From 8a4497a8d32355e29f7008db25b4f0e0ae4f1235 Mon Sep 17 00:00:00 2001
From: Daniel Kirchner <daniel@ekpyron.org>
Date: Thu, 15 Apr 2021 15:13:31 +0200
Subject: [PATCH] Fix argument stack slot reuse for functions without return
 variables.

---
 libyul/backends/evm/EVMCodeTransform.cpp      |  6 ++--
 libyul/backends/evm/EVMCodeTransform.h        |  4 +++
 ...ction_argument_reuse_without_retparams.yul | 29 +++++++++++++++++++
 3 files changed, 37 insertions(+), 2 deletions(-)
 create mode 100644 test/libyul/evmCodeTransform/stackReuse/function_argument_reuse_without_retparams.yul

diff --git a/libyul/backends/evm/EVMCodeTransform.cpp b/libyul/backends/evm/EVMCodeTransform.cpp
index 8c8efe46d..ba4eb5135 100644
--- a/libyul/backends/evm/EVMCodeTransform.cpp
+++ b/libyul/backends/evm/EVMCodeTransform.cpp
@@ -402,7 +402,7 @@ void CodeTransform::operator()(FunctionDefinition const& _function)
 				subTransform.deleteVariable(var);
 		}
 
-	if (!m_allowStackOpt || _function.returnVariables.empty())
+	if (!m_allowStackOpt)
 		subTransform.setupReturnVariablesAndFunctionExit();
 
 	subTransform(_function.body);
@@ -592,6 +592,7 @@ void CodeTransform::visitExpression(Expression const& _expression)
 
 void CodeTransform::setupReturnVariablesAndFunctionExit()
 {
+	yulAssert(isInsideFunction(), "");
 	yulAssert(!returnVariablesAndFunctionExitAreSetup(), "");
 	yulAssert(m_scope, "");
 
@@ -654,7 +655,8 @@ void CodeTransform::visitStatements(vector<Statement> const& _statements)
 	{
 		freeUnusedVariables();
 		if (
-			!m_delayedReturnVariables.empty() &&
+			isInsideFunction() &&
+			!returnVariablesAndFunctionExitAreSetup() &&
 			statementNeedsReturnVariableSetup(statement, m_delayedReturnVariables)
 		)
 			setupReturnVariablesAndFunctionExit();
diff --git a/libyul/backends/evm/EVMCodeTransform.h b/libyul/backends/evm/EVMCodeTransform.h
index be7fef528..bf4f8520d 100644
--- a/libyul/backends/evm/EVMCodeTransform.h
+++ b/libyul/backends/evm/EVMCodeTransform.h
@@ -183,6 +183,10 @@ private:
 	{
 		return m_functionExitStackHeight.has_value();
 	}
+	bool isInsideFunction() const
+	{
+		return m_functionExitLabel.has_value();
+	}
 
 	AbstractAssembly& m_assembly;
 	AsmAnalysisInfo& m_info;
diff --git a/test/libyul/evmCodeTransform/stackReuse/function_argument_reuse_without_retparams.yul b/test/libyul/evmCodeTransform/stackReuse/function_argument_reuse_without_retparams.yul
new file mode 100644
index 000000000..d1f6b5bdc
--- /dev/null
+++ b/test/libyul/evmCodeTransform/stackReuse/function_argument_reuse_without_retparams.yul
@@ -0,0 +1,29 @@
+{
+  function f(x, y) {
+    mstore(0x80, x)
+    if calldataload(0) { sstore(y, y) }
+  }
+}
+// ====
+// stackOptimization: true
+// ----
+// PUSH1 0x17
+// JUMP
+// JUMPDEST
+// DUP1
+// PUSH1 0x80
+// MSTORE
+// POP
+// PUSH1 0x0
+// CALLDATALOAD
+// ISZERO
+// PUSH1 0x13
+// JUMPI
+// DUP1
+// DUP2
+// SSTORE
+// JUMPDEST
+// POP
+// JUMPDEST
+// JUMP
+// JUMPDEST