Node: Inlining of Subprograms, Previous: Debugging Optimized Code, Up: Performance Considerations



Inlining of Subprograms

A call to a subprogram in the current unit is inlined if all the following conditions are met:

Calls to subprograms in with'ed units are normally not inlined. To achieve this level of inlining, the following conditions must all be true:

Note that specifying the -gnatn switch causes additional compilation dependencies. Consider the following:

     
package R is procedure Q; pragma Inline (Q); end R; package body R is ... end R; with R; procedure Main is begin ... R.Q; end Main;

With the default behavior (no -gnatn switch specified), the compilation of the Main procedure depends only on its own source, main.adb, and the spec of the package in file r.ads. This means that editing the body of R does not require recompiling Main.

On the other hand, the call R.Q is not inlined under these circumstances. If the -gnatn switch is present when Main is compiled, the call will be inlined if the body of Q is small enough, but now Main depends on the body of R in r.adb as well as on the spec. This means that if this body is edited, the main program must be recompiled. Note that this extra dependency occurs whether or not the call is in fact inlined by gcc.

The use of front end inlining with -gnatN generates similar additional dependencies.

Note: The -fno-inline switch can be used to prevent all inlining. This switch overrides all other conditions and ensures that no inlining occurs. The extra dependences resulting from -gnatn will still be active, even if this switch is used to suppress the resulting inlining actions.