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Hi, Anton > On Win64 general purpose registers shadow xmm and vice versa, so, say, > if you put argument into ecx, the xmm0 is marked as already occupied, > if you put argument into xmm1, edx is marked as occupied, etc. I think ecx and xmm0 are physical different registers (not like ecx and cx), right? So why we cannot use xmm0 while ecx has been used? Is it just a rule or there are

Objects compiled for the MS-ABI don't conform to it! Data types beyond 64 bit MUST BE returned by the callee via the hidden first argument allocated by the caller, NOT in XMM0! Demo/proof: from this source --- llvm-bug.c --- #ifndef __clang__ typedef struct { unsigned __int64 low; unsigned __int64 high; } __uint128_t; #else __attribute__((ms_abi)) #endif __uint128_t