[Bug tree-optimization/68840] New: Wrong code in loop optimization

[michael.chapman at cortus dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68840

            Bug ID: 68840
           Summary: Wrong code in loop optimization
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: michael.chapman at cortus dot com
  Target Milestone: ---

Created attachment 36983
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36983&action=edit
Test case

The loop counter (i) in the attached code runs of the end. The test (i < 4)
seems to have been optimized away in the cunrolli pass.

The attached test program exits with status 0 when compiled with gcc -O1. It
aborts when compiled with gcc -O2 (and higher optimizations).

Version information:-

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
5.1.0-0ubuntu11~14.04.1' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-5 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=c++98 --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --with-system-zlib
--disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-amd64/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 5.1.0 (Ubuntu 5.1.0-0ubuntu11~14.04.1)