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2013 Apr 09
1
[LLVMdev] inefficient code generation for 128-bit->256-bit typecast intrinsics
Hello,
LLVM generates two additional instructions for 128->256 bit typecasts
(e.g. _mm256_castsi128_si256()) to clear out the upper 128 bits of YMM register corresponding to source XMM register.
vxorps xmm2,xmm2,xmm2
vinsertf128 ymm0,ymm2,xmm0,0x0
Most of the industry-standard C/C++ compilers (GCC, Intel's compiler, Visual Studio compiler) don't
generate any extra moves