When a function template instance is called, it is called indirectly, likely
due to being "weak" function (arm.c:arm_encode_section_info).
However when the same call is subject of a tail call optimization, it is called
directly.
The function is also called directly when there is no function template
definition visible in the source, e.g. when old style template organization
makes template definitions visible in a single source file only.
What is the reasoning behind the distinction between between weak and normal
functions made in arm.c:arm_encode_section_info? It falls a bit short because
it treats function calls inconsistently, depending on the visibility of their
definition. And while it could simply be treated as a bug in the tail call
optimization, I'd rather suggest to not treat "weak" functions differently,
because (1) efficiency of template based code is greatly affected and (2) I can
see little reason to use long-calls for known "weak" functions but short-calls
for all other external functions including those which are not yet known to be
"weak".
Invocation:
arm-elf-gcc -O2 -S source.cpp
Sample code:
template<class T> class Q {
public:
Q();
void f ();
};
// called directly if this definition is removed.
template<class T> void Q<T>::f() { }
class U {
public:
int g();
Q<char>& rx;
};
int U::g()
{
rx.f(); // indirect call is used
rx.f(); // turned into direct call by tail call optimization
}
--
Summary: inconsistent code for template function calls
Product: gcc
Version: 4.0.1
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: a dot kaiser at gmx dot net
GCC target triplet: arm-elf
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25249
