import std.algorithm;
import std.range;

void main() {
    auto N2 = sequence!"n"(cast(size_t)1).map!"a";
}


When compiling with dmd -O (latest git for dmd, druntime, phobos), this produces the following errors:

/usr/src/d/phobos/std/range.d(4590): Error: variable upper used before set
/usr/src/d/phobos/std/range.d(4590): Error: variable lower used before set

The referenced line of code occurs in this context:

    auto opSlice(size_t lower, size_t upper)
    in
    {  
        assert(upper >= lower); // this is line 4590
    }
    body
    {  
        auto s = typeof(this)(this._state, this._n + lower);
        return takeExactly(s, upper - lower);
    }

Which makes no sense, because there is nothing wrong with the reference to upper and lower (they are function parameters). Perhaps the optimizer inadvertently permuted the order of stuff in a way that caused the contract to run before the parameters are initialized?

If -O is not specified, the compile is successful. This problem appears to be independent of whether I specify -m32 or -m64.