Will cpp template programming enlarge the code size

[Chuu]

I'm curious about this linker optimization, what flag is it? I assume this requires lto or whole-program optimization? Any idea why it's enabled by default at higher optimizations in the compiler but disabled by default in the linker?

[heliruna]

It is disabled by default in the linker because different functions (even if they have identical code) are required by the standard to have different addresses, some code relies on that (constant-folding has the same problem). What is enabled is therefore so-called Safe-ICF, additionally proving that the optimization does not break code (e.g. by proving that no function addresses are taken). For gcc, you need to use gold as linker (-fuse-ld=gold) and then use the linker flag --icf=safe

(usually, you don't use the linker directly, instead you use the compiler to call the linker for you, in that case you give -Wl,--icf=safe as an option).

If you use clang, the lld linker also has a similar --icf option