From 04c8a7f0c6b74170d39d4210e9e7ea130f3fae3a Mon Sep 17 00:00:00 2001
From: chriseth <chris@ethereum.org>
Date: Wed, 9 Mar 2022 09:18:32 +0100
Subject: [PATCH] Less destructive switch processing.

---
 libyul/optimiser/DataFlowAnalyzer.cpp         |  9 ++++--
 .../fullSuite/loadrestest.yul                 | 28 +++++++++++++++++++
 2 files changed, 34 insertions(+), 3 deletions(-)
 create mode 100644 test/libyul/yulOptimizerTests/fullSuite/loadrestest.yul

diff --git a/libyul/optimiser/DataFlowAnalyzer.cpp b/libyul/optimiser/DataFlowAnalyzer.cpp
index af25cde59..19ba2822d 100644
--- a/libyul/optimiser/DataFlowAnalyzer.cpp
+++ b/libyul/optimiser/DataFlowAnalyzer.cpp
@@ -136,16 +136,18 @@ void DataFlowAnalyzer::operator()(Switch& _switch)
 		unordered_map<YulString, YulString> storage = m_storage;
 		unordered_map<YulString, YulString> memory = m_memory;
 		(*this)(_case.body);
+		//TODO throw away knowledge if it is terminating
 		joinKnowledge(storage, memory);
 
 		set<YulString> variables = assignedVariableNames(_case.body);
 		assignedVariables += variables;
 		// This is a little too destructive, we could retain the old values.
 		clearValues(variables);
-		clearKnowledgeIfInvalidated(_case.body);
+		//clearKnowledgeIfInvalidated(_case.body);
 	}
-	for (auto& _case: _switch.cases)
-		clearKnowledgeIfInvalidated(_case.body);
+	// TODO Handle special case where we have a default switch body?
+	//for (auto& _case: _switch.cases)
+//		clearKnowledgeIfInvalidated(_case.body);
 	clearValues(assignedVariables);
 }
 
@@ -341,6 +343,7 @@ void DataFlowAnalyzer::clearKnowledgeIfInvalidated(Block const& _block)
 
 void DataFlowAnalyzer::clearKnowledgeIfInvalidated(Expression const& _expr)
 {
+	// TODO with the extended side-effects, this could also be more precise now.
 	SideEffectsCollector sideEffects(m_dialect, _expr, &m_functionSideEffects);
 	if (sideEffects.invalidatesStorage())
 		m_storage.clear();
diff --git a/test/libyul/yulOptimizerTests/fullSuite/loadrestest.yul b/test/libyul/yulOptimizerTests/fullSuite/loadrestest.yul
new file mode 100644
index 000000000..8cd05ece3
--- /dev/null
+++ b/test/libyul/yulOptimizerTests/fullSuite/loadrestest.yul
@@ -0,0 +1,28 @@
+{
+    let _1 := memoryguard(0x80)
+    mstore(64, _1)
+    let _2 := 0
+    switch shr(224, calldataload(_2))
+    case 0x06661abd {
+        mstore(_1, sload(_2))
+        return(_1, 32)
+    }
+    case 0xc2985578 {
+        return(mload(64), _2)
+    }
+}
+// ----
+// step: fullSuite
+//
+// {
+//     {
+//         let _1 := memoryguard(0x80)
+//         mstore(64, _1)
+//         switch shr(224, calldataload(0))
+//         case 0x06661abd {
+//             mstore(_1, sload(0))
+//             return(_1, 32)
+//         }
+//         case 0xc2985578 { return(mload(64), 0) }
+//     }
+// }