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Peephole optimizer for unreacheable code.

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This commit is contained in:
chriseth
2016-11-25 16:10:02 +01:00
parent 721b6a9696
commit f2872bfa99
2 changed files with 116 additions and 42 deletions
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libevmasm/PeepholeOptimiser.cpp
+73 -37
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@@ -30,36 +30,55 @@ using namespace dev;
// TODO: Extend this to use the tools from ExpressionClasses.cpp
struct Identity
struct OptimiserState
{
static size_t windowSize() { return 1; }
static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
AssemblyItems const& items;
size_t i;
std::back_insert_iterator<AssemblyItems> out;
};
template <class Method, size_t WindowSize>
struct SimplePeepholeOptimizerMethod
{
static bool apply(OptimiserState& _state)
{
if (
_state.i + WindowSize <= _state.items.size() &&
Method::applySimple(_state.items.begin() + _state.i, _state.out)
)
{
_state.i += WindowSize;
return true;
}
else
return false;
}
};
struct Identity: SimplePeepholeOptimizerMethod<Identity, 1>
{
static bool applySimple(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
{
*_out = *_in;
return true;
}
};
struct PushPop
struct PushPop: SimplePeepholeOptimizerMethod<PushPop, 2>
{
static size_t windowSize() { return 2; }
static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems>)
static size_t applySimple(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems>)
{
auto t = _in[0].type();
if (_in[1] == Instruction::POP && (
return _in[1] == Instruction::POP && (
SemanticInformation::isDupInstruction(_in[0]) ||
t == Push || t == PushString || t == PushTag || t == PushSub ||
t == PushSubSize || t == PushProgramSize || t == PushData || t == PushLibraryAddress
))
return true;
else
return false;
);
}
};
struct AddPop
struct AddPop: SimplePeepholeOptimizerMethod<AddPop, 2>
{
static size_t windowSize() { return 2; }
static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
{
if (_in[1] == Instruction::POP &&
@@ -83,22 +102,17 @@ struct AddPop
}
};
struct DoubleSwap
struct DoubleSwap: SimplePeepholeOptimizerMethod<DoubleSwap, 2>
{
static size_t windowSize() { return 2; }
static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems>)
static size_t applySimple(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems>)
{
if (_in[0] == _in[1] && SemanticInformation::isSwapInstruction(_in[0]))
return true;
else
return false;
return _in[0] == _in[1] && SemanticInformation::isSwapInstruction(_in[0]);
}
};
struct JumpToNext
struct JumpToNext: SimplePeepholeOptimizerMethod<JumpToNext, 3>
{
static size_t windowSize() { return 3; }
static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
static size_t applySimple(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
{
if (
_in[0].type() == PushTag &&
@@ -117,10 +131,41 @@ struct JumpToNext
}
};
struct TagConjunctions
/// Removes everything after a JUMP (or similar) until the next JUMPDEST.
struct UnreachableCode
{
static size_t windowSize() { return 3; }
static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
static bool apply(OptimiserState& _state)
{
auto it = _state.items.begin() + _state.i;
auto end = _state.items.end();
if (it == end)
return false;
if (
it[0] != Instruction::JUMP &&
it[0] != Instruction::RETURN &&
it[0] != Instruction::STOP &&
it[0] != Instruction::SUICIDE
)
return false;
size_t i = 1;
while (it + i != end && it[i].type() != Tag)
i++;
if (i > 1)
{
*_state.out = it[0];
_state.i += i;
return true;
}
else
return false;
}
};
struct TagConjunctions: SimplePeepholeOptimizerMethod<TagConjunctions, 3>
{
static bool applySimple(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
{
if (
_in[0].type() == PushTag &&
@@ -137,13 +182,6 @@ struct TagConjunctions
}
};
struct OptimiserState
{
AssemblyItems const& items;
size_t i;
std::back_insert_iterator<AssemblyItems> out;
};
void applyMethods(OptimiserState&)
{
assertThrow(false, OptimizerException, "Peephole optimizer failed to apply identity.");
@@ -152,9 +190,7 @@ void applyMethods(OptimiserState&)
template <typename Method, typename... OtherMethods>
void applyMethods(OptimiserState& _state, Method, OtherMethods... _other)
{
if (_state.i + Method::windowSize() <= _state.items.size() && Method::apply(_state.items.begin() + _state.i, _state.out))
_state.i += Method::windowSize();
else
if (!Method::apply(_state))
applyMethods(_state, _other...);
}
@@ -162,7 +198,7 @@ bool PeepholeOptimiser::optimise()
{
OptimiserState state {m_items, 0, std::back_inserter(m_optimisedItems)};
while (state.i < m_items.size())
applyMethods(state, PushPop(), AddPop(), DoubleSwap(), JumpToNext(), TagConjunctions(), Identity());
applyMethods(state, PushPop(), AddPop(), DoubleSwap(), JumpToNext(), UnreachableCode(), TagConjunctions(), Identity());
if (m_optimisedItems.size() < m_items.size())
{
m_items = std::move(m_optimisedItems);