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’

‘arc600’

Compile for ARC600. Aliases: -mA6, -mARC600.

‘ARC601’

‘arc601’

Compile for ARC601. Alias: -mARC601.

‘ARC700’

‘arc700’

Compile for ARC700. Aliases: -mA7, -mARC700. This is the default when configured with --with-cpu=arc700.

‘ARCEM’

‘arcem’

Compile for ARC EM.

‘ARCHS’

‘archs’

Compile for ARC HS.

-mdpfp

-mdpfp-compact

FPX: Generate Double Precision FPX instructions, tuned for the compact implementation.

-mdpfp-fast

FPX: 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 instructions for ARC700.

-mmul32x16

Generate 32x16 bit multiply and mac instructions.

-mmul64

Generate mul64 and mulu64 instructions. Only valid for -mcpu=ARC600.

-mnorm

Generate norm instruction. This is the default if -mcpu=ARC700 is in effect.

-mspfp

-mspfp-compact

FPX: Generate Single Precision FPX instructions, tuned for the compact implementation.

-mspfp-fast

FPX: 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 Locked Load/Store Conditional extension to implement atomic memopry built-in functions. Not available for ARC 6xx or ARC EM cores.

-mdiv-rem

Enable DIV/REM instructions for ARCv2 cores.

-mcode-density

Enable code density instructions for ARC EM, default on for ARC HS.

-mll64

Enable double load/store operations for ARC HS cores.

-mmpy-option=multo

Compile ARCv2 code with a multiplier design option. ‘wlh1’ is the default value. The recognized values for multo are:

‘0’

No multiplier available.

‘1’

The multiply option is set to w: 16x16 multiplier, fully pipelined. The following instructions are enabled: MPYW, and MPYUW.

‘2’

The multiply option is set to wlh1: 32x32 multiplier, fully pipelined (1 stage). The following instructions are additionally enabled: MPY, MPYU, MPYM, MPYMU, and MPY_S.

‘3’

The multiply option is set to wlh2: 32x32 multiplier, fully pipelined (2 stages). The following instructions are additionally enabled: MPY, MPYU, MPYM, MPYMU, and MPY_S.

‘4’

The multiply option is set to wlh3: Two 16x16 multiplier, blocking, sequential. The following instructions are additionally enabled: MPY, MPYU, MPYM, MPYMU, and MPY_S.

‘5’

The multiply option is set to wlh4: One 16x16 multiplier, blocking, sequential. The following instructions are additionally enabled: MPY, MPYU, MPYM, MPYMU, and MPY_S.

‘6’

The multiply option is set to wlh5: One 32x4 multiplier, blocking, sequential. The following instructions are additionally enabled: MPY, MPYU, MPYM, MPYMU, and MPY_S.

This option is only available for ARCv2 cores.

-mfpu=fpu

Enables specific floating-point hardware extension for ARCv2 core. 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, and simple precision square-root and divide hardware extensions. The single precision floating point extension is 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, and simple precision fused multiple and add hardware extension. The single precision floating point extension is 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, and all simple precision hardware extensions. The single precision floating point extension is also enabled. This option is only available for ARC EM.

‘fpus_div’

Enables support for single precision floating point, and single precision square-root and divide hardware extensions.

‘fpud_div’

Enables support for double precision floating point, and double precision 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 single precision fused multiple and add hardware extensions.

‘fpud_fma’

Enables support for double precision floating point, and double precision fused multiple 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.

-mdvbf

Passed down to the assembler to enable the dual viterbi butterfly extension. Also sets the preprocessor symbol __Xdvbf.

-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.

-mmac-24

Passed down to the assembler. Also sets the preprocessor symbol __Xxmac_24.

-mrtsc

Passed down to the assembler to enable the 64-bit Time-Stamp Counter extension instruction. Also sets the preprocessor symbol __Xrtsc.

-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.

-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 call insns 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.

-mucb-mcount

Instrument with mcount calls as used in UCB code. I.e. do the counting in the callee, not the caller. By default ARC instrumentation counts in the caller.

-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 BRcc instructions. It has no effect on BRcc generation driven by the combiner pass.

-mcase-vector-pcrel

Use pc-relative switch case tables - this enables case table shortening. This is the default for -Os.

-mcompact-casesi

Enable compact casesi pattern. This is the default for -Os.

-mno-cond-exec

Disable 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 generating 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 - 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. Users wanting big-endian code, should use the arceb-elf32 and arceb-linux-uclibc targets when building the tool chain, for which big-endian is the default.

-mlittle-endian

-EL

Compile code for little endian targets. Use of these options is now deprecated. Users wanting little-endian code should use the arc-elf32 and arc-linux-uclibc targets when building the tool chain, 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.