Link-time optimisation (LTO)

[Cecil Ward via Digitalmars-d-learn]

Say that I use say GDC or LDC. I want to declare a routine as 
public in one compilation unit (.d src file) and be able to 
access it from other compilation units.

Do I simply declare the routine with the word keyword public 
before the usual declaration?

Or maybe that is the default, like not using the keyword static 
with function declarations in C?

My principal question: If I successfully do this, with GCC or 
LDC, will I be able to get the code for the externally defined 
short routine expanded inline and fully integrated into the 
generated code that corresponds to the calling source code? (So 
no ‘call’ instruction is even found.)