3.18.3 ARC Options

The following options control the architecture variant for which code is being compiled:

-mbarrel-shifter
Generate instructions supported by barrel shifter. This is the default unless -mcpu=ARC601 or ‘ -mcpu=ARCEM ’ is in effect.
-mcpu= cpu
Set architecture type, register usage, and instruction scheduling parameters for cpu . There are also shortcut alias options available for backward compatibility and convenience. Supported values for cpu are
arc600
Compile for ARC600. Aliases: -mA6 , -mARC600 .
arc601
Compile for ARC601. Alias: -mARC601 .
arc700
Compile for ARC700. Aliases: -mA7 , -mARC700 . This is the default when configured with --with-cpu=arc700 .
arcem
Compile for ARC EM.
archs
Compile for ARC HS.
em
Compile for ARC EM CPU with no hardware extensions.
em4
Compile for ARC EM4 CPU.
em4_dmips
Compile for ARC EM4 DMIPS CPU.
em4_fpus
Compile for ARC EM4 DMIPS CPU with the single-precision floating-point extension.
em4_fpuda
Compile for ARC EM4 DMIPS CPU with single-precision floating-point and double assist instructions.
hs
Compile for ARC HS CPU with no hardware extensions except the atomic instructions.
hs34
Compile for ARC HS34 CPU.
hs38
Compile for ARC HS38 CPU.
hs38_linux
Compile for ARC HS38 CPU with all hardware extensions on.
arc600_norm
Compile for ARC 600 CPU with norm instructions enabled.
arc600_mul32x16
Compile for ARC 600 CPU with norm and 32x16-bit multiply instructions enabled.
arc600_mul64
Compile for ARC 600 CPU with norm and mul64 -family instructions enabled.
arc601_norm
Compile for ARC 601 CPU with norm instructions enabled.
arc601_mul32x16
Compile for ARC 601 CPU with norm and 32x16-bit multiply instructions enabled.
arc601_mul64
Compile for ARC 601 CPU with norm and mul64 -family instructions enabled.
nps400
Compile for ARC 700 on NPS400 chip.

-mdpfp
-mdpfp-compact
Generate double-precision FPX instructions, tuned for the compact implementation.
-mdpfp-fast
Generate double-precision FPX instructions, tuned for the fast implementation.
-mno-dpfp-lrsr
Disable lr and sr instructions from using FPX extension aux registers.
-mea
Generate extended arithmetic instructions. Currently only divaw , adds , subs , and sat16 are supported. This is always enabled for -mcpu=ARC700 .
-mno-mpy
Do not generate mpy -family instructions for ARC700. This option is deprecated.
-mmul32x16
Generate 32x16-bit multiply and multiply-accumulate instructions.
-mmul64
Generate mul64 and mulu64 instructions. Only valid for -mcpu=ARC600 .
-mnorm
Generate norm instructions. This is the default if -mcpu=ARC700 is in effect.
-mspfp
-mspfp-compact
Generate single-precision FPX instructions, tuned for the compact implementation.
-mspfp-fast
Generate single-precision FPX instructions, tuned for the fast implementation.
-msimd
Enable generation of ARC SIMD instructions via target-specific builtins. Only valid for -mcpu=ARC700 .
-msoft-float
This option ignored; it is provided for compatibility purposes only. Software floating-point code is emitted by default, and this default can overridden by FPX options; -mspfp , -mspfp-compact , or -mspfp-fast for single precision, and -mdpfp , -mdpfp-compact , or -mdpfp-fast for double precision.
-mswap
Generate swap instructions.
-matomic
This enables use of the locked load/store conditional extension to implement atomic memory built-in functions. Not available for ARC 6xx or ARC EM cores.
-mdiv-rem
Enable div and rem instructions for ARCv2 cores.
-mcode-density
Enable code density instructions for ARC EM. This option is on by default for ARC HS.
-mll64
Enable double load/store operations for ARC HS cores.
-mtp-regno= regno
Specify thread pointer register number.
-mmpy-option= multo
Compile ARCv2 code with a multiplier design option. You can specify the option using either a string or numeric value for multo . ‘ wlh1 ’ is the default value. The recognized values are:
0
none
No multiplier available.
1
w
16x16 multiplier, fully pipelined. The following instructions are enabled: mpyw and mpyuw .
2
wlh1
32x32 multiplier, fully pipelined (1 stage). The following instructions are additionally enabled: mpy , mpyu , mpym , mpymu , and mpy_s .
3
wlh2
32x32 multiplier, fully pipelined (2 stages). The following instructions are additionally enabled: mpy , mpyu , mpym , mpymu , and mpy_s .
4
wlh3
Two 16x16 multipliers, blocking, sequential. The following instructions are additionally enabled: mpy , mpyu , mpym , mpymu , and mpy_s .
5
wlh4
One 16x16 multiplier, blocking, sequential. The following instructions are additionally enabled: mpy , mpyu , mpym , mpymu , and mpy_s .
6
wlh5
One 32x4 multiplier, blocking, sequential. The following instructions are additionally enabled: mpy , mpyu , mpym , mpymu , and mpy_s .
7
plus_dmpy
ARC HS SIMD support.
8
plus_macd
ARC HS SIMD support.
9
plus_qmacw
ARC HS SIMD support.

This option is only available for ARCv2 cores.

-mfpu= fpu
Enables support for specific floating-point hardware extensions for ARCv2 cores. Supported values for fpu are:
fpus
Enables support for single-precision floating-point hardware extensions.
fpud
Enables support for double-precision floating-point hardware extensions. The single-precision floating-point extension is also enabled. Not available for ARC EM.
fpuda
Enables support for double-precision floating-point hardware extensions using double-precision assist instructions. The single-precision floating-point extension is also enabled. This option is only available for ARC EM.
fpuda_div
Enables support for double-precision floating-point hardware extensions using double-precision assist instructions. The single-precision floating-point, square-root, and divide extensions are also enabled. This option is only available for ARC EM.
fpuda_fma
Enables support for double-precision floating-point hardware extensions using double-precision assist instructions. The single-precision floating-point and fused multiply and add hardware extensions are also enabled. This option is only available for ARC EM.
fpuda_all
Enables support for double-precision floating-point hardware extensions using double-precision assist instructions. All single-precision floating-point hardware extensions are also enabled. This option is only available for ARC EM.
fpus_div
Enables support for single-precision floating-point, square-root and divide hardware extensions.
fpud_div
Enables support for double-precision floating-point, square-root and divide hardware extensions. This option includes option ‘ fpus_div ’. Not available for ARC EM.
fpus_fma
Enables support for single-precision floating-point and fused multiply and add hardware extensions.
fpud_fma
Enables support for double-precision floating-point and fused multiply and add hardware extensions. This option includes option ‘ fpus_fma ’. Not available for ARC EM.
fpus_all
Enables support for all single-precision floating-point hardware extensions.
fpud_all
Enables support for all single- and double-precision floating-point hardware extensions. Not available for ARC EM.

The following options are passed through to the assembler, and also define preprocessor macro symbols.

-mdsp-packa
Passed down to the assembler to enable the DSP Pack A extensions. Also sets the preprocessor symbol __Xdsp_packa . This option is deprecated.
-mdvbf
Passed down to the assembler to enable the dual Viterbi butterfly extension. Also sets the preprocessor symbol __Xdvbf . This option is deprecated.
-mlock
Passed down to the assembler to enable the locked load/store conditional extension. Also sets the preprocessor symbol __Xlock .
-mmac-d16
Passed down to the assembler. Also sets the preprocessor symbol __Xxmac_d16 . This option is deprecated.
-mmac-24
Passed down to the assembler. Also sets the preprocessor symbol __Xxmac_24 . This option is deprecated.
-mrtsc
Passed down to the assembler to enable the 64-bit time-stamp counter extension instruction. Also sets the preprocessor symbol __Xrtsc . This option is deprecated.
-mswape
Passed down to the assembler to enable the swap byte ordering extension instruction. Also sets the preprocessor symbol __Xswape .
-mtelephony
Passed down to the assembler to enable dual- and single-operand instructions for telephony. Also sets the preprocessor symbol __Xtelephony . This option is deprecated.
-mxy
Passed down to the assembler to enable the XY memory extension. Also sets the preprocessor symbol __Xxy .

The following options control how the assembly code is annotated:

-misize
Annotate assembler instructions with estimated addresses.
-mannotate-align
Explain what alignment considerations lead to the decision to make an instruction short or long.

The following options are passed through to the linker:

-marclinux
Passed through to the linker, to specify use of the arclinux emulation. This option is enabled by default in tool chains built for arc-linux-uclibc and arceb-linux-uclibc targets when profiling is not requested.
-marclinux_prof
Passed through to the linker, to specify use of the arclinux_prof emulation. This option is enabled by default in tool chains built for arc-linux-uclibc and arceb-linux-uclibc targets when profiling is requested.

The following options control the semantics of generated code:

-mlong-calls
Generate calls as register indirect calls, thus providing access to the full 32-bit address range.
-mmedium-calls
Don't use less than 25-bit addressing range for calls, which is the offset available for an unconditional branch-and-link instruction. Conditional execution of function calls is suppressed, to allow use of the 25-bit range, rather than the 21-bit range with conditional branch-and-link. This is the default for tool chains built for arc-linux-uclibc and arceb-linux-uclibc targets.
-mno-sdata
Do not generate sdata references. This is the default for tool chains built for arc-linux-uclibc and arceb-linux-uclibc targets.
-mvolatile-cache
Use ordinarily cached memory accesses for volatile references. This is the default.
-mno-volatile-cache
Enable cache bypass for volatile references.

The following options fine tune code generation:

-malign-call
Do alignment optimizations for call instructions.
-mauto-modify-reg
Enable the use of pre/post modify with register displacement.
-mbbit-peephole
Enable bbit peephole2.
-mno-brcc
This option disables a target-specific pass in arc_reorg to generate compare-and-branch (br cc ) instructions. It has no effect on generation of these instructions driven by the combiner pass.
-mcase-vector-pcrel
Use PC-relative switch case tables to enable case table shortening. This is the default for -Os .
-mcompact-casesi
Enable compact casesi pattern. This is the default for -Os , and only available for ARCv1 cores.
-mno-cond-exec
Disable the ARCompact-specific pass to generate conditional execution instructions.

Due to delay slot scheduling and interactions between operand numbers, literal sizes, instruction lengths, and the support for conditional execution, the target-independent pass to generate conditional execution is often lacking, so the ARC port has kept a special pass around that tries to find more conditional execution generation opportunities after register allocation, branch shortening, and delay slot scheduling have been done. This pass generally, but not always, improves performance and code size, at the cost of extra compilation time, which is why there is an option to switch it off. If you have a problem with call instructions exceeding their allowable offset range because they are conditionalized, you should consider using -mmedium-calls instead.

-mearly-cbranchsi
Enable pre-reload use of the cbranchsi pattern.
-mexpand-adddi
Expand adddi3 and subdi3 at RTL generation time into add.f , adc etc.
-mindexed-loads
Enable the use of indexed loads. This can be problematic because some optimizers then assume that indexed stores exist, which is not the case.

Enable Local Register Allocation. This is still experimental for ARC, so by default the compiler uses standard reload (i.e. -mno-lra ).

-mlra-priority-none
Don't indicate any priority for target registers.
-mlra-priority-compact
Indicate target register priority for r0..r3 / r12..r15.
-mlra-priority-noncompact
Reduce target register priority for r0..r3 / r12..r15.
-mno-millicode
When optimizing for size (using -Os ), prologues and epilogues that have to save or restore a large number of registers are often shortened by using call to a special function in libgcc; this is referred to as a millicode call. As these calls can pose performance issues, and/or cause linking issues when linking in a nonstandard way, this option is provided to turn off millicode call generation.
-mmixed-code
Tweak register allocation to help 16-bit instruction generation. This generally has the effect of decreasing the average instruction size while increasing the instruction count.
-mq-class
Enable ‘ q ’ instruction alternatives. This is the default for -Os .
-mRcq
Enable ‘ Rcq ’ constraint handling. Most short code generation depends on this. This is the default.
-mRcw
Enable ‘ Rcw ’ constraint handling. Most ccfsm condexec mostly depends on this. This is the default.
-msize-level= level
Fine-tune size optimization with regards to instruction lengths and alignment. The recognized values for level are:
0
No size optimization. This level is deprecated and treated like ‘ 1 ’.
1
Short instructions are used opportunistically.
2
In addition, alignment of loops and of code after barriers are dropped.
3
In addition, optional data alignment is dropped, and the option Os is enabled.

This defaults to ‘ 3 ’ when -Os is in effect. Otherwise, the behavior when this is not set is equivalent to level ‘ 1 ’.

-mtune= cpu
Set instruction scheduling parameters for cpu , overriding any implied by -mcpu= .

Supported values for cpu are

ARC600
Tune for ARC600 CPU.
ARC601
Tune for ARC601 CPU.
ARC700
Tune for ARC700 CPU with standard multiplier block.
ARC700-xmac
Tune for ARC700 CPU with XMAC block.
ARC725D
Tune for ARC725D CPU.
ARC750D
Tune for ARC750D CPU.

-mmultcost= num
Cost to assume for a multiply instruction, with ‘ 4 ’ being equal to a normal instruction.
-munalign-prob-threshold= probability
Set probability threshold for unaligning branches. When tuning for ‘ ARC700 ’ and optimizing for speed, branches without filled delay slot are preferably emitted unaligned and long, unless profiling indicates that the probability for the branch to be taken is below probability . See Cross-profiling . The default is (REG_BR_PROB_BASE/2), i.e. 5000.

The following options are maintained for backward compatibility, but are now deprecated and will be removed in a future release:

-margonaut
Obsolete FPX.
-mbig-endian
-EB
Compile code for big-endian targets. Use of these options is now deprecated. Big-endian code is supported by configuring GCC to build arceb-elf32 and arceb-linux-uclibc targets, for which big endian is the default.
-mlittle-endian
-EL
Compile code for little-endian targets. Use of these options is now deprecated. Little-endian code is supported by configuring GCC to build arc-elf32 and arc-linux-uclibc targets, for which little endian is the default.
-mbarrel_shifter
Replaced by -mbarrel-shifter .
-mdpfp_compact
Replaced by -mdpfp-compact .
-mdpfp_fast
Replaced by -mdpfp-fast .
-mdsp_packa
Replaced by -mdsp-packa .
-mEA
Replaced by -mea .
-mmac_24
Replaced by -mmac-24 .
-mmac_d16
Replaced by -mmac-d16 .
-mspfp_compact
Replaced by -mspfp-compact .
-mspfp_fast
Replaced by -mspfp-fast .
-mtune= cpu
Values ‘ arc600 ’, ‘ arc601 ’, ‘ arc700 ’ and ‘ arc700-xmac ’ for cpu are replaced by ‘ ARC600 ’, ‘ ARC601 ’, ‘ ARC700 ’ and ‘ ARC700-xmac ’ respectively.
-multcost= num
Replaced by -mmultcost .