!isfinite(Expression) does not compile. This is becuase

Tensor<bool,....> res = !isfinite(Expression); 

is a nested expression that calls the eval function for ! and isfinite. The first call is to eval<bool> for ! and the second (nested) call is to eval<EVAL_TYPE> for isfinite.

Now EVAL_TYPE is a macro alias to scalar_type so we get eval<bool>(eval<EVAL_TYPE>). The return type of the inner function is SIMDVector<bool,simd_abi::fixed<4>> say for SSE float, but the return type of the outer function given that the type is bool is SIMDVector<bool,simd_abi::fixed<16>> (again under SSE). If Instead we use something like result_scalar_type = typename result_type::scalar_type we will resolve the evaluation at least as far as types are concerned but given that we use simd_abi::fixed the size of SIMDVectors will not be the same as the nested eval<EVAL_TYPE==bool> is now initialised with simd vector of different sizes (one for bool 16/32/64 and one for float 4/8/16 for SSE/AVX/AVX512).

We need proper mask types for these to be resolved.