3.18.37 PowerPC SPE Options

These ‘-m’ options are defined for PowerPC SPE:

-mmfcrf

-mno-mfcrf

-mpopcntb

-mno-popcntb

You use these options to specify which instructions are available on the processor you are using. The default value of these options is determined when configuring GCC. Specifying the -mcpu=cpu_type overrides the specification of these options. We recommend you use the -mcpu=cpu_type option rather than the options listed above.

The -mmfcrf option allows GCC to generate the move from condition register field instruction implemented on the POWER4 processor and other processors that support the PowerPC V2.01 architecture. The -mpopcntb option allows GCC to generate the popcount and double-precision FP reciprocal estimate instruction implemented on the POWER5 processor and other processors that support the PowerPC V2.02 architecture.

-mcpu=cpu_type

Set architecture type, register usage, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are ‘8540’, ‘8548’, and ‘native’.

-mcpu=powerpc specifies pure 32-bit PowerPC (either endian), with an appropriate, generic processor model assumed for scheduling purposes.

Specifying ‘native’ as cpu type detects and selects the architecture option that corresponds to the host processor of the system performing the compilation. -mcpu=native has no effect if GCC does not recognize the processor.

The other options specify a specific processor. Code generated under those options runs best on that processor, and may not run at all on others.

The -mcpu options automatically enable or disable the following options:

-mhard-float  -mmfcrf  -mmultiple 
-mpopcntb -mpopcntd 
-msingle-float -mdouble-float 
-mfloat128

The particular options set for any particular CPU varies between compiler versions, depending on what setting seems to produce optimal code for that CPU; it doesn’t necessarily reflect the actual hardware’s capabilities. If you wish to set an individual option to a particular value, you may specify it after the -mcpu option, like -mcpu=8548.

-mtune=cpu_type

Set the instruction scheduling parameters for machine type cpu_type, but do not set the architecture type or register usage, as -mcpu=cpu_type does. The same values for cpu_type are used for -mtune as for -mcpu. If both are specified, the code generated uses the architecture and registers set by -mcpu, but the scheduling parameters set by -mtune.

-msecure-plt

Generate code that allows ld and ld.so to build executables and shared libraries with non-executable .plt and .got sections. This is a PowerPC 32-bit SYSV ABI option.

-mbss-plt

Generate code that uses a BSS .plt section that ld.so fills in, and requires .plt and .got sections that are both writable and executable. This is a PowerPC 32-bit SYSV ABI option.

-misel

-mno-isel

This switch enables or disables the generation of ISEL instructions.

-misel=yes/no

This switch has been deprecated. Use -misel and -mno-isel instead.

-mspe

-mno-spe

This switch enables or disables the generation of SPE simd instructions.

-mspe=yes/no

This option has been deprecated. Use -mspe and -mno-spe instead.

-mfloat128

-mno-float128

Enable/disable the __float128 keyword for IEEE 128-bit floating point and use either software emulation for IEEE 128-bit floating point or hardware instructions.

-mfloat-gprs=yes/single/double/no

-mfloat-gprs

This switch enables or disables the generation of floating-point operations on the general-purpose registers for architectures that support it.

The argument ‘yes’ or ‘single’ enables the use of single-precision floating-point operations.

The argument ‘double’ enables the use of single and double-precision floating-point operations.

The argument ‘no’ disables floating-point operations on the general-purpose registers.

This option is currently only available on the MPC854x.

-mfull-toc

-mno-fp-in-toc

-mno-sum-in-toc

-mminimal-toc

Modify generation of the TOC (Table Of Contents), which is created for every executable file. The -mfull-toc option is selected by default. In that case, GCC allocates at least one TOC entry for each unique non-automatic variable reference in your program. GCC also places floating-point constants in the TOC. However, only 16,384 entries are available in the TOC.

If you receive a linker error message that saying you have overflowed the available TOC space, you can reduce the amount of TOC space used with the -mno-fp-in-toc and -mno-sum-in-toc options. -mno-fp-in-toc prevents GCC from putting floating-point constants in the TOC and -mno-sum-in-toc forces GCC to generate code to calculate the sum of an address and a constant at run time instead of putting that sum into the TOC. You may specify one or both of these options. Each causes GCC to produce very slightly slower and larger code at the expense of conserving TOC space.

If you still run out of space in the TOC even when you specify both of these options, specify -mminimal-toc instead. This option causes GCC to make only one TOC entry for every file. When you specify this option, GCC produces code that is slower and larger but which uses extremely little TOC space. You may wish to use this option only on files that contain less frequently-executed code.

-maix32

Disables the 64-bit ABI. GCC defaults to -maix32.

-mxl-compat

-mno-xl-compat

Produce code that conforms more closely to IBM XL compiler semantics when using AIX-compatible ABI. Pass floating-point arguments to prototyped functions beyond the register save area (RSA) on the stack in addition to argument FPRs. Do not assume that most significant double in 128-bit long double value is properly rounded when comparing values and converting to double. Use XL symbol names for long double support routines.

The AIX calling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of its arguments with fewer arguments than declared. IBM XL compilers access floating-point arguments that do not fit in the RSA from the stack when a subroutine is compiled without optimization. Because always storing floating-point arguments on the stack is inefficient and rarely needed, this option is not enabled by default and only is necessary when calling subroutines compiled by IBM XL compilers without optimization.

-malign-natural

-malign-power

On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option -malign-natural overrides the ABI-defined alignment of larger types, such as floating-point doubles, on their natural size-based boundary. The option -malign-power instructs GCC to follow the ABI-specified alignment rules. GCC defaults to the standard alignment defined in the ABI.

On 64-bit Darwin, natural alignment is the default, and -malign-power is not supported.

-msoft-float

-mhard-float

Generate code that does not use (uses) the floating-point register set. Software floating-point emulation is provided if you use the -msoft-float option, and pass the option to GCC when linking.

-msingle-float

-mdouble-float

Generate code for single- or double-precision floating-point operations. -mdouble-float implies -msingle-float.

-mmultiple

-mno-multiple

Generate code that uses (does not use) the load multiple word instructions and the store multiple word instructions. These instructions are generated by default on POWER systems, and not generated on PowerPC systems. Do not use -mmultiple on little-endian PowerPC systems, since those instructions do not work when the processor is in little-endian mode. The exceptions are PPC740 and PPC750 which permit these instructions in little-endian mode.

-mupdate

-mno-update

Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated memory location. These instructions are generated by default. If you use -mno-update, there is a small window between the time that the stack pointer is updated and the address of the previous frame is stored, which means code that walks the stack frame across interrupts or signals may get corrupted data.

-mavoid-indexed-addresses

-mno-avoid-indexed-addresses

Generate code that tries to avoid (not avoid) the use of indexed load or store instructions. These instructions can incur a performance penalty on Power6 processors in certain situations, such as when stepping through large arrays that cross a 16M boundary. This option is enabled by default when targeting Power6 and disabled otherwise.

-mfused-madd

-mno-fused-madd

Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine-dependent -mfused-madd option is now mapped to the machine-independent -ffp-contract=fast option, and -mno-fused-madd is mapped to -ffp-contract=off.

-mno-strict-align

-mstrict-align

On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references are handled by the system.

-mrelocatable

-mno-relocatable

Generate code that allows (does not allow) a static executable to be relocated to a different address at run time. A simple embedded PowerPC system loader should relocate the entire contents of .got2 and 4-byte locations listed in the .fixup section, a table of 32-bit addresses generated by this option. For this to work, all objects linked together must be compiled with -mrelocatable or -mrelocatable-lib. -mrelocatable code aligns the stack to an 8-byte boundary.

-mrelocatable-lib

-mno-relocatable-lib

Like -mrelocatable, -mrelocatable-lib generates a .fixup section to allow static executables to be relocated at run time, but -mrelocatable-lib does not use the smaller stack alignment of -mrelocatable. Objects compiled with -mrelocatable-lib may be linked with objects compiled with any combination of the -mrelocatable options.

-mno-toc

-mtoc

On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a global area pointing to the addresses used in the program.

-mlittle

-mlittle-endian

On System V.4 and embedded PowerPC systems compile code for the processor in little-endian mode. The -mlittle-endian option is the same as -mlittle.

-mbig

-mbig-endian

On System V.4 and embedded PowerPC systems compile code for the processor in big-endian mode. The -mbig-endian option is the same as -mbig.

-mdynamic-no-pic

On Darwin and Mac OS X systems, compile code so that it is not relocatable, but that its external references are relocatable. The resulting code is suitable for applications, but not shared libraries.

-msingle-pic-base

Treat the register used for PIC addressing as read-only, rather than loading it in the prologue for each function. The runtime system is responsible for initializing this register with an appropriate value before execution begins.

-mprioritize-restricted-insns=priority

This option controls the priority that is assigned to dispatch-slot restricted instructions during the second scheduling pass. The argument priority takes the value ‘0’, ‘1’, or ‘2’ to assign no, highest, or second-highest (respectively) priority to dispatch-slot restricted instructions.

-msched-costly-dep=dependence_type

This option controls which dependences are considered costly by the target during instruction scheduling. The argument dependence_type takes one of the following values:

‘no’

No dependence is costly.

‘all’

All dependences are costly.

‘true_store_to_load’

A true dependence from store to load is costly.

‘store_to_load’

Any dependence from store to load is costly.

number

Any dependence for which the latency is greater than or equal to number is costly.

-minsert-sched-nops=scheme

This option controls which NOP insertion scheme is used during the second scheduling pass. The argument scheme takes one of the following values:

‘no’

Don’t insert NOPs.

‘pad’

Pad with NOPs any dispatch group that has vacant issue slots, according to the scheduler’s grouping.

‘regroup_exact’

Insert NOPs to force costly dependent insns into separate groups. Insert exactly as many NOPs as needed to force an insn to a new group, according to the estimated processor grouping.

number

Insert NOPs to force costly dependent insns into separate groups. Insert number NOPs to force an insn to a new group.

-mcall-sysv

On System V.4 and embedded PowerPC systems compile code using calling conventions that adhere to the March 1995 draft of the System V Application Binary Interface, PowerPC processor supplement. This is the default unless you configured GCC using ‘powerpc-*-eabiaix’.

-mcall-sysv-eabi

-mcall-eabi

Specify both -mcall-sysv and -meabi options.

-mcall-sysv-noeabi

Specify both -mcall-sysv and -mno-eabi options.

-mcall-aixdesc

On System V.4 and embedded PowerPC systems compile code for the AIX operating system.

-mcall-linux

On System V.4 and embedded PowerPC systems compile code for the Linux-based GNU system.

-mcall-freebsd

On System V.4 and embedded PowerPC systems compile code for the FreeBSD operating system.

-mcall-netbsd

On System V.4 and embedded PowerPC systems compile code for the NetBSD operating system.

-mcall-openbsd

On System V.4 and embedded PowerPC systems compile code for the OpenBSD operating system.

-maix-struct-return

Return all structures in memory (as specified by the AIX ABI).

-msvr4-struct-return

Return structures smaller than 8 bytes in registers (as specified by the SVR4 ABI).

-mabi=abi-type

Extend the current ABI with a particular extension, or remove such extension. Valid values are ‘altivec’, ‘no-altivec’, ‘spe’, ‘no-spe’, ‘ibmlongdouble’, ‘ieeelongdouble’, ‘elfv1’, ‘elfv2’.

-mabi=spe

Extend the current ABI with SPE ABI extensions. This does not change the default ABI, instead it adds the SPE ABI extensions to the current ABI.

-mabi=no-spe

Disable Book-E SPE ABI extensions for the current ABI.

-mabi=ibmlongdouble

Change the current ABI to use IBM extended-precision long double. This is not likely to work if your system defaults to using IEEE extended-precision long double. If you change the long double type from IEEE extended-precision, the compiler will issue a warning unless you use the -Wno-psabi option. Requires -mlong-double-128 to be enabled.

-mabi=ieeelongdouble

Change the current ABI to use IEEE extended-precision long double. This is not likely to work if your system defaults to using IBM extended-precision long double. If you change the long double type from IBM extended-precision, the compiler will issue a warning unless you use the -Wno-psabi option. Requires -mlong-double-128 to be enabled.

-mabi=elfv1

Change the current ABI to use the ELFv1 ABI. This is the default ABI for big-endian PowerPC 64-bit Linux. Overriding the default ABI requires special system support and is likely to fail in spectacular ways.

-mabi=elfv2

Change the current ABI to use the ELFv2 ABI. This is the default ABI for little-endian PowerPC 64-bit Linux. Overriding the default ABI requires special system support and is likely to fail in spectacular ways.

-mgnu-attribute

-mno-gnu-attribute

Emit .gnu_attribute assembly directives to set tag/value pairs in a .gnu.attributes section that specify ABI variations in function parameters or return values.

-mprototype

-mno-prototype

On System V.4 and embedded PowerPC systems assume that all calls to variable argument functions are properly prototyped. Otherwise, the compiler must insert an instruction before every non-prototyped call to set or clear bit 6 of the condition code register (CR) to indicate whether floating-point values are passed in the floating-point registers in case the function takes variable arguments. With -mprototype, only calls to prototyped variable argument functions set or clear the bit.

-msim

On embedded PowerPC systems, assume that the startup module is called sim-crt0.o and that the standard C libraries are libsim.a and libc.a. This is the default for ‘powerpc-*-eabisim’ configurations.

-mmvme

On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C libraries are libmvme.a and libc.a.

-mads

On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C libraries are libads.a and libc.a.

-myellowknife

On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C libraries are libyk.a and libc.a.

-mvxworks

On System V.4 and embedded PowerPC systems, specify that you are compiling for a VxWorks system.

-memb

On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags header to indicate that ‘eabi’ extended relocations are used.

-meabi

-mno-eabi

On System V.4 and embedded PowerPC systems do (do not) adhere to the Embedded Applications Binary Interface (EABI), which is a set of modifications to the System V.4 specifications. Selecting -meabi means that the stack is aligned to an 8-byte boundary, a function __eabi is called from main to set up the EABI environment, and the -msdata option can use both r2 and r13 to point to two separate small data areas. Selecting -mno-eabi means that the stack is aligned to a 16-byte boundary, no EABI initialization function is called from main, and the -msdata option only uses r13 to point to a single small data area. The -meabi option is on by default if you configured GCC using one of the ‘powerpc*-*-eabi*’ options.

-msdata=eabi

On System V.4 and embedded PowerPC systems, put small initialized const global and static data in the .sdata2 section, which is pointed to by register r2. Put small initialized non-const global and static data in the .sdata section, which is pointed to by register r13. Put small uninitialized global and static data in the .sbss section, which is adjacent to the .sdata section. The -msdata=eabi option is incompatible with the -mrelocatable option. The -msdata=eabi option also sets the -memb option.

-msdata=sysv

On System V.4 and embedded PowerPC systems, put small global and static data in the .sdata section, which is pointed to by register r13. Put small uninitialized global and static data in the .sbss section, which is adjacent to the .sdata section. The -msdata=sysv option is incompatible with the -mrelocatable option.

-msdata=default

-msdata

On System V.4 and embedded PowerPC systems, if -meabi is used, compile code the same as -msdata=eabi, otherwise compile code the same as -msdata=sysv.

-msdata=data

On System V.4 and embedded PowerPC systems, put small global data in the .sdata section. Put small uninitialized global data in the .sbss section. Do not use register r13 to address small data however. This is the default behavior unless other -msdata options are used.

-msdata=none

-mno-sdata

On embedded PowerPC systems, put all initialized global and static data in the .data section, and all uninitialized data in the .bss section.

-mblock-move-inline-limit=num

Inline all block moves (such as calls to memcpy or structure copies) less than or equal to num bytes. The minimum value for num is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets. The default value is target-specific.

-G num

On embedded PowerPC systems, put global and static items less than or equal to num bytes into the small data or BSS sections instead of the normal data or BSS section. By default, num is 8. The -G num switch is also passed to the linker. All modules should be compiled with the same -G num value.

-mregnames

-mno-regnames

On System V.4 and embedded PowerPC systems do (do not) emit register names in the assembly language output using symbolic forms.

-mlongcall

-mno-longcall

By default assume that all calls are far away so that a longer and more expensive calling sequence is required. This is required for calls farther than 32 megabytes (33,554,432 bytes) from the current location. A short call is generated if the compiler knows the call cannot be that far away. This setting can be overridden by the shortcall function attribute, or by #pragma longcall(0).

Some linkers are capable of detecting out-of-range calls and generating glue code on the fly. On these systems, long calls are unnecessary and generate slower code. As of this writing, the AIX linker can do this, as can the GNU linker for PowerPC/64. It is planned to add this feature to the GNU linker for 32-bit PowerPC systems as well.

In the future, GCC may ignore all longcall specifications when the linker is known to generate glue.

-mtls-markers

-mno-tls-markers

Mark (do not mark) calls to __tls_get_addr with a relocation specifying the function argument. The relocation allows the linker to reliably associate function call with argument setup instructions for TLS optimization, which in turn allows GCC to better schedule the sequence.

-mrecip

-mno-recip

This option enables use of the reciprocal estimate and reciprocal square root estimate instructions with additional Newton-Raphson steps to increase precision instead of doing a divide or square root and divide for floating-point arguments. You should use the -ffast-math option when using -mrecip (or at least -funsafe-math-optimizations, -ffinite-math-only, -freciprocal-math and -fno-trapping-math). Note that while the throughput of the sequence is generally higher than the throughput of the non-reciprocal instruction, the precision of the sequence can be decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994) for reciprocal square roots.

-mrecip=opt

This option controls which reciprocal estimate instructions may be used. opt is a comma-separated list of options, which may be preceded by a ! to invert the option:

‘all’

Enable all estimate instructions.

‘default’

Enable the default instructions, equivalent to -mrecip.

‘none’

Disable all estimate instructions, equivalent to -mno-recip.

‘div’

Enable the reciprocal approximation instructions for both single and double precision.

‘divf’

Enable the single-precision reciprocal approximation instructions.

‘divd’

Enable the double-precision reciprocal approximation instructions.

‘rsqrt’

Enable the reciprocal square root approximation instructions for both single and double precision.

‘rsqrtf’

Enable the single-precision reciprocal square root approximation instructions.

‘rsqrtd’

Enable the double-precision reciprocal square root approximation instructions.

So, for example, -mrecip=all,!rsqrtd enables all of the reciprocal estimate instructions, except for the FRSQRTE, XSRSQRTEDP, and XVRSQRTEDP instructions which handle the double-precision reciprocal square root calculations.

-mrecip-precision

-mno-recip-precision

Assume (do not assume) that the reciprocal estimate instructions provide higher-precision estimates than is mandated by the PowerPC ABI. Selecting -mcpu=power6, -mcpu=power7 or -mcpu=power8 automatically selects -mrecip-precision. The double-precision square root estimate instructions are not generated by default on low-precision machines, since they do not provide an estimate that converges after three steps.

-mpointers-to-nested-functions

-mno-pointers-to-nested-functions

Generate (do not generate) code to load up the static chain register (r11) when calling through a pointer on AIX and 64-bit Linux systems where a function pointer points to a 3-word descriptor giving the function address, TOC value to be loaded in register r2, and static chain value to be loaded in register r11. The -mpointers-to-nested-functions is on by default. You cannot call through pointers to nested functions or pointers to functions compiled in other languages that use the static chain if you use -mno-pointers-to-nested-functions.

-msave-toc-indirect

-mno-save-toc-indirect

Generate (do not generate) code to save the TOC value in the reserved stack location in the function prologue if the function calls through a pointer on AIX and 64-bit Linux systems. If the TOC value is not saved in the prologue, it is saved just before the call through the pointer. The -mno-save-toc-indirect option is the default.

-mcompat-align-parm

-mno-compat-align-parm

Generate (do not generate) code to pass structure parameters with a maximum alignment of 64 bits, for compatibility with older versions of GCC.

Older versions of GCC (prior to 4.9.0) incorrectly did not align a structure parameter on a 128-bit boundary when that structure contained a member requiring 128-bit alignment. This is corrected in more recent versions of GCC. This option may be used to generate code that is compatible with functions compiled with older versions of GCC.

The -mno-compat-align-parm option is the default.

-mstack-protector-guard=guard

-mstack-protector-guard-reg=reg

-mstack-protector-guard-offset=offset

-mstack-protector-guard-symbol=symbol

Generate stack protection code using canary at guard. Supported locations are ‘global’ for global canary or ‘tls’ for per-thread canary in the TLS block (the default with GNU libc version 2.4 or later).

With the latter choice the options -mstack-protector-guard-reg=reg and -mstack-protector-guard-offset=offset furthermore specify which register to use as base register for reading the canary, and from what offset from that base register. The default for those is as specified in the relevant ABI. -mstack-protector-guard-symbol=symbol overrides the offset with a symbol reference to a canary in the TLS block.