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Allow duplicate code removal for loops.

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This commit is contained in:
chriseth 2015-05-28 14:43:46 +02:00
parent 7f55e26eb8
commit beab869e14
3 changed files with 72 additions and 29 deletions
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10
Assembly.cpp
View File

@ -307,6 +307,11 @@ Assembly& Assembly::optimise(bool _enable)
count = 0;
copt << "Performing optimisation...";
// This only modifies PushTags, we have to run again to actually remove code.
BlockDeduplicator dedup(m_items);
if (dedup.deduplicate())
count++;
{
ControlFlowGraph cfg(m_items);
AssemblyItems optimisedItems;
@ -349,11 +354,6 @@ Assembly& Assembly::optimise(bool _enable)
m_items = move(optimisedItems);
count++;
}
// This only modifies PushTags, we have to run again to actually remove code.
BlockDeduplicator dedup(m_items);
if (dedup.deduplicate())
count++;
}
}

75
BlockDeduplicator.cpp
View File

@ -35,13 +35,33 @@ bool BlockDeduplicator::deduplicate()
{
// Compares indices based on the suffix that starts there, ignoring tags and stopping at
// opcodes that stop the control flow.
// Virtual tag that signifies "the current block" and which is used to optimise loops.
// We abort if this virtual tag actually exists.
AssemblyItem pushSelf(PushTag, u256(-4));
if (
std::count(m_items.cbegin(), m_items.cend(), pushSelf.tag()) ||
std::count(m_items.cbegin(), m_items.cend(), pushSelf.pushTag())
)
return false;
function<bool(size_t, size_t)> comparator = [&](size_t _i, size_t _j)
{
if (_i == _j)
return false;
BlockIterator first(m_items.begin() + _i, m_items.end());
BlockIterator second(m_items.begin() + _j, m_items.end());
// To compare recursive loops, we have to already unify PushTag opcodes of the
// block's own tag.
AssemblyItem pushFirstTag(pushSelf);
AssemblyItem pushSecondTag(pushSelf);
if (_i < m_items.size() && m_items.at(_i).type() == Tag)
pushFirstTag = m_items.at(_i).pushTag();
if (_j < m_items.size() && m_items.at(_j).type() == Tag)
pushSecondTag = m_items.at(_j).pushTag();
BlockIterator first(m_items.begin() + _i, m_items.end(), &pushFirstTag, &pushSelf);
BlockIterator second(m_items.begin() + _j, m_items.end(), &pushSecondTag, &pushSelf);
BlockIterator end(m_items.end(), m_items.end());
if (first != end && (*first).type() == Tag)
@ -52,27 +72,34 @@ bool BlockDeduplicator::deduplicate()
return std::lexicographical_compare(first, end, second, end);
};
set<size_t, function<bool(size_t, size_t)>> blocksSeen(comparator);
map<u256, u256> tagReplacement;
for (size_t i = 0; i < m_items.size(); ++i)
size_t iterations = 0;
for (; ; ++iterations)
{
if (m_items.at(i).type() != Tag)
continue;
auto it = blocksSeen.find(i);
if (it == blocksSeen.end())
blocksSeen.insert(i);
else
tagReplacement[m_items.at(i).data()] = m_items.at(*it).data();
}
bool ret = false;
for (AssemblyItem& item: m_items)
if (item.type() == PushTag && tagReplacement.count(item.data()))
//@todo this should probably be optimized.
set<size_t, function<bool(size_t, size_t)>> blocksSeen(comparator);
map<u256, u256> tagReplacement;
for (size_t i = 0; i < m_items.size(); ++i)
{
ret = true;
item.setData(tagReplacement.at(item.data()));
if (m_items.at(i).type() != Tag)
continue;
auto it = blocksSeen.find(i);
if (it == blocksSeen.end())
blocksSeen.insert(i);
else
tagReplacement[m_items.at(i).data()] = m_items.at(*it).data();
}
return ret;
bool changed = false;
for (AssemblyItem& item: m_items)
if (item.type() == PushTag && tagReplacement.count(item.data()))
{
changed = true;
item.setData(tagReplacement.at(item.data()));
}
if (!changed)
break;
}
return iterations > 0;
}
BlockDeduplicator::BlockIterator& BlockDeduplicator::BlockIterator::operator++()
@ -89,3 +116,11 @@ BlockDeduplicator::BlockIterator& BlockDeduplicator::BlockIterator::operator++()
}
return *this;
}
AssemblyItem const& BlockDeduplicator::BlockIterator::operator*() const
{
if (replaceItem && replaceWith && *it == *replaceItem)
return *replaceWith;
else
return *it;
}

16
BlockDeduplicator.h
View File

@ -47,19 +47,27 @@ public:
bool deduplicate();
private:
/// Iterator that skips tags skips to the end if (all branches of) the control
/// Iterator that skips tags and skips to the end if (all branches of) the control
/// flow does not continue to the next instruction.
/// If the arguments are supplied to the constructor, replaces items on the fly.
struct BlockIterator: std::iterator<std::forward_iterator_tag, AssemblyItem const>
{
public:
BlockIterator(AssemblyItems::const_iterator _it, AssemblyItems::const_iterator _end):
it(_it), end(_end) { }
BlockIterator(
AssemblyItems::const_iterator _it,
AssemblyItems::const_iterator _end,
AssemblyItem const* _replaceItem = nullptr,
AssemblyItem const* _replaceWith = nullptr
):
it(_it), end(_end), replaceItem(_replaceItem), replaceWith(_replaceWith) {}
BlockIterator& operator++();
bool operator==(BlockIterator const& _other) const { return it == _other.it; }
bool operator!=(BlockIterator const& _other) const { return it != _other.it; }
AssemblyItem const& operator*() const { return *it; }
AssemblyItem const& operator*() const;
AssemblyItems::const_iterator it;
AssemblyItems::const_iterator end;
AssemblyItem const* replaceItem;
AssemblyItem const* replaceWith;
};
AssemblyItems& m_items;