https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83133
--- Comment #9 from Uroš Bizjak <ubizjak at gmail dot com> --- (In reply to Maxim Egorushkin from comment #6) > This code underflows a signed integer, which is undefined behaviour, if I am > not mistaken. So, this would not be a valid example, would it? An example of "dangerous optimization" from Comment #2 was requested. The optimization is valid, but this code happens as well. As shown in the example, the program, compiled with clang declared 2147483647 as nonpositive when compiled with -O2 and as positive when compiled with -O0. We can sweep the issue under the carpet as "undefined behaviour", but I don't want to jeopardize the robustness of an industrial-strength compiler with the implementation of this relatively minor optimization.
