https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72785
--- Comment #28 from James Greenhalgh <jgreenhalgh at gcc dot gnu.org> --- > As far as I can tell the kernel is the only project where this issue ever > popped up. The fix is straightforward. It just needs to be send to the > correct kernel maintainer. Right, but getting the patch in mainline is the easy bit! This bug hits many released kernels. > Why do you think this case is any different from any other buggy application > code that needs adjustments as gcc improves? In most cases we improve GCC to exploit well defined behaviors of the standard. In this case we created defined __builtin_constant_p with insufficient documentation to allow a user to reasonably predict the surprising behavior shown in this testcase. GCC has created a path which will never be executed and used that to introduce a constant which does not exist in the source. Unless you know what jump-threading can do, this transformation isn't obvious.
