https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103308
Bug ID: 103308
Summary: gcc regression after version 8, simple double loop
exiting early with optimizations
Product: gcc
Version: 11.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: pallansson at gmail dot com
Target Milestone: ---
Picked up from here:
https://cboard.cprogramming.com/c-programming/180520-interesting-bug-gcc-9-above.html
I have tested gcc-9/10/11 as included in Ubuntu and they all give the same
results, as well as builds from gcc.git of latest gcc-11 and gcc-12, specific
results from gcc 11.1.0 in Ubuntu 21.04 below:
$ gcc-11 -Og -o el earlyloop.c
$ ./el
a=0, c=1
a=0, c=2
a=1, c=3
a=1, c=4
a=2, c=5
a=2, c=6
a=3, c=7
a=3, c=8
a=4, c=9
a=4, c=10
a=5, c=11
a=5, c=12
a=6, c=13
a=6, c=14
a=7, c=15
a=7, c=16
a=8, c=17
a=8, c=18
a=9, c=19
a=9, c=20
$ gcc-11 -O3 -o el earlyloop.c
$ ./el
a=0, c=1
a=0, c=2
a=1, c=3
$ gcc-11 -v
Using built-in specs.
COLLECT_GCC=gcc-11
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/11/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
11.1.0-1ubuntu1~21.04' --with-bugurl=file:///usr/share/doc/gcc-11/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-11
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-11-RPS7jb/gcc-11-11.1.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-11-RPS7jb/gcc-11-11.1.0/debian/tmp-gcn/usr
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
--with-build-config=bootstrap-lto-lean --enable-link-serialization=2
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.1.0 (Ubuntu 11.1.0-1ubuntu1~21.04)
