CODEWITHSUNDEEP
coptimizationcompiler-construction
Mark
Mark

Reputation: 6494

many small sized functions

in computer literature it is generally recommended to write short functions as much as possible. I understand it may increase readability (although not always), and such approach also provides more flexibility. But does it have something to do with optimization as well? I mean -- does it matter to a compiler to compile a bunch of small routines rather than a few large routines?

Thanks.

Upvotes: 1

Views: 125

Answers (2)

Jerry Coffin
Jerry Coffin

Reputation: 490663

That depends on the compiler. Many older compilers only optimized a single function at a time, so writing larger functions (up to to some limit) could improve optimization -- but (with most of them) exceeding that limit turned optimization off completely.

Most reasonably current compilers can generate inline code for functions (and C99 added the ineline keyword to facilitate that) and do global (cross-function) optimization, in which case it normally makes no difference at all.

Upvotes: 6

Ethan Brown
Ethan Brown

Reputation: 27292

@twain249 and @Jerry are both correct; breaking a program into multiple functions can have a negative effect on performance, but it depends on whether or not the compiler can optimize the functions into inline code.

The only way to know for sure is to examine the assembler output of your program and do some profiling. For example, if you know a particular code path is causing a performance problem, you can look at the assembler, and see how many functions are getting called, how many times parameters are being pushed onto the stack, etc. In that case, you may want to consolidate small functions into one larger one.

This has been a concern for me in the past: doing very tight optimization for embedded projects, I have consciously tried to reduce the number of function calls, especially in tight loops. However, this does produce ungainly functions, sometimes several pages long. To mitigate the maintenance cost of this, you can use macros, which I have leveraged heavily and successfully to make sure there are no function calls while at the same time preserving readability.

Upvotes: 1

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