From a3a9630d8b0d9b6fb032f282af23771785fe5fd5 Mon Sep 17 00:00:00 2001
From: chriseth <chris@ethereum.org>
Date: Tue, 4 Aug 2020 11:25:09 +0200
Subject: [PATCH] Optimize byte-after-shr for shift amounts that are not
 multiples of 8.

---
 libevmasm/RuleList.h                                     | 4 +---
 test/formal/combine_byte_shr_2.py                        | 5 +----
 .../expressionSimplifier/byte_after_shr_non_mul_of_8.yul | 9 +++++++++
 3 files changed, 11 insertions(+), 7 deletions(-)
 create mode 100644 test/libyul/yulOptimizerTests/expressionSimplifier/byte_after_shr_non_mul_of_8.yul

diff --git a/libevmasm/RuleList.h b/libevmasm/RuleList.h
index 1e3fd7800..c2cf1eef3 100644
--- a/libevmasm/RuleList.h
+++ b/libevmasm/RuleList.h
@@ -583,9 +583,7 @@ std::vector<SimplificationRule<Pattern>> simplificationRuleListPart7(
 		Builtins::BYTE(A, Builtins::SHR(B, X)),
 		[=]() -> Pattern { return Word(0); },
 		true,
-		[=] {
-			return B.d() % 8 == 0 && A.d() < Pattern::WordSize / 8 && B.d() <= Pattern::WordSize && A.d() < B.d() / 8;
-		}
+		[=] { return A.d() < B.d() / 8; }
 	});
 
 	rules.push_back({
diff --git a/test/formal/combine_byte_shr_2.py b/test/formal/combine_byte_shr_2.py
index d74114e85..4f9be05a4 100644
--- a/test/formal/combine_byte_shr_2.py
+++ b/test/formal/combine_byte_shr_2.py
@@ -3,7 +3,7 @@ from opcodes import *
 
 """
 byte(A, shr(B, X))
-given B % 8 == 0 && A < n_bits/8 && B <= n_bits && A < B / 8
+given A < B / 8
 ->
 0
 """
@@ -22,9 +22,6 @@ nonopt = BYTE(A, SHR(B, X))
 # Optimized result
 opt = 0
 
-rule.require(B % 8 == 0)
-rule.require(ULT(A, n_bits/8))
-rule.require(ULE(B, n_bits))
 rule.require(ULT(A, DIV(B,8)))
 
 rule.check(nonopt, opt)
diff --git a/test/libyul/yulOptimizerTests/expressionSimplifier/byte_after_shr_non_mul_of_8.yul b/test/libyul/yulOptimizerTests/expressionSimplifier/byte_after_shr_non_mul_of_8.yul
new file mode 100644
index 000000000..e7c7bbf88
--- /dev/null
+++ b/test/libyul/yulOptimizerTests/expressionSimplifier/byte_after_shr_non_mul_of_8.yul
@@ -0,0 +1,9 @@
+{
+  sstore(0, byte(0, shr(0x9, calldataload(0))))
+}
+// ====
+// EVMVersion: >=constantinople
+// ----
+// step: expressionSimplifier
+//
+// { sstore(0, 0) }