https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68431
Bug ID: 68431
Summary: Regression in GCC-6.0.0's optimizer
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
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-5.2.1 and GCC-6.0.0 with -O3 option.
GCC-5.2.1 performed better optimization than GCC-6.0.0.
Note that "unsigned int" is 32 bit and "long long int" is 64 bit.
(A.c)
unsigned int x = 1;
int main (void)
{
long long int a = -2LL;
int t = 1<=(a/x);
if (t != 0) { __builtin_abort(); }
return 0;
}
+---------------------------------------+--------------------------------------+
| gcc-5.2.1s (gcc-5.2.1 A.c -O3 -S) | gcc-6.0.0.s (gcc-6.0.0 A.c -O3 -S)
|
+---------------------------------------+--------------------------------------+
|main: |main:
|
|.LFB0: |.LFB0:
|
| .cfi_startproc | .cfi_startproc
|
| | movl x(%rip), %ecx
|
| | movq $-2, %rax
|
| | cqto
|
| | idivq %rcx
|
| | testq %rax, %rax
|
| | jg .L7
|
| xorl %eax, %eax | xorl %eax, %eax
|
| ret | ret
|
| |.L7:
|
| | pushq %rax
|
| | .cfi_def_cfa_offset 16
|
| | call abort
|
| .cfi_endproc | .cfi_endproc
|
|.LFE0: |.LFE0:
|
| .size main, .-main | .size main, .-main
|
| .section .text.unlikely |
|
|.LCOLDE0: |
|
| .section .text.startup |
|
|.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: (Ubuntu 5.2.1 ...| .ident "GCC: (GNU) 6.0.0
...|
| .section .note.GNU- ...| .section .note.GNU-
...|
+---------------------------------------+--------------------------------------+
$ gcc-6.0 -v
Using built-in specs.
COLLECT_GCC=gcc-6.0
COLLECT_LTO_WRAPPER=/home/iwatsuji/opt/gcc-6.0.0/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
configured with: ../gcc/configure --prefix=/home/iwatsuji/opt/gcc-6.0.0
--program-suffix=-6.0 --disable-multilib --enable-languages=c
Thread model: posix
gcc versin 6.0.0 20151119 (experimental) (GCC)
$ gcc-5 -v
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
5.2.1-23ubuntu1~14.04.2' --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=gcc4-compatible --disable-libstdcxx-dual-abi
--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 20151031 (Ubuntu 5.2.1-23ubuntu1~14.04.2)
