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 Settlement ... is an experimental effort to aid in the solution of the social and industrial problems which are engendered by the modern conditions of life in a great city. It insists that these problems are not confined to any one portion of the city. It is an attempt to relieve, at the same time, the overaccumulation at one end of society and the destitution at the other ...”
—Jane Addams (1860–1935)
“Nothing in the world can take the place of Persistence. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts. Persistence and Determination alone are omnipotent. The slogan “Press On”, has solved and will always solve the problems of the human race.”
—Calvin Coolidge (1872–1933)
“We are all adult learners. Most of us have learned a good deal more out of school than in it. We have learned from our families, our work, our friends. We have learned from problems resolved and tasks achieved but also from mistakes confronted and illusions unmasked. . . . Some of what we have learned is trivial: some has changed our lives forever.”
—Laurent A. Daloz (20th century)