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Merge pull request #6817 from ethereum/const-opt-comments

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Document copyRoutine in ConstantOptimiser
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chriseth 2019-05-22 17:22:19 +02:00 committed by GitHub
commit 8ebf057b5c
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1 changed files with 13 additions and 2 deletions
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15
libevmasm/ConstantOptimiser.cpp
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@ -151,6 +151,7 @@ bigint CodeCopyMethod::gasNeeded() const
AssemblyItems CodeCopyMethod::execute(Assembly& _assembly) const
{
bytes data = toBigEndian(m_value);
assertThrow(data.size() == 32, OptimizerException, "Invalid number encoding.");
AssemblyItems actualCopyRoutine = copyRoutine();
actualCopyRoutine[4] = _assembly.newData(data);
return actualCopyRoutine;
@ -159,15 +160,25 @@ AssemblyItems CodeCopyMethod::execute(Assembly& _assembly) const
AssemblyItems const& CodeCopyMethod::copyRoutine()
{
AssemblyItems static copyRoutine{
// constant to be reused 3+ times
u256(0),
// back up memory
// mload(0)
Instruction::DUP1,
Instruction::MLOAD, // back up memory
Instruction::MLOAD,
// codecopy(0, <offset>, 32)
u256(32),
AssemblyItem(PushData, u256(1) << 16), // has to be replaced
AssemblyItem(PushData, u256(1) << 16), // replaced above in actualCopyRoutine[4]
Instruction::DUP4,
Instruction::CODECOPY,
// mload(0)
Instruction::DUP2,
Instruction::MLOAD,
// restore original memory
Instruction::SWAP2,
Instruction::MSTORE
};