Created attachment 1498 [details]
example code

This example, compiled as "dmd -O -release -inline -m64" on Win64, reproducibly crashes with dmd 2.067.0-b2 and later up to dmd 2.067.0 release, and reproducibly does not crash with dmd 2.066.1 and earlier.

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import std.algorithm, std.conv, std.range, std.stdio;
void main () {
    auto arr = [7, 5, 7, 3, 3, 5, 3, 3, 0, 3, 1, 1, 5, 1, 
1, 1, 2, 2, 8, 5, 8, 8];
    arr.sort !((x, y) => arr.count (x) > arr.count (y) ||
        (arr.count (x) == arr.count (y) && x < y), SwapStrategy.stable)
        .map !(to !(string))
        .join (" ")
        .writeln;
    // prints 1 1 1 1 1 3 3 3 3 3 5 5 5 5 8 8 8 2 2 7 7 0
}
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The D.learn discussion resulting in this example:
http://forum.dlang.org/thread/fqbojlyocmsovrpzilhu@forum.dlang.org

A somewhat minimized example:

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import std.algorithm, std.conv, std.stdio;
void main () {
    auto arr = [1];
    version (S1) sort (arr);
    version (S2) sort !(q{a < b}, SwapStrategy.stable) (arr);
    auto s = map !(to !(string)) (arr);
    if (s.front != "1") {
        writeln ("?");
    }
}
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Crashes with either
dmd -O -release -inline -m64 -version=S1
or
dmd -O -release -inline -m64 -version=S2