[Bug c/64136] New: gcc tree optimization removes basic block containing break condition

["ecd at brainaid dot de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64136

            Bug ID: 64136
           Summary: gcc tree optimization removes basic block containing
                    break condition
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ecd at brainaid dot de

Created attachment 34152
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34152&action=edit
bug.i source code

When compiling the following code the loop does not terminate properly, if day
is greater than 334 and leap equal 0 or day is greater than 335 and leap equals
1:

#include <stdint.h>

static const uint16_t days_on_first[2][12] =
            {
                { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 },
                { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335 }
            };

int
foo(int leap, int32_t days)
{
        int i = 0;

        while ((days <= days_on_first[leap][i + 1]) && (i < 11)) {
                i++;
        }

        return i;
}

The test for (i << 11) is removed from the loop. This is verified by looking at
the generated output bug.c.056t.cunrolli.

The bug can be reproduced on gcc for x86 with the following options:

gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-cygwin/4.8.3/lto-wrapper.exe
Target: x86_64-pc-cygwin
Configured with:
/cygdrive/i/szsz/tmpp/gcc/gcc-4.8.3-3.x86_64/src/gcc-4.8.3/configure
--srcdir=/cygdrive/i/szsz/tmpp/gcc/gcc-4.8.3-3.x86_64/src/gcc-4.8.3
--prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin
--libexecdir=/usr/libexec --datadir=/usr/share --localstatedir=/var
--sysconfdir=/etc --libdir=/usr/lib --datarootdir=/usr/share
--docdir=/usr/share/doc/gcc --htmldir=/usr/share/doc/gcc/html -C
--build=x86_64-pc-cygwin --host=x86_64-pc-cygwin --target=x86_64-pc-cygwin
--without-libiconv-prefix --without-libintl-prefix --libexecdir=/usr/lib
--enable-shared --enable-shared-libgcc --enable-static
--enable-version-specific-runtime-libs --enable-bootstrap --enable-__cxa_atexit
--with-dwarf2 --with-tune=generic
--enable-languages=ada,c,c++,fortran,lto,objc,obj-c++ --enable-graphite
--enable-threads=posix --enable-libatomic --enable-libgomp --disable-libitm
--enable-libquadmath --enable-libquadmath-support --enable-libssp
--enable-libada --enable-libgcj-sublibs --disable-java-awt --disable-symvers
--with-ecj-jar=/usr/share/java/ecj.jar --with-gnu-ld --with-gnu-as
--with-cloog-include=/usr/include/cloog-isl --without-libiconv-prefix
--without-libintl-prefix --with-system-zlib --enable-linker-build-id
Thread model: posix
gcc version 4.8.3 (GCC)

and on arm-none-eabi-gcc compiled with these options:

arm-none-eabi-gcc -v
Using built-in specs.
COLLECT_GCC=arm-none-eabi-gcc
COLLECT_LTO_WRAPPER=/opt/gcc-arm-none-eabi-4_8-2014q4/bin/../lib/gcc/arm-none-eabi/4.8.4/lto-wrapper
Target: arm-none-eabi
Configured with:
/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/src/gcc/configure
--target=arm-none-eabi
--prefix=/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/install-native
--libexecdir=/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/install-native/lib
--infodir=/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/install-native/share/doc/gcc-arm-none-eabi/info
--mandir=/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/install-native/share/doc/gcc-arm-none-eabi/man
--htmldir=/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/install-native/share/doc/gcc-arm-none-eabi/html
--pdfdir=/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/install-native/share/doc/gcc-arm-none-eabi/pdf
--enable-languages=c,c++ --enable-plugins --disable-decimal-float
--disable-libffi --disable-libgomp --disable-libmudflap --disable-libquadmath
--disable-libssp --disable-libstdcxx-pch --disable-nls --disable-shared
--disable-threads --disable-tls --with-gnu-as --with-gnu-ld --with-newlib
--with-headers=yes --with-python-dir=share/gcc-arm-none-eabi
--with-sysroot=/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/install-native/arm-none-eabi
--build=x86_64-linux-gnu --host=x86_64-linux-gnu
--with-gmp=/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/build-native/host-libs/usr
--with-mpfr=/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/build-native/host-libs/usr
--with-mpc=/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/build-native/host-libs/usr
--with-isl=/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/build-native/host-libs/usr
--with-cloog=/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/build-native/host-libs/usr
--with-libelf=/home/IS/ecd/src/gcc-arm-none-eabi-4_8-2014q3-20140805/build-native/host-libs/usr
--with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++,-Bdynamic -lm'
--with-pkgversion='GNU Tools for ARM Embedded Processors'
--with-multilib-list=armv6-m,armv7-m,armv7e-m,armv7-r
Thread model: single
gcc version 4.8.4 20140725 (release) [ARM/embedded-4_8-branch revision 213147]
(GNU Tools for ARM Embedded Processors)

The problem goes away, when the code is compiled with
-fno-aggressive-loop-optimizations.

The systems this can be reproduced are Debian Linux 7 (wheezy) and
Cygwin_NT-6.1.

Command line used to trigger the bug is:

gcc -O2 -c bug.i -save-temps -fdump-tree-all -fopt-info-all

Please find attached the files bug.i and bug.i.056t.cunrolli.