Use -ip and -ipo to enable interprocedural optimizations (IPO), which enable the compiler to analyze your code to determine where you can benefit from the optimizations listed in tables that follow. See IPO options summary.
IA-32 and Itanium™-based applications
Optimization |
Affected Aspect of Program |
|
inline function expansion |
calls, jumps, branches, and loops |
|
interprocedural constant propagation |
arguments, global variables, and return values |
|
monitoring module-level static variables |
further optimizations, loop invariant code |
|
dead code elimination |
code size |
|
propagation of function characteristics |
call deletion and call movement |
|
multifile optimization |
affects the same aspects as -ip, but across multiple files |
IA-32 applications only
|
Optimization |
Affected Aspect of Program |
|
passing arguments in registers |
calls, register usage |
|
loop-invariant code motion |
further optimizations, loop invariant code |
Inline function expansion is one of the main optimizations performed by the interprocedural optimizer. For function calls that the compiler believes are frequently executed, the compiler might decide to replace the instructions of the call with code for the function itself.
With -ip, the compiler performs inline function expansion for calls to procedures defined within the current source file. However, when you use -ipo to specify multifile IPO, the compiler performs inline function expansion for calls to procedures defined in separate files.
To disable the IPO optimizations, use the -O0 option.