[benchmark] Add DictionaryOfObjects benchmark

This tests performance of dictionary when both key and value are objects.

(We have fast paths otherwise because we know that the dictionary cannot be
backed by an objective c dictionary)

benchmark/single-source/DictTest.swift

@@ -145,3 +145,156 @@ public func run_Dictionary(scale: Int) {
   CheckResults(count == N*541,
                "IncorrectResults in DictTest: \(count) != \(N*541).")
 }
+
+class Box<T : Hashable where T : Equatable> : Hashable {
+  var value: T
+
+  init(_ v: T) {
+    value = v
+  }
+
+  var hashValue : Int {
+    return value.hashValue
+  }
+}
+
+extension Box : Equatable {
+}
+
+func ==<T: Equatable>(lhs: Box<T>,  rhs: Box<T>) -> Bool {
+  return lhs.value == rhs.value
+}
+
+@inline(never)
+public func run_DictionaryOfObjects(scale: Int) {
+  let Input = [
+    // Text from http://en.wikipedia.org/wiki/Hash_table
+    "hash", "table",
+      "in", "computing", "a", "hash", "table", "also", "hash", "map", "is",
+      "a", "data", "structure", "used", "to", "implement", "an", "associative",
+      "array", "a", "structure", "that", "can", "map", "keys", "to", "values",
+      "a", "hash", "table", "uses", "a", "hash", "function", "to", "compute",
+      "an", "index", "into", "an", "array", "of", "buckets", "or", "slots",
+      "from", "which", "the", "correct", "value", "can", "be", "found",
+      "ideally", "the", "hash", "function", "will", "assign", "each", "key",
+      "to", "a", "unique", "bucket", "but", "this", "situation", "is",
+      "rarely", "achievable", "in", "practice", "usually", "some", "keys",
+      "will", "hash", "to", "the", "same", "bucket", "instead", "most", "hash",
+      "table", "designs", "assume", "that", "hash", "collisions", "different",
+      "keys", "that", "are", "assigned", "by", "the", "hash", "function", "to",
+      "the", "same", "bucket", "will", "occur", "and", "must", "be",
+      "accommodated", "in", "some", "way", "in", "a", "well", "dimensioned",
+      "hash", "table", "the", "average", "cost", "number", "of",
+      "instructions", "for", "each", "lookup", "is", "independent", "of",
+      "the", "number", "of", "elements", "stored", "in", "the", "table",
+      "many", "hash", "table", "designs", "also", "allow", "arbitrary",
+      "insertions", "and", "deletions", "of", "key", "value", "pairs", "at",
+      "amortized", "constant", "average", "cost", "per", "operation", "in",
+      "many", "situations", "hash", "tables", "turn", "out", "to", "be",
+      "more", "efficient", "than", "search", "trees", "or", "any", "other",
+      "table", "lookup", "structure", "for", "this", "reason", "they", "are",
+      "widely", "used", "in", "many", "kinds", "of", "computer", "software",
+      "particularly", "for", "associative", "arrays", "database", "indexing",
+      "caches", "and", "sets",
+
+    "hashing",
+      "the", "idea", "of", "hashing", "is", "to", "distribute", "the",
+      "entries", "key", "value", "pairs", "across", "an", "array", "of",
+      "buckets", "given", "a", "key", "the", "algorithm", "computes", "an",
+      "index", "that", "suggests", "where", "the", "entry", "can", "be",
+      "found", "index", "f", "key", "array", "size", "often", "this", "is",
+      "done", "in", "two", "steps", "hash", "hashfunc", "key", "index", "hash",
+      "array", "size", "in", "this", "method", "the", "hash", "is",
+      "independent", "of", "the", "array", "size", "and", "it", "is", "then",
+      "reduced", "to", "an", "index", "a", "number", "between", "and", "array",
+      "size", "using", "the", "modulus", "operator", "in", "the", "case",
+      "that", "the", "array", "size", "is", "a", "power", "of", "two", "the",
+      "remainder", "operation", "is", "reduced", "to", "masking", "which",
+      "improves", "speed", "but", "can", "increase", "problems", "with", "a",
+      "poor", "hash", "function",
+
+    "choosing", "a", "good", "hash", "function",
+      "a", "good", "hash", "function", "and", "implementation", "algorithm",
+      "are", "essential", "for", "good", "hash", "table", "performance", "but",
+      "may", "be", "difficult", "to", "achieve", "a", "basic", "requirement",
+      "is", "that", "the", "function", "should", "provide", "a", "uniform",
+      "distribution", "of", "hash", "values", "a", "non", "uniform",
+      "distribution", "increases", "the", "number", "of", "collisions", "and",
+      "the", "cost", "of", "resolving", "them", "uniformity", "is",
+      "sometimes", "difficult", "to", "ensure", "by", "design", "but", "may",
+      "be", "evaluated", "empirically", "using", "statistical", "tests", "e",
+      "g", "a", "pearson", "s", "chi", "squared", "test", "for", "discrete",
+      "uniform", "distributions", "the", "distribution", "needs", "to", "be",
+      "uniform", "only", "for", "table", "sizes", "that", "occur", "in", "the",
+      "application", "in", "particular", "if", "one", "uses", "dynamic",
+      "resizing", "with", "exact", "doubling", "and", "halving", "of", "the",
+      "table", "size", "s", "then", "the", "hash", "function", "needs", "to",
+      "be", "uniform", "only", "when", "s", "is", "a", "power", "of", "two",
+      "on", "the", "other", "hand", "some", "hashing", "algorithms", "provide",
+      "uniform", "hashes", "only", "when", "s", "is", "a", "prime", "number",
+      "for", "open", "addressing", "schemes", "the", "hash", "function",
+      "should", "also", "avoid", "clustering", "the", "mapping", "of", "two",
+      "or", "more", "keys", "to", "consecutive", "slots", "such", "clustering",
+      "may", "cause", "the", "lookup", "cost", "to", "skyrocket", "even", "if",
+      "the", "load", "factor", "is", "low", "and", "collisions", "are",
+      "infrequent", "the", "popular", "multiplicative", "hash", "3", "is",
+      "claimed", "to", "have", "particularly", "poor", "clustering",
+      "behavior", "cryptographic", "hash", "functions", "are", "believed",
+      "to", "provide", "good", "hash", "functions", "for", "any", "table",
+      "size", "s", "either", "by", "modulo", "reduction", "or", "by", "bit",
+      "masking", "they", "may", "also", "be", "appropriate", "if", "there",
+      "is", "a", "risk", "of", "malicious", "users", "trying", "to",
+      "sabotage", "a", "network", "service", "by", "submitting", "requests",
+      "designed", "to", "generate", "a", "large", "number", "of", "collisions",
+      "in", "the", "server", "s", "hash", "tables", "however", "the", "risk",
+      "of", "sabotage", "can", "also", "be", "avoided", "by", "cheaper",
+      "methods", "such", "as", "applying", "a", "secret", "salt", "to", "the",
+      "data", "or", "using", "a", "universal", "hash", "function",
+
+    "perfect", "hash", "function",
+      "if", "all", "keys", "are", "known", "ahead", "of", "time", "a",
+      "perfect", "hash", "function", "can", "be", "used", "to", "create", "a",
+      "perfect", "hash", "table", "that", "has", "no", "collisions", "if",
+      "minimal", "perfect", "hashing", "is", "used", "every", "location", "in",
+      "the", "hash", "table", "can", "be", "used", "as", "well", "perfect",
+      "hashing", "allows", "for", "constant", "time", "lookups", "in", "the",
+      "worst", "case", "this", "is", "in", "contrast", "to", "most",
+      "chaining", "and", "open", "addressing", "methods", "where", "the",
+      "time", "for", "lookup", "is", "low", "on", "average", "but", "may",
+      "be", "very", "large", "proportional", "to", "the", "number", "of",
+      "entries", "for", "some", "sets", "of", "keys"
+  ]
+
+  var Dict: Dictionary<Box<String>, Box<Bool>> = [:]
+  let N = 5*scale
+
+  // Check performance of filling the dictionary:
+  for _ in 1...N {
+    Dict = [:]
+    for word in Input {
+      Dict[Box(word)] = Box(true);
+    }
+  }
+  CheckResults(Dict.count == 270,
+               "IncorrectResults in DictTest: \(Dict.count) != 270.")
+
+  // Check performance of searching in the dictionary:
+  // Fill the dictionary with words from the first half of the text
+  Dict = [:]
+  for i in 0 ..< Input.count/2 {
+    let word = Input[i]
+    Dict[Box(word)] = Box(true)
+  }
+
+  // Count number of words from the first half in the entire text
+  var count = 0
+  for _ in 1...N {
+    for word in Input {
+      if Dict[Box(word)] != nil {
+        count += 1
+      }
+    }
+  }
+  CheckResults(count == N*541,
+               "IncorrectResults in DictTestAllObjects: \(count) != \(N*541).")
+}