gcc optimizes template recursion better - Thank You!!!

["Hite, Christopher" <Christopher dot Hite at partner dot commerzbank dot com>]

The following code is a simplified version of what someone doing C++ metaprogramming would hand the optimizer for example via boost::mpl::for_each().

#include <iostream>

void foo(int i){
	std::cout<<i<<std::endl;
}


template<int N>
void bar(){
	bar<N-1>();
	foo(N);
}

template<>
void bar<-1>(){}

int main(){
	bar<1024>();
	return 0;
}

gcc used to generate a bunch of bars that could be inlined, but weren't.

g++ -O3 -ftemplate-depth=1034 template_recurision_ctest.cpp
objdump -f -d  -C  a.out  | grep bar |grep ">:"
08048700 <void bar<-1>()>:
08048720 <void bar<19>()>:
08048fb0 <void bar<39>()>:
08049840 <void bar<59>()>:
0804a0d0 <void bar<79>()>:
0804a960 <void bar<99>()>:
0804b1f0 <void bar<159>()>:
0804cb60 <void bar<179>()>:
0804d3f0 <void bar<319>()>:
0804fc00 <void bar<339>()>:
08050490 <void bar<959>()>:
080535a0 <void bar<979>()>:
08053e30 <void bar<1019>()>:

The only way to prevent this was turning on LTO, which then realized that all these functions were called only from one place and could be inlined.

g++ 4.7.1 does it right an inlines all calls to foo() into main().  Awesome!!!  What changed?  Who do I thank?

Even more cool is the debug information lets gdb attribute the code to a stack of 1000 bar()s.

Chris