The Gentoo bug tracker has a specific meta-bug for tracking packages that break when built with LTO. The vast majority of the bugs are "failed to compile". It s

The Gentoo bug tracker has a specific meta-bug for tracking packages that break when built with LTO. The vast majority of the bugs are "failed to compile". It seems like that is the most common issue by far. There are cases where it causes runtime errors as well. Sometimes software is written incorrectly and has "undefined behavior" (you probably know this already). The thing with UB is that it may or may not cause a visible bug at runtime. Sometimes these bugs go unnoticed for a long time. It's really common for code with UB to run without visible errors when compiled without optimizations, but when you compile it with optimizations it segfaults at runtime. LTO is adding another form of optimization and sometimes the transformations the compiler made just happen to cause already existing UB to "surface". This is what I meant by LTO "causing" runtime issues to appear! There are cases of this happening in the Gentoo bug tracker, and in the Linux kernel! https://lwn.net/Articles/512548/ https://lwn.net/Articles/512548/