Remove an old workaround that was kept around for ABI-compatibility on x86-64 between different LLVM versions. This means LLVM r67588 is required if you want to compile for x86-64, otherwise the backend will assert when you try to return e.g. struct { int i; char c; } from a function. (In particular, this is no longer compatible with LLVM 2.5) It also means that any code returning small structs on x86-64 will probably need to be recompiled in order to be linkable to code compiled with this change.

extern(C) int printf(char*, ...);

ulong retval() {
    version (X86)
    asm { naked; mov EAX, 0xff; mov EDX, 0xaa; ret; }
    else version (X86_64)
    asm { naked; mov RAX, 0xaa000000ff; ret; }
}

ulong retval2() {
    return (cast(ulong)0xaa << 32) | 0xff;
}

void main() {
    auto a = retval();
    auto b = retval2();
    printf("%llu\n%llu\n", retval(), retval2());
    assert(a == 0xaa000000ff);
    assert(a == b);
}