Rewrite LLVM's generalized support library for hashing to follow the API

of the proposed standard hashing interfaces (N3333), and to use
a modified and tuned version of the CityHash algorithm.

Some of the highlights of this change:
 -- Significantly higher quality hashing algorithm with very well
    distributed results, and extremely few collisions. Should be close to
    a checksum for up to 64-bit keys. Very little clustering or clumping of
    hash codes, to better distribute load on probed hash tables.
 -- Built-in support for reserved values.
 -- Simplified API that composes cleanly with other C++ idioms and APIs.
 -- Better scaling performance as keys grow. This is the fastest
    algorithm I've found and measured for moderately sized keys (such as
    show up in some of the uniquing and folding use cases)
 -- Support for enabling per-execution seeds to prevent table ordering
    or other artifacts of hashing algorithms to impact the output of
    LLVM. The seeding would make each run different and highlight these
    problems during bootstrap.

This implementation was tested extensively using the SMHasher test
suite, and pased with flying colors, doing better than the original
CityHash algorithm even.

I've included a unittest, although it is somewhat minimal at the moment.
I've also added (or refactored into the proper location) type traits
necessary to implement this, and converted users of GeneralHash over.

My only immediate concerns with this implementation is the performance
of hashing small keys. I've already started working to improve this, and
will continue to do so. Currently, the only algorithms faster produce
lower quality results, but it is likely there is a better compromise
than the current one.

Many thanks to Jeffrey Yasskin who did most of the work on the N3333
paper, pair-programmed some of this code, and reviewed much of it. Many
thanks also go to Geoff Pike Pike and Jyrki Alakuijala, the original
authors of CityHash on which this is heavily based, and Austin Appleby
who created MurmurHash and the SMHasher test suite.

Also thanks to Nadav, Tobias, Howard, Jay, Nick, Ahmed, and Duncan for
all of the review comments! If there are further comments or concerns,
please let me know and I'll jump on 'em.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151822 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 286 insertions, 25 deletions

diff --git a/unittests/ADT/HashingTest.cpp b/unittests/ADT/HashingTest.cpp
index 18bfb722f4..1f4e4793fc 100644
--- a/unittests/ADT/HashingTest.cpp
+++ b/unittests/ADT/HashingTest.cpp
@@ -13,45 +13,306 @@
 
 #include "gtest/gtest.h"
 #include "llvm/ADT/Hashing.h"
+#include "llvm/Support/DataTypes.h"
+#include <deque>
+#include <list>
+#include <map>
+#include <vector>
+
+namespace llvm {
+
+// Helper for test code to print hash codes.
+void PrintTo(const hash_code &code, std::ostream *os) {
+  *os << static_cast<size_t>(code);
+}
+
+// Fake an object that is recognized as hashable data to test super large
+// objects.
+struct LargeTestInteger { uint64_t arr[8]; };
+
+namespace hashing {
+namespace detail {
+template <> struct is_hashable_data<LargeTestInteger> : true_type {};
+} // namespace detail
+} // namespace hashing
+
+} // namespace llvm
 
 using namespace llvm;
 
 namespace {
 
-TEST(HashingTest, EmptyHashTest) {
-  GeneralHash Hash;
-  ASSERT_EQ(0u, Hash.finish());
+TEST(HashingTest, HashValueBasicTest) {
+  int x = 42, y = 43, c = 'x';
+  void *p = 0;
+  uint64_t i = 71;
+  const unsigned ci = 71;
+  volatile int vi = 71;
+  const volatile int cvi = 71;
+  uintptr_t addr = reinterpret_cast<uintptr_t>(&y);
+  EXPECT_EQ(hash_value(42), hash_value(x));
+  EXPECT_NE(hash_value(42), hash_value(y));
+  EXPECT_NE(hash_value(42), hash_value(p));
+  EXPECT_NE(hash_code::get_null_code(), hash_value(p));
+  EXPECT_EQ(hash_value(71), hash_value(i));
+  EXPECT_EQ(hash_value(71), hash_value(ci));
+  EXPECT_EQ(hash_value(71), hash_value(vi));
+  EXPECT_EQ(hash_value(71), hash_value(cvi));
+  EXPECT_EQ(hash_value(c), hash_value('x'));
+  EXPECT_EQ(hash_value('4'), hash_value('0' + 4));
+  EXPECT_EQ(hash_value(addr), hash_value(&y));
 }
 
-TEST(HashingTest, IntegerHashTest) {
-  ASSERT_TRUE(GeneralHash().add(1).finish() == GeneralHash().add(1).finish());
-  ASSERT_TRUE(GeneralHash().add(1).finish() != GeneralHash().add(2).finish());
-}
+template <typename T, size_t N> T *begin(T (&arr)[N]) { return arr; }
+template <typename T, size_t N> T *end(T (&arr)[N]) { return arr + N; }
+
+// Provide a dummy, hashable type designed for easy verification: its hash is
+// the same as its value.
+struct HashableDummy { size_t value; };
+hash_code hash_value(HashableDummy dummy) { return dummy.value; }
+
+TEST(HashingTest, HashCombineRangeBasicTest) {
+  // Leave this uninitialized in the hope that valgrind will catch bad reads.
+  int dummy;
+  hash_code dummy_hash = hash_combine_range(&dummy, &dummy);
+  EXPECT_NE(hash_code::get_null_code(), dummy_hash);
+  EXPECT_NE(hash_code::get_invalid_code(), dummy_hash);
+
+  const int arr1[] = { 1, 2, 3 };
+  hash_code arr1_hash = hash_combine_range(begin(arr1), end(arr1));
+  EXPECT_NE(hash_code::get_null_code(), arr1_hash);
+  EXPECT_NE(hash_code::get_invalid_code(), arr1_hash);
+  EXPECT_NE(dummy_hash, arr1_hash);
+  EXPECT_EQ(arr1_hash, hash_combine_range(begin(arr1), end(arr1)));
 
-TEST(HashingTest, StringHashTest) {
-  ASSERT_TRUE(
-    GeneralHash().add("abc").finish() == GeneralHash().add("abc").finish());
-  ASSERT_TRUE(
-    GeneralHash().add("abc").finish() != GeneralHash().add("abcd").finish());
+  const std::vector<int> vec(begin(arr1), end(arr1));
+  EXPECT_EQ(arr1_hash, hash_combine_range(vec.begin(), vec.end()));
+
+  const std::list<int> list(begin(arr1), end(arr1));
+  EXPECT_EQ(arr1_hash, hash_combine_range(list.begin(), list.end()));
+
+  const std::deque<int> deque(begin(arr1), end(arr1));
+  EXPECT_EQ(arr1_hash, hash_combine_range(deque.begin(), deque.end()));
+
+  const int arr2[] = { 3, 2, 1 };
+  hash_code arr2_hash = hash_combine_range(begin(arr2), end(arr2));
+  EXPECT_NE(hash_code::get_null_code(), arr2_hash);
+  EXPECT_NE(hash_code::get_invalid_code(), arr2_hash);
+  EXPECT_NE(dummy_hash, arr2_hash);
+  EXPECT_NE(arr1_hash, arr2_hash);
+
+  const int arr3[] = { 1, 1, 2, 3 };
+  hash_code arr3_hash = hash_combine_range(begin(arr3), end(arr3));
+  EXPECT_NE(hash_code::get_null_code(), arr3_hash);
+  EXPECT_NE(hash_code::get_invalid_code(), arr3_hash);
+  EXPECT_NE(dummy_hash, arr3_hash);
+  EXPECT_NE(arr1_hash, arr3_hash);
+
+  const int arr4[] = { 1, 2, 3, 3 };
+  hash_code arr4_hash = hash_combine_range(begin(arr4), end(arr4));
+  EXPECT_NE(hash_code::get_null_code(), arr4_hash);
+  EXPECT_NE(hash_code::get_invalid_code(), arr4_hash);
+  EXPECT_NE(dummy_hash, arr4_hash);
+  EXPECT_NE(arr1_hash, arr4_hash);
+
+  const size_t arr5[] = { 1, 2, 3 };
+  const HashableDummy d_arr5[] = { {1}, {2}, {3} };
+  hash_code arr5_hash = hash_combine_range(begin(arr5), end(arr5));
+  hash_code d_arr5_hash = hash_combine_range(begin(d_arr5), end(d_arr5));
+  EXPECT_EQ(arr5_hash, d_arr5_hash);
 }
 
-TEST(HashingTest, FloatHashTest) {
-  ASSERT_TRUE(
-    GeneralHash().add(1.0f).finish() == GeneralHash().add(1.0f).finish());
-  ASSERT_TRUE(
-    GeneralHash().add(1.0f).finish() != GeneralHash().add(2.0f).finish());
+TEST(HashingTest, HashCombineRangeLengthDiff) {
+  // Test that as only the length varies, we compute different hash codes for
+  // sequences.
+  std::map<size_t, size_t> code_to_size;
+  std::vector<char> all_one_c(256, '\xff');
+  for (unsigned Idx = 1, Size = all_one_c.size(); Idx < Size; ++Idx) {
+    hash_code code = hash_combine_range(&all_one_c[0], &all_one_c[0] + Idx);
+    std::map<size_t, size_t>::iterator
+      I = code_to_size.insert(std::make_pair(code, Idx)).first;
+    EXPECT_EQ(Idx, I->second);
+  }
+  code_to_size.clear();
+  std::vector<char> all_zero_c(256, '\0');
+  for (unsigned Idx = 1, Size = all_zero_c.size(); Idx < Size; ++Idx) {
+    hash_code code = hash_combine_range(&all_zero_c[0], &all_zero_c[0] + Idx);
+    std::map<size_t, size_t>::iterator
+      I = code_to_size.insert(std::make_pair(code, Idx)).first;
+    EXPECT_EQ(Idx, I->second);
+  }
+  code_to_size.clear();
+  std::vector<unsigned> all_one_int(512, -1);
+  for (unsigned Idx = 1, Size = all_one_int.size(); Idx < Size; ++Idx) {
+    hash_code code = hash_combine_range(&all_one_int[0], &all_one_int[0] + Idx);
+    std::map<size_t, size_t>::iterator
+      I = code_to_size.insert(std::make_pair(code, Idx)).first;
+    EXPECT_EQ(Idx, I->second);
+  }
+  code_to_size.clear();
+  std::vector<unsigned> all_zero_int(512, 0);
+  for (unsigned Idx = 1, Size = all_zero_int.size(); Idx < Size; ++Idx) {
+    hash_code code = hash_combine_range(&all_zero_int[0], &all_zero_int[0] + Idx);
+    std::map<size_t, size_t>::iterator
+      I = code_to_size.insert(std::make_pair(code, Idx)).first;
+    EXPECT_EQ(Idx, I->second);
+  }
 }
 
-TEST(HashingTest, DoubleHashTest) {
-  ASSERT_TRUE(GeneralHash().add(1.).finish() == GeneralHash().add(1.).finish());
-  ASSERT_TRUE(GeneralHash().add(1.).finish() != GeneralHash().add(2.).finish());
+TEST(HashingTest, HashCombineRangeGoldenTest) {
+  struct { const char *s; uint64_t hash; } golden_data[] = {
+    { "a",                                0xaeb6f9d5517c61f8ULL },
+    { "ab",                               0x7ab1edb96be496b4ULL },
+    { "abc",                              0xe38e60bf19c71a3fULL },
+    { "abcde",                            0xd24461a66de97f6eULL },
+    { "abcdefgh",                         0x4ef872ec411dec9dULL },
+    { "abcdefghijklm",                    0xe8a865539f4eadfeULL },
+    { "abcdefghijklmnopqrstu",            0x261cdf85faaf4e79ULL },
+    { "abcdefghijklmnopqrstuvwxyzabcdef", 0x43ba70e4198e3b2aULL },
+    { "abcdefghijklmnopqrstuvwxyzabcdef"
+      "abcdefghijklmnopqrstuvwxyzghijkl"
+      "abcdefghijklmnopqrstuvwxyzmnopqr"
+      "abcdefghijklmnopqrstuvwxyzstuvwx"
+      "abcdefghijklmnopqrstuvwxyzyzabcd", 0xdcd57fb2afdf72beULL },
+    { "a",                                0xaeb6f9d5517c61f8ULL },
+    { "aa",                               0xf2b3b69a9736a1ebULL },
+    { "aaa",                              0xf752eb6f07b1cafeULL },
+    { "aaaaa",                            0x812bd21e1236954cULL },
+    { "aaaaaaaa",                         0xff07a2cff08ac587ULL },
+    { "aaaaaaaaaaaaa",                    0x84ac949d54d704ecULL },
+    { "aaaaaaaaaaaaaaaaaaaaa",            0xcb2c8fb6be8f5648ULL },
+    { "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", 0xcc40ab7f164091b6ULL },
+    { "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+      "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+      "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+      "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+      "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", 0xc58e174c1e78ffe9ULL },
+    { "z",                                0x1ba160d7e8f8785cULL },
+    { "zz",                               0x2c5c03172f1285d7ULL },
+    { "zzz",                              0x9d2c4f4b507a2ac3ULL },
+    { "zzzzz",                            0x0f03b9031735693aULL },
+    { "zzzzzzzz",                         0xe674147c8582c08eULL },
+    { "zzzzzzzzzzzzz",                    0x3162d9fa6938db83ULL },
+    { "zzzzzzzzzzzzzzzzzzzzz",            0x37b9a549e013620cULL },
+    { "zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz", 0x8921470aff885016ULL },
+    { "zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz"
+      "zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz"
+      "zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz"
+      "zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz"
+      "zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz", 0xf60fdcd9beb08441ULL },
+    { "a",                                0xaeb6f9d5517c61f8ULL },
+    { "ab",                               0x7ab1edb96be496b4ULL },
+    { "aba",                              0x3edb049950884d0aULL },
+    { "ababa",                            0x8f2de9e73a97714bULL },
+    { "abababab",                         0xee14a29ddf0ce54cULL },
+    { "ababababababa",                    0x38b3ddaada2d52b4ULL },
+    { "ababababababababababa",            0xd3665364219f2b85ULL },
+    { "abababababababababababababababab"
+      "abababababababababababababababab"
+      "abababababababababababababababab"
+      "abababababababababababababababab"
+      "abababababababababababababababab", 0x840192d129f7a22bULL }
+  };
+  for (unsigned i = 0; i < sizeof(golden_data)/sizeof(*golden_data); ++i) {
+    StringRef str = golden_data[i].s;
+    hash_code hash = hash_combine_range(str.begin(), str.end());
+#if 0 // Enable this to generate paste-able text for the above structure.
+    std::string member_str = "\"" + str.str() + "\",";
+    fprintf(stderr, " { %-35s 0x%016lxULL },\n",
+            member_str.c_str(), (size_t)hash);
+#endif
+    EXPECT_EQ(static_cast<size_t>(golden_data[i].hash),
+              static_cast<size_t>(hash));
+  }
 }
 
-TEST(HashingTest, IntegerArrayHashTest) {
-  int a[] = { 1, 2 };
-  int b[] = { 1, 3 };
-  ASSERT_TRUE(GeneralHash().add(a).finish() == GeneralHash().add(a).finish());
-  ASSERT_TRUE(GeneralHash().add(a).finish() != GeneralHash().add(b).finish());
+TEST(HashingTest, HashCombineBasicTest) {
+  // Hashing a sequence of homogenous types matches range hashing.
+  const int i1 = 42, i2 = 43, i3 = 123, i4 = 999, i5 = 0, i6 = 79;
+  const int arr1[] = { i1, i2, i3, i4, i5, i6 };
+  EXPECT_EQ(hash_combine_range(arr1, arr1 + 1), hash_combine(i1));
+  EXPECT_EQ(hash_combine_range(arr1, arr1 + 2), hash_combine(i1, i2));
+  EXPECT_EQ(hash_combine_range(arr1, arr1 + 3), hash_combine(i1, i2, i3));
+  EXPECT_EQ(hash_combine_range(arr1, arr1 + 4), hash_combine(i1, i2, i3, i4));
+  EXPECT_EQ(hash_combine_range(arr1, arr1 + 5),
+            hash_combine(i1, i2, i3, i4, i5));
+  EXPECT_EQ(hash_combine_range(arr1, arr1 + 6),
+            hash_combine(i1, i2, i3, i4, i5, i6));
+
+  // Hashing a sequence of heterogenous types which *happen* to all produce the
+  // same data for hashing produces the same as a range-based hash of the
+  // fundamental values.
+  const size_t s1 = 1024, s2 = 8888, s3 = 9000000;
+  const HashableDummy d1 = { 1024 }, d2 = { 8888 }, d3 = { 9000000 };
+  const size_t arr2[] = { s1, s2, s3 };
+  EXPECT_EQ(hash_combine_range(begin(arr2), end(arr2)),
+            hash_combine(s1, s2, s3));
+  EXPECT_EQ(hash_combine(s1, s2, s3), hash_combine(s1, s2, d3));
+  EXPECT_EQ(hash_combine(s1, s2, s3), hash_combine(s1, d2, s3));
+  EXPECT_EQ(hash_combine(s1, s2, s3), hash_combine(d1, s2, s3));
+  EXPECT_EQ(hash_combine(s1, s2, s3), hash_combine(d1, d2, s3));
+  EXPECT_EQ(hash_combine(s1, s2, s3), hash_combine(d1, d2, d3));
+
+  // Permuting values causes hashes to change.
+  EXPECT_NE(hash_combine(i1, i1, i1), hash_combine(i1, i1, i2));
+  EXPECT_NE(hash_combine(i1, i1, i1), hash_combine(i1, i2, i1));
+  EXPECT_NE(hash_combine(i1, i1, i1), hash_combine(i2, i1, i1));
+  EXPECT_NE(hash_combine(i1, i1, i1), hash_combine(i2, i2, i1));
+  EXPECT_NE(hash_combine(i1, i1, i1), hash_combine(i2, i2, i2));
+  EXPECT_NE(hash_combine(i2, i1, i1), hash_combine(i1, i1, i2));
+  EXPECT_NE(hash_combine(i1, i1, i2), hash_combine(i1, i2, i1));
+  EXPECT_NE(hash_combine(i1, i2, i1), hash_combine(i2, i1, i1));
+
+  // Changing type w/o changing value causes hashes to change.
+  EXPECT_NE(hash_combine(i1, i2, i3), hash_combine((char)i1, i2, i3));
+  EXPECT_NE(hash_combine(i1, i2, i3), hash_combine(i1, (char)i2, i3));
+  EXPECT_NE(hash_combine(i1, i2, i3), hash_combine(i1, i2, (char)i3));
+
+  // This is array of uint64, but it should have the exact same byte pattern as
+  // an array of LargeTestIntegers.
+  const uint64_t bigarr[] = {
+    0xaaaaaaaaababababULL, 0xacacacacbcbcbcbcULL, 0xccddeeffeeddccbbULL,
+    0xdeadbeafdeadbeefULL, 0xfefefefededededeULL, 0xafafafafededededULL,
+    0xffffeeeeddddccccULL, 0xaaaacbcbffffababULL,
+    0xaaaaaaaaababababULL, 0xacacacacbcbcbcbcULL, 0xccddeeffeeddccbbULL,
+    0xdeadbeafdeadbeefULL, 0xfefefefededededeULL, 0xafafafafededededULL,
+    0xffffeeeeddddccccULL, 0xaaaacbcbffffababULL,
+    0xaaaaaaaaababababULL, 0xacacacacbcbcbcbcULL, 0xccddeeffeeddccbbULL,
+    0xdeadbeafdeadbeefULL, 0xfefefefededededeULL, 0xafafafafededededULL,
+    0xffffeeeeddddccccULL, 0xaaaacbcbffffababULL
+  };
+  // Hash a preposterously large integer, both aligned with the buffer and
+  // misaligned.
+  const LargeTestInteger li = { {
+    0xaaaaaaaaababababULL, 0xacacacacbcbcbcbcULL, 0xccddeeffeeddccbbULL,
+    0xdeadbeafdeadbeefULL, 0xfefefefededededeULL, 0xafafafafededededULL,
+    0xffffeeeeddddccccULL, 0xaaaacbcbffffababULL
+  } };
+  // Rotate the storage from 'li'.
+  const LargeTestInteger l2 = { {
+    0xacacacacbcbcbcbcULL, 0xccddeeffeeddccbbULL, 0xdeadbeafdeadbeefULL,
+    0xfefefefededededeULL, 0xafafafafededededULL, 0xffffeeeeddddccccULL,
+    0xaaaacbcbffffababULL, 0xaaaaaaaaababababULL
+  } };
+  const LargeTestInteger l3 = { {
+    0xccddeeffeeddccbbULL, 0xdeadbeafdeadbeefULL, 0xfefefefededededeULL,
+    0xafafafafededededULL, 0xffffeeeeddddccccULL, 0xaaaacbcbffffababULL,
+    0xaaaaaaaaababababULL, 0xacacacacbcbcbcbcULL
+  } };
+  EXPECT_EQ(hash_combine_range(begin(bigarr), end(bigarr)),
+            hash_combine(li, li, li));
+  EXPECT_EQ(hash_combine_range(bigarr, bigarr + 9),
+            hash_combine(bigarr[0], l2));
+  EXPECT_EQ(hash_combine_range(bigarr, bigarr + 10),
+            hash_combine(bigarr[0], bigarr[1], l3));
+  EXPECT_EQ(hash_combine_range(bigarr, bigarr + 17),
+            hash_combine(li, bigarr[0], l2));
+  EXPECT_EQ(hash_combine_range(bigarr, bigarr + 18),
+            hash_combine(li, bigarr[0], bigarr[1], l3));
+  EXPECT_EQ(hash_combine_range(bigarr, bigarr + 18),
+            hash_combine(bigarr[0], l2, bigarr[9], l3));
+  EXPECT_EQ(hash_combine_range(bigarr, bigarr + 20),
+            hash_combine(bigarr[0], l2, bigarr[9], l3, bigarr[18], bigarr[19]));
 }
 
 }