You’ll need to also add -flto to your LDFLAGS.

mgaunard · on Nov 10, 2023

I don't think that's required. The linker driver will use LTO automatically if the object files it's given contain LTO IR.

If anything you might want to explicitly do -fno-lto to not use LTO when you have fat objects.

synergy20 · on Nov 10, 2023

Thanks. confirmed with chatgpt, and, if you're doing debug build, you probably do not want to use -flto, otherwise it's great for release build.

mgaunard · on Nov 10, 2023

LTO is required to detect ODR errors and to do a bunch of other checks.

It does more than optimize.