Extract side effects into their own struct.

libyul/SideEffects.h

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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/>.
+*/
+
+#pragma once
+
+#include <set>
+
+namespace yul
+{
+
+/**
+ * Side effects of code.
+ *
+ * The default-constructed value applies to the "empty code".
+ */
+struct SideEffects
+{
+	/// If true, expressions in this code can be freely moved and copied without altering the
+	/// semantics.
+	/// At statement level, it means that functions containing this code can be
+	/// called multiple times, their calls can be rearranged and calls can also be
+	/// deleted without changing the semantics.
+	/// This means it cannot depend on storage or memory, cannot have any side-effects,
+	/// but it can depend on state that is constant across an EVM-call.
+	bool movable = true;
+	/// If true, the code can be removed without changing the semantics.
+	bool sideEffectFree = true;
+	/// If true, the code can be removed without changing the semantics as long as
+	/// the whole program does not contain the msize instruction.
+	bool sideEffectFreeIfNoMSize = true;
+	/// If false, storage is guaranteed to be unchanged by the code under all
+	/// circumstances.
+	bool invalidatesStorage = false;
+	/// If false, memory is guaranteed to be unchanged by the code under all
+	/// circumstances.
+	bool invalidatesMemory = false;
+
+	/// @returns the worst-case side effects.
+	static SideEffects worst()
+	{
+		return SideEffects{false, false, false, true, true};
+	}
+
+	/// @returns the combined side effects of two pieces of code.
+	SideEffects operator+(SideEffects const& _other)
+	{
+		return SideEffects{
+			movable && _other.movable,
+			sideEffectFree && _other.sideEffectFree,
+			sideEffectFreeIfNoMSize && _other.sideEffectFreeIfNoMSize,
+			invalidatesStorage || _other.invalidatesStorage,
+			invalidatesMemory || _other.invalidatesMemory
+		};
+	}
+
+	/// Adds the side effects of another piece of code to this side effect.
+	SideEffects& operator+=(SideEffects const& _other)
+	{
+		*this = *this + _other;
+		return *this;
+	}
+};
+
+}