"How NOT To Program an Out-of-order Vector Processor" slides are public. static.sched.com/hosted_files...

Fuzzing tip: use VLA instead of fixed-size buffers or malloc 1. with fixed-size buffers asan won't catch everything. 2. VLAs are faster than malloc, in my case I get 15% faster fuzzing. If VLAs aren't portable enough, just check __STDC_NO_VLA__ and select between the other options.

Tenstorrent decided to publish the first benchmark data for Ascalon's RVV implementation using the instruction throughput benchmark of my rvv-bench benchmark suite. <3 camel-cdr.github.io/rvv-bench-re... Overall, the results look really good so far:

So if you are currently involved with ISA-level decisions about inclusion of any pext/pdep-like instructions: Please consider including SAG/inverse-SAG with bit-reversal of the goats. No matter which of the two implementation methods you are using: All you need to do is not mask the goat bits.

TIL about Trace Cache: www.realworldtech.com/forum/?threa... (thread on Apples Trace Cache) Ventanas Veyron V2/V3 seem to also use something like a trace cache.

The sixth Championship of Branch Prediction (CBP2025) happened a week ago: ericrotenberg.wordpress.ncsu.edu/cbp2025-work...

I wrote a reference implementation for a SAG without bit reflection: github.com/clairexen/ed..., and I wrote a parametric SAG core for any bit width: github.com/clairexen/ed...

edu-sag/param.v at main · clairexen/edu-sag

Educational 8-Bit Sheep-And-Goats (SAG) Verilog Reference IP - clairexen/edu-sag

github.com

SiFive X280 RVV benchmarks: camel-cdr.github.io/rvv-bench-re... Civil was so nice run my RVV benchmark on the SiFive X280 cores on the Tenstorrent Blackhole.

TIL you can't do forward compatible syscalls with inline assembly because the kernel can decide to clobber architectural state that was added after you wrote the code. If you use svc with inline assembly, you have to explicitly clobber SVE registers. Good luck doing this back in 2015 when you wrote

@clairexen.bsky.social Hi Claire, we are trying to propose some of the dropped bitmanip instructions for RVV: lists.riscv.org/g/sig-vector... Since you were deeply involved in the development of the bitmanip spec, I was wondering if you could answer some questions about your bextdep implementation.

oh no > When source and destination registers overlap and have different EEW, the instruction is mask- and tail-agnostic, regardless of the setting of the vta and vma bits in vtype.

"Efficient Implementation of RISC-V Vector Permutation Instructions" -- arxiv.org/abs/2505.07112 "Efficient Architecture for RISC-V Vector Memory Access" -- arxiv.org/abs/2504.08334 I love how these two were released so close to each other.

I recently learned that the godbolt executor for Arm has Neoverse V1 cores, with 256-bit SVE. Here is a SVE vs NEON benchmark with 1/2/4x unrolled for each: godbolt.org/z/47T9oaf97 SVE is faster across the board, with the fastest SVE version being about 30% faster than the fastest NEON version.

Compiler Explorer

Compiler Explorer is an interactive online compiler which shows the assembly output of compiled C++, Rust, Go (and many more) code.

godbolt.org

Hello you fine Internet folks, Today's article is on Alibaba/T-Head's Xuantie C910 core which has in part been open sourced and is T-Head's first out of order core. Hope y'all enjoy! open.substack.com/pub/chipsand... old.chipsandcheese.com/2025/02/03/a...

Alibaba/T-HEAD's Xuantie C910

T-HEAD is a wholly owned subsidiary of Alibaba, one of China's largest tech companies.

open.substack.com

"Using the Ziggurat Method for Sampling Random Coordinates From a Unit Circle" gist.github.com/camel-cdr/d1... I got inspired yesterday, after I saw the article "When Greedy Algorithms Can Be Faster" (16bpp.net/blog/post/wh...) It ended up about 2x faster then the simple rejection sampling.

Using the Ziggurat Method for Sampling Random Coordinates From a Unit Circle

Using the Ziggurat Method for Sampling Random Coordinates From a Unit Circle - dist_circle.h

gist.github.com

Some neat tricks for computing bit-wise prefix-or and segmented-prefix-or within scalar registers.

Falvyu@falvyu.bsky.social · 2y ago

It turns that the 'unrolled loop' for the 64-bits bitwise-or segmented scan can actually be reduced down to a few instructions. (not sure if that's a known trick) Note: compilers optimize `((~mreset) | v)` so that it is only computed once.

I've taken a look at the problem: github.com/natmaurice/s... (code on master branch also handle quotes) The segmented scan is done in scalar/SWP to avoid inter-lane overheads. I've tested it, but not benchmarked it yet.

GitHub - natmaurice/simd-comment at comment-simple

Contribute to natmaurice/simd-comment development by creating an account on GitHub.

github.com

Removing single line comments in multiple lines in parallel with RVV. If anyone has a good AVX512 solution, please share. Inspired by this reddit post: www.reddit.com/r/simd/comme... #RVV #RISC-V #SIMD

For my fellow GFNI fans. Here is Knuth introducing the MMIX instruction MXOR, which Intel later defined on vector registers under the name vgf2p8affineqb. www.youtube.com/watch?v=r_pP... (55:00)

There's been a lot of discourse on fixed-length SIMD (e.g. SSE, AVX512, NEON) vs variable-length/vector (SVE, RVV) ISAs. It's probably too early for a definite answer. But as I've designed SIMD image processing algorithms, I'll share a few results.

rvv-bench now has RSS feeds: camel-cdr.github.io/rvv-bench-re... New articles feed: camel-cdr.github.io/rvv-bench-re... Benchmark updates feed: camel-cdr.github.io/rvv-bench-re...

Here are some slightly tricky RVV mask patterns.