The following code:

// START of CODE, FILE 'try.cpp'
template<class A,class B> 
typeof(A(0)+B(0)) add( A a , B b )
{
	return a + b;
}

void f( double & S , double X , int Y )
{
	S = add( X , Y );
}
// END OF CODE

causes g++ to emit an ICE error, as shown of the following sessions transcript.
I joined the try.ii file even if I think it can be easily re-created, as the bug-triggering code contains non "#include<...>" statement.

-----------------------------------------------------------------------------------------
> gcc -v -save-temps try.cpp
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --enable-nls --program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug --enable-mpfr --with-tune=i686 --enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)
 /usr/lib/gcc/i486-linux-gnu/4.1.2/cc1plus -E -quiet -v -D_GNU_SOURCE try.cpp -mtune=i686 -fpch-preprocess -o try.ii
ignoring nonexistent directory "/usr/local/include/i486-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/i486-linux-gnu/4.1.2/../../../../i486-linux-gnu/include"
ignoring nonexistent directory "/usr/include/i486-linux-gnu"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/i486-linux-gnu/4.1.2/../../../../include/c++/4.1.2
 /usr/lib/gcc/i486-linux-gnu/4.1.2/../../../../include/c++/4.1.2/i486-linux-gnu
 /usr/lib/gcc/i486-linux-gnu/4.1.2/../../../../include/c++/4.1.2/backward
 /usr/local/include
 /usr/lib/gcc/i486-linux-gnu/4.1.2/include
 /usr/include
End of search list.
 /usr/lib/gcc/i486-linux-gnu/4.1.2/cc1plus -fpreprocessed try.ii -quiet -dumpbase try.cpp -mtune=i686 -auxbase try -version -o try.s
GNU C++ version 4.1.2 20061115 (prerelease) (Debian 4.1.1-21) (i486-linux-gnu)
        compiled by GNU C version 4.1.2 20061115 (prerelease) (Debian 4.1.1-21).
GGC heuristics: --param ggc-min-expand=64 --param ggc-min-heapsize=64575
Compiler executable checksum: 183d42a838ed2b7313bffcb8f2f2fda7
try.cpp: In function '__typeof__ (((A)(0) + (B)(0))) add(A, B) [with A = double, B = int]':
try.cpp:4: internal compiler error: in write_type, at cp/mangle.c:1651
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.
For Debian GNU/Linux specific bug reporting instructions,
see <URL:file:///usr/share/doc/gcc-4.1/README.Bugs>.
Preprocessed source stored into /tmp/ccAaaM0z.out file, please attach this to your bugreport.
-----------------------------------------------------------------------------------------
> cat try.ii 
# 1 "try.cpp"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "try.cpp"
template<class A,class B>
typeof(A(0)+B(0)) add( A a , B b )
{
 return a + b;
}

void f( double & S , double X , int Y )
{
 S = add( X , Y );
}
-----------------------------------------------------------------------------------------