Target Specific Options¶
Overview¶
In addition GCC options common to all targets, ARC GNU toolchains supports a set of -m<value>
target specific options.
Each of them configures a particular feature. For example, -mno-code-density
option disables generating
code density instructions.
-mcpu=<core>
selects a particular ISA and CPU family and enables/disables a set of other -m
options.
Each -mcpu
value leads to linking with a prebuilt library which corresponds to this particular
-mcpu=<value>
and is built using this -mcpu=<value>
.
For example, options combination -mcpu=em4 -mno-code-density
generates code that doesn't
use code density instructions, however it is linked with standard library that has been built
with just -mcpu=em4
, which uses code density instructions. Therefore a final application still may
use code density instructions.
All available target specific options may be found in an official GCC manual.
ARCv1 and ARCv2 Toolchains¶
Target Options¶
Here is a table of target options for ARCv1 and ARCv2 CPU families with default values for CPU families (On, Off or N/A).
Options | ARC HS | ARC EM | ARC 700 | ARC 600 |
---|---|---|---|---|
-mbarrel-shifter |
On | Off | On | Off |
-mnorm |
On | Off | On | Off |
-mswap |
On | Off | On | Off |
-rf16 |
Off | Off | Off | Off |
-mfpu=<...> |
Off | Off | — | — |
-mmpy-option=<...> |
Off | Off | — | — |
-mcode-density |
On | Off | — | — |
-mdiv-rem |
Off | Off | — | — |
-matomic |
On | — | Off | — |
-mll64 |
Off | — | — | — |
-mspfp |
— | Off | Off | Off |
-mdpfp |
— | Off | Off | Off |
-msimd |
— | Off | Off | — |
-mmargonaut |
— | — | Off | Off |
-mea |
— | — | Off | — |
-mmul64 |
— | — | — | Off |
-mmul32x16 |
— | — | — | Off |
-munaligned-access |
You can find a short description for all target options using --target-help
option. For example:
$ arc-elf32-gcc --target-help
...
-mbranch-index Enable use of BI/BIH instructions when available.
-mcase-vector-pcrel Use pc-relative switch case tables - this enables case table shortening.
-mcmem Enable use of NPS400 xld/xst extension.
-mcode-density Enable code density instructions for ARCv2.
-mcode-density-frame Enable ENTER_S and LEAVE_S opcodes for ARCv2.
-mcompact-casesi Enable compact casesi pattern. Uses of this option are diagnosed.
-mcpu=CPU Compile code for ARC variant CPU.
-mcrc Enable variable polynomial CRC extension. Uses of this option are diagnosed.
-mdiv-rem Enable DIV-REM instructions for ARCv2.
-mdpfp FPX: Generate Double Precision FPX (compact) instructions.
-mdpfp-compact FPX: Generate Double Precision FPX (compact) instructions.
...
You can find what target options are enabled or disabled by a particular -mcpu=<...>
using
-Q
options. For example:
$ arc-elf32-gcc -Q --target-help -mcpu=archs
...
-mbranch-index [disabled]
-mcase-vector-pcrel [disabled]
-mcmem [disabled]
-mcode-density [enabled]
-mcode-density-frame [disabled]
-mcompact-casesi [disabled]
-mcpu=CPU archs
-mcrc [disabled]
-mdiv-rem [enabled]
-mdpfp [disabled]
-mdpfp-compact [disabled]
...
Also, there are several configuration files in GCC's source tree that describe
target options for all targets. All of them may be found in gcc/config/arc
directory:
arc-options.def
,arc-opts.h
,arc.opt
- definitions and descriptions for all target options.arc-arches.def
- definitions of CPU families with all available and default target options.arc-cpus.def
- definitions of particular-mcpu=<core>
targets.
Values of -mcpu
for ARC HS3x and HS4x Families¶
-mcpu= |
-mdiv-rem |
-matomic |
-mll64 |
-mmpy-option= |
-mfpu= |
---|---|---|---|---|---|
hs |
Y | ||||
hs34 |
Y | mpy |
|||
archs |
Y | Y | Y | mpy |
|
hs38 |
Y | Y | Y | plus_qmacw |
|
hs4x |
Y | Y | Y | plus_qmacw |
|
hs4xd |
Y | Y | Y | plus_qmacw |
|
hs38_linux |
Y | Y | Y | plus_qmacw |
fpud_all |
The above -mcpu
values correspond to specific ARC EM Processor templates presented in the ARChitect tool.
-mcpu=hs
corresponds to a basic ARC HS with only atomic instructions enabled. It corresponds to the following ARC HS templates in ARChitect:hs34_base
,hs36_base
andhs38_base
.-mcpu=hs34
is likehs
but with with additional support for standard hardware multiplier. It corresponds to the following ARC HS templates in ARChitect:hs34
,hs36
andhs38
.-mcpu=archs
is a generic configuration, which corresponds to the default configuration in older GNU toolchain versions.-mcpu=hs38
is a full-featured ARC HS. It corresponds to the following ARC HS template in ARChitect:hs38_full
.-mcpu=hs4x
and-mcpu=hs4xd
have the same option set as-mcpu=hs38
, but compiler will optimize instruction scheduling for specified processors.-mcpu=hs38_linux
is a full-featured ARC HS with additional support of double-precision FPU.
Values of -mcpu
for ARC EM Family¶
-mcpu |
-mcode-density |
-mnorm |
-mswap |
-mbarrel-shifter |
-mdiv-rem |
-mmpy-option= |
-mfpu= |
-mrf16 |
-mspfp |
-mdpfp |
---|---|---|---|---|---|---|---|---|---|---|
em |
||||||||||
em_mini |
Y | |||||||||
em4 |
Y | |||||||||
arcem |
Y | Y | wlh1 |
|||||||
em4_dmips |
Y | Y | Y | Y | Y | wlh1 |
||||
em4_fpus |
Y | Y | Y | Y | Y | wlh1 |
fpus |
|||
em4_fpuda |
Y | Y | Y | Y | Y | wlh1 |
fpuda |
|||
quarkse_em |
Y | Y | Y | Y | Y | wlh2 |
quark |
Y | Y |
The above -mcpu
values correspond to specific ARC EM Processor templates presented in the ARChitect tool.
It should be noted however that some ARC features are not currently supported in the GNU toolchain, for
example DSP instruction support.
-mcpu=em
doesn't correspond to any specific template, it simply defines the base ARC EM configuration without any optional instructions.-mcpu=em_mini
is same asem
, but uses reduced register file with only 16 core registers.-mcpu=em4
is a base ARC EM core configuration with-mcode-density
option. It corresponds to the following ARC EM templates in ARChitect:em4_mini
,em4_sensor
,em4_ecc
,em6_mini
,em5d_mini
,em5d_mini_v3
,em5d_nrg
,em7d_nrg
,em9d_mini
. Note that those mini templates have a reduced core register file, but-mcpu=em4
doesn't enable this feature.-mcpu=arcem
doesn't correspond to any specific template, it is a legacy flag preserved for compatibility with older GNU toolchain versions, where-mcpu
used to select only a CPU family, while optional features were enabled or disabled by individual-m<something>
options.-mcpu=em4_dmips
is a full-featured ARC EM configuration for integer operations. It corresponds to the following ARC EM templates in ARChitect:em4_dmips
,em4_rtos
,em6_dmips
,em4_dmips_v3
,em4_parity
,em6_dmips_v3
,em6_gp
,em5d_voice_audio
,em5d_nrg_v3
,em7d_nrg_v3
,em7d_voice_audio
,em9d_nrg
,em9d_voice_audio
,em11d_nrg
andem11d_voice_audio
.-mcpu=em4_fpus
is likeem4_dmips
but with additional support for single-precision floating point unit. It corresponds to the following ARC EM templates in ARChitect:em4_dmips_fpusp
,em4_dmips_fpusp_v3
,em5d_nrg_fpusp
andem9d_nrg_fpusp
.-mcpu=em4_fpuda
is likeem4_fpus
but with additional support for double-precision assist instructions. It corresponds to the following ARC EM templates in ARChitect:em4_dmips_fpuspdp
andem4_dmips_fpuspdp_v3
.-mcpu=quarkse_em
is a configuration for ARC processor in Intel Quark SE chip. It enables additional floating point instructions which cannot be enable using a particular target option.
Values of -mcpu
for ARC 600 and 700 Families¶
-mcpu= |
-mnorm |
-mswap |
-mbarrel-shifter |
Multiplier |
---|---|---|---|---|
arc700 |
Y | Y | Y | -mmpy |
arc600 |
Y | |||
arc600_norm |
Y | Y | ||
arc600_mul64 |
Y | Y | -mmul64 |
|
arc600_mul32x16 |
Y | Y | -mmul32x16 |
|
arc601 |
||||
arc601_norm |
Y | |||
arc601_mul64 |
Y | -mmul64 |
||
arc601_mul32x16 |
Y | -mmul32x16 |
Controlling the Memory Model¶
-mcmodel |
Memory size for Data/Code |
---|---|
small |
1MB region |
medium |
4GB region (used by -fpic ) |
large |
Full memory (used by -fPIC ) |
Other Tweaking Options¶
Option | Description |
---|---|
-mfpmov |
Reduces the pressure on GPRs by using FPRs for inline memory operations. |
-mbrcc |
Generate BRcc instructions early on. |
-mbbit |
Likewise but for BBITx instructions. |
ARCv3 Toolchain¶
Values of -mcpu
for ARC HS5x and ARC HS6x Families¶
-mcpu= |
-msimd |
-m128 |
-mll64 |
---|---|---|---|
hs5x |
Y | N/A | |
hs58 |
Y | N/A | Y |
hs6x |
Y | N/A | |
hs68 |
Y | Y | N/A |