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/*
This file is part of solidity.
solidity is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
solidity is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with solidity. If not, see <http://www.gnu.org/licenses/>.
*/
// SPDX-License-Identifier: GPL-3.0
/**
* Stack layout generator for Yul to EVM code generation.
*/
#pragma once
#include <libyul/backends/evm/ControlFlowGraph.h>
#include <map>
namespace solidity::yul
{
struct StackLayout
{
struct BlockInfo
{
/// Complete stack layout that is required for entering a block.
Stack entryLayout;
/// The resulting stack layout after executing the block.
Stack exitLayout;
};
std::map<CFG::BasicBlock const*, BlockInfo> blockInfos;
/// For each operation the complete stack layout that:
/// - has the slots required for the operation at the stack top.
/// - will have the operation result in a layout that makes it easy to achieve the next desired layout.
std::map<CFG::Operation const*, Stack> operationEntryLayout;
};
class StackLayoutGenerator
{
public:
struct StackTooDeep
{
/// Number of slots that need to be saved.
size_t deficit = 0;
/// Set of variables, eliminating which would decrease the stack deficit.
std::vector<YulString> variableChoices;
};
static StackLayout run(CFG const& _cfg);
/// @returns a map from function names to the stack too deep errors occurring in that function.
/// Requires @a _cfg to be a control flow graph generated from disambiguated Yul.
/// The empty string is mapped to the stack too deep errors of the main entry point.
static std::map<YulString, std::vector<StackTooDeep>> reportStackTooDeep(CFG const& _cfg);
/// @returns all stack too deep errors in the function named @a _functionName.
/// Requires @a _cfg to be a control flow graph generated from disambiguated Yul.
/// If @a _functionName is empty, the stack too deep errors of the main entry point are reported instead.
static std::vector<StackTooDeep> reportStackTooDeep(CFG const& _cfg, YulString _functionName);
private:
StackLayoutGenerator(StackLayout& _context);
/// @returns the optimal entry stack layout, s.t. @a _operation can be applied to it and
/// the result can be transformed to @a _exitStack with minimal stack shuffling.
/// Simultaneously stores the entry layout required for executing the operation in m_layout.
Stack propagateStackThroughOperation(Stack _exitStack, CFG::Operation const& _operation, bool _aggressiveStackCompression = false);
/// @returns the desired stack layout at the entry of @a _block, assuming the layout after
/// executing the block should be @a _exitStack.
Stack propagateStackThroughBlock(Stack _exitStack, CFG::BasicBlock const& _block, bool _aggressiveStackCompression = false);
/// Main algorithm walking the graph from entry to exit and propagating back the stack layouts to the entries.
/// Iteratively reruns itself along backwards jumps until the layout is stabilized.
void processEntryPoint(CFG::BasicBlock const& _entry);
/// @returns the best known exit layout of @a _block, if all dependencies are already @a _visited.
/// If not, adds the dependencies to @a _dependencyList and @returns std::nullopt.
std::optional<Stack> getExitLayoutOrStageDependencies(
CFG::BasicBlock const& _block,
std::set<CFG::BasicBlock const*> const& _visited,
std::list<CFG::BasicBlock const*>& _dependencyList
) const;
/// @returns a pair of ``{jumpingBlock, targetBlock}`` for each backwards jump in the graph starting at @a _entry.
std::list<std::pair<CFG::BasicBlock const*, CFG::BasicBlock const*>> collectBackwardsJumps(CFG::BasicBlock const& _entry) const;
/// After the main algorithms, layouts at conditional jumps are merely compatible, i.e. the exit layout of the
/// jumping block is a superset of the entry layout of the target block. This function modifies the entry layouts
/// of conditional jump targets, s.t. the entry layout of target blocks match the exit layout of the jumping block
/// exactly, except that slots not required after the jump are marked as `JunkSlot`s.
void stitchConditionalJumps(CFG::BasicBlock const& _block);
/// Calculates the ideal stack layout, s.t. both @a _stack1 and @a _stack2 can be achieved with minimal
/// stack shuffling when starting from the returned layout.
static Stack combineStack(Stack const& _stack1, Stack const& _stack2);
/// Walks through the CFG and reports any stack too deep errors that would occur when generating code for it
/// without countermeasures.
std::vector<StackTooDeep> reportStackTooDeep(CFG::BasicBlock const& _entry) const;
/// @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
/// stack @a _stack.
static Stack compressStack(Stack _stack);
//// Fills in junk when entering branches that do not need a clean stack in case the result is cheaper.
void fillInJunk(CFG::BasicBlock const& _block);
StackLayout& m_layout;
};
}