{{short description|Subroutines in computer science}}
A '''leaf routine''', '''leaf subroutine''', '''leaf function''', or '''leaf procedure''' is a [[subroutinefunction (computer programming)|function]] whichthat cannotdoes not in turn call another subroutinefunction. Some compilers can apply special program optimizations to leaf subroutinesroutines 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 subroutinesroutines call more than one other subroutinefunction. When this is the case, the majority of subroutinefunction calls in the call graph are calls to leaf subroutinesroutines, 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 subroutineroutines often has a significant effect on the efficiency of the whole program.{{fact|date=July 2025}}
