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This commit is contained in:
Daniel Kirchner 2021-08-10 15:35:59 +02:00
parent 387c248601
commit 3bb7414703
1 changed files with 13 additions and 2 deletions
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15
libyul/backends/evm/StackHelpers.h
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@ -91,7 +91,9 @@ concept ShuffleOperationConcept = requires(ShuffleOperations ops, size_t sourceO
// In terms of EVM opcodes this is supposed to be a `SWAP<depth>`.
// In terms of vectors this is supposed to be `std::swap(source.at(source.size() - depth - 1, source.top))`.
{ ops.swap(depth) };
// Pops the top most slot in the source.
// Pops the top most slot in the source, i.e. the slot at offset ops.sourceSize() - 1.
// In terms of EVM opcodes this is `POP`.
// In terms of vectors this is `source.pop();`.
{ ops.pop() };
// Dups or pushes the slot that is supposed to end up at the given target offset.
{ ops.pushOrDupTarget(targetOffset) };
@ -150,6 +152,15 @@ private:
}
return false;
}
/// Finds a slot to dups or pushes with the aim of eventually fixing @a _targetOffset in the target.
/// In the simplest case, the slot at @a _targetOffset has a multiplicity > 0, i.e. it can directly be dupped or pushed
/// and the next iteration will fix @a _targetOffset.
/// But, in general, there may already be enough copies of the slot that is supposed to end up at @a _targetOffset
/// on stack, s.t. it cannot be dupped again. In that case there has to be a copy of the desired slot on stack already
/// elsewhere that is not yet in place (`nextOffset` below). The fact that ``nextOffset`` is not in place means that
/// we can (recursively) try bringing up the slot that is supposed to end up at ``nextOffset`` in the *target*.
/// When the target slot at ``nextOffset`` is fixed, the current source slot at ``nextOffset`` will be
/// at the stack top, which is the slot required at @a _targetOffset.
static void bringUpTargetSlot(ShuffleOperations& _ops, size_t _targetOffset)
{
std::list<size_t> toVisit{_targetOffset};
@ -203,7 +214,7 @@ private:
// in the target.
if (
ops.sourceMultiplicity(sourceTop) < 0 &&
!(ops.targetSize() >= ops.sourceSize() && ops.targetIsArbitrary(sourceTop))
!ops.targetIsArbitrary(sourceTop)
)
{
ops.pop();