Merge pull request #10683 from ethereum/optSubEq

Optimize iszero(sub(x, y)) to eq(x, y).

Changelog.md

@@ -4,6 +4,7 @@ Language Features:
  * Possibility to use ``catch Panic(uint code)`` to catch a panic failure from an external call.
 
 Compiler Features:
+ * Optimizer: Add rule to replace ``iszero(sub(x,y))`` by ``eq(x,y)``.
  * Parser: Report meaningful error if parsing a version pragma failed.
  * SMTChecker: Support ABI functions as uninterpreted functions.
  * SMTChecker: Use checked arithmetic by default and support ``unchecked`` blocks.

libevmasm/RuleList.h

@@ -365,6 +365,11 @@ std::vector<SimplificationRule<Pattern>> simplificationRuleListPart6(
 		[=]() -> Pattern { return Builtins::EQ(X, Y); }
 	});
 
+	rules.push_back({
+		Builtins::ISZERO(Builtins::SUB(X, Y)),
+		[=]() -> Pattern { return Builtins::EQ(X, Y); }
+	});
+
 	return rules;
 }
 

test/formal/eq_sub.py

@@ -0,0 +1,23 @@
+from rule import Rule
+from opcodes import *
+
+"""
+Rule:
+ISZERO(SUB(X, Y)) -> EQ(X, Y)
+"""
+
+rule = Rule()
+
+n_bits = 256
+
+# Input vars
+X = BitVec('X', n_bits)
+Y = BitVec('Y', n_bits)
+
+# Non optimized result
+nonopt = ISZERO(SUB(X, Y))
+
+# Optimized result
+opt = EQ(X, Y)
+
+rule.check(nonopt, opt)

test/libyul/yulOptimizerTests/expressionSimplifier/iszero_sub_to_eq.yul

@@ -0,0 +1,16 @@
+{
+    let a := calldataload(0)
+    let b := calldataload(0x20)
+    let x := sub(a, b)
+    if iszero(x) {
+        sstore(0, 1)
+    }
+}
+// ----
+// step: expressionSimplifier
+//
+// {
+//     let _1 := 0
+//     let a := calldataload(_1)
+//     if eq(a, calldataload(0x20)) { sstore(_1, 1) }
+// }