[Bug tree-optimization/14703] Inadequate optimization of inline templated functions

["rguenth at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #7 from rguenth at gcc dot gnu dot org  2006-03-03 10:29 -------
Note that using functions as in fibconst is not really an efficient way to do
this.  Still, with gcc 4.1.0 you now have the ability to use

template<unsigned long long L> inline __attribute__((flatten)) unsigned long
long fibconst()
{
   return fibconst<L - 1>() + fibconst<L - 2>();
}

which will result in one call in main and a fibconst that returns the constant
requested.  Of course for big numbers you'll hit interesting quadraticness in
time and memory required to build the program - so the limits in place actually
prevent you from running into this issue.  It's like

rguenther@g148:/tmp> ~/bin/maxmem2.sh
/space/rguenther/install/gcc-4.1.0/bin/gcc -O2 -S t.C -DVAL=23
total: 149886 kB
rguenther@g148:/tmp> ~/bin/maxmem2.sh
/space/rguenther/install/gcc-4.1.0/bin/gcc -O2 -S t.C -DVAL=24
total: 238102 kB
rguenther@g148:/tmp> ~/bin/maxmem2.sh
/space/rguenther/install/gcc-4.1.0/bin/gcc -O2 -S t.C -DVAL=25
total: 385738 kB
rguenther@g148:/tmp> ~/bin/maxmem2.sh
/space/rguenther/install/gcc-4.1.0/bin/gcc -O2 -S t.C -DVAL=26
total: 623094 kB

so, an exponential growth in memory usage due to the way we're doing the
inlining.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14703