texas	O
Instruments	O
,	O
Hewlett	O
Packard	O
,	O
Sharp	O
,	O
and	O
Casio	O
programmable	O
graphing	O
calculators	O
.	O
</s>
<s>
GCC	B-Application
is	O
licensed	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
version	O
3	O
.	O
</s>
<s>
The	O
GCC	B-Application
runtime	O
exception	O
permits	O
compilation	B-Language
of	O
proprietary	B-Application
programs	I-Application
(	O
in	O
addition	O
to	O
free	B-Application
software	I-Application
)	O
with	O
GCC	B-Application
.	O
</s>
<s>
This	O
does	O
not	O
impact	O
the	O
license	O
terms	O
of	O
GCC	B-Application
source	O
code	O
.	O
</s>
