Use rematerializer if variable is unreferenced or value is "cheap".

1 files changed, 12 insertions, 1 deletions

diff --git a/libyul/optimiser/Rematerialiser.h b/libyul/optimiser/Rematerialiser.h
index b3841519..c34353de 100644
--- a/libyul/optimiser/Rematerialiser.h
+++ b/libyul/optimiser/Rematerialiser.h
@@ -26,16 +26,27 @@ namespace yul
 {
 
 /**
- * Optimisation stage that replaces variables by their most recently assigned expressions.
+ * Optimisation stage that replaces variables by their most recently assigned expressions,
+ * but only if the expression is movable and one of the following holds:
+ *  - the variable is referenced exactly once
+ *  - the value is extremely cheap ("cost" of zero like ``caller()``)
+ *  - the variable is referenced at most 5 times and the value is rather cheap
+ *    ("cost" of at most 1 like a constant up to 0xff)
  *
  * Prerequisite: Disambiguator
  */
 class Rematerialiser: public DataFlowAnalyzer
 {
+public:
+	static void run(Block& _ast);
+
 protected:
+	Rematerialiser(Block& _ast);
+
 	using ASTModifier::visit;
 	void visit(Expression& _e) override;
 
+	std::map<YulString, size_t> m_referenceCounts;
 };
 
 }