Move prefetch() out of TT

This code is platform specific and has nothing to
do with TT class, so move to misc.cpp

This patch is a prerequisite to use extend prefetch use
also to other hash tables apart from Transposition Table.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/misc.cpp

@@ -39,6 +39,10 @@
 
 #endif
 
+#if !defined(NO_PREFETCH)
+#  include <xmmintrin.h>
+#endif
+
 #include <cassert>
 #include <cstdio>
 #include <iomanip>
@@ -287,4 +291,26 @@ int Bioskey()
         return 0;
     }
 }
+
+/// prefetch() preloads the given address in L1/L2 cache. This is a non
+/// blocking function and do not stalls the CPU waiting for data to be
+/// loaded from RAM, that can be very slow.
+#if defined(NO_PREFETCH)
+void prefetch(char*) {}
+#else
+
+void prefetch(char* addr) {
+
+#if defined(__INTEL_COMPILER) || defined(__ICL)
+   // This hack prevents prefetches to be optimized away by
+   // Intel compiler. Both MSVC and gcc seems not affected.
+   __asm__ ("");
+#endif
+
+  _mm_prefetch(addr, _MM_HINT_T2);
+  _mm_prefetch(addr+64, _MM_HINT_T2); // 64 bytes ahead
+}
+
+#endif
+
 #endif

src/misc.h

@@ -55,6 +55,7 @@ extern const std::string engine_name();
 extern int get_system_time();
 extern int cpu_count();
 extern int Bioskey();
+extern void prefetch(char* addr);
 
 
 ////

src/position.cpp

@@ -772,7 +772,7 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
   }
 
   // Prefetch TT access as soon as we know key is updated
-  TT.prefetch(key);
+  prefetch((char*)TT.first_entry(key));
 
   // Move the piece
   Bitboard move_bb = make_move_bb(from, to);
@@ -1250,7 +1250,7 @@ void Position::do_null_move(StateInfo& backupSt) {
       st->key ^= zobEp[st->epSquare];
 
   st->key ^= zobSideToMove;
-  TT.prefetch(st->key);
+  prefetch((char*)TT.first_entry(st->key));
 
   sideToMove = opposite_color(sideToMove);
   st->epSquare = SQ_NONE;

src/tt.cpp

@@ -25,9 +25,6 @@
 #include <cassert>
 #include <cmath>
 #include <cstring>
-#if !defined(NO_PREFETCH)
-#  include <xmmintrin.h>
-#endif
 
 #include "movegen.h"
 #include "tt.h"
@@ -91,16 +88,6 @@ void TranspositionTable::clear() {
 }
 
 
-/// TranspositionTable::first_entry returns a pointer to the first
-/// entry of a cluster given a position. The low 32 bits of the key
-/// are used to get the index in the table.
-
-inline TTEntry* TranspositionTable::first_entry(const Key posKey) const {
-
-  return entries[uint32_t(posKey) & (size - 1)].data;
-}
-
-
 /// TranspositionTable::store writes a new entry containing a position,
 /// a value, a value type, a search depth, and a best move to the
 /// transposition table. Transposition table is organized in clusters of
@@ -160,31 +147,6 @@ TTEntry* TranspositionTable::retrieve(const Key posKey) const {
 }
 
 
-/// TranspositionTable::prefetch looks up the current position in the
-/// transposition table and load it in L1/L2 cache. This is a non
-/// blocking function and do not stalls the CPU waiting for data
-/// to be loaded from RAM, that can be very slow. When we will
-/// subsequently call retrieve() the TT data will be already
-/// quickly accessible in L1/L2 CPU cache.
-#if defined(NO_PREFETCH)
-void TranspositionTable::prefetch(const Key) const {}
-#else
-
-void TranspositionTable::prefetch(const Key posKey) const {
-
-#if defined(__INTEL_COMPILER) || defined(__ICL)
-   // This hack prevents prefetches to be optimized away by
-   // Intel compiler. Both MSVC and gcc seems not affected.
-   __asm__ ("");
-#endif
-
-   char const* addr = (char*)first_entry(posKey);
-  _mm_prefetch(addr, _MM_HINT_T2);
-  _mm_prefetch(addr+64, _MM_HINT_T2); // 64 bytes ahead
-}
-
-#endif
-
 /// TranspositionTable::new_search() is called at the beginning of every new
 /// search. It increments the "generation" variable, which is used to
 /// distinguish transposition table entries from previous searches from

src/tt.h

@@ -108,15 +108,13 @@ public:
   void clear();
   void store(const Key posKey, Value v, ValueType type, Depth d, Move m, Value statV, Value kingD);
   TTEntry* retrieve(const Key posKey) const;
-  void prefetch(const Key posKey) const;
   void new_search();
   void insert_pv(const Position& pos, Move pv[]);
   void extract_pv(const Position& pos, Move pv[], const int PLY_MAX);
   int full() const;
+  TTEntry* first_entry(const Key posKey) const;
 
 private:
-  inline TTEntry* first_entry(const Key posKey) const;
-
   // Be sure 'writes' is at least one cache line away
   // from read only variables.
   unsigned char pad_before[64 - sizeof(unsigned)];
@@ -130,4 +128,14 @@ private:
 
 extern TranspositionTable TT;
 
+
+/// TranspositionTable::first_entry returns a pointer to the first
+/// entry of a cluster given a position. The low 32 bits of the key
+/// are used to get the index in the table.
+
+inline TTEntry* TranspositionTable::first_entry(const Key posKey) const {
+
+  return entries[uint32_t(posKey) & (size - 1)].data;
+}
+
 #endif // !defined(TT_H_INCLUDED)