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Remove fixStackTooDeep and adjust combineStack comments.

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This commit is contained in:
Daniel Kirchner 2021-08-13 14:33:10 +02:00
parent 3bb7414703
commit 556bd9adfc
2 changed files with 6 additions and 19 deletions
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21
libyul/backends/evm/StackLayoutGenerator.cpp
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@ -302,7 +302,6 @@ void StackLayoutGenerator::processEntryPoint(CFG::BasicBlock const& _entry)
} }
stitchConditionalJumps(_entry); stitchConditionalJumps(_entry);
fixStackTooDeep(_entry);
} }
optional<Stack> StackLayoutGenerator::getExitLayoutOrStageDependencies( optional<Stack> StackLayoutGenerator::getExitLayoutOrStageDependencies(
@ -446,8 +445,9 @@ void StackLayoutGenerator::stitchConditionalJumps(CFG::BasicBlock const& _block)
Stack StackLayoutGenerator::combineStack(Stack const& _stack1, Stack const& _stack2) Stack StackLayoutGenerator::combineStack(Stack const& _stack1, Stack const& _stack2)
{ {
// TODO: there is probably a better way than brute-forcing. This has n! complexity or worse, so // TODO: it would be nicer to replace this by a constructive algorithm.
// we can't keep it like this. // Currently it uses a reduced version of the Heap Algorithm to partly brute-force, which seems
// to work decently well.
Stack commonPrefix; Stack commonPrefix;
for (auto&& [slot1, slot2]: ranges::zip_view(_stack1, _stack2)) for (auto&& [slot1, slot2]: ranges::zip_view(_stack1, _stack2))
@ -478,13 +478,6 @@ Stack StackLayoutGenerator::combineStack(Stack const& _stack1, Stack const& _sta
std::map<size_t, Stack> sortedCandidates; std::map<size_t, Stack> sortedCandidates;
// TODO: surprisingly this works for rather comparably large candidate size, but we should probably
// set up some limit, since this will quickly explode otherwise.
// Ideally we would then have a better fallback mechanism - although returning any naive union of both stacks
// like ``candidate`` itself may just be fine.
// if (candidate.size() > 8)
// return candidate;
auto evaluate = [&](Stack const& _candidate) -> size_t { auto evaluate = [&](Stack const& _candidate) -> size_t {
size_t numOps = 0; size_t numOps = 0;
Stack testStack = _candidate; Stack testStack = _candidate;
@ -518,6 +511,9 @@ Stack StackLayoutGenerator::combineStack(Stack const& _stack1, Stack const& _sta
std::swap(candidate[c[i]], candidate[i]); std::swap(candidate[c[i]], candidate[i]);
sortedCandidates.insert(std::make_pair(evaluate(candidate), candidate)); sortedCandidates.insert(std::make_pair(evaluate(candidate), candidate));
++c[i]; ++c[i];
// Note that for a proper implementation of the Heap algorithm this would need to revert back to ``i = 1.``
// However, the incorrect implementation produces decent result and the proper version would have n!
// complexity and is thereby not feasible.
++i; ++i;
} }
else else
@ -530,11 +526,6 @@ Stack StackLayoutGenerator::combineStack(Stack const& _stack1, Stack const& _sta
return commonPrefix + sortedCandidates.begin()->second; return commonPrefix + sortedCandidates.begin()->second;
} }
void StackLayoutGenerator::fixStackTooDeep(CFG::BasicBlock const&)
{
// TODO
}
Stack StackLayoutGenerator::compressStack(Stack _stack) Stack StackLayoutGenerator::compressStack(Stack _stack)
{ {
optional<size_t> firstDupOffset; optional<size_t> firstDupOffset;

4
libyul/backends/evm/StackLayoutGenerator.h
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@ -85,10 +85,6 @@ private:
/// stack shuffling when starting from the returned layout. /// stack shuffling when starting from the returned layout.
static Stack combineStack(Stack const& _stack1, Stack const& _stack2); static Stack combineStack(Stack const& _stack1, Stack const& _stack2);
/// Tries to detect stack layout transitions that are bound to cause stack too deep errors and
/// attempts to reorganize the layout to avoid those cases.
void fixStackTooDeep(CFG::BasicBlock const& _entry);
/// @returns a copy of @a _stack stripped of all duplicates and slots that can be freely generated. /// @returns a copy of @a _stack stripped of all duplicates and slots that can be freely generated.
/// Attempts to create a layout that requires a minimal amount of operations to reconstruct the original /// Attempts to create a layout that requires a minimal amount of operations to reconstruct the original
/// stack @a _stack. /// stack @a _stack.