[Bug c/47255] New: Missed optimization with loops, inline functions, and __attribute__((const))

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47255

           Summary: Missed optimization with loops, inline functions, and
                    __attribute__((const))
           Product: gcc
           Version: 4.5.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: in-gnu@baka.org


Created attachment 22942
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=22942
Test program exhibiting missed optimization

Using gcc 4.5.2 on gentoo (or gcc 4.1.2 on RHEL 5.5), gcc fails to optimize a
case where a const function is called in a const way inside a loop, if the
const function is elgible for inlining.

The test case should print three lines if it succeeds.  In fact, the "World"
line is printed once per loop iteration.

How-To-Repeat:

Compile the attach test-case with -O3 or "-O -finline-small-functions
-finline-functions" -- more than three lines are printed.  Compile with -O2,
the correct number of lines (three) for full optimization are printed.

Release:
----------------------------------------------------------------------
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-libgcj-multifile
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk
--disable-dssi --enable-plugin
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre --with-cpu=generic
--host=x86_64-redhat-linux
Thread model: posix
gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)
----------------------------------------------------------------------
Using built-in specs.
COLLECT_GCC=/usr/x86_64-pc-linux-gnu/gcc-bin/4.5.2/gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/4.5.2/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with:
/n/startide/proj/startide/var-tmp/portage/sys-devel/gcc-4.5.2/work/gcc-4.5.2/configure
--prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.5.2
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.5.2/include
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.5.2
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.5.2/man
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.5.2/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.5.2/include/g++-v4
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-altivec
--disable-fixed-point --without-ppl --without-cloog --disable-lto --enable-nls
--without-included-gettext --with-system-zlib --disable-werror
--enable-secureplt --enable-multilib --enable-libmudflap --disable-libssp
--enable-libgomp --enable-cld
--with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/4.5.2/python
--enable-checking=release --disable-libgcj --enable-languages=c,c++
--enable-shared --enable-threads=posix --enable-__cxa_atexit
--enable-clocale=gnu --with-bugurl=http://bugs.gentoo.org/
--with-pkgversion='Gentoo 4.5.2 p1.0, pie-0.4.5'
Thread model: posix
gcc version 4.5.2 (Gentoo 4.5.2 p1.0, pie-0.4.5)
----------------------------------------------------------------------