Update contrib/libs/snappy to 1.1.9

ref:8e094c2e0f44b866d354257c6a902b6d4394b8f0

1 files changed, 110 insertions, 24 deletions

diff --git a/contrib/libs/snappy/snappy-internal.h b/contrib/libs/snappy/snappy-internal.h
index 1e1c307fef..720ccd8282 100644
--- a/contrib/libs/snappy/snappy-internal.h
+++ b/contrib/libs/snappy/snappy-internal.h
@@ -46,16 +46,16 @@ class WorkingMemory {
   // Allocates and clears a hash table using memory in "*this",
   // stores the number of buckets in "*table_size" and returns a pointer to
   // the base of the hash table.
-  uint16* GetHashTable(size_t fragment_size, int* table_size) const;
+  uint16_t* GetHashTable(size_t fragment_size, int* table_size) const;
   char* GetScratchInput() const { return input_; }
   char* GetScratchOutput() const { return output_; }
 
  private:
-  char* mem_;      // the allocated memory, never nullptr
-  size_t size_;    // the size of the allocated memory, never 0
-  uint16* table_;  // the pointer to the hashtable
-  char* input_;    // the pointer to the input scratch buffer
-  char* output_;   // the pointer to the output scratch buffer
+  char* mem_;        // the allocated memory, never nullptr
+  size_t size_;      // the size of the allocated memory, never 0
+  uint16_t* table_;  // the pointer to the hashtable
+  char* input_;      // the pointer to the input scratch buffer
+  char* output_;     // the pointer to the output scratch buffer
 
   // No copying
   WorkingMemory(const WorkingMemory&);
@@ -76,7 +76,7 @@ class WorkingMemory {
 char* CompressFragment(const char* input,
                        size_t input_length,
                        char* op,
-                       uint16* table,
+                       uint16_t* table,
                        const int table_size);
 
 // Find the largest n such that
@@ -89,12 +89,18 @@ char* CompressFragment(const char* input,
 // Does not read *(s1 + (s2_limit - s2)) or beyond.
 // Requires that s2_limit >= s2.
 //
+// In addition populate *data with the next 5 bytes from the end of the match.
+// This is only done if 8 bytes are available (s2_limit - s2 >= 8). The point is
+// that on some arch's this can be done faster in this routine than subsequent
+// loading from s2 + n.
+//
 // Separate implementation for 64-bit, little-endian cpus.
 #if !defined(SNAPPY_IS_BIG_ENDIAN) && \
-    (defined(ARCH_K8) || defined(ARCH_PPC) || defined(ARCH_ARM))
+    (defined(__x86_64__) || defined(_M_X64) || defined(ARCH_PPC) || defined(ARCH_ARM))
 static inline std::pair<size_t, bool> FindMatchLength(const char* s1,
                                                       const char* s2,
-                                                      const char* s2_limit) {
+                                                      const char* s2_limit,
+                                                      uint64_t* data) {
   assert(s2_limit >= s2);
   size_t matched = 0;
 
@@ -103,12 +109,71 @@ static inline std::pair<size_t, bool> FindMatchLength(const char* s1,
   // uncommon code paths that determine, without extra effort, whether the match
   // length is less than 8.  In short, we are hoping to avoid a conditional
   // branch, and perhaps get better code layout from the C++ compiler.
-  if (SNAPPY_PREDICT_TRUE(s2 <= s2_limit - 8)) {
-    uint64 a1 = UNALIGNED_LOAD64(s1);
-    uint64 a2 = UNALIGNED_LOAD64(s2);
-    if (a1 != a2) {
-      return std::pair<size_t, bool>(Bits::FindLSBSetNonZero64(a1 ^ a2) >> 3,
-                                     true);
+  if (SNAPPY_PREDICT_TRUE(s2 <= s2_limit - 16)) {
+    uint64_t a1 = UNALIGNED_LOAD64(s1);
+    uint64_t a2 = UNALIGNED_LOAD64(s2);
+    if (SNAPPY_PREDICT_TRUE(a1 != a2)) {
+      // This code is critical for performance. The reason is that it determines
+      // how much to advance `ip` (s2). This obviously depends on both the loads
+      // from the `candidate` (s1) and `ip`. Furthermore the next `candidate`
+      // depends on the advanced `ip` calculated here through a load, hash and
+      // new candidate hash lookup (a lot of cycles). This makes s1 (ie.
+      // `candidate`) the variable that limits throughput. This is the reason we
+      // go through hoops to have this function update `data` for the next iter.
+      // The straightforward code would use *data, given by
+      //
+      // *data = UNALIGNED_LOAD64(s2 + matched_bytes) (Latency of 5 cycles),
+      //
+      // as input for the hash table lookup to find next candidate. However
+      // this forces the load on the data dependency chain of s1, because
+      // matched_bytes directly depends on s1. However matched_bytes is 0..7, so
+      // we can also calculate *data by
+      //
+      // *data = AlignRight(UNALIGNED_LOAD64(s2), UNALIGNED_LOAD64(s2 + 8),
+      //                    matched_bytes);
+      //
+      // The loads do not depend on s1 anymore and are thus off the bottleneck.
+      // The straightforward implementation on x86_64 would be to use
+      //
+      // shrd rax, rdx, cl  (cl being matched_bytes * 8)
+      //
+      // unfortunately shrd with a variable shift has a 4 cycle latency. So this
+      // only wins 1 cycle. The BMI2 shrx instruction is a 1 cycle variable
+      // shift instruction but can only shift 64 bits. If we focus on just
+      // obtaining the least significant 4 bytes, we can obtain this by
+      //
+      // *data = ConditionalMove(matched_bytes < 4, UNALIGNED_LOAD64(s2),
+      //     UNALIGNED_LOAD64(s2 + 4) >> ((matched_bytes & 3) * 8);
+      //
+      // Writen like above this is not a big win, the conditional move would be
+      // a cmp followed by a cmov (2 cycles) followed by a shift (1 cycle).
+      // However matched_bytes < 4 is equal to
+      // static_cast<uint32_t>(xorval) != 0. Writen that way, the conditional
+      // move (2 cycles) can execute in parallel with FindLSBSetNonZero64
+      // (tzcnt), which takes 3 cycles.
+      uint64_t xorval = a1 ^ a2;
+      int shift = Bits::FindLSBSetNonZero64(xorval);
+      size_t matched_bytes = shift >> 3;
+#ifndef __x86_64__
+      *data = UNALIGNED_LOAD64(s2 + matched_bytes);
+#else
+      // Ideally this would just be
+      //
+      // a2 = static_cast<uint32_t>(xorval) == 0 ? a3 : a2;
+      //
+      // However clang correctly infers that the above statement participates on
+      // a critical data dependency chain and thus, unfortunately, refuses to
+      // use a conditional move (it's tuned to cut data dependencies). In this
+      // case there is a longer parallel chain anyway AND this will be fairly
+      // unpredictable.
+      uint64_t a3 = UNALIGNED_LOAD64(s2 + 4);
+      asm("testl %k2, %k2\n\t"
+          "cmovzq %1, %0\n\t"
+          : "+r"(a2)
+          : "r"(a3), "r"(xorval));
+      *data = a2 >> (shift & (3 * 8));
+#endif
+      return std::pair<size_t, bool>(matched_bytes, true);
     } else {
       matched = 8;
       s2 += 8;
@@ -119,14 +184,27 @@ static inline std::pair<size_t, bool> FindMatchLength(const char* s1,
   // time until we find a 64-bit block that doesn't match; then we find
   // the first non-matching bit and use that to calculate the total
   // length of the match.
-  while (SNAPPY_PREDICT_TRUE(s2 <= s2_limit - 8)) {
-    if (UNALIGNED_LOAD64(s2) == UNALIGNED_LOAD64(s1 + matched)) {
+  while (SNAPPY_PREDICT_TRUE(s2 <= s2_limit - 16)) {
+    uint64_t a1 = UNALIGNED_LOAD64(s1 + matched);
+    uint64_t a2 = UNALIGNED_LOAD64(s2);
+    if (a1 == a2) {
       s2 += 8;
       matched += 8;
     } else {
-      uint64 x = UNALIGNED_LOAD64(s2) ^ UNALIGNED_LOAD64(s1 + matched);
-      int matching_bits = Bits::FindLSBSetNonZero64(x);
-      matched += matching_bits >> 3;
+      uint64_t xorval = a1 ^ a2;
+      int shift = Bits::FindLSBSetNonZero64(xorval);
+      size_t matched_bytes = shift >> 3;
+#ifndef __x86_64__
+      *data = UNALIGNED_LOAD64(s2 + matched_bytes);
+#else
+      uint64_t a3 = UNALIGNED_LOAD64(s2 + 4);
+      asm("testl %k2, %k2\n\t"
+          "cmovzq %1, %0\n\t"
+          : "+r"(a2)
+          : "r"(a3), "r"(xorval));
+      *data = a2 >> (shift & (3 * 8));
+#endif
+      matched += matched_bytes;
       assert(matched >= 8);
       return std::pair<size_t, bool>(matched, false);
     }
@@ -136,6 +214,9 @@ static inline std::pair<size_t, bool> FindMatchLength(const char* s1,
       ++s2;
       ++matched;
     } else {
+      if (s2 <= s2_limit - 8) {
+        *data = UNALIGNED_LOAD64(s2);
+      }
       return std::pair<size_t, bool>(matched, matched < 8);
     }
   }
@@ -144,7 +225,8 @@ static inline std::pair<size_t, bool> FindMatchLength(const char* s1,
 #else
 static inline std::pair<size_t, bool> FindMatchLength(const char* s1,
                                                       const char* s2,
-                                                      const char* s2_limit) {
+                                                      const char* s2_limit,
+                                                      uint64_t* data) {
   // Implementation based on the x86-64 version, above.
   assert(s2_limit >= s2);
   int matched = 0;
@@ -155,15 +237,17 @@ static inline std::pair<size_t, bool> FindMatchLength(const char* s1,
     matched += 4;
   }
   if (LittleEndian::IsLittleEndian() && s2 <= s2_limit - 4) {
-    uint32 x = UNALIGNED_LOAD32(s2) ^ UNALIGNED_LOAD32(s1 + matched);
+    uint32_t x = UNALIGNED_LOAD32(s2) ^ UNALIGNED_LOAD32(s1 + matched);
     int matching_bits = Bits::FindLSBSetNonZero(x);
     matched += matching_bits >> 3;
+    s2 += matching_bits >> 3;
   } else {
     while ((s2 < s2_limit) && (s1[matched] == *s2)) {
       ++s2;
       ++matched;
     }
   }
+  if (s2 <= s2_limit - 8) *data = LittleEndian::Load64(s2);
   return std::pair<size_t, bool>(matched, matched < 8);
 }
 #endif
@@ -190,7 +274,8 @@ static const int kMaximumTagLength = 5;  // COPY_4_BYTE_OFFSET plus the actual o
 // because of efficiency reasons:
 //      (1) Extracting a byte is faster than a bit-field
 //      (2) It properly aligns copy offset so we do not need a <<8
-static const uint16 char_table[256] = {
+static constexpr uint16_t char_table[256] = {
+    // clang-format off
   0x0001, 0x0804, 0x1001, 0x2001, 0x0002, 0x0805, 0x1002, 0x2002,
   0x0003, 0x0806, 0x1003, 0x2003, 0x0004, 0x0807, 0x1004, 0x2004,
   0x0005, 0x0808, 0x1005, 0x2005, 0x0006, 0x0809, 0x1006, 0x2006,
@@ -222,7 +307,8 @@ static const uint16 char_table[256] = {
   0x0039, 0x0f04, 0x1039, 0x2039, 0x003a, 0x0f05, 0x103a, 0x203a,
   0x003b, 0x0f06, 0x103b, 0x203b, 0x003c, 0x0f07, 0x103c, 0x203c,
   0x0801, 0x0f08, 0x103d, 0x203d, 0x1001, 0x0f09, 0x103e, 0x203e,
-  0x1801, 0x0f0a, 0x103f, 0x203f, 0x2001, 0x0f0b, 0x1040, 0x2040
+  0x1801, 0x0f0a, 0x103f, 0x203f, 0x2001, 0x0f0b, 0x1040, 0x2040,
+    // clang-format on
 };
 
 }  // end namespace internal