View source for SVE2

[[Category:ARM]]
The Armv9 '''Scalable Vector Extensions verision 2''' (SVE2) provide a variable-witdh SIMD capability for [[AArch64]] systems. Note that SVE2 is a minor refinement and standardization of the original Scalable Vector Extensions (used on the [https://www.r-ccs.riken.jp/en/fugaku/ Fugaku] supercomputer), so most materials discussing SVE are also applicable to SVE2 (which will be used on systems ranging from smartphones to servers to supercomputers).

== Resources ==
* Arm Armv9-A A64 Instruction Set Architecture - https://developer.arm.com/documentation/ddi0602/2021-12/
* '''Introduction to SVE2''' - https://developer.arm.com/documentation/102340/0001/?lang=en
* Intrinsics - Arm C Language Extensions for SVE (ACLE) - https://developer.arm.com/documentation/100987/latest
* SVE Coding Considerations with Arm Compiler - Note that this documentation is specific to Arm's own compiler, but most of it will be applicable to other compilers including gcc - https://developer.arm.com/documentation/100748/0616/SVE-Coding-Considerations-with-Arm-Compiler
* [[AArch64 Emulation]]

== Building SVE2 Code ==

=== C Compiler Options ===

At the time of writing (March 2022), most compilers do not have a specific target for Armv9 systems. Therefore, to build code that includes SVE2 instructions, you will need to instruct the complier to emit code for an Armv8-a processor that also understands the SVE2 instructions; on the GCC compiler, this is performed using the <code>-march=</code> option (which is read as "machine architecture"). '''You must do this regardless of whether you're using autovectorization, inline assembler, or intrinsics.''' The architecture specification for this target is currently "armv8-a+sve2":

 gcc -march=armv8-a+sve2 ...

Remember that in order to invoke the autovectorizer in GCC version 11, you must use <code>-O3</code> ''or'' the appropriate feature options (<code>-ftree-vectorize</code>):

 gcc -O3 -march=armv8-a+sve2 ...
 
 gcc -O2 -march=armv8-a+sve2 -ftree-vectorize ...

=== Using SVE2 Intrinsics Header Files ===

To use SVE2 intrinsics in a C program, include the header file <code>arm_sve.h</code>:

 #include <arm_sve.h>

Note: some ARM documentation will refer to <code><arm_sve2.h></code>, but in gcc, the correct file is <code><arm_sve.h></code>

=== Macro for SVE2 ===

To detect SVE2 capability in the compilation target, use the macro <code>__ARM_FEATURE_SVE2</code>:

 #if __ARM_FEATURE_SVE2
 ...
 #endif

== Running SVE2 Code ==

To run SVE2 code on an Armv8 computer, you can use the [[AArch64 Emulation|QEMU usermode]] software. This will trap SVE2 instructions and emulate them in software, while executing Armv8a instructions directly on the hardware:

 qemu-aarch64 ''./binary''

{{Admon/tip|Running AArch64 code on x86_64|The QEMU user mode software can also be used to run AArch64 code on an x86_64 system (albeit slowly). However, this requires a full AArch64 userspace (applications and tools, such as ld) to be installed on the x86_64 system. See [[AArch64 Emulation]] for details.}}