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Enable POPCNT only through Makefile

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Also remove some fallback templates that prevent a
compile error in case the user runs 'make icc-profile-popcnt'
from a non supported machine.

We want to loudly fail in that case instead of silently
fallback in a non-popcount compilation.

Updated documentation too.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2009-11-06 17:23:02 +01:00
parent 53ce6ce49c
commit 7c0cb8e73d
2 changed files with 5 additions and 24 deletions
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3
Readme.txt
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@ -58,8 +58,7 @@ flag changing from -DNBIGENDIAN to -DBIGENDIAN in the Makefile.
Stockfish has POPCNT instruction runtime detection and support. This can Stockfish has POPCNT instruction runtime detection and support. This can
give an extra speed on Core i7 or similar systems. To enable this feature give an extra speed on Core i7 or similar systems. To enable this feature
(disabled by default) simply uncomment #define USE_POPCNT in bitcount.h compile with 'make icc-profile-popcnt'
before to compile.
On 64 bit Unix-like systems the 'bsfq' assembly instruction will be used On 64 bit Unix-like systems the 'bsfq' assembly instruction will be used
for bit counting. Detection is automatic at compile time, but in case you for bit counting. Detection is automatic at compile time, but in case you

26
src/bitcount.h
View file

@ -22,19 +22,12 @@
#if !defined(BITCOUNT_H_INCLUDED) #if !defined(BITCOUNT_H_INCLUDED)
#define BITCOUNT_H_INCLUDED #define BITCOUNT_H_INCLUDED
// To enable POPCNT support uncomment USE_POPCNT define. For PGO compile on a Core i7
// you may want to collect profile data first with USE_POPCNT disabled and then, in a
// second profiling session, with USE_POPCNT enabled so to exercise both paths. Don't
// forget to leave USE_POPCNT enabled for the final optimized compile though ;-)
//#define USE_POPCNT
#include "types.h" #include "types.h"
// Select type of intrinsic bit count instruction to use // Select type of intrinsic bit count instruction to use, see
// README.txt on how to pgo compile with POPCNT support.
#if defined(__INTEL_COMPILER) && defined(IS_64BIT) && defined(USE_POPCNT) // Intel compiler #if defined(__INTEL_COMPILER) && defined(USE_POPCNT) // Intel compiler
#include <nmmintrin.h> #include <nmmintrin.h>
@ -45,17 +38,9 @@ inline bool cpu_has_popcnt() {
return (CPUInfo[2] >> 23) & 1; return (CPUInfo[2] >> 23) & 1;
} }
// Define a dummy template to workaround a compile error if _mm_popcnt_u64() is not defined.
//
// If _mm_popcnt_u64() is defined in <nmmintrin.h> it will be choosen first due to
// C++ overload rules that always prefer a function to a template with the same name.
// If not, we avoid a compile error and because cpu_has_popcnt() should return false,
// our templetized _mm_popcnt_u64() is never called anyway.
template<typename T> inline unsigned _mm_popcnt_u64(T) { return 0; } // Is never called
#define POPCNT_INTRINSIC(x) _mm_popcnt_u64(x) #define POPCNT_INTRINSIC(x) _mm_popcnt_u64(x)
#elif defined(_MSC_VER) && defined(IS_64BIT) && defined(USE_POPCNT) // Microsoft compiler #elif defined(_MSC_VER) && defined(USE_POPCNT) // Microsoft compiler
#include <intrin.h> #include <intrin.h>
@ -66,9 +51,6 @@ inline bool cpu_has_popcnt() {
return (CPUInfo[2] >> 23) & 1; return (CPUInfo[2] >> 23) & 1;
} }
// See comment of _mm_popcnt_u64<>() few lines above for an explanation.
template<typename T> inline unsigned __popcnt64(T) { return 0; } // Is never called
#define POPCNT_INTRINSIC(x) __popcnt64(x) #define POPCNT_INTRINSIC(x) __popcnt64(x)
#else // Safe fallback for unsupported compilers or when USE_POPCNT is disabled #else // Safe fallback for unsupported compilers or when USE_POPCNT is disabled