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3.17.34 IBM RS/6000 and PowerPC Options

These ‘-m’ options are defined for the IBM RS/6000 and PowerPC:

-mpowerpc-gpopt
-mno-powerpc-gpopt
-mpowerpc-gfxopt
-mno-powerpc-gfxopt
-mpowerpc64
-mno-powerpc64
-mmfcrf
-mno-mfcrf
-mpopcntb
-mno-popcntb
-mpopcntd
-mno-popcntd
-mfprnd
-mno-fprnd
-mcmpb
-mno-cmpb
-mmfpgpr
-mno-mfpgpr
-mhard-dfp
-mno-hard-dfp

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.

Specifying ‘-mpowerpc-gpopt’ allows GCC to use the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root. Specifying ‘-mpowerpc-gfxopt’ allows GCC to use the optional PowerPC architecture instructions in the Graphics group, including floating-point select.

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. The ‘-mpopcntd’ option allows GCC to generate the popcount instruction implemented on the POWER7 processor and other processors that support the PowerPC V2.06 architecture. The ‘-mfprnd’ option allows GCC to generate the FP round to integer instructions implemented on the POWER5+ processor and other processors that support the PowerPC V2.03 architecture. The ‘-mcmpb’ option allows GCC to generate the compare bytes instruction implemented on the POWER6 processor and other processors that support the PowerPC V2.05 architecture. The ‘-mmfpgpr’ option allows GCC to generate the FP move to/from general-purpose register instructions implemented on the POWER6X processor and other processors that support the extended PowerPC V2.05 architecture. The ‘-mhard-dfp’ option allows GCC to generate the decimal floating-point instructions implemented on some POWER processors.

The ‘-mpowerpc64’ option allows GCC to generate the additional 64-bit instructions that are found in the full PowerPC64 architecture and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to ‘-mno-powerpc64’.

-mcpu=cpu_type

Set architecture type, register usage, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are ‘401’, ‘403’, ‘405’, ‘405fp’, ‘440’, ‘440fp’, ‘464’, ‘464fp’, ‘476’, ‘476fp’, ‘505’, ‘601’, ‘602’, ‘603’, ‘603e’, ‘604’, ‘604e’, ‘620’, ‘630’, ‘740’, ‘7400’, ‘7450’, ‘750’, ‘801’, ‘821’, ‘823’, ‘860’, ‘970’, ‘8540’, ‘a2’, ‘e300c2’, ‘e300c3’, ‘e500mc’, ‘e500mc64’, ‘e5500’, ‘e6500’, ‘ec603e’, ‘G3’, ‘G4’, ‘G5’, ‘titan’, ‘power3’, ‘power4’, ‘power5’, ‘power5+’, ‘power6’, ‘power6x’, ‘power7’, ‘power8’, ‘powerpc’, ‘powerpc64’, and ‘rs64’.

-mcpu=powerpc’, and ‘-mcpu=powerpc64’ specify pure 32-bit PowerPC and 64-bit PowerPC architecture machine types, with an appropriate, generic processor model assumed for scheduling purposes.

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:

-maltivec  -mfprnd  -mhard-float  -mmfcrf  -mmultiple 
-mpopcntb -mpopcntd  -mpowerpc64 
-mpowerpc-gpopt  -mpowerpc-gfxopt  -msingle-float -mdouble-float 
-msimple-fpu -mstring  -mmulhw  -mdlmzb  -mmfpgpr -mvsx

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=970 -mno-altivec’.

On AIX, the ‘-maltivec’ and ‘-mpowerpc64’ options are not enabled or disabled by the ‘-mcpu’ option at present because AIX does not have full support for these options. You may still enable or disable them individually if you’re sure it’ll work in your environment.

-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’.

-mcmodel=small

Generate PowerPC64 code for the small model: The TOC is limited to 64k.

-mcmodel=medium

Generate PowerPC64 code for the medium model: The TOC and other static data may be up to a total of 4G in size.

-mcmodel=large

Generate PowerPC64 code for the large model: The TOC may be up to 4G in size. Other data and code is only limited by the 64-bit address space.

-maltivec
-mno-altivec

Generate code that uses (does not use) AltiVec instructions, and also enable the use of built-in functions that allow more direct access to the AltiVec instruction set. You may also need to set ‘-mabi=altivec’ to adjust the current ABI with AltiVec ABI enhancements.

-mvrsave
-mno-vrsave

Generate VRSAVE instructions when generating AltiVec code.

-mgen-cell-microcode

Generate Cell microcode instructions.

-mwarn-cell-microcode

Warn when a Cell microcode instruction is emitted. An example of a Cell microcode instruction is a variable shift.

-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.

-mpaired
-mno-paired

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

-mspe=yes/no

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

-mvsx
-mno-vsx

Generate code that uses (does not use) vector/scalar (VSX) instructions, and also enable the use of built-in functions that allow more direct access to the VSX instruction set.

-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.

-m32
-m64

Generate code for 32-bit or 64-bit environments of Darwin and SVR4 targets (including GNU/Linux). The 32-bit environment sets int, long and pointer to 32 bits and generates code that runs on any PowerPC variant. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits, and generates code for PowerPC64, as for ‘-mpowerpc64’.

-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.

-maix64
-maix32

Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit long type, and the infrastructure needed to support them. Specifying ‘-maix64’ implies ‘-mpowerpc64’, while ‘-maix32’ disables the 64-bit ABI and implies ‘-mno-powerpc64’. 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.

-mpe

Support IBM RS/6000 SP Parallel Environment (PE). Link an application written to use message passing with special startup code to enable the application to run. The system must have PE installed in the standard location (‘/usr/lpp/ppe.poe/’), or the ‘specs’ file must be overridden with the ‘-specs=’ option to specify the appropriate directory location. The Parallel Environment does not support threads, so the ‘-mpe’ option and the ‘-pthread’ option are incompatible.

-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’.

-msimple-fpu

Do not generate sqrt and div instructions for hardware floating-point unit.

-mfpu=name

Specify type of floating-point unit. Valid values for name are ‘sp_lite’ (equivalent to ‘-msingle-float -msimple-fpu’), ‘dp_lite’ (equivalent to ‘-mdouble-float -msimple-fpu’), ‘sp_full’ (equivalent to ‘-msingle-float’), and ‘dp_full’ (equivalent to ‘-mdouble-float’).

-mxilinx-fpu

Perform optimizations for the floating-point unit on Xilinx PPC 405/440.

-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.

-mstring
-mno-string

Generate code that uses (does not use) the load string instructions and the store string word instructions to save multiple registers and do small block moves. These instructions are generated by default on POWER systems, and not generated on PowerPC systems. Do not use ‘-mstring’ 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’.

-mmulhw
-mno-mulhw

Generate code that uses (does not use) the half-word multiply and multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors. These instructions are generated by default when targeting those processors.

-mdlmzb
-mno-dlmzb

Generate code that uses (does not use) the string-search ‘dlmzb’ instruction on the IBM 405, 440, 464 and 476 processors. This instruction is generated by default when targeting those processors.

-mno-bit-align
-mbit-align

On System V.4 and embedded PowerPC systems do not (do) force structures and unions that contain bit-fields to be aligned to the base type of the bit-field.

For example, by default a structure containing nothing but 8 unsigned bit-fields of length 1 is aligned to a 4-byte boundary and has a size of 4 bytes. By using ‘-mno-bit-align’, the structure is aligned to a 1-byte boundary and is 1 byte in size.

-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.

-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 a PowerPC 32-bit SYSV ABI option.

-mabi=ieeelongdouble

Change the current ABI to use IEEE extended-precision long double. This is a PowerPC 32-bit Linux ABI option.

-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.

On Darwin/PPC systems, #pragma longcall generates jbsr callee, L42, plus a branch island (glue code). The two target addresses represent the callee and the branch island. The Darwin/PPC linker prefers the first address and generates a bl callee if the PPC bl instruction reaches the callee directly; otherwise, the linker generates bl L42 to call the branch island. The branch island is appended to the body of the calling function; it computes the full 32-bit address of the callee and jumps to it.

On Mach-O (Darwin) systems, this option directs the compiler emit to the glue for every direct call, and the Darwin linker decides whether to use or discard it.

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.

-pthread

Adds support for multithreading with the pthreads library. This option sets flags for both the preprocessor and linker.

-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’, ‘-finite-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.

-mveclibabi=type

Specifies the ABI type to use for vectorizing intrinsics using an external library. The only type supported at present is mass, which specifies to use IBM’s Mathematical Acceleration Subsystem (MASS) libraries for vectorizing intrinsics using external libraries. GCC currently emits calls to acosd2, acosf4, acoshd2, acoshf4, asind2, asinf4, asinhd2, asinhf4, atan2d2, atan2f4, atand2, atanf4, atanhd2, atanhf4, cbrtd2, cbrtf4, cosd2, cosf4, coshd2, coshf4, erfcd2, erfcf4, erfd2, erff4, exp2d2, exp2f4, expd2, expf4, expm1d2, expm1f4, hypotd2, hypotf4, lgammad2, lgammaf4, log10d2, log10f4, log1pd2, log1pf4, log2d2, log2f4, logd2, logf4, powd2, powf4, sind2, sinf4, sinhd2, sinhf4, sqrtd2, sqrtf4, tand2, tanf4, tanhd2, and tanhf4 when generating code for power7. Both ‘-ftree-vectorize’ and ‘-funsafe-math-optimizations’ must also be enabled. The MASS libraries must be specified at link time.

-mfriz
-mno-friz

Generate (do not generate) the friz instruction when the ‘-funsafe-math-optimizations’ option is used to optimize rounding of floating-point values to 64-bit integer and back to floating point. The friz instruction does not return the same value if the floating-point number is too large to fit in an integer.

-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 the ‘-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.


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