[[!tag standards]]

# Simple-V Vectorisation for the OpenPOWER ISA

**SV is in DRAFT STATUS**. SV has not yet been submitted to the OpenPOWER Foundation ISA WG for review.

<https://bugs.libre-soc.org/show_bug.cgi?id=213>

Fundamental design principles:

* Simplicity of introduction and implementation on the existing OpenPOWER ISA
* Effectively a hardware for-loop, pausing PC, issuing multiple scalar operations
* Preserving the underlying scalar execution dependencies as if the for-loop had been expanded as actual scalar instructions
  (termed "preserving Program Order")
* Augments ("tags") existing instructions, providing Vectorisation "context" rather than adding new ones.
* Does not modify or deviate from the underly scalar OpenPOWER ISA unless it provides significant performance or other advantage to do so in the Vector space (dropping XER.SO and OE=1 for example)

Advantages of these design principles:

* It is therefore easy to create a first (and sometimes only) implementation as literally a for-loop in hardware, simulators, and compilers.
* More complex HDL can be done by repeating existing scalar ALUs and pipelines as blocks.
* As (mostly) a high-level "context" that does not (significantly) deviate from scalar OpenPOWER ISA and, in its purest form being "a for loop around scalar instructions", it is minimally-disruptive and consequently stands a reasonable chance of broad community adoption and acceptance
* Completely wipes not just SIMD opcode proliferation off the
  map (SIMD is O(N^6) opcode proliferation)
  but off of Vectorisation ISAs as well.  No more separate Vector
  instructions.

Pages being developed and examples

* [[sv/overview]] explaining the basics.
* [[sv/implementation]] implementation planning and coordination
* [[sv/predication]] discussion on predication concepts
* [[sv/masked_vector_chaining]]
* [[sv/discussion]]
* [[sv/example_dep_matrices]]
* [[sv/prefix]]
* [[sv/major_opcode_allocation]]
* [[opcode_regs_deduped]]
* [[sv/vector_swizzle]]
* [[sv/mv.swizzle]]
* [[sv/mv.x]]
* [[sv/fcvt]] FP Conversion (due to OpenPOWER Scalar FP32)
* [[sv/mv.vec]] move to and from vec2/3/4
* [[sv/16_bit_compressed]]
* [[sv/toc_data_pointer]]
* [[sv/cr_int_predication]]
* [[sv/setvl]]
* [[sv/svp64]]
* [[sv/ldst]] Load and Store
* [[sv/sprs]] SPRs
* [[sv/bitmanip]]
* [[sv/remap]] "Remapping" for Matrix Multiply and RGB "Structure Packing"
* [[sv/propagation]] Context propagation including svp64, swizzle and remap
* [[sv/vector_ops]] Vector ops needed to make a "complete" Vector ISA
* [[sv/av_opcodes]] scalar opcodes for Audio/Video
* [[sv/byteswap]]
* TODO: OpenPOWER [[openpower/transcendentals]]

Additional links:

* <https://www.sigarch.org/simd-instructions-considered-harmful/>
* [[simple_v_extension]] old (deprecated) version