Add comments, fix typo

Change-Id: I2988cca3d11a89693ed79b0137b61bcf4c273dee
Reviewed-on: https://chrome-internal-review.googlesource.com/c/v8/fuzzilli/+/7977730
Reviewed-by: Carl Smith <cffsmith@google.com>
Commit-Queue: Eva Herencsárová <evih@google.com>

Author: evicy

Sources/Fuzzilli/FuzzIL/TypeSystem.swift

@@ -30,7 +30,7 @@
 // The following base types are defined:
 //     .undefined
 //     .integer
-//     .biging
+//     .bigint
 //     .float
 //     .boolean
 //     .string
@@ -473,7 +473,8 @@ public struct ILType: Hashable {
         let definiteType = self.definiteType.intersection(other.definiteType)
         let possibleType = self.possibleType.union(other.possibleType)
 
-        // Fast union case
+        // Fast union case.
+        // Identity comparison avoids comparing each property of the class.
         if self.ext === other.ext {
             return ILType(definiteType: definiteType, possibleType: possibleType, ext: self.ext)
         }
@@ -520,7 +521,8 @@ public struct ILType: Hashable {
         // "add back" the definite type to the possible type (which at this point would just be String).
         possibleType.formUnion(definiteType)
 
-        // Fast intersection case
+        // Fast intersection case.
+        // Identity comparison avoids comparing each property of the class.
         if self.ext === other.ext {
             return ILType(definiteType: definiteType, possibleType: possibleType, ext: self.ext)
         }

Tests/FuzzilliTests/TypeSystemTest.swift

@@ -1058,6 +1058,7 @@ class TypeSystemTests: XCTestCase {
     let primitiveTypes: [ILType] = [.undefined, .integer, .float, .string, .boolean, .bigint, .regexp]
 
     // A set of different types used by various tests.
+    // TODO(cffsmith): Test and adjust types with a WasmTypeExtension.
     let typeSuite: [ILType] = [.undefined,
                                .integer,
                                .float,