Successful compilation of SSE instruction with qmake (but SSE2 is not recognized)

Question

I'm trying to compile and run my code migrated from Unix to windows. My code is pure C++ and not using Qt classes. it is fine in Unix.

I'm also using Qt creator as an IDE and qmake.exe with -spec win32-g++ for compiling. As I have sse instructions within my code, I have to include emmintrin.h header.

I added:

QMAKE_FLAGS_RELEASE += -O3 -msse4.1 -mssse3 -msse3 -msse2 -msse

QMAKE_CXXFLAGS_RELEASE += -O3 -msse4.1 -mssse3 -msse3 -msse2 -msse

In the .pro file. I have been able to compile my code without errors. but after running it gives run-time error while going through some functions containing __m128 or like that.

When I open emmintrin.h, I see:

#ifndef __SSE2__
# error "SSE2 instruction set not enabled"
#else

and It is undefined after #else.

I don't know how to enable SSE in my computer.

Platform: Windows Vista

System type: 64-bit

Processor: intel(R) Core(TM) i5-2430M CPU @ 2.40Hz

Does anyone know the solution?

Thanks in advance.

Answer 1

It sounds like your data is not 16 byte aligned, which is a requirement for SSE loads such as mm_load_ps. You can either:

• use _mm_loadu_ps as a temporary workaround. On newer CPUs the performance hit for misaligned loads such as this is fairly small (on older CPUs it's much more significant), but it should still be avoided if possible

or

• fix your memory alignment. On Windows/Visual Studio you can use the declspec(align(16)) attribute for static allocations or _aligned_malloc for dynamic allocations. For gcc and most other civilised platforms/compilers use __attribute__ ((align(16))) for the former and posix_memalign for the latter.