This test inside std.array.back causes a segfault: assert(a.length, "Attempting to fetch the back of an empty array"); This doesn't: assert(a.length); The bug seems to manifest itself only on Linux and only in release mode. To reproduce, build Phobos on Linux like this: make -f linux.mak unittest BUILD=release DMDEXTRAFLAGS="-version=bugXXXX" where XXXX is the number of this bug report.
The workaround is gone from std.array.back.