Itanium® Architecture for Programmers: Understanding 64-Bit Processors and EPIC Principles

7.5. Calling Conventions

Software development requires standardization, not only to minimize confusion and maximize understandability, but also to reduce redundant operations when saving and restoring the contents of registers. The use of libraries of subroutines, while increasing programmer efficiency, has the potential to decrease machine performance.

Should a subroutine conservatively save every register that it uses? That may be wasteful if the calling program did not actually require preservation of the contents of those registers for its own functioning. Should a caller conservatively save copies of the contents from all those registers? That may also be wasteful if the called routine did not need all those registers. The negative side ...