[edit] i386 Note: Gentoo's minimum hardware requirement for x86 CPUs is the i486. This is due to glibc-2.4 dropping linuxthreads support and requiring NPTL which doesn't work on i386.
If you would like to use a newer machine (eg. a Pentium III) to compile code that will still run on i386 machines use the following:

CHOST="i386-pc-linux-gnu"
CFLAGS="-mtune=pentium3 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

or

CHOST="i386-pc-linux-gnu"
CFLAGS="-march=i386 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

The former will create code optimized for a PIII that will still run on a i386, while the latter will be optimized for the i386 alone.

[edit] i486 CHOST="i486-pc-linux-gnu"
CFLAGS="-march=i486 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Intel Processors [edit] Pentium vendor_id : GenuineIntel
cpu family : 5
model : 2
model name : Pentium 75 - 200

CHOST="i586-pc-linux-gnu"
CFLAGS="-march=pentium -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Pentium w/ MMX CHOST="i586-pc-linux-gnu"
CFLAGS="-march=pentium-mmx -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Cyrix MediaGX / AMD Geode GX1 CFLAGS="-march=pentium-mmx -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Pentium Pro CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentiumpro -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

or

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=i686 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

(these are identical)

[edit] Pentium II vendor_id : GenuineIntel
cpu family : 6
model : 3, 5

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium2 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 6
model name      : Mobile Pentium II
stepping        : 10
cpu MHz         : 397.082
cache size      : 256 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov pat pse36 mmx fxsr
bogomips        : 794.75
clflush size    : 32

[edit] Celeron (Mendocino), aka Celeron1 vendor_id : GenuineIntel
cpu family : 6
model : 6
stepping : 0

processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 6
model name      : Celeron (Mendocino)
stepping        : 0
cpu MHz         : 400.932
cache size      : 128 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov pat pse36 mmx fxsr up
bogomips        : 802.49
clflush size    : 32

[edit] Pentium III vendor_id : GenuineIntel
cpu family : 6
model : 7, 8

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium3 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 8
model name      : Pentium III (Coppermine)
stepping        : 6
cpu MHz         : 863.934
cache size      : 256 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr sse
bogomips        : 1728.97
clflush size    : 32

[edit] Celeron (Coppermine) vendor_id  : GenuineIntel
cpu family  : 6
model  : 8
stepping  : 10

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium3 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Celeron (Willamette) vendor_id  : GenuineIntel
cpu family  : 15
model  : 1
model name  : Intel(R) Celeron(R) CPU 1.70GHz
stepping  : 3

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium4 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Pentium M(Centrino)/Celeron M vendor_id  : GenuineIntel
cpu family  : 6
model  : 9 or 13
model name  : Intel(R) Pentium(R) M processor XXXXMHz

For gcc 3.3 or older (Warning: dev-java/sun-jdk needs old libstdc++-3.3.so on X86 Systems) :

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium3 -msse2 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

For gcc 3.4 and later:

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium-m -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

The Celeron M is based on the Pentium M but it has half the L2 cache and does not support the SpeedStep technology.

[edit] Mobile Pentium 4-M (Northwood) vendor_id  : GenuineIntel
cpu family  : 15
model  : 2
model name  : Mobile Intel(R) Pentium(R) 4 - M CPU X.XXGHz

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium4 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Pentium 4 vendor_id  : GenuineIntel
cpu family  : 15
model  : 0 or 1 or 2
model name  : Intel(R) Pentium(R) 4 CPU XXXXMHz

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium4 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Pentium 4 (Prescott) / Celeron D vendor_id : GenuineIntel
cpu family : 15
model : 3 or 4
model name  : Intel(R) Pentium(R) 4 CPU XXXGHz -or- Intel(R) Celeron(R) CPU XXXGHz

32-bit profile (x86)

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=prescott -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

64-bit profile (amd64)

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=nocona -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

Note: You can verify the chip is a Prescott by looking for pni in the flags section of /proc/cpuinfo. This indicates support for SSE3.
In 2004, Intel started branding processors with the Prescott core as Intel Celeron D.

[edit] Pentium D 8xx / 9xx vendor_id : GenuineIntel
cpu family : 15
model  : 4, 6
model name  : Intel(R) Pentium(R) D CPU x.xxGHz

32-bit profile (x86)

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=prescott -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

64-bit profile (amd64)

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=nocona -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Xeon w/o EM64T vendor_id  : GenuineIntel
cpu family  : 15
model  : 2
model name  : Intel(R) Xeon(R) CPU XXXXMHz

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium4 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Xeon w/EM64T (also Pentium 4 P6xx) vendor_id  : GenuineIntel
cpu family  : 15
model  : 4, 6
model name  : Intel(R) Xeon(R) CPU XXXXMHz

32-bit profile (x86)

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=prescott -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

64-bit profile (amd64)

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=nocona -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Intel Core Solo/Duo vendor_id  : GenuineIntel
cpu family  : 6
model  : 14
model name  : Genuine Intel(R) CPU TXXXX @ XXXGHz

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=prescott -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

Notes:

It has been confirmed by hongjiu.lu@intel.com that prescott is the correct microarchitecture to use with this CPU. http://article.gmane.org/gmane.comp.gcc.devel/83870
The newer (eg. 420) Celeron-M processors are Core Solo based, not Pentium-M based. If your processor's family and model are 6 and 14, then you should use the -march=prescott option.
[edit] Intel Core 2 Duo/Quad / Xeon 51xx/53xx vendor_id  : GenuineIntel
cpu family  : 6
model  : 15
model name  : Intel(R) Core(TM)2 CPU XXXX @ XXXGHz

32 bit profile (x86)

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=prescott -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

64 bit profile (amd64)

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=nocona -O2 -pipe"
CXXFLAGS="${CFLAGS}"

Note:

GCC 4.3 has -march=core2[1], but Gentoo has nothing above 4.2 in portage.
[edit] VIA Processors Note: EPIA is the name of all VIA's mini-ITX and nano-ITX motherboards with onboard VIA processor. Eden is low-power CPU variant, this name itself also does not tell anything about CPU core.
[edit] Esther C5J (Via C7) vendor_id  : CentaurHauls
cpu family  : 6
model  : 10
model name  : VIA Esther processor 2000MHz

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=i686 -mmmx -msse -msse2 -msse3 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

As the C7 has the pni flag in /proc/cpuinfo, it supports SSE3. Search for pni on this page to get the explanation.

[edit] C3 Nehemiah (C5X/C5XL/C5P) (VIA) vendor_id : CentaurHauls
cpu family : 6
model : 9
model name : VIA Nehemiah

Note: Despite the C5 core name, these processors are marketed as C3s.
GCC 3.3 and earlier

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=i686 -msse -mmmx -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

GCC 3.4 and later

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=c3-2 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

Note: These cores do support the cmov instruction and hence are supported by i686 - and of course c3-2. If you must be compatible with all VIA C3 versions, do not use the settings in this section and instead use the flags in the C3 entry below.
[edit] C3 Samuel/Ezra (Via EPIA) CHOST="i586-pc-linux-gnu"
CFLAGS="-march=c3 -m3dnow -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

Warning: Do not use any stages or packages containing i686 instructions (such as cmov) with the Samuel 2 and Ezra versions of the C3.
The Ezra doesn't have any special instructions that you could optimize for, just consider it a K6-3 - basically a Pentium 2 with 3DNow.

Note: The Mini-ITX EPIA-SP features a VIA C3 Eden processor, even if /proc/cpuinfo answers: model name: VIA Nehemiah
[edit] Transmeta Processors [edit] Transmeta Crusoe vendor_id  : GenuineTMx86
cpu family  : 6
model  : 4
model name  : Transmeta(tm) Crusoe(tm) Processor TM5800
stepping  : 3

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=i686 -Os -mmmx -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Transmeta Efficeon vendor_id  : GenuineTMx86
cpu family  : 15
model  : 2
model name  : Transmeta Efficeon(tm) Processor TM8000
stepping  : 4

CHOST="i686-pc-linux-gnu"
CFLAGS="-mtune=pentium3 -msse2 -O2 -pipe -falign-functions=0 -falign-jumps=0 -falign-loops=0"
CXXFLAGS="${CFLAGS}"

Note: The Efficeon processor will reorder and realign instructions on translating from x86 to VLIW (Very Large Instruction Word), so not aligning functions/jumps/loops will produce smaller executable without any effect on speed.

[edit] AMD Processors [edit] K6 (AMD) CHOST="i586-pc-linux-gnu"
CFLAGS="-march=k6 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] K6-2 (AMD) vendor_id  : AuthenticAMD
cpu family  : 5
model  : 8

CHOST="i586-pc-linux-gnu"
CFLAGS="-march=k6-2 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

# cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 5
model           : 8
model name      : AMD-K6(tm) 3D processor
stepping        : 12
cpu MHz         : 451.031
cache size      : 64 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr mce cx8 pge mmx syscall 3dnow k6_mtrr up
bogomips        : 902.84
clflush size    : 32

Note: /proc/cpuinfo may be confusing. The model name may say "AMD-K6(tm) 3D Processor" but it is not a AMD K6-3. Rely on the vendor_id, CPU family, and model number.Note: If you get "Illegal Instruction" errors on compiles (especially long ones), you may be running into a cooling problem, or worse yet, a Sig11 (segmentation fault/bad ram) problem. Bug #24379 has a discussion about it.

[edit] Geode LX (AMD) vendor_id  : AuthenticAMD
cpu family  : 5
model  : 10

CHOST="i586-pc-linux-gnu"
CFLAGS="-march=k6-2 -Os -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] K6-3 (AMD) CHOST="i586-pc-linux-gnu"
CFLAGS="-march=k6-3 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Duron (AMD) From 600 to 900 MHz (these models have a tbird-alike core model)

product: AMD Duron(tm) Processor version: 6.3.1

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-tbird -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Mobile Duron (AMD) vendor_id : AuthenticAMD
cpu family : 6
model : 3
model name : AMD Duron(tm) Processor

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-tbird -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Duron Morgan (AMD) From 900 to 1300 MHz
The Morgan Durons are based on the Palomino core, and hence can be treated as Athlon XP's.

vendor_id : AuthenticAMD
cpu family : 6
model : 7
model name : AMD Duron(tm) Processor
stepping : 1

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-xp -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Athlon (AMD) vendor_id : AuthenticAMD
cpu family : 6
model : 4 or 2 or 1
model name : AMD Athlon(TM)Processor or AMD-K7(TM)Processor
stepping : 4 or 2

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Athlon-tbird, aka K75 (AMD) vendor_id : AuthenticAMD
cpu family : 6
model : 4
model name : AMD Athlon(tm) Processor

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-tbird -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Athlon-tbird XP/Duron (AMD) vendor_id  : AuthenticAMD
cpu family  : 6
model  : 8
model name  : AMD Athlon(tm)

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-xp -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

Sempron 2400+ (2000MHz) is also identified as cpu family:6 model:8 model_name:AMD Sempron(TM) 2400+ (256kB cache) The Duron 1800+ is also included in this list.

[edit] Athlon 4 (AMD) CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-4 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Athlon XP/Geode NX (AMD) vendor_id  : AuthenticAMD
cpu family  : 6
model  : 6
stepping  : 2
Some CPUs have also been observed with the following:
model : 10
model name : AMD Athlon(tm) XP 2500+
stepping : 0

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-xp -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

# cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 6
model           : 6
model name      : AMD Athlon(tm) XP 2000+
stepping        : 2
cpu MHz         : 1670.597
cache size      : 256 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr sse syscall mmxext 3dnowext 3dnow up ts
bogomips        : 3343.54

# cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 6
model           : 8
model name      : AMD Geode NX 1750 
stepping        : 1
cpu MHz         : 1400.115
cache size      : 256 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr sse syscall mp mmxext 3dnowext 3dnow up ts fid vid
bogomips        : 2801.55
clflush size    : 32

[edit] Athlon MP (AMD) vendor_id  : AuthenticAMD
cpu family  : 6
model  : 10
model name  : AMD Sempron(tm)
stepping  : 0

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-mp -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Athlon 64 (AMD) 32 bit

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=k8 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

64 bit
cpu family  :15
model  :4
model name  :AMD Athlon(tm) 64 Processor 3200+
stepping  :8

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=k8 -O2 -pipe"
CXXFLAGS="${CFLAGS}"

# cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 63
model name      : AMD Athlon(tm) 64 Processor 3200+
stepping        : 2
cpu MHz         : 1999.821
cache size      : 512 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx mmxext fxsr_opt lm 3dnowext 3dnow pni lahf_lm
bogomips        : 4001.79
TLB size        : 1024 4K pages
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management: ts fid vid ttp

[edit] Athlon 64 X2 (AMD) vendor_id: AuthenticAMD
cpu family: 15
model: 35, 43, or 75
stepping: 1 or 2
model name: AMD Athlon(tm) X2 Dual Core Processor

32 bit

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=k8 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

64 bit

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=athlon64 -O2 -pipe"
CXXFLAGS="${CFLAGS}"

If you have a newer Athlon64("Venice" or "San Diego")/Athlon64-X2("Manchester", "Toledo", or "Windsor") (check for pni in cat /proc/cpuinfo) you can also add -msse3 to your CFLAGS to enable SSE3 support. Any chip using the 90nm process except for the "Winchester" class Athlon64 supports SSE3.

Also bear in mind that all Athlon64 X2 and Opteron 165, 170, 175, 180, and 185 processors are dual-core CPUs so make sure that you use MAKEOPTS="-j3" in your make.conf. This doesn't affect the code but might reduce compile times.

All socket AM2 processors are SSE3 capable as well.

[edit] 1xx Opteron (AMD) vendor_id : AuthenticAMD
cpu family : 15
model : 5
model name : AMD Opteron(tm) Processor 1xx
stepping : 8

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=opteron -O2 -pipe"
CXXFLAGS="${CFLAGS}"

socket 939
# cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 39
model name      : AMD Opteron(tm) Processor 144
stepping        : 1
cpu MHz         : 1800.000
cache size      : 1024 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx mmxext fxsr_opt lm 3dnowext 3dnow up pni lahf_lm
bogomips        : 3593.50
TLB size        : 1024 4K pages
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management: ts fid vid ttp

[edit] 2xx/8xx Opteron (AMD) vendor_id : AuthenticAMD
cpu family : 15
model : 5
model name : AMD Opteron(tm) Processor xxx
stepping : 8

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=opteron -O2 -pipe"
CXXFLAGS="${CFLAGS}"

[edit] 22xx Dual-Core Opteron (AMD) vendor_id : AuthenticAMD
cpu family : 15
model : 65
model name : Dual-Core AMD Opteron(tm) Processor 22xx
stepping : 2

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=opteron -O2 -pipe"
CXXFLAGS="${CFLAGS}"

[edit] 23xx Quad-Core Barcelona (AMD) vendor_id  : AuthenticAMD
cpu family  : 16
model  : 2
model name  : Quad-Core AMD Opteron(tm) Processor 23xx
stepping  : 10

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=k8 -O2 -pipe"
CXXFLAGS="${CFLAGS}"

[edit] Sempron/Sempron64 (AMD) If it is a Socket A (Socket 462) Sempron you can be sure it is neither 64-bit capable nor SSE2/SSE3 capable.
If it is a Socket AM2 Sempron you can be sure it is both 64-bit and SSE3 capable.
If it is a Socket 754 it depends on the stepping (part number):
Steppings: CG (Part No.: *AX) or D0 (Part No.: *BA) have neither SSE3 nor AMD64
Stepping: E3 (Part No.: *BO) has SSE3
Stepping: E6 (Part No.: *BX) has SSE3 and AMD64
Anyway you should check /proc/cpuinfo for pni (SSE3) string before using -msse3.
vendor_id : AuthenticAMD
cpu family : 15
model : 44
model name : AMD Sempron(tm) Processor

Note: The model number may differ.

32 bit (Socket A)

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-xp -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

64 bit

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=k8 -O2 -pipe"
CXXFLAGS="${CFLAGS}"

64 bit (SSE3 capable)

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=k8 -msse3 -O2 -pipe"
CXXFLAGS="${CFLAGS}"

Sempron64 - 32 bit

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=k8 -msse3 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

Sempron64 - 64 bit

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=k8 -msse3 -O2 -pipe"
CXXFLAGS="${CFLAGS}"

[edit] Turion64 (AMD) 32 bit

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=k8 -msse3 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

64 bit

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=k8 -msse3 -O2 -pipe"
CXXFLAGS="${CFLAGS}"

SSE3 is called pni in /proc/cpuinfo for this Central Processing Unit.

[edit] Mobile Sempron (AMD) vendor_id : AuthenticAMD
cpu family : 15
model : 8
model name : Mobile AMD Sempron Processor 2800+

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-xp -msse3 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

If you have a Sempron without SSE3 (earlier chips), omit "-msse3".
SSE3 is called pni (prescott new instuction) by cpuinfo (cat /proc/cpuinfo).

Check it out, there are many different sempron mobile CPUs on sale, those that work at 1.8GHz are K8 (i.e. AMD SM 3000+), some others, older, aren't yet k8 but they're still k7 so you must specify athlon-xp instead of athlon64, anyway AMD announced in 2006 there will be 64bit Sempron Mobile CPUs so be carefull and pay attention, run a cat /proc/cpuinfo and then ask on AMD forums if you don't know what to do.

[edit] PowerPC Processors [edit] PowerPC 601 The PowerPC 601 CPU is a mixture between POWER and PowerPC architectures and it is a must you specify -mcpu=601 for taking advantage of the POWER part of the processor and do not use unimplemented PowerPC instructions (implementation of both ISAs is incomplete on 601).

CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=601 -O2 -pipe"
CXXFLAGS="${CFLAGS}"

NOTE: Code created with this flags will not run in any other CPU but PowerPC 601, if you want to run on 601 and others use -mcpu=common and code will run in ANY POWER or PowerPC CPU.

[edit] PowerPC 603 CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=603 -O2 -pipe"
CXXFLAGS="${CFLAGS}"

[edit] PowerPC 603e CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=603e -O2 -pipe"
CXXFLAGS="${CFLAGS}"

[edit] PowerPC 604 CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=604 -O2 -pipe"
CXXFLAGS="${CFLAGS}"

[edit] PowerPC 604e CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=604e -O2 -pipe"
CXXFLAGS="${CFLAGS}"

-Os may be beneficial on older processors (of any kind, not just PowerPCs).

[edit] PowerPC 604e CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=604e -O2 -pipe -fno-strict-aliasing"
CXXFLAGS="${CFLAGS}"

[edit] PowerPC 750 (G3) CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=750 -Os -pipe -fno-strict-aliasing"
CXXFLAGS="${CFLAGS}"

Given the smaller cache sizes, and the fact that the L2 cache is off-die on the G3, better performance may be achieved with -Os rather than -O2.

[edit] PowerPC 750cx (G3e) CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=750 -O2 -pipe -fno-strict-aliasing"
CXXFLAGS="${CFLAGS}"

The 750cx offers more L2 cache than its predecessor, and moves it on-die for a performance boost. Better performance may be achieved with -O2.

[edit] PowerPC 7400 (G4) CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=7400 -O2 -pipe -maltivec -mabi=altivec"
CXXFLAGS="${CFLAGS}"

Note: -O3 is unstable on G4

[edit] PowerPC 7450 (G4 second generation) CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=7450 -O2 -pipe -maltivec -mabi=altivec"
CXXFLAGS="${CFLAGS}"

[edit] PowerPC 970 (G5) CHOST="powerpc64-unknown-linux-gnu"
CFLAGS="-mcpu=G5 -O2 -pipe -maltivec -mabi=altivec -fno-strict-aliasing"
CXXFLAGS="${CFLAGS}"
LDFLAGS="-Wl,-O1"

[edit] Cell Broadband Engine (Playstation 3) Don't use -mcpu=970 it will make the PS3 slower due to the different pipeline (after all it is a CELL B.E and not a G5). GCC 4.3 or SDK 2.1+ is recommended. A second hint: Unlike x86-64 architecture, it is better to use 32bit user land on a PowerPC with a 64bit kernel. The benefit is, that pointers are 32bits so memory usage goes down slightly. In fact unlike x86_64, the number of registers don't change and the register size does not change (though the Linux kernel has issues with interrupts) and the kernel will save all 64bits of the register across context switches.

CHOST="powerpc64-unknown-linux-gnu"
CFLAGS="-O2 -pipe -mcpu=cell -mabi=altivec"
CXXFLAGS="${CFLAGS}"
LDFLAGS=""

[edit] PowerPC (If you don't know which one) CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-O2 -pipe"
CXXFLAGS="${CFLAGS}"

[edit] Embedded PowerPC CPUs You should check /proc/cpuinfo for the CPU model and then for a correct -mcpu flag on man gcc. If you do not find it, use powerpc.

CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=<flag> -Os -pipe"
CXXFLAGS="${CFLAGS}"

[edit] Other Processors [edit] Sparc CHOST="sparc-unknown-linux-gnu"
CFLAGS="-O2 -pipe"
CXXFLAGS="${CFLAGS}"

[edit] Sparc 64 CHOST="sparc-unknown-linux-gnu"
CFLAGS="-mcpu=ultrasparc -mtune=ultrasparc -O2 -pipe"
CXXFLAGS="${CFLAGS}"

Be careful! The CHOST for Sparc64 is still sparc-unknown-linux-gnu, not sparc64-!

[edit] HPPA 1.1 CHOST="hppa1.1-unknown-linux-gnu"
CFLAGS="-O2 -pipe -mschedule=7100LC -march=1.1 -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] HPPA 2.0 CHOST="hppa2.0-unknown-linux-gnu"
CFLAGS="-O2 -pipe -mschedule=8000 -march=2.0 -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

[edit] Alpha ev56 CHOST="alpha-unknown-linux-gnu"
CFLAGS="-mcpu=ev56 -mieee -O2 -pipe"
CXXFLAGS="${CFLAGS}"

[edit] Alpha ev67 CHOST="alpha-unknown-linux-gnu"
CFLAGS="-mieee -mcpu=ev67 -Wa,-mev6 -O2 -pipe "
CXXFLAGS="${CFLAGS}"

This applies to ev68 (Compaq Alpha DS25) machines too. Without -mcpu=ev67 -Wa,-mev6 flags it cannot bootstrap at all.