From d3abbd5610824ad82337d9926655da02d45063ea Mon Sep 17 00:00:00 2001
From: chriseth <chris@ethereum.org>
Date: Wed, 8 Jul 2020 20:13:11 +0200
Subject: [PATCH] Remove unneccessary masking of tags.

---
 Changelog.md                    |  1 +
 libevmasm/PeepholeOptimiser.cpp | 13 ++++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/Changelog.md b/Changelog.md
index 9795ecb51..ca81e04d8 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -2,6 +2,7 @@
 
 Compiler Features:
  * Code Generator: Evaluate ``keccak256`` of string literals at compile-time.
+ * Peephole Optimizer: Remove unnecessary masking of tags.
 
 Bugfixes:
  * Type Checker: Fix overload resolution in combination with ``{value: ...}``.
diff --git a/libevmasm/PeepholeOptimiser.cpp b/libevmasm/PeepholeOptimiser.cpp
index 861cae0f2..dd5f9399c 100644
--- a/libevmasm/PeepholeOptimiser.cpp
+++ b/libevmasm/PeepholeOptimiser.cpp
@@ -266,9 +266,10 @@ struct TagConjunctions: SimplePeepholeOptimizerMethod<TagConjunctions, 3>
 		std::back_insert_iterator<AssemblyItems> _out
 	)
 	{
+		if (_and != Instruction::AND)
+			return false;
 		if (
 			_pushTag.type() == PushTag &&
-			_and == Instruction::AND &&
 			_pushConstant.type() == Push &&
 			(_pushConstant.data() & u256(0xFFFFFFFF)) == u256(0xFFFFFFFF)
 		)
@@ -276,6 +277,16 @@ struct TagConjunctions: SimplePeepholeOptimizerMethod<TagConjunctions, 3>
 			*_out = _pushTag;
 			return true;
 		}
+		else if (
+			// tag and constant are swapped
+			_pushConstant.type() == PushTag &&
+			_pushTag.type() == Push &&
+			(_pushTag.data() & u256(0xFFFFFFFF)) == u256(0xFFFFFFFF)
+		)
+		{
+			*_out = _pushConstant;
+			return true;
+		}
 		else
 			return false;
 	}