https://github.com/bitcoin/bitcoin/blob/5f0c6a7b0e47e03f848dc992d37fe209dd9c6975/src/crypto/sha256.cpp#L183

This checks whether the CPU supports SSE4. It should also check if the OS supports SSE4. See this [StackOverflow answer](https://stackoverflow.com/a/22521619/6557621).
Round(c, d, e, f, g, h, a, b, 0x6ed41a95ul);
    Round(b, c, d, e, f, g, h, a, 0x6d437890ul);
    Round(a, b, c, d, e, f, g, h, 0xc39c91f2ul);
    Round(h, a, b, c, d, e, f, g, 0x9eccabbdul);
    Round(g, h, a, b, c, d, e, f, 0xb5c9a0e6ul);
    Round(f, g, h, a, b, c, d, e, 0x532fb63cul);
    Round(e, f, g, h, a, b, c, d, 0xd2c741c6ul);
    Round(d, e, f, g, h, a, b, c, 0x07237ea3ul);
    Round(c, d, e, f, g, h, a, b, 0xa4954b68ul);
    Round(b, c, d, e, f, g, h, a, 0x4c191d76ul);
    w0 = t0 + a;
    w1 = t1 + b;
    w2 = t2 + c;
    w3 = t3 + d;
    w4 = t4 + e;
    w5 = t5 + f;
    w6 = t6 + g;
    w7 = t7 + h;
    
    a = 0x6a09e667ul;
    b = 0xbb67ae85ul;
    c = 0x3c6ef372ul;
    d = 0xa54ff53aul;
    e = 0x510e527ful;
    f = 0x9b05688cul;
    g = 0x1f83d9abul;
    h = 0x5be0cd19ul;
    Round(a, b, c, d, e, f, g, h, 0x428a2f98ul + w0);
    Round(h, a, b, c, d, e, f, g, 0x71374491ul + w1);
    Round(g, h, a, b, c, d, e, f, 0xb5c0fbcful + w2);