In JEM3.0 when this macro is off the encoder compresses the first I-frame then quits.

In the JEM7.0, the following code is added in the “TComTrQuant.cpp” #if 1800 < _MSC_VER && _MSC_VER < 2000 #pragma optimize("", off) #endif The macro value “_MSC_VER”= 1900 for visual studio 2015. So for the VS2015, the above code makes the encoding time double for AI, and around 20-30% higher for RA and LD configurations. Maybe the purpose of that code is to prevent some potential compiler failure for VS2015. But for our VS2015, there is no problem found to remove that code. So, if you use VS2015, you may try to speedup JEM7.0 by remove that code.

Trying to build git HEAD in MSYS2/MinGW with GCC 9.2.0:

CFLAGS: -mthreads -mtune=generic -O2 -pipe
LDFLAGS: -pipe -static-libgcc -static-libstdc++
ninja 
...
[72/191] Building CXX object source/Lib/CommonLib/CMakeFiles/CommonLib.dir/Slice.cpp.o
FAILED: source/Lib/CommonLib/CMakeFiles/CommonLib.dir/Slice.cpp.o 
E:\MABS\local32\bin\g++.bat  -DENABLE_SPLIT_PARALLELISM=0 -I../source/Lib/CommonLib/. -I../source/Lib/CommonLib/.. -I../source/Lib/CommonLib/./x86 -I../source/Lib/CommonLib/../libmd5 -mthreads -mtune=generic -O2 -pipe -fopenmp -O3 -DNDEBUG   -Wall -fdiagnostics-show-option -Werror -Wno-sign-compare -Wno-class-memaccess -msse4.1 -mthreads -std=gnu++11 -MD -MT source/Lib/CommonLib/CMakeFiles/CommonLib.dir/Slice.cpp.o -MF source\Lib\CommonLib\CMakeFiles\CommonLib.dir\Slice.cpp.o.d -o source/Lib/CommonLib/CMakeFiles/CommonLib.dir/Slice.cpp.o -c ../source/Lib/CommonLib/Slice.cpp
../source/Lib/CommonLib/Slice.cpp: In member function 'bool ScalingList::isNotDefaultScalingList()':
../source/Lib/CommonLib/Slice.cpp:2015:23: error: 'int __builtin_memcmp_eq(const void*, const void*, unsigned int)' reading 256 bytes from a region of size 64 [-Werror=stringop-overflow=]
 2015 |       if( !( !::memcmp(getScalingListAddress(sizeId, listId), getScalingListDefaultAddress(sizeId, listId), sizeof(int)*std::min(MAX_MATRIX_COEF_NUM, (int)g_scalingListSize[sizeId])) // check value of matrix
      |               ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../source/Lib/CommonLib/Slice.cpp:2015:23: error: 'int __builtin_memcmp_eq(const void*, const void*, unsigned int)' reading 256 bytes from a region of size 64 [-Werror=stringop-overflow=]
../source/Lib/CommonLib/Slice.cpp:2015:23: error: 'int __builtin_memcmp_eq(const void*, const void*, unsigned int)' reading 256 bytes from a region of size 64 [-Werror=stringop-overflow=]
../source/Lib/CommonLib/Slice.cpp:2015:23: error: 'int __builtin_memcmp_eq(const void*, const void*, unsigned int)' reading 256 bytes from a region of size 64 [-Werror=stringop-overflow=]
../source/Lib/CommonLib/Slice.cpp:2015:23: error: 'int __builtin_memcmp_eq(const void*, const void*, unsigned int)' reading 256 bytes from a region of size 64 [-Werror=stringop-overflow=]
../source/Lib/CommonLib/Slice.cpp:2015:23: error: 'int __builtin_memcmp_eq(const void*, const void*, unsigned int)' reading 256 bytes from a region of size 64 [-Werror=stringop-overflow=]
../source/Lib/CommonLib/Slice.cpp:2015:23: error: 'int __builtin_memcmp_eq(const void*, const void*, unsigned int)' reading 256 bytes from a region of size 64 [-Werror=stringop-overflow=]
../source/Lib/CommonLib/Slice.cpp:2015:23: error: 'int __builtin_memcmp_eq(const void*, const void*, unsigned int)' reading 256 bytes from a region of size 64 [-Werror=stringop-overflow=]
cc1plus.exe: all warnings being treated as errors