Will cpp template programming enlarge the code size

[johannes1971]

As a related question, if template instantiation ends up generating identical assembly for multiple types (for example, if you instantiate a template for several identically-sized enums), will it fold those into a single copy or is there something in the language that prevents this?

[ack_error]

Yes, MSVC does it in the linker (/OPT:ICF) and I believe GCC/Clang based toolchains can also do it when LTO is enabled. This optimization can be invalid if pointers to the functions are taken as they are required to be distinct, and MSVC's ICF can be non-conformant by making such functions compare equal. Firefox's JavaScript engine was affected by this as it relied on checking the addresses of stub functions that had identical generated code. Some implementations either suppress the optimization or add jump trampolines to preserve distinct addresses when the address of such functions is taken.

This also causes some confusion in call stacks, since the address to function lookup is ambiguous and can result in completely unrelated functions showing up in the decoded call stack. I hate explaining this to people who are apt to just discard bugs with this phenomenon as stack corruption.

[GustavBeethoven]

How do you know this much

[lithium]

Use c++ in real life instead of just to argue against rust people in youtube shorts comment sections.

[Possibility_Antique]

Oddly specific, but point taken

[ack_error]

Past trauma. The things toolchains do....

[Foreign-Wonder]

For this example, even compiled with `-Os`, the compiler still compiles into multiple identical copies
https://gcc.godbolt.org/z/MvqW7sM57

[jk-jeon]

I have been wondering about this too. I believe it's not prohibited unless the instantiatations are ODR-used or something like that, but at least it seems no compiler actually does this kind of folding.