Stockfish haswell optimized build

[j_romang]

Here is the attack code, with no changes elsewhere :
https://github.com/jromang/Stockfish/bl ... ard.h#L271

[Gerd Isenberg]

Here is the attack code, with no changes elsewhere :
https://github.com/jromang/Stockfish/bl ... ard.h#L271

Thanks, yes Ronald's PDEP/PEXT 210.5k lookup approach. Wow, 4% is a huge speedup considering only attack-getters are changed, but of course affecting other memory and cache issues in other areas of the program. Assuming you also tried the PEXT only approach with 4 times greater tables, Ronald had the right sense, congratulations!

http://www.talkchess.com/forum/viewtopi ... 11&start=3

Cheers,
Gerd

[phenri]

I would probably have no utility of this patch before some months, or even some years.
But thank you for the future.

I have a question that has nothing to do with BMI2.
I'm asking you because I do not really expect a response from Marco.

I probably be wrong, but I want to understand.
Why in the makefile, POPCNT comes with the flag -msse3 instead of -msse4.2 while POPCNT is present only for architectures with a minimum SSE4.2.

And why the flag -mpopcnt is not included?

Code: Select all

### 3.9 popcnt
ifeq ($(popcnt),yes)
	CXXFLAGS += -msse3 -DUSE_POPCNT
endif

Same for preftech why the flag is so low?

Code: Select all

### 3.7 prefetch
ifeq ($(prefetch),yes)
	ifeq ($(sse),yes)
		CXXFLAGS += -msse
		DEPENDFLAGS += -msse
	endif
else
	CXXFLAGS += -DNO_PREFETCH
endif

Regards,

Paul

[syzygy]

It might be interesting to try this.
In bitboard.h change

Code: Select all

struct BMI2Info {
  unsigned short *data;
  uint64_t mask1;
  uint64_t mask2;
};

extern unsigned short attack_table[107648];
extern struct BMI2Info bishop_bmi2[64];
extern struct BMI2Info rook_bmi2[64];

template<PieceType Pt>
inline Bitboard attacks_bb(Square s, Bitboard occ) {
  struct BMI2Info *info = (Pt == ROOK ? &rook_bmi2[s] : &bishop_bmi2[s]);
  return _pdep_u64(info->data[_pext_u64(occ, info->mask1)], info->mask2);
}

into

Code: Select all

struct BMI2Info {
  uint64_t *data;
  uint64_t mask;
};

extern struct BMI2Info bishop_bmi2[64];
extern struct BMI2Info rook_bmi2[64];

template<PieceType Pt>
inline Bitboard attacks_bb(Square s, Bitboard occ) {
  struct BMI2Info *info = (Pt == ROOK ? &rook_bmi2[s] : &bishop_bmi2[s]);
  return info->data[_pext_u64(occ, info->mask)];
}

In bitboard.cpp change the lines

Code: Select all

static unsigned short attacks_table[107648];
...
        info[sq].mask1 = bb
...
          if (i == 0)
        info[sq].mask2 = bb2;
          attacks_table[idx++] = _pext_u64(bb2, info[sq].mask2);

into

Code: Select all

static uint64_t attacks_table[107648];
...
        info[sq].mask = bb
...
          attacks_table[idx++] = bb2;

I did not test this, so maybe something is wrong or missing.

This might be faster and this might be slower, but it would be interesting to know.

[syzygy]

Assuming you also tried the PEXT only approach with 4 times greater tables, Ronald had the right sense, congratulations!

I don't think he tried, but we can now find out

[Gerd Isenberg]

Assuming you also tried the PEXT only approach with 4 times greater tables, Ronald had the right sense, congratulations!

I don't think he tried, but we can now find out

Would be nice if Jean-Francois or you could try and report. U64 versus pdep_u64(U16, mask2).

[j_romang]

I didn't try

[j_romang]

Wow, 4% is a huge speedup considering only attack-getters are changed, but of course affecting other memory and cache issues in other areas of the program.

According to my profiling experiments stockfish spends about 5-6% of time computing attack bitboards, that's we I wanted to give a try to the pext solution.

[syzygy]

Why in the makefile, POPCNT comes with the flag -msse3 instead of -msse4.2 while POPCNT is present only for architectures with a minimum SSE4.2.

It is not entirely true that POPCNT needs SSE4.2. On AMD native popcnt came with SSE4a.

I tried compiling with -msse4.2. It did not improve the speed.

And why the flag -mpopcnt is not included?

Code: Select all

### 3.9 popcnt
ifeq ($(popcnt),yes)
	CXXFLAGS += -msse3 -DUSE_POPCNT
endif

Because stockfish uses inline assembly for native popcount, so the compiler does not need to be told it can generate the popcnt instruction. It would be different if stockfish used the __builtin_popcountll() compiler intrinsic.

Same for preftech why the flag is so low?

Code: Select all

### 3.7 prefetch[/quote]
I did not check, but I suppose the prefetch instruction is available on systems with sse. So no need to generate executables that don't work on systems that do not have sse2 or higher.

[syzygy]

I didn't try

See the suggested code changes I posted above. They try.