Bug 9720 – OSX wrong code with -O Illegal instruction

Investigated from: https://github.com/D-Programming-Language/phobos/pull/878 http://d.puremagic.com/test-results/pull-history.ghtml?projectid=1&repoid=3&pullid=878 Happens with OSX, when compile with -O. Below a reduced test case: //---- import std.stdio; //Simplified RefCounted struct MyRef(T) { private struct Impl { T _payload; size_t _count; } Impl* _store; this(int i) { _store = new Impl; _store._payload = T.init; _store._count = 1; } ~this() { if (!_store) return; writeln("d: ", _store._count); //Comment me --_store._count; } } //Extracted from Array struct Payload { size_t _capacity; //Comment me int[] _pay; //Comment me size_t insertBack(Stuff)(Stuff /+stuff+/) { immutable newLen = _pay.length + 3; _pay.length = newLen; _pay = _pay[0 .. newLen]; //Comment me return 3; } } alias Data = MyRef!Payload; unittest { auto a = Data(1); auto b = Data(1); writeln(__LINE__); a._store._payload.insertBack(1); //Passes writeln(__LINE__); a._store._payload.insertBack(b); //Fails writeln(__LINE__); } //---- rdmd -w -d -property -O --main -unittest test2.d 47 49 d: 1 Illegal instruction //--- I was not able to simplify much more, as the compile-time behavior is non deterministic: EG: removing an unused variable such as "capacity" is enough to make the problem "disappear" (or at least, unobservable). AFAIK, this code contains nothing unsafe, and the only requirement to reproduce is as simple as "pass by value something with a destructor"... (!)

64 bit only.

Reduced test case: ------------------ import core.stdc.stdio; struct Payload { size_t _capacity; //Comment me int[] _pay; //Comment me size_t insertBack(Data d) { immutable newLen = _pay.length + 3; _pay.length = newLen; _pay = _pay[0 .. newLen]; //Comment me return 3; } } struct Impl { Payload _payload; size_t _count; } struct Data { Impl* _store; this(int i) { _store = new Impl; _store._payload = Payload.init; } ~this() { printf("%d\n", _store._count); --_store._count; } } void main() { auto a = Data(1); auto b = Data(1); a._store._payload.insertBack(b); //Fails }

Commits pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/8176c41cb828b9800928d947926b9c0749222e1f fix Issue 9720 - OSX wrong code with -O Illegal instruction https://github.com/D-Programming-Language/dmd/commit/614878714a702ca923b4910e487e4635226bc62c Merge pull request #1823 from WalterBright/fix9720 fix Issue 9720 - OSX wrong code with -O Illegal instruction

Commit pushed to dmd-1.x at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/6b2fb00442c38f9200d7d10a07e5435807651a7e Merge pull request #1823 from WalterBright/fix9720 fix Issue 9720 - OSX wrong code with -O Illegal instruction