Replace byte(A, X) by zero if A >= 32

Changelog.md

@@ -5,6 +5,7 @@ Language Features:
 
 
 Compiler Features:
+ * Optimizer: Add rule that replaces the BYTE opcode by 0 if the first argument is larger than 31.
 
 
 Bugfixes:

libevmasm/RuleList.h

@@ -259,6 +259,14 @@ std::vector<SimplificationRule<Pattern>> simplificationRuleListPart5(
 		[=]() { return A.d() >= 256; }
 	});
 
+	// Replace BYTE(A, X), A >= 32 with 0
+	rules.push_back({
+		{Instruction::BYTE, {A, X}},
+		[=]() -> Pattern { return u256(0); },
+		true,
+		[=]() { return A.d() >= 32; }
+	});
+
 	for (auto const& op: std::vector<Instruction>{
 		Instruction::ADDRESS,
 		Instruction::CALLER,

test/libyul/yulOptimizerTests/expressionSimplifier/large_byte_access.yul

@@ -0,0 +1,16 @@
+{
+    let a := calldataload(0)
+    let b := byte(33, a)
+    let c := byte(20, a)
+    // create cannot be removed.
+    let d := byte(33, create(0, 0, 0x20))
+}
+// ====
+// step: expressionSimplifier
+// ----
+// {
+//     let a := calldataload(0)
+//     let b := 0
+//     let c := byte(20, a)
+//     let d := byte(33, create(0, 0, 0x20))
+// }