1 **ISA Comparison Table** - discussion and research at <https://bugs.libre-soc.org/show_bug.cgi?id=893>
3 |ISA <br>name |Num <br>opcodes|Num <br>intrinsics|Taxonomy / <br> Class|setvl <br> scalable|Predicate <br> Masks|Twin <br> Predication|Explicit <br> Vector regs|128-bit <br> ops|Bigint |LDST <br> Fault-First|Data-dep<br> Fail-first|Pred-<br> Result|Matrix HW<br> support|DCT/FFT HW<br? support |
4 |--------------|---------------|------------------|---------------------|-------------------|--------------------|---------------------|-------------------------|----------------|--------|---------------------|-----------------------|----------------|---------------------|-----------------------|
5 |Draft SVP64 |5 (1) |see (25) |Scalable (2) |yes |yes |yes (3) |no (4) |see (5) |yes (6) |yes (7) |yes (8) |yes (9) |yes (10) | yes(11) |
6 |VSX |700+ |700+? (26) |Packed SIMD |no |no |no |yes (12) |yes |no |no |no |no |yes (13) | no |
7 |NEON |~250 (14) |7088 (28) |Packed SIMD |no |no |no |yes |yes |no |no |no |no |no | no |
8 |SVE2 |~1000 (15) |6040 (29) |Predicated SIMD(16) |no (16) |yes |no |yes |yes |no |yes (7) |no |no |yes (33) | no |
9 |AVX512 (17) |~1000s (18) |7256 (30) |Predicated SIMD |no |yes |no |yes |yes |no |no |no |no |no | no |
10 |RVV (19) |~190 (20) |~25000 (31) |Scalable (21) |yes |yes |no |yes |yes (22) |no |yes |no |no |no | no |
11 |Aurora SX(23) |~200 (24) |unknown (32) |Scalable (25) |yes |yes |no |yes |no |no |no |no |no |? | no |
13 * (1): plus EXT001 24-bit prefixing using 25% of EXT001 space. See [[sv/svp64]]
14 * (2): A 2-Dimensional Scalable Vector ISA **specifically designed for the Power ISA** with both Horizontal-First and Vertical-First Modes. See [[sv/vector_isa_comparison]]
15 * (3): on specific operations. See [[opcode_regs_deduped]] for full list. Key: 2P - Twin Predication, 1P - Single-Predicate
16 * (4): SVP64 provides a Vector concept on top of the **Scalar** GPR, FPR and CR Fields, extended to 128 entries.
17 * (5): SVP64 Vectorises Scalar ops. It is up to the **implementor** to choose (**optionally**) whether to apply SVP64 to e.g. VSX Quad-Precision (128-bit) instructions, to create 128-bit Vector ops.
18 * (6): big-integer add is just `sv.adde`. For optimal performance Bigint Mul and divide first require addition of two scalar operations (in turn, naturally Vectorised by SVP64). See [[sv/biginteger/analysis]]
19 * (7): See [[sv/svp64/appendix]] and [ARM SVE Fault-First](https://alastairreid.github.io/papers/sve-ieee-micro-2017.pdf)
20 * (8): Based on LD/ST Fail-first, extended to data. See [[sv/svp64/appendix]]
21 * (9): Predicate-result effectively turns any standard op into a type of "cmp". See [[sv/svp64/appendix]]
22 * (10): Any non-power-of-two Matrices up to 127 FMACs (or other FMA-style op), full triple-loop Schedule. See [[sv/remap]]
23 * (11): DCT (Lee) and FFT Full Triple-loops supported, RADIX2-only. Normally only found in VLIW DSPs (TI MSP30, Qualcom Hexagon). See [[sv/remap]]
24 * (12): VSX's Vector Registers are mis-named: they are 100% PackedSIMD. AVX-512 is not a Vector ISA either. See [Flynn's Taxonomy](https://en.wikipedia.org/wiki/Flynn%27s_taxonomy)
25 * (13): Power ISA v3.1 contains "Matrix Multiply Assist" (MMA) which due to PackedSIMD is restricted to RADIX2 and requires inline assembler loop-unrolling for non-power-of-two Matrix dimensions
26 * (14): difficult to ascertain, see [NEON/VFP](https://developer.arm.com/documentation/den0018/a/NEON-and-VFP-Instruction-Summary/List-of-all-NEON-and-VFP-instructions).
27 Critically depends on ARM Scalar instructions
28 * (15): difficult to exactly ascertain, see ARM Architecture Reference Manual Supplement, DDI 0584. Critically depends on ARM Scalar instructions.
29 * (16): ARM states that the Scalability is a [Silicon-partner choice](https://developer.arm.com/-/media/Arm%20Developer%20Community/PDF/102340_0001_00_en_introduction-to-sve2.pdf?revision=aae96dd2-5334-4ad3-9a47-393086a20fea).
30 Scalability in the ISA is **not available to the programmer**: there is no `setvl` instruction in SVE2, which is already causing assembler programmer difficulties.
31 [quote](https://gist.github.com/zingaburga/805669eb891c820bd220418ee3f0d6bd#file-sve2-md) **"you may be stuck with only using the bottom 128 bits of the vector, or need to code specifically for each width"**
32 * (17): [AVX512 Wikipedia](https://en.wikipedia.org/wiki/AVX-512), [Lifecycle of an instruction set](https://media.handmade-seattle.com/tom-forsyth/) including full slides
33 * (18): difficult to exactly ascertain, contains subsets. Critically depends on ISA support from earlier x86 ISA subsets (several more thousand instructions). See [SIMD ISA listing](https://www.officedaytime.com/simd512e/)
34 * (19): [RVV Spec](https://github.com/riscv/riscv-v-spec/blob/master/v-spec.adoc)
35 * (20): RISC-V Vectors are not stand-alone, i.e. like SVE2 and AVX-512 are critically dependent on the Scalar ISA (an additional ~96 instructions for the Scalar RV64GC set, needed for Linux).
36 * (21): Like the original Cray RVV is a truly scalable Vector ISA (Cray setvl instruction). However, like SVE2, the Maximum Vector length is a Silicon-partner choice, which creates similar limitations that SVP64 does not have.
37 The RISC-V Founders strongly discourage efforts by programmers to find out the Silicon's Maximum Vector Length, as an effort to steer programmers towards Silicon-independent assembler. This requires **all** algorithms to contain a loop construct.
38 MAXVL in SVP64 is a Spec-hard-fixed quantity therefore loop constructs are not necessary 100% of the time.
39 * (22): like SVP64 it is up to the hardware implementor (Silicon partner) to choose whether to support 128-bit elements.
40 * (23): [NEC SX Aurora](https://ftp.libre-soc.org/NEC_SX_Aurora_TSUBASA_VectorEngine-as-manual-v1.2.pdf) is based on the original Cray Vectors
41 * (24): [Aurora ISA guide](https://sxauroratsubasa.sakura.ne.jp/documents/guide/pdfs/Aurora_ISA_guide.pdf) Appendix-3 11.1 p508
42 * (25): Like the original Cray Vectors, the ISA Vector Length is independent of the underlying hardware, however Generation 1 has 256 elements per Vector register (3.2.4 p24, Aurora ISA guide)
43 * (26): If treated as a 1-Dimensional ISA, and designed badly, the 24-bit Prefix expands 200+ scalar instructions to well over a million intrinsics (N~=10^4 **times** M~=10^2).
44 If treated as a 2-Dimensional ISA and designed well, there are far less. N prefix intrinsics **plus** M scalar instruction intrinsics, where N is likely to be of the order of 10^2 and M of the order of 10^2.
45 * (27): [Altivec gcc intrinsics](https://gcc.gnu.org/onlinedocs/gcc/PowerPC-AltiVec_002fVSX-Built-in-Functions.html), contains links to additional VSX intrinsics for ISA 2.05/6/7, 3.0 and 3.1
46 * (28): NEON 32-bit 2754 intrinsics, NEON 64-bit 4334 intrinsics.
47 * (29): SVE: 4140 intrinsics, SVE2 1900 intrinsics
48 * (30): Count includes SSE, SSE2, AVX, AVX2 and all AVX512 variants
49 * (31): [RVV intrinsics listing](https://raw.githubusercontent.com/riscv-non-isa/rvv-intrinsic-doc/master/intrinsic_funcs.md) page is 25,000 lines long.
50 * (32): Unknown. estimated to be of the order of length of RVV due to also being a Cray-style Scalable ISA.
51 * (33): [Scalable Matrix Optional Extension](https://community.arm.com/arm-community-blogs/b/architectures-and-processors-blog/posts/scalable-matrix-extension-armv9-a-architecture)
52 the key is an outer-product instruction [SMOPA](https://developer.arm.com/documentation/ddi0602/2022-06/SME-Instructions/SMOPA--Signed-integer-sum-of-outer-products-and-accumulate-?lang=en) which is very hard to tell at a glance if it is power-2 or non-power-2
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