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Adjust and extend comments for the stack shuffling operations.

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This commit is contained in:
Daniel Kirchner 2021-08-10 12:46:04 +02:00
parent 20956a7a19
commit eca4fb6781
1 changed files with 15 additions and 3 deletions
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18
libyul/backends/evm/StackHelpers.h
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@ -56,6 +56,14 @@ inline std::string stackToString(Stack const& _stack)
// Abstraction of stack shuffling operations. Can be defined as actual concept once we switch to C++20.
// Used as an interface for the stack shuffler below.
// The shuffle operation class is expected to internally keep track of a current stack layout (the "source layout")
// that the shuffler is supposed to shuffle to a fixed target stack layout.
// The shuffler works iteratively. At each iteration it instantiates an instance of the shuffle operations and
// queries it for various information about the current source stack layout and the target layout, as described
// in the interface below.
// Based on that information the shuffler decides which is the next optimal operation to perform on the stack
// and calls the corresponding entry point in the shuffling operations (swap, pushOrDupTarget or pop).
/*
template<typename ShuffleOperations>
concept ShuffleOperationConcept = requires(ShuffleOperations ops, size_t sourceOffset, size_t targetOffset, size_t depth) {
@ -65,11 +73,13 @@ concept ShuffleOperationConcept = requires(ShuffleOperations ops, size_t sourceO
{ ops.sourceIsSame(sourceOffset, sourceOffset) } -> std::convertible_to<bool>;
// Returns a positive integer n, if the slot at the given source offset needs n more copies.
// Returns a negative integer -n, if the slot at the given source offsets occurs n times too many.
// Returns zero if the amount of occurrences, in the current source layout, of the slot at the given source offset matches the desired amount of occurrences in the target.
// Returns zero if the amount of occurrences, in the current source layout, of the slot at the given source offset
// matches the desired amount of occurrences in the target.
{ ops.sourceMultiplicity(sourceOffset) } -> std::convertible_to<int>;
// Returns a positive integer n, if the slot at the given target offset needs n more copies.
// Returns a negative integer -n, if the slot at the given target offsets occurs n times too many.
// Returns zero if the amount of occurrences, in the current source layout, of the slot at the given target offset matches the desired amount of occurrences in the target.
// Returns zero if the amount of occurrences, in the current source layout, of the slot at the given target offset
// matches the desired amount of occurrences in the target.
{ ops.targetMultiplicity(targetOffset) } -> std::convertible_to<int>;
// Returns true, iff any slot is compatible with the given target offset.
{ ops.targetIsArbitrary(targetOffset) } -> std::convertible_to<bool>;
@ -77,7 +87,9 @@ concept ShuffleOperationConcept = requires(ShuffleOperations ops, size_t sourceO
{ ops.sourceSize() } -> std::convertible_to<size_t>;
// Returns the number of slots in the target layout.
{ ops.targetSize() } -> std::convertible_to<size_t>;
// Swaps the top most slot in the source with the slot at depth.
// Swaps the top most slot in the source with the slot `depth` slots below the top.
// 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.
{ ops.pop() };