From: Luboš Luňák <l.lunak@centrum.cz>
Date: Tue, 23 Nov 2021 18:33:34 +0000 (+0100)
Subject: fix: Make AVX2 code work also with MSVC (#963)
X-Git-Tag: v4.6~77
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7b86803c799b9ab57dd30bd301eeca8b34026ce2;p=thirdparty%2Fccache.git

fix: Make AVX2 code work also with MSVC (#963)
---

diff --git a/cmake/GenerateConfigurationFile.cmake b/cmake/GenerateConfigurationFile.cmake
index ee6716bea..df909337f 100644
--- a/cmake/GenerateConfigurationFile.cmake
+++ b/cmake/GenerateConfigurationFile.cmake
@@ -73,7 +73,9 @@ include(CheckCXXSourceCompiles)
 check_cxx_source_compiles(
   [=[
     #include <immintrin.h>
+    #ifndef _MSC_VER // MSVC does not need explicit enabling of AVX2.
     void func() __attribute__((target("avx2")));
+    #endif
     void func() { _mm256_abs_epi8(_mm256_set1_epi32(42)); }
     int main()
     {
diff --git a/src/hashutil.cpp b/src/hashutil.cpp
index 9e30cd019..d61282fcc 100644
--- a/src/hashutil.cpp
+++ b/src/hashutil.cpp
@@ -120,8 +120,10 @@ check_for_temporal_macros_bmh(string_view str)
 }
 
 #ifdef HAVE_AVX2
+#  ifndef _MSC_VER // MSVC does not need explicit enabling of AVX2.
 int check_for_temporal_macros_avx2(string_view str)
   __attribute__((target("avx2")));
+#  endif
 
 // The following algorithm, which uses AVX2 instructions to find __DATE__,
 // __TIME__ and __TIMESTAMP__, is heavily inspired by
@@ -157,7 +159,13 @@ check_for_temporal_macros_avx2(string_view str)
     // A bit set in mask now indicates a possible location for a temporal macro.
     while (mask != 0) {
       // The start position + 1 (as we know the first char is _).
+#  ifndef _MSC_VER
       const auto start = pos + __builtin_ctz(mask) + 1;
+#  else
+      unsigned long index;
+      _BitScanForward(&index, mask);
+      const auto start = pos + index + 1;
+#  endif
 
       // Clear the least significant bit set.
       mask = mask & (mask - 1);