From 6d15c229fa03cda85b9db90d2ef2cbd8ac7d4143 Mon Sep 17 00:00:00 2001
From: Daniel Kirchner <daniel@ekpyron.org>
Date: Tue, 13 Apr 2021 12:26:13 +0200
Subject: [PATCH] Support multi-variable-declarations without value.

---
 libyul/optimiser/StackToMemoryMover.cpp       | 16 +++++++++-----
 ...lti_variable_declaration_without_value.yul | 21 +++++++++++++++++++
 2 files changed, 32 insertions(+), 5 deletions(-)
 create mode 100644 test/libyul/yulOptimizerTests/fakeStackLimitEvader/multi_variable_declaration_without_value.yul

diff --git a/libyul/optimiser/StackToMemoryMover.cpp b/libyul/optimiser/StackToMemoryMover.cpp
index 04b3cd0e4..7c859bfba 100644
--- a/libyul/optimiser/StackToMemoryMover.cpp
+++ b/libyul/optimiser/StackToMemoryMover.cpp
@@ -213,11 +213,17 @@ void StackToMemoryMover::operator()(Block& _block)
 			else
 				return {};
 		}
-		FunctionCall const* functionCall = get_if<FunctionCall>(_stmt.value.get());
-		yulAssert(functionCall, "");
-		auto rhsMemorySlots = m_functionReturnVariables.at(functionCall->functionName.name) |
-			ranges::views::transform(m_memoryOffsetTracker) |
-			ranges::to<vector<optional<YulString>>>;
+		vector<optional<YulString>> rhsMemorySlots;
+		if (_stmt.value)
+		{
+			FunctionCall const* functionCall = get_if<FunctionCall>(_stmt.value.get());
+			yulAssert(functionCall, "");
+			rhsMemorySlots = m_functionReturnVariables.at(functionCall->functionName.name) |
+				ranges::views::transform(m_memoryOffsetTracker) |
+				ranges::to<vector<optional<YulString>>>;
+		}
+		else
+			rhsMemorySlots = vector<optional<YulString>>(_lhsVars.size(), nullopt);
 
 		// Nothing to do, if the right-hand-side remains entirely on the stack and
 		// none of the variables in the left-hand-side are moved.
diff --git a/test/libyul/yulOptimizerTests/fakeStackLimitEvader/multi_variable_declaration_without_value.yul b/test/libyul/yulOptimizerTests/fakeStackLimitEvader/multi_variable_declaration_without_value.yul
new file mode 100644
index 000000000..5650b580d
--- /dev/null
+++ b/test/libyul/yulOptimizerTests/fakeStackLimitEvader/multi_variable_declaration_without_value.yul
@@ -0,0 +1,21 @@
+{
+  mstore(0x40, memoryguard(0x60))
+  {
+    let x, y
+  }
+  {
+    let z, $w
+  }
+}
+// ----
+// step: fakeStackLimitEvader
+//
+// {
+//     mstore(0x40, memoryguard(0x80))
+//     { let x, y }
+//     {
+//         let z_1, $w_2
+//         mstore(0x60, $w_2)
+//         let z := z_1
+//     }
+// }