Enable POPCNT only through Makefile

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>

diff --git a/Readme.txt b/Readme.txt
index 85139105b0f1ca3bf84b3a1a541da8172acbdb23..a79e73025ffab11055e08aff25f295a29fbf6218 100644 (file)
--- a/Readme.txt
+++ b/Readme.txt
@@ -58,8 +58,7 @@ flag changing from -DNBIGENDIAN to -DBIGENDIAN in the Makefile.
 
 Stockfish has POPCNT instruction runtime detection and support. This can
 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
-before to compile.
+compile with 'make icc-profile-popcnt'
 
 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

diff --git a/src/bitcount.h b/src/bitcount.h
index 6b5f5b5789bb5f8b0b895fafa650566ceba107c2..aa27c049415bcc3ce98750d48a9194152f8d8486 100644 (file)
--- a/src/bitcount.h
+++ b/src/bitcount.h
@@ -22,19 +22,12 @@
 #if !defined(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"
 
-// 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>
 
@@ -45,17 +38,9 @@ inline bool cpu_has_popcnt() {
   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)
 
-#elif defined(_MSC_VER) && defined(IS_64BIT) && defined(USE_POPCNT) // Microsoft compiler
+#elif defined(_MSC_VER) && defined(USE_POPCNT) // Microsoft compiler
 
 #include <intrin.h>
 
@@ -66,9 +51,6 @@ inline bool cpu_has_popcnt() {
   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)
 
 #else // Safe fallback for unsupported compilers or when USE_POPCNT is disabled