How safe is it to turn LTO on?

[revolting_peasant]

I noticed that, when I CMake-configure Wesnoth for building, LTO is turned off by default. Is this because it's somehow unsafe/unstable? If it is, can someone describe what behavior one can expect with LTO turned on?

[Pentarctagon]

It's basically just another level of optimization, and the more you tell a compiler to optimize something the more likely it is to do something unintended because of some undefined behavior in the code base. It should be relatively safe though - the Steam Linux build has had LTO enabled for years now.

[ahyangyi]

LTO also tends to make building longer (a very slow linking step that cannot be relieved by parallelism). So turning off LTO by default could have much more benign reasons.

[egallager]

LTO also tends to make building longer (a very slow linking step that cannot be relieved by parallelism). So turning off LTO by default could have much more benign reasons.

GCC does actually support parallelism for LTO; see documentation of the -flto= option.

[ahyangyi]

Nice!