Consider:

bool b1search(int[] a, int x) {
    if (!a.length) return 0;
    auto mid = a.length / 2;
    auto e = a[mid];
    return x == e ? true
        : x < e ? b1search(a[0 .. mid], x)
        : b1search(a[mid + 1 .. $], x);
}

bool b2search(int[] a, int x) {
    if (!a.length) return 0;
    auto mid = a.length / 2;
    auto e = a[mid];
    if (x == e) return true;
    return x < e ? b2search(a[0 .. mid], x)
        : b2search(a[mid + 1 .. $], x);
}

bool b3search(int[] a, int x) {
    if (!a.length) return 0;
    auto mid = a.length / 2;
    auto e = a[mid];
    if (x == e) return true;
    if (x < e) return b3search(a[0 .. mid], x);
    return b3search(a[mid + 1 .. $], x);
}

bool b4search(int[] a, int x) {
    if (!a.length) return 0;
    auto mid = a.length / 2;
    auto e = a[mid];
    if (x == e) return true;
    return b4search(x < e ? a[0 .. mid] : a[mid + 1 .. $], x);
}

void main()
{
}

After compiling with:

dmd -O -release test

and looking at the generated object file, only b3search and b4search are tail-call optimized, but not b1search and b2search. Tail-call optimization doesn't seem to work when a ternary expression is used with return.