B.2.68.1 -xarch Flags for SPARC (Sun Studio 12: C User's Guide)

Sun Studio 12: C User's Guide

B.2.68.1 `-xarch` Flags for SPARC

The following table details the performance of an executable that is compiled with a given-xarch option and then executed by various SPARC processors. The purpose of this table is to help you identify the best-xarch option for your executable given a particular target machine. Start by identifying the range of machines that are of interest to you and then consider the cost of maintaining multiple binaries versus the benefit of extracting the last iota of performance from newer machines.

Table B–12 The -xarch Matrix


	Instruction Set of SPARC Machine:
		V8a	V8	V9 (Non-Sun Processor)	V9 (Sun processor)	V9b
	v8a	N	S	S	S	S
-xarch compilation option	v8	PD	N	S	S	S
	v8plus	NE	NE	N	S	S
	v8plusa	NE	NE	**	N	S
	v8plusb	NE	NE	**	NE	N
	v9	NE	NE	N	S	S
	v9a	NE	NE	**	N	S
	v9b	NE	NE	[** ]	NE	N
** Note: An executable compiled with this instruction set may perform nominally on a V9 non-Sun processor chip or it may not execute at all. Check with your hardware vendor to make sure your executable can run on its target machine.

N reflects Nominal performance. The program executes and takes full advantage of the processor’s instruction set.
S reflects Satisfactory performance. The program executes but may not exploit all available processor instructions.
PD reflects Performance Degradation. The program executes, but depending on the instructions used, may experience slight to significant performance degradation. The degradation occurs when instructions that are not implemented by the processor are emulated by the kernel.
NE means Not Executable. The program will not execute because the kernel does not emulate the instructions that are not implemented by the processor.

If you are compiling your executable with the v8plus or v8plusa instruction set, consider compiling with v9 or v9a instead. The v8plus and v8plusa options are provided so that programs can take advantage of some SPARC V9 and UltraSPARC features prior to the availability of Solaris 8 software with its support for 64-bit programs. Programs compiled with the v8plus or v8plusa option are not portable to SPARC V8 or older machines. You can recompile such programs with v9 or v9a, respectively, to take full advantage of all the features of SPARC V9 and UltraSPARC. The V8+ Technical Specification white paper, part number 802-7447-10, is available through your Sun representative and explains the limitations of v8plus and v8plusa.

SPARC instruction set architectures V8 and V8a are binary compatible.
Object binary files (.o) compiled with v8plus and v8plusa can be linked and can execute together, but only on a SPARC V8plusa compatible platform.
Object binary files (.o) compiled with v8plus, v8plusa, and v8plusb can be linked and can execute together, but only on a SPARC V8plusb compatible platform.
-xarch values v9, v9a, and v9b are only available on UltraSPARC 64-bit Solaris operating systems.
Object binary files (.o) compiled with v9 and v9a can be linked and can execute together, but will run only on a SPARC V9a compatible platform.
Object binary files (.o) compiled with v9, v9a, and v9b can be linked and can execute together, but will run only on a SPARC V9b compatible platform.

For any particular choice, the generated executable may run much more slowly on earlier architectures. Also, although quad-precision (REAL*16 and long double) floating-point instructions are available in many of these instruction set architectures, the compiler does not use these instructions in the code it generates.

The following table gives details for each of the-xarch keywords on SPARC platforms.

Table B–13 The -xarch Flags for SPARC Platforms


Flag	Meaning
`generic`	Uses the instruction set common to most processors. This is the default.
`generic`64	Compile for good performance on most 64-bit platforms. (Solaris only). This option is equivalent to `-m64` `-xarch=generic` and is provided for compatibility with earlier releases. Use `-m64` to specify 64-bit compilation instead of `-xarch=generic64`.
`native`	Compile for good performance on this system. The compiler chooses the appropriate setting for the current system processor it is running on.
`native`64	Compile for good performance on this system (Solaris only). This option is equivalent to `-m64` `-xarch=native` and is provided for compatibility with earlier releases.
`sparc`	Compile for the SPARC-V9 ISA, but without the Visual Instruction Set (VIS), and without other implementation-specific ISA extensions. This option enables the compiler to generate code for good performance on the V9 ISA.
`sparcvis`	Compile for SPARC-V9 plus the Visual Instruction Set (VIS) version 1.0, and with UltraSPARC extensions. This option enables the compiler to generate code for good performance on the UltraSPARC architecture.
`sparcvis2`	Enables the compiler to generate object code for the UltraSPARC architecture, plus the Visual Instruction Set (VIS) version 2.0, and with UltraSPARC III extensions.
`sparcfmaf`	Enables the compiler to use instructions from the SPARC-V9 instruction set, plus the UltraSPARC extensions, including the Visual Instruction Set (VIS) version 1.0, the UltraSPARC-III extensions, including the Visual Instruction Set (VIS) version 2.0, and the SPARC64 VI extensions for floating-point multiply-add. You must use `-xarch=sparcfmaf` in conjunction with `fma=fused` and some optimization level to get the compiler to attempt to find opportunities to use the multiply-add instructions automatically.
`v7`	Compile for the SPARC-V7 ISA. (Obsolete) Current Solaris operating systems no longer support the SPARC V7 architecture, and programs compiled with this option run slower on current platforms. The default is `-xarch=v8plus`. Examples: SPARCstation 1, SPARCstation 2.
`v8a`	Compile for the V8a version of the SPARC-V8 ISA. By definition, V8a means the V8 ISA, but without the `fsmuld` instruction. This option enables the compiler to generate code for good performance on the V8a ISA. Example: Any system based on the microSPARC I chip architecture
`v8`	Compile for the SPARC-V8 ISA. Enables the compiler to generate code for good performance on the V8 architecture. Example: SPARCstation 10
`v8plus`	Compile for the V8plus version of the SPARC-V9 ISA. By definition, `V8plus` means the V9 ISA, but limited to the 32–bit subset defined by the V8plus ISA specification, without the Visual Instruction Set (VIS), and without other implementation-specific ISA extensions. This option enables the compiler to generate code for good performance on the V8plus ISA. The resulting object code is in SPARC-V8+ ELF32 format and only executes in a Solaris UltraSPARC environment—it does not run on a V7 or V8 processor. Example: Any system based on the UltraSPARC chip architecture
`v8plusa`	Compile for the V8plusa version of the SPARC-V9 ISA. By definition, `V8plusa` means the V8plus architecture, plus the Visual Instruction Set (VIS) version 1.0, and with UltraSPARC extensions. This option enables the compiler to generate code for good performance on the UltraSPARC architecture, but limited to the 32–bit subset defined by the V8plus specification. The resulting object code is in SPARC-V8+ ELF32 format and only executes in a Solaris UltraSPARC environment—it does not run on a V8 processor. Example: Any system based on the UltraSPARC chip architecture
`v8plusb`	Compile for the V8plusb version of the SPARC-V8plus ISA with UltraSPARC III extensions. Enables the compiler to generate object code for the UltraSPARC architecture, plus the Visual Instruction Set (VIS) version 2.0, and with UltraSPARC III extensions. The resulting object code is in SPARC-V8+ ELF32 format and executes only in a Solaris UltraSPARC III environment. Compiling with this option uses the best instruction set for good performance on the UltraSPARC III architecture.
`v9`	Is equivalent to `-m64` `-xarch=sparc`. Legacy makefiles and scripts that use `-xarch=v9` to obtain the 64-bit memory model need only use `-m64`.
`v9a`	Is equivalent to `-m64` `-xarch=sparcvis` and is provided for compatibility with earlier releases.
`v9b`	Is equivalent to `-m64` `-xarch=sparcvis2` and is provided for compatibility with earlier releases.