mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
4553b8c0d5
Optimization rule that rewrites functions whose return parameters are not used at callsite.
71 lines
2.2 KiB
C++
71 lines
2.2 KiB
C++
/*
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This file is part of solidity.
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solidity is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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solidity is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with solidity. If not, see <http://www.gnu.org/licenses/>.
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*/
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// SPDX-License-Identifier: GPL-3.0
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#pragma once
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#include <libyul/optimiser/OptimiserStep.h>
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namespace solidity::yul
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{
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/**
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* UnusedFunctionReturnParameterPruner: Optimiser step that removes unused return parameters at function callsite.
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*
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* If a parameter is unused, like `z` and correspondingly `x` in the following snippet:
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*
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* {
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* let z := f(sload(1), sload(2))
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* function f(a,b) -> x { x := div(a,b) }
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* }
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*
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* We remove the parameter and create a new "linking" function `f2` as follows:
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*
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* function f(a,b) {
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* let x
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* x := div(a,b)
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* }
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*
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* function f2(a,b) -> x { x := f(a,b) }
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*
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* and replace all references to `f` by `f2`.
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* The inliner should be run afterwards to make sure that all references to `f2` are replaced by
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* `f`.
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*
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* Prerequisites: Disambiguator, FunctionHoister, SSATransform, ExpressionSplitter
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*
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* Only Disambiguator and FunctionHoister are needed for correctness.
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*
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* Ideally, we want all function calls to appear in the code in the following form:
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* `let x_1, ..., x_n = f(y_1, ..., y_m)`.
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*
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* ExpressionSplitter can reduce expressions into the above form. SSATransform allows us to realize
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* that the variable `x` is unused in the following example:
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*
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* let x := f()
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* x := 1
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*
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* Note that ForLoopConditionIntoBody and ForLoopInitRewriter are prerequisites for ExpressionSplitter and SSATransform.
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*/
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struct UnusedFunctionReturnParameterPruner
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{
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static constexpr char const* name{"UnusedFunctionReturnParameterPruner"};
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static void run(OptimiserStepContext& _context, Block& _ast);
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};
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}
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