On Sun, 19 Sep 2021, Allin Cottrell via Gcc wrote:
Should this perhaps be considered a bug? Below is a minimal test case for a type of calculation that occurs in my real code. It works as expected when compiled without optimization, but produces what seems like a wrong result when compiled with -O2, using both gcc 10.3.1 20210422 on Fedora and gcc 11.1.0-1 on Arch Linux. I realize there's a newer gcc release but it's not yet available for Arch, and looking at https://gcc.gnu.org/gcc-11/changes.html I didn't see anything to suggest that something relevant has changed.
https://gcc.gnu.org/bugs/ says that you should first try compiling your code with -fsanitize=undefined, which tells you at runtime that your code is broken.
Apart from that, bug reports should go to https://gcc.gnu.org/bugzilla/ and questions to gcc-h...@gcc.gnu.org.
-- Marc Glisse
