[Bug tree-optimization/71521] New: Regression in GCC-7.0.0's optimizer

[ishiura-compiler at ml dot kwansei.ac.jp]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71521

            Bug ID: 71521
           Summary: Regression in GCC-7.0.0's optimizer
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ishiura-compiler at ml dot kwansei.ac.jp
  Target Milestone: ---

We compiled a program (A.c) by GCC-7.0.0 and GCC-5.2.1 with -O3 option.
GCC-5.2.1 performed better optimization than GCC-7.0.0.

(A.c)
int x = 1;

int main ()
{
        int t = (1/(1>=x))>>1;
        if (t != 0) __builtin_abort();
        return 0;
}

+--------------------------------------+------------------------------------+
|gcc-7.0.0.s (gcc-7.0.0 A.c -O3 -S)    |gcc-5.2.1.s (gcc-5.2.1 A.c -O3 -S)  |
+--------------------------------------+------------------------------------+
|main:                                 |main:                               |
|.LFB0:                                |.LFB0:                              |
|        .cfi_startproc                |        .cfi_startproc              |
|        cmpl    $1, x(%rip)           |                                    |
|        jle     .L2                   |                                    |
|        movl    $1, %eax              |                                    |
|        xorl    %ecx, %ecx            |                                    |
|        cltd                          |                                    |
|        idivl   %ecx                  |                                    |
|        testl   %eax, %eax            |                                    |
|        js      .L10                  |                                    |
|.L2:                                  |                                    |
|        xorl    %eax, %eax            |        xorl    %eax, %eax          |
|        ret                           |        ret                         |
|.L10:                                 |                                    |
|        subq    $8, %rsp              |                                    |
|        .cfi_def_cfa_offset 16        |                                    |
|        call    abort                 |                                    |
|        .cfi_endproc                  |        .cfi_endproc                |
|.LFE0:                                |.LFE0:                              |
|        .size   main, .-main          |        .size   main, .-main        |
|                                      |        .section        .text.unl...|
|                                      |.LCOLDE0:                           |
|                                      |        .section        .text.sta...|
|                                      |.LHOTE0:                            |
|        .globl  x                     |        .globl  x                   |
|        .data                         |        .data                       |
|        .align 4                      |        .align 4                    |
+--------------------------------------+------------------------------------+
|        .size   x, 4                  |        .size   x, 4                |
|x:                                    |x:                                  |
|        .long   1                     |        .long   1                   |
|        .ident  "GCC: (GNU) 7.0.0 ... |        .ident  "GCC: (Ubuntu 5.2...|
|        .section        .note.GNU-... |        .section        .note.GNU...|
+--------------------------------------+------------------------------------+


using built-in spacs.
COLLECT_GCC=gcc-7.0-0612
COLLECT_LTO_WRAPPER=/home/kota_kitaura/opt/gcc-7.0-0612/libexec/gcc/x86_64-pc-linux-gnu/7.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
configure with: ../gcc/configure --prefix=/home/kota_kitaura/opt/gcc-7.0-0612
--program-suffix=-7.0-0612 --enable-languages=c
Thread model: posix
gcc version 7.0.0 20160612 (experimental) (GCC) 

Using built-in specs.
COLLECT_GCC=gcc-5
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
5.2.1-23ubuntu1~15.10' --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=new --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 5.2.1 20151028 (Ubuntu 5.2.1-23ubuntu1~15.10)