I believe this is a known problem, but I couldn't find it anywhere.
The inliner at -O2 will attempt to inline any small functions. It will not
however try to inline functions will external linkage, which includes all
templated functions.
As much C++ code (including libstdc++) contains many small templated functions,
this means it is necessary to mark all these functions as inline to ensure they
are even considered at -O2.
Example: given:
void foo() {}
void foo2() {foo();}
int main() {foo2();}
then main() is optimised away to an empty function at -O2. However:
template<class T>
void foo() {}
template<class T>
void foo2() {foo<T>();}
int main() {foo2<int>();}
leaves the calls to foo2 and foo in at -O2.
Is there a good reason to not pull inlining of small functions (which in C++
typically consist of simply calling a new function with almost identical
parameters) into -O2, even when they have external linkage? (or make an
exception for templated functions?)
--
Summary: Templated functions no inlined at -O2
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: minor
Priority: P2
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: chris at bubblescope dot net
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20411
