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EIP-7939 CLZ for Osaka #16122

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EIP-7939 CLZ for Osaka #16122

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Saw-mon-and-Natalie
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@Saw-mon-and-Natalie Saw-mon-and-Natalie commented Jul 16, 2025 •
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This PR addresses:

By adding a new YUL builtin function clz for EVM versions greater than or equal to Osaka.

Followed the patterns from #14757 to create these modifications:

Tests

Currently the tests in semanticTests/inlineAssembly/clz.sol fail due to evmone not having implemented CLZ:

solidity/test/EVMHost.cpp

Line 420 in 779daec

evmc::Result result = m_vm.execute(*this, m_evmRevision, message, code.data(), code.size());

In the above line m_vm.execute(...) returns EVMC_UNDEFINED_INSTRUCTION and the m_vm is:

{
    abi_version: 12,
    name: "evmone",
    version: "0.15.0",
    destroy: ... ,
    execute: ... ,
    get_capabilities: ... ,
    set_option: ...
}

References:

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Vectorized
Vectorized reviewed Jul 19, 2025
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libevmasm/Instruction.cpp
@@ -219,6 +220,7 @@ static std::map<Instruction, InstructionInfo> const c_instructionInfo =
{Instruction::SHL, {"SHL", 0, 2, 1, false, Tier::VeryLow}},
{Instruction::SHR, {"SHR", 0, 2, 1, false, Tier::VeryLow}},
{Instruction::SAR, {"SAR", 0, 2, 1, false, Tier::VeryLow}},
{Instruction::CLZ, {"CLZ", 0, 1, 1, false, Tier::Low}},
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CLZ has the same gas cost as ADD, which is in the Tier::VeryLow.

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I think it was updated. Also it is 5 in geth. Plus in the EIP it mentions:

The cost of the opcode is 5, matching MUL (raised from 3 to avoid under-pricing DoS risk).

matheusaaguiar
matheusaaguiar reviewed Jul 23, 2025
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Hi @Saw-mon-and-Natalie , thanks for the PR!
Looking good.

@Saw-mon-and-Natalie
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clz also got added to evmone which should solve the test issues (see PR description) here in this PR. But it has not assigned a new version I think yet. So in this repo, one might need to use the compiled binary from the HEAD of that repo.

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@Saw-mon-and-Natalie @Vectorized @matheusaaguiar