SIMD Feature Build Failing as of nightly-2020-09-15 (on x86_64)

[danieldjewell]

Opening issue here after tracking it upstream:

Build of ripgrep failing as of nightly-2020-09-15 because of a build failure in packed_simd: rust-lang/packed_simd#288

This, in turn, appears to have been caused by rust-lang/stdarch#890

[danieldjewell]

Also see rust-lang/rust#76295

[BurntSushi]

Thanks, but as you've helpfully linked, this isn't really an issue with ripgrep and the simd feature is nightly only for exactly this reason.

In any case, I'd suggest not using the simd feature unless you know you need it. The only benefit you get is when searching UTF-16 files. (ripgrep uses lots of SIMD in other places, but decoding UTF-16 is maintained by others and refuses to use the non-portable but stable SIMD APIs.)

[danieldjewell]

In any case, I'd suggest not using the simd feature unless you know you need it. The only benefit you get is when searching UTF-16 files.

This is great info! Thank you for the clarification.

Perhaps this would be good to add into the readme? Maybe somewhere in here: 😁

ripgrep/README.md

Lines 369 to 390 in f511849

	If you have a Rust nightly compiler and a recent Intel CPU, then you can enable
	additional optional SIMD acceleration like so:
	```
	RUSTFLAGS="-C target-cpu=native" cargo build --release --features 'simd-accel'
	```
	The `simd-accel` feature enables SIMD support in certain ripgrep dependencies
	(responsible for transcoding). They are not necessary to get SIMD optimizations
	for search; those are enabled automatically. Hopefully, some day, the
	`simd-accel` feature will similarly become unnecessary. **WARNING:** Currently,
	enabling this option can increase compilation times dramatically.
	Finally, optional PCRE2 support can be built with ripgrep by enabling the
	`pcre2` feature:
	```
	$ cargo build --release --features 'pcre2'
	```
	(Tip: use `--features 'pcre2 simd-accel'` to also include compile time SIMD
	optimizations, which will only work with a nightly compiler.)

[BurntSushi]

It is already, right in the section you quoted:

The simd-accel feature enables SIMD support in certain ripgrep dependencies (responsible for transcoding). They are not necessary to get SIMD optimizations for search; those are enabled automatically. Hopefully, some day, the simd-accel feature will similarly become unnecessary.

[BurntSushi]

If you think it could be clearer, please submit a PR with a clarification. :)