From f95388011b287497c3983b9110b871ab8b366e47 Mon Sep 17 00:00:00 2001
From: Alex Beregszaszi <alex@rtfs.hu>
Date: Mon, 25 Feb 2019 11:31:35 +0000
Subject: [PATCH] Allow simplification patterns to signal failure

---
 libevmasm/ExpressionClasses.cpp          |  1 +
 libevmasm/SimplificationRule.h           | 13 +++++++++++++
 libevmasm/SimplificationRules.cpp        |  4 +++-
 libyul/optimiser/SimplificationRules.cpp |  3 ++-
 4 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/libevmasm/ExpressionClasses.cpp b/libevmasm/ExpressionClasses.cpp
index abbbbc2c5..db60d15bf 100644
--- a/libevmasm/ExpressionClasses.cpp
+++ b/libevmasm/ExpressionClasses.cpp
@@ -203,6 +203,7 @@ ExpressionClasses::Id ExpressionClasses::tryToSimplify(Expression const& _expr)
 		//cout << "with rule " << match->first.toString() << endl;
 		//ExpressionTemplate t(match->second());
 		//cout << "to " << match->second().toString() << endl;
+
 		return rebuildExpression(ExpressionTemplate(match->action(), _expr.item->location()));
 	}
 
diff --git a/libevmasm/SimplificationRule.h b/libevmasm/SimplificationRule.h
index 7b4dea687..fa1d50691 100644
--- a/libevmasm/SimplificationRule.h
+++ b/libevmasm/SimplificationRule.h
@@ -36,9 +36,22 @@ namespace solidity
 template <class Pattern>
 struct SimplificationRule
 {
+	SimplificationRule(
+		Pattern _pattern,
+		std::function<Pattern()> _action,
+		bool _removesNonConstants,
+		std::function<bool()> _feasible = {}
+	):
+		pattern(std::move(_pattern)),
+		action(std::move(_action)),
+		removesNonConstants(_removesNonConstants),
+		feasible(std::move(_feasible))
+	{}
+
 	Pattern pattern;
 	std::function<Pattern()> action;
 	bool removesNonConstants;
+	std::function<bool()> feasible;
 };
 
 }
diff --git a/libevmasm/SimplificationRules.cpp b/libevmasm/SimplificationRules.cpp
index b812cecc3..9fee79cf4 100644
--- a/libevmasm/SimplificationRules.cpp
+++ b/libevmasm/SimplificationRules.cpp
@@ -51,7 +51,9 @@ SimplificationRule<Pattern> const* Rules::findFirstMatch(
 	for (auto const& rule: m_rules[uint8_t(_expr.item->instruction())])
 	{
 		if (rule.pattern.matches(_expr, _classes))
-			return &rule;
+			if (!rule.feasible || rule.feasible())
+				return &rule;
+
 		resetMatchGroups();
 	}
 	return nullptr;
diff --git a/libyul/optimiser/SimplificationRules.cpp b/libyul/optimiser/SimplificationRules.cpp
index 1b620b641..c70ed2061 100644
--- a/libyul/optimiser/SimplificationRules.cpp
+++ b/libyul/optimiser/SimplificationRules.cpp
@@ -51,7 +51,8 @@ SimplificationRule<Pattern> const* SimplificationRules::findFirstMatch(
 	{
 		rules.resetMatchGroups();
 		if (rule.pattern.matches(_expr, _dialect, _ssaValues))
-			return &rule;
+			if (!rule.feasible || rule.feasible())
+				return &rule;
 	}
 	return nullptr;
 }