Fix expression simplifying by moving from SSAValueTracker to DataFlowAnalyzer as a base.

Changelog.md

@@ -25,6 +25,7 @@ Bugfixes:
  * TypeChecker: Fix internal error and disallow index access on contracts and libraries.
  * Yul: Properly detect name clashes with functions before their declaration.
  * Yul: Take builtin functions into account in the compilability checker.
+ * Yul Optimizer: Properly take reassignments to variables in sub-expressions into account when replacing in the ExpressionSimplifier.
 
 
 Build System:

libyul/optimiser/ExpressionSimplifier.cpp

@@ -36,7 +36,7 @@ using namespace dev::solidity;
 void ExpressionSimplifier::visit(Expression& _expression)
 {
 	ASTModifier::visit(_expression);
-	while (auto match = SimplificationRules::findFirstMatch(_expression, m_dialect, m_ssaValues))
+	while (auto match = SimplificationRules::findFirstMatch(_expression, m_dialect, m_value))
 	{
 		// Do not apply the rule if it removes non-constant parts of the expression.
 		// TODO: The check could actually be less strict than "movable".
@@ -53,7 +53,5 @@ void ExpressionSimplifier::visit(Expression& _expression)
 
 void ExpressionSimplifier::run(Dialect const& _dialect, Block& _ast)
 {
-	SSAValueTracker ssaValues;
+	ExpressionSimplifier{_dialect}(_ast);
-	ssaValues(_ast);
-	ExpressionSimplifier{_dialect, ssaValues.values()}(_ast);
 }

libyul/optimiser/ExpressionSimplifier.h

@@ -22,7 +22,7 @@
 
 #include <libyul/AsmDataForward.h>
 
-#include <libyul/optimiser/ASTWalker.h>
+#include <libyul/optimiser/DataFlowAnalyzer.h>
 
 namespace yul
 {
@@ -33,9 +33,12 @@ struct Dialect;
  * The component will work best if the code is in SSA form, but
  * this is not required for correctness.
  *
+ * It tracks the current values of variables using the DataFlowAnalyzer
+ * and takes them into account for replacements.
+ *
  * Prerequisite: Disambiguator.
  */
-class ExpressionSimplifier: public ASTModifier
+class ExpressionSimplifier: public DataFlowAnalyzer
 {
 public:
 	using ASTModifier::operator();
@@ -43,12 +46,7 @@ public:
 
 	static void run(Dialect const& _dialect, Block& _ast);
 private:
-	explicit ExpressionSimplifier(Dialect const& _dialect, std::map<YulString, Expression const*> _ssaValues):
+	explicit ExpressionSimplifier(Dialect const& _dialect): DataFlowAnalyzer(_dialect) {}
-		m_dialect(_dialect), m_ssaValues(std::move(_ssaValues))
-	{}
-
-	Dialect const& m_dialect;
-	std::map<YulString, Expression const*> m_ssaValues;
 };
 
 }

test/libyul/yulOptimizerTests/expressionSimplifier/reassign.yul

@@ -0,0 +1,12 @@
+{
+	let x := mload(0)
+	x := 0
+	mstore(0, add(7, x))
+}
+// ----
+// expressionSimplifier
+// {
+//     let x := mload(0)
+//     x := 0
+//     mstore(0, 7)
+// }

test/libyul/yulOptimizerTests/fullSuite/reuse_vars_bug_in_simplifier.yul

@@ -0,0 +1,16 @@
+{
+	// This tests that a bug is fixed that was related to just taking
+	// values of SSA variables in account and not clearing them when
+	// a dependency was reassigned.
+	pop(foo())
+	function foo() -> x_9
+	{
+		x_9 := sub(1,sub(x_9,1))
+		mstore(sub(1,div(sub(x_9,1),sub(1,sub(x_9,1)))), 1)
+	}
+}
+// ----
+// fullSuite
+// {
+//     mstore(1, 1)
+// }