Problems
Replacing a call site with an expanded function body can worsen performance in several ways :
- In applications where code size is more important than speed, such as many embedded systems, inlining is usually disadvantageous except for very small functions, such as trivial mutator methods.
- The increase in code size may cause a small, critical section of code to no longer fit in the cache, causing cache misses and slowdown.
- The added variables from the inlined procedure may consume additional registers, and in an area where register pressure is already high this may force spilling, which causes additional RAM accesses.
- A language specification may allow a program to make additional assumptions about arguments to procedures that it can no longer make after the procedure is inlined.
- If code size is increased too much, resource constraints such as RAM size may be exceeded, leading to programs that either cannot be run or that cause thrashing. Today, this is unlikely to be an issue with desktop or server computers except with very aggressive inlining, but it can still be an issue for embedded systems.
Typically, compiler developers keep these issues in mind, and incorporate heuristics into their compilers that choose which functions to inline so as to improve performance, rather than worsening it, in most cases.
Read more about this topic: Inline Expansion
Famous quotes containing the word problems:
“The problems of society will also be the problems of the predominant language of that society. It is the carrier of its perceptions, its attitudes, and its goals, for through it, the speakers absorb entrenched attitudes. The guilt of English then must be recognized and appreciated before its continued use can be advocated.”
—Njabulo Ndebele (b. 1948)
“Men decide far more problems by hate, love, lust, rage, sorrow, joy, hope, fear, illusion, or some other inward emotion than by reality, authority, any legal standard, judicial precedent, or statute.”
—Marcus Tullius Cicero (106–43 B.C.)
“To be a philosopher is not merely to have subtle thoughts, nor even to found a school, but so to love wisdom as to live according to its dictates a life of simplicity, independence, magnanimity, and trust. It is to solve some of the problems of life, not only theoretically, but practically.”
—Henry David Thoreau (1817–1862)