[Bug c/22633] New: recursivity -O3 pessimization

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

Using built-in specs.
Target: powerpc-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f95,objc,ada,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib --enable-nls
--without-included-gettext --enable-threads=posix --program-suffix=-4.0
--enable-__cxa_atexit --enable-libstdcxx-allocator=mt --enable-clocale=gnu
--enable-libstdcxx-debug --enable-java-gc=boehm --enable-java-awt=gtk
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-4.0-1.4.2.0/jre --enable-mpfr
--disable-multilib --disable-werror --enable-checking=release powerpc-linux-gnu
Thread model: posix
gcc version 4.0.1 (Debian 4.0.1-2)


unsigned factorial(unsigned i)
{
	if(i <= 1)
		return 1;
	else
		return i * factorial(i - 1);
}


gcc < 4.0 was never able to optimize this kind of function the right way.
gcc-4.0 is :)

At level -O1, -O2 and -Os, gcc optimizes the recursive call away turning the
function into a simple loop. Impressive. Great :)
But at level -O3, gcc tries to optimize in a very different way : it unrolls 10
times factorial() body, and then makes a recursive call. Bad.

-- 
           Summary: recursivity -O3 pessimization
           Product: gcc
           Version: 4.0.1
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: TazForEver at dlfp dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: powerpc-linux-gnu
  GCC host triplet: powerpc-linux-gnu
GCC target triplet: powerpc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22633