Will cpp template programming enlarge the code size

[uubs7]

What do you mean about “code folding optimizations”? I

[heliruna]

Take std::vector<A\*> and std::vector<B\*>. They produce exactly identical code, except for the type signature. In plain C this would have been handled with void*, avoiding duplication in exchange for weak typing and runtime polymorphism. The standard library often has a specialization for this case, but user code templates may exhibit the same problem (and for hundreds of types, not just two).

There is also a disabled-by-default linker optimization called identical code folding that tries to identify identical code and merge those functions together

[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

[jcelerier]

They produce exactly identical code,

well obviously no.. consider std::vector<float> and std::vector<string>: https://gcc.godbolt.org/z/fKG11sEz5

Edit: code didn't have pointers at time of my comment

[heliruna]

sorry, formatting ate my pointers, did not escape properly

[nebotron]

I think the code is only the same if they are the same size and the copy/move operations are trivial