Criteria for Inline Function Expansion

Once the criteria are met, the compiler picks the routines whose inline expansion will provide the greatest benefit to program performance. The inlining heuristics used by the compiler differ, based on whether or not you use profile-guided optimizations (-prof_use). When you use profile-guided optimizations with -ip or -ipo, the compiler uses the following heuristics:

• The default heuristic focuses on the most frequently executed call sites, based on the profile information gathered for the program.
• By default, the compiler will not inline functions with more than 230 intermediate statements.  You can change this value by specifying the option -Qoption,c,-ip_ninl_max_stats=new_value.  Note: there is a higher limit for functions declared by the user as inline or __inline.
• The default inline heuristic will stop inlining when direct recursion is detected.
• The default heuristic will always inline very small functions that meet the minimum inline criteria.
• Default for Itanium®-based applications: ip_ninl_min_stats=15.
• Default for IA-32 applications: ip_ninl_min_stats=7. This limit can be modified with the option -Qoption,c,-ip_ninl_min_stats=new_value.

If you do not use profile-guided optimizations with -ip or -ipo, the compiler uses less aggressive inlining heuristics:

• Inline a function if the inline expansion will not increase the size of the final program.
• Inline a function if it is declared with the inline or __inline keywords.