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Replace comparison operators with opposites if preceded by SWAP1

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This commit is contained in:
Alex Beregszaszi 2018-04-04 15:28:15 +02:00
parent efa0ccaf9e
commit 02ea0e547f
3 changed files with 66 additions and 6 deletions
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1
Changelog.md
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@ -6,6 +6,7 @@ Features:
* General: Support accessing dynamic return data in post-byzantium EVMs.
* Interfaces: Allow overriding external functions in interfaces with public in an implementing contract.
* Optimizer: Remove useless ``SWAP1`` instruction preceding a commutative instruction (such as ``ADD``, ``MUL``, etc).
* Optimizer: Replace comparison operators (``LT``, ``GT``, etc) with opposites if preceded by ``SWAP1``, e.g. ``SWAP1 LT`` is replaced with ``GT``.
* Optimizer: Optimize across ``mload`` if ``msize()`` is not used.
* Syntax Checker: Issue warning for empty structs (or error as experimental 0.5.0 feature).
* General: Introduce new constructor syntax using the ``constructor`` keyword as experimental 0.5.0 feature.

28
libevmasm/PeepholeOptimiser.cpp
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@ -173,6 +173,32 @@ struct CommutativeSwap: SimplePeepholeOptimizerMethod<CommutativeSwap, 2>
}
};
struct SwapComparison: SimplePeepholeOptimizerMethod<SwapComparison, 2>
{
static bool applySimple(AssemblyItem const& _swap, AssemblyItem const& _op, std::back_insert_iterator<AssemblyItems> _out)
{
map<Instruction, Instruction> swappableOps{
{ Instruction::LT, Instruction::GT },
{ Instruction::GT, Instruction::LT },
{ Instruction::SLT, Instruction::SGT },
{ Instruction::SGT, Instruction::SLT }
};
if (
_swap.type() == Operation &&
_swap.instruction() == Instruction::SWAP1 &&
_op.type() == Operation &&
swappableOps.count(_op.instruction())
)
{
*_out = swappableOps.at(_op.instruction());
return true;
}
else
return false;
}
};
struct JumpToNext: SimplePeepholeOptimizerMethod<JumpToNext, 3>
{
static size_t applySimple(
@ -279,7 +305,7 @@ bool PeepholeOptimiser::optimise()
{
OptimiserState state {m_items, 0, std::back_inserter(m_optimisedItems)};
while (state.i < m_items.size())
applyMethods(state, PushPop(), OpPop(), DoublePush(), DoubleSwap(), CommutativeSwap(), JumpToNext(), UnreachableCode(), TagConjunctions(), Identity());
applyMethods(state, PushPop(), OpPop(), DoublePush(), DoubleSwap(), CommutativeSwap(), SwapComparison(), JumpToNext(), UnreachableCode(), TagConjunctions(), Identity());
if (m_optimisedItems.size() < m_items.size() || (
m_optimisedItems.size() == m_items.size() && (
eth::bytesRequired(m_optimisedItems, 3) < eth::bytesRequired(m_items, 3) ||

39
test/libevmasm/Optimiser.cpp
View File

@ -903,9 +903,7 @@ BOOST_AUTO_TEST_CASE(peephole_noncommutative_swap1)
Instruction::SDIV,
Instruction::MOD,
Instruction::SMOD,
Instruction::EXP,
Instruction::LT,
Instruction::GT
Instruction::EXP
};
for (Instruction const op: ops)
{
@ -934,6 +932,41 @@ BOOST_AUTO_TEST_CASE(peephole_noncommutative_swap1)
}
}
BOOST_AUTO_TEST_CASE(peephole_swap_comparison)
{
map<Instruction, Instruction> swappableOps{
{ Instruction::LT, Instruction::GT },
{ Instruction::GT, Instruction::LT },
{ Instruction::SLT, Instruction::SGT },
{ Instruction::SGT, Instruction::SLT }
};
for (auto const& op: swappableOps)
{
AssemblyItems items{
u256(1),
u256(2),
Instruction::SWAP1,
op.first,
u256(4),
u256(5)
};
AssemblyItems expectation{
u256(1),
u256(2),
op.second,
u256(4),
u256(5)
};
PeepholeOptimiser peepOpt(items);
BOOST_REQUIRE(peepOpt.optimise());
BOOST_CHECK_EQUAL_COLLECTIONS(
items.begin(), items.end(),
expectation.begin(), expectation.end()
);
}
}
BOOST_AUTO_TEST_CASE(jumpdest_removal)
{
AssemblyItems items{