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# Solidity Optimizer Overview

@chriseth / February 2023

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## Different Kinds of Optimizers

- Currently no optimization on Solidity AST basis
- Yul Optimizer (IR-level)
- EVMASM optimizer (opcode-level)

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## EVMASM optimizer

- Entry point is ``Assembly::optimise``
- Inliner (uses size/cost tradeoff)
- Jumpdest Remover
- Peephole Optimizer
- Block Deduplicator
- CSE (does more thas just CSE)
- Constant Optimizer (uses size/cost tradeoff)

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## Yul Optimizer

- Built from different easy to understand steps.
- Proper Yul code between each step.
- No "hidden" data structures or analysis information.
- If a job can be done by combining two simple steps, split it.

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### Optimizer Step Details

- Each step has name and unique letter:
- `static constexpr char const* name{"SSATransform"};`
- `OptimiserSuite::stepNameToAbbreviationMap`
- Use `yulopti` tool to run individual steps on Yul code

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### Some Important Steps

- Disambiguator
- CSE
- Conditional Simplifier
- DeadCodeEliminator
- ExpressionSplitter / ExpressionJoiner
- SSATransform
- LoadResolver
- NameSimplifier

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### Some More Important Steps

- StackToMemoryMover
- UnusedAssignEliminator
- UnusedStoreEliminator
- UnusedPruner
- FullInliner
- ExpressionInliner