The following program

void main(string[] args)
{
    import core.simd;
    float4 a = 1, b = 2;
    float4 c = __simd(XMM.ADDSS, a, b);
}

fails to compile with gdc. The compiler aborts with

test.d:5: error: undefined identifier __simd
test.d:5: error: undefined identifier XMM

My running gdc on Linux.
gdc (crosstool-NG hg+unknown-20131212.080758) 4.8.2
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

How do I generate SSE instructions with gdc?