Leaf routine: Difference between revisions

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{{short description|Subroutines in computer science}}

A '''leaf subroutine''' is a [[subroutine]] which cannot in turn call another subroutine. Some compilers can apply special program optimizations to leaf subroutines, such as the use of [[link register]]s to avoid having to push the return address on the stack.

A '''leaf routine''', '''leaf subroutine''', '''leaf function''', or '''leaf procedure''' is a [[function (computer programming)|function]] that does not in turn call another function. Some compilers can apply special program optimizations to leaf routines to make them more efficient, such as the use of [[link register]]s to avoid having to push the return address on the stack, or not allocating a [[register window]] on CPU architectures descended from [[Berkeley RISC]].<ref>{{cite web|url=https://gcc.gnu.org/onlinedocs/gccint/Leaf-Functions.html|title=Leaf Functions (GCC (GNU Compiler Collection) Internals Manual)}}</ref>

The term "leaf" refers to their position as [[leaf node]]s in the [[call graph]] of the program.

Usually, most non-leaf routines call more than one other function. When this is the case, the majority of function calls in the call graph are calls to leaf routines, because a [[binary tree]] has more leaf nodes than non-leaf nodes (assuming that all non-leaf nodes have two children). Consequently, the efficiency of calls to leaf routines often has a significant effect on the efficiency of the whole program.{{fact|date=July 2025}}

== References ==

{{Reflist}}

[[Category:Subroutines]]