https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77620
Bug ID: 77620
Summary: Generic compile time regression of 7.0
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: petschy at gmail dot com
Target Milestone: ---
I noticed that compiling my C++ project with 7.0 at -O3 took twice as much time
as before with earlier major versions. First I thought that it might be that
7.0 used more optimizations, but a significant time difference remained even
with -O0:
5.4.1 6.2.1 7.0.0
-O0 2m10 2m18 3m43
-O1 2m45 2m51 5m38
-O2 3m24 3m26 6m46
-O3 3m25 3m34 7m05
Also did measurements with the gcc source, compiling the master branch
(b55f1f4) with
for o in 0 1 2 3; do for v in 4.9.2 5.4.1 6.2.1 7.0.0; do rm -Rf *;
../configure CC=gcc-$v CXX=g++-$v --enable-languages=c,c++ --disable-multilib
--program-suffix=-`cat ../gcc/BASE-VER` --disable-bootstrap CFLAGS="-O$o
-march=native" CXXFLAGS="-O$o -march=native"; time make -j8; echo "-O$o $v";
echo hit enter to continue; read x; done; done
4.9.2 5.4.1 6.2.1 7.0.0
-O0 7m15 7m12 7m28 8m18
-O1 7m11 7m13 7m02 9m11
-O2 8m19 8m17 8m24 10m57
-O3 8m53 8m57 9m05 12m03
The tests were done on a PC with Debian Jessie 64bit, AMD FX-8150 @ 4GHz, 16GB
RAM, XFS on SSD.
$ gcc-4.9.2 -v
Using built-in specs.
COLLECT_GCC=gcc-4.9.2
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-unknown-linux-gnu/4.9.2/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ./configure --enable-languages=c,c++ --disable-multilib
--program-suffix=-4.9.2
Thread model: posix
gcc version 4.9.2 20140808 (prerelease) (GCC)
$ gcc-5.4.1 -v
Using built-in specs.
COLLECT_GCC=gcc-5.4.1
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-unknown-linux-gnu/5.4.1/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --enable-languages=c,c++ --disable-multilib
--program-suffix=-5.4.1 --disable-bootstrap CFLAGS='-O2 -march=native'
CXXFLAGS='-O2 -march=native'
Thread model: posix
gcc version 5.4.1 20160829 (GCC)
$ gcc-6.2.1 -v
Using built-in specs.
COLLECT_GCC=gcc-6.2.1
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-pc-linux-gnu/6.2.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --enable-languages=c,c++ --disable-multilib
--program-suffix=-6.2.1 --disable-bootstrap CFLAGS='-O2 -march=native'
CXXFLAGS='-O2 -march=native'
Thread model: posix
gcc version 6.2.1 20160831 (GCC)
$ gcc-7.0.0 -v
Using built-in specs.
COLLECT_GCC=gcc-7.0.0
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-pc-linux-gnu/7.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --enable-languages=c,c++ --disable-multilib
--program-suffix=-7.0.0 --disable-bootstrap CFLAGS='-O2 -march=native'
CXXFLAGS='-O2 -march=native'
Thread model: posix
gcc version 7.0.0 20160831 (experimental) (GCC)
