Merge pull request #6935 from ethereum/subMaxValueXNotXRule

Add optimization rule SUB(~0, X) -> NOT(X).

test/formal/sub_not_zero_x_to_not_x_256.py

@@ -0,0 +1,26 @@
+from rule import Rule
+from opcodes import *
+
+"""
+Rule:
+SUB(~0, X) -> NOT(X)
+Requirements:
+"""
+
+rule = Rule()
+
+n_bits = 256
+
+# Input vars
+X = BitVec('X', n_bits)
+
+# Constants
+ZERO = BitVecVal(0, n_bits)
+
+# Non optimized result
+nonopt = SUB(~ZERO, X)
+
+# Optimized result
+opt = NOT(X)
+
+rule.check(nonopt, opt)