Add support for EIP-7939 CLZ

[Vectorized]

Abstract

EIP-7939 (CLZ) is an opcode that is scheduled for inclusion in the Fusaka hardfork.

https://eips.ethereum.org/EIPS/eip-7607#core-eips

Motivation

Support for the CLZ opcode.

Specification

The mathematical specification is outlined in the EIP.

Minimally, expose the clz opcode in inline-assembly (and pure yul).

Optionally, expose it in regular Solidity. However, this includes the added risk of breaking existing codebases which have a clz identifier in regular Solidity namespace.

As most existing use-cases of clz are in low level inline-assembly, implementing it just for inline-assembly may suffice.

Backwards Compatibility

Existing codebases which use clz as an identifier may break.

[gakonst]

Hi folks -- when can we expect this upstream?

Revm: https://github.com/bluealloy/revm/blob/0edd22014012ff425283787957e0a07e61959227/crates/interpreter/src/instructions/bitwise.rs#L25

[cameel]

We will aim to get this into the next release, for which we do not have a concrete date yet, but we need it at the latest just before Devconnect.

The PR should have some semantic tests and this is blocked by not having CLZ support in the latest evmone release (pinging @chfast) - it's only in the master branch for now. Once we get a release we'll be able to update the CI and proceed with the PR.

[chfast]

I'm busy with other projects, but I can make evmone's release if someone contributes the CHANGELOG for the release.

Have you tested evmone/master with solidity though?

[chfast]

New release: https://github.com/ipsilon/evmone/releases/tag/v0.16.0.
The EVMC is unchanged since 0.15 so the upgrade may be easy.

[moodysalem]

We need clz in yul for our audit starting mid October and targeting Fusaka in December, so it would be great to have this ASAP. I think the work is trivial to add it now that evmone is released. @cameel could a 0.8.31 pre-release be cut sooner?

[cameel]

Sure, why not. We'd rather still aim for Devconnect with a full release, but a prerelease would be doable. We haven't really done those in the past, but not so long ago in the team we discussed starting doing them as a way to make experimental features available earlier. I think it would fit this case perfectly. We can make the binaries available in solc-bin like with a normal release, but with a special version string and skipping the rest of the overhead of a release.

So yeah, there's not that much work in CLZ so we'll aim to have that ready by next week and do a prerelease then.