Merge pull request #6242 from ethereum/yul-bc-dataflow

Yul dataflow analysis for continue/break statements

libyul/optimiser/DataFlowAnalyzer.cpp

@@ -117,6 +117,9 @@ void DataFlowAnalyzer::operator()(ForLoop& _for)
 	for (auto& statement: _for.pre.statements)
 		visit(statement);
 
+	AssignmentsSinceContinue assignmentsSinceCont;
+	assignmentsSinceCont(_for.body);
+
 	Assignments assignments;
 	assignments(_for.body);
 	assignments(_for.post);
@@ -124,22 +127,13 @@ void DataFlowAnalyzer::operator()(ForLoop& _for)
 
 	visit(*_for.condition);
 	(*this)(_for.body);
+	clearValues(assignmentsSinceCont.names());
 	(*this)(_for.post);
-
 	clearValues(assignments.names());
+
 	popScope();
 }
 
-void DataFlowAnalyzer::operator()(Break&)
-{
-	yulAssert(false, "Not implemented yet.");
-}
-
-void DataFlowAnalyzer::operator()(Continue&)
-{
-	yulAssert(false, "Not implemented yet.");
-}
-
 void DataFlowAnalyzer::operator()(Block& _block)
 {
 	size_t numScopes = m_variableScopes.size();

libyul/optimiser/DataFlowAnalyzer.h

@@ -53,8 +53,6 @@ public:
 	void operator()(Switch& _switch) override;
 	void operator()(FunctionDefinition&) override;
 	void operator()(ForLoop&) override;
-	void operator()(Break& _continue) override;
-	void operator()(Continue& _continue) override;
 	void operator()(Block& _block) override;
 
 protected:

libyul/optimiser/NameCollector.cpp

@@ -79,3 +79,29 @@ void Assignments::operator()(Assignment const& _assignment)
 	for (auto const& var: _assignment.variableNames)
 		m_names.emplace(var.name);
 }
+
+
+void AssignmentsSinceContinue::operator()(ForLoop const& _forLoop)
+{
+	m_forLoopDepth++;
+	ASTWalker::operator()(_forLoop);
+	m_forLoopDepth--;
+}
+
+void AssignmentsSinceContinue::operator()(Continue const&)
+{
+	if (m_forLoopDepth == 0)
+		m_continueFound = true;
+}
+
+void AssignmentsSinceContinue::operator()(Assignment const& _assignment)
+{
+	if (m_continueFound)
+		for (auto const& var: _assignment.variableNames)
+			m_names.emplace(var.name);
+}
+
+void AssignmentsSinceContinue::operator()(FunctionDefinition const&)
+{
+	yulAssert(false, "");
+}

libyul/optimiser/NameCollector.h

@@ -81,4 +81,29 @@ private:
 	std::set<YulString> m_names;
 };
 
+/**
+ * Collects all names from a given continue statement on onwards.
+ *
+ * It makes only sense to be invoked from within a body of an outer for loop, that is,
+ * it will only collect all names from the beginning of the first continue statement
+ * of the outer-most ForLoop.
+ */
+class AssignmentsSinceContinue: public ASTWalker
+{
+public:
+	using ASTWalker::operator();
+	void operator()(ForLoop const& _forLoop) override;
+	void operator()(Continue const&) override;
+	void operator()(Assignment const& _assignment) override;
+	void operator()(FunctionDefinition const& _funDef) override;
+
+	std::set<YulString> const& names() const { return m_names; }
+	bool empty() const noexcept { return m_names.empty(); }
+
+private:
+	size_t m_forLoopDepth = 0;
+	bool m_continueFound = false;
+	std::set<YulString> m_names;
+};
+
 }

test/libyul/yulOptimizerTests/rematerialiser/for_break.yul

@@ -0,0 +1,38 @@
+{
+	let a
+	let b
+	for {let i := 0} lt(i, 10) {i := add(a, b)} {
+		a := origin()
+		b := origin()
+		b := caller()
+		// a=origin, b=caller
+		if callvalue() { break }
+		// a=origin, b=caller
+		a := caller()
+	}
+	mstore(a, b)
+}
+// ----
+// rematerialiser
+// {
+//     let a
+//     let b
+//     for {
+//         let i := 0
+//     }
+//     lt(i, 10)
+//     {
+//         i := add(caller(), caller())
+//     }
+//     {
+//         a := origin()
+//         b := origin()
+//         b := caller()
+//         if callvalue()
+//         {
+//             break
+//         }
+//         a := caller()
+//     }
+//     mstore(a, b)
+// }

test/libyul/yulOptimizerTests/rematerialiser/for_continue.yul

@@ -0,0 +1,40 @@
+{
+	let a
+	let b
+	for { let i := 0 }
+		lt(i, 10)
+		{ i := add(a, b) } // `b` is always known to be caller() but `a` may be origin() or caller().
+	{
+		a := origin()
+		b := origin()
+
+		b := caller()
+		if callvalue() { continue }
+		a := caller()
+	}
+	mstore(a, b)
+}
+// ----
+// rematerialiser
+// {
+//     let a
+//     let b
+//     for {
+//         let i := 0
+//     }
+//     lt(i, 10)
+//     {
+//         i := add(a, caller())
+//     }
+//     {
+//         a := origin()
+//         b := origin()
+//         b := caller()
+//         if callvalue()
+//         {
+//             continue
+//         }
+//         a := caller()
+//     }
+//     mstore(a, b)
+// }

test/libyul/yulOptimizerTests/rematerialiser/for_continue_with_assignment_in_post.yul

@@ -0,0 +1,54 @@
+{
+	let a
+	let b
+	let c
+	for {
+		let i := 0
+		b := origin()
+		c := origin()
+	}
+	lt(i, 10)
+	{
+		i := add(a, b)
+		b := callvalue()
+		c := caller()
+	}
+	{
+		a := origin()
+
+		b := caller()
+		if callvalue() { continue }
+		a := caller()
+	}
+	let x := b // does not rematerialize as b may be either origin() or callvalue() (btw: not caller())
+	let y := c // does not rematerialize as c may be either origin() or caller()
+}
+// ----
+// rematerialiser
+// {
+//     let a
+//     let b
+//     let c
+//     for {
+//         let i := 0
+//         b := origin()
+//         c := origin()
+//     }
+//     lt(i, 10)
+//     {
+//         i := add(a, caller())
+//         b := callvalue()
+//         c := caller()
+//     }
+//     {
+//         a := origin()
+//         b := caller()
+//         if callvalue()
+//         {
+//             continue
+//         }
+//         a := caller()
+//     }
+//     let x := b
+//     let y := c
+// }