https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71384
Bug ID: 71384
Summary: Global constructors (init_array) emitted for trivial
initialisation depending on source code ordering
Product: gcc
Version: 5.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: niels at penneman dot org
Target Milestone: ---
GCC versions 4.7.2/5.3.0/5.3.1 are emitting a global constructor (to the
.init_array section) for the following piece of trivial code:
===
struct X
{
constexpr X(int a);
const int m_a;
};
X x(999);
inline constexpr X::X(int a):m_a(a) {}
===
Swapping the last two lines, i.e. placing the constructor implementation before
the declaration of 'x', causes 'x' to be emitted to the '.data' section with
value 999 instead. The latter is desirable as the generate binary is far
smaller and does not require global constructors.
How to reproduce:
g++ -std=c++11 -c -save-temps=obj global-constructor.cxx
Occurs regardless of whether you specify -O0, -O1, -O2, -O3. In a complete
program, -flto cannot resolve this. The issue occurs on both x86_64 and ARM, so
not in the backend. Also occurs with -std=c++14 and -std=c++17 on GCC 5.3.x.
Compiler versions used:
$ g++ -###
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/5.3.1/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap
--enable-languages=c,c++,objc,obj-c++,fortran,ada,go,lto --prefix=/usr
--mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared
--enable-threads=posix --enable-checking=release --enable-multilib
--with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions
--enable-gnu-unique-object --enable-linker-build-id
--with-linker-hash-style=gnu --enable-plugin --enable-initfini-array
--disable-libgcj --with-isl --enable-libmpx --enable-gnu-indirect-function
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 5.3.1 20160406 (Red Hat 5.3.1-6) (GCC)
$ ${CROSS_COMPILE}g++ -###
Using built-in specs.
COLLECT_GCC=/home/niels/workspace/toolchains/build/arm-none-eabi/output/bin/arm-none-eabi-g++
COLLECT_LTO_WRAPPER=/home/niels/workspace/toolchains/build/arm-none-eabi/output/libexec/gcc/arm-none-eabi/5.3.0/lto-wrapper
Target: arm-none-eabi
Configured with:
/home/niels/workspace/toolchains/build/arm-none-eabi/work/src/gcc-5.3.0/configure
--build=x86_64-build_pc-linux-gnu --host=x86_64-build_pc-linux-gnu
--target=arm-none-eabi
--prefix=/home/niels/workspace/toolchains/build/arm-none-eabi/output
--with-local-prefix=/home/niels/workspace/toolchains/build/arm-none-eabi/output/arm-none-eabi/sysroot
--with-sysroot=/home/niels/workspace/toolchains/build/arm-none-eabi/output/arm-none-eabi/sysroot
--with-newlib --enable-threads=no --disable-shared --with-float=soft
--with-pkgversion='crosstool-NG crosstool-ng-1.22.0-134-ge1d494a'
--enable-__cxa_atexit --disable-libgomp --disable-libmudflap --disable-libssp
--disable-libquadmath --disable-libquadmath-support
--with-gmp=/home/niels/workspace/toolchains/build/arm-none-eabi/work/arm-none-eabi/buildtools
--with-mpfr=/home/niels/workspace/toolchains/build/arm-none-eabi/work/arm-none-eabi/buildtools
--with-mpc=/home/niels/workspace/toolchains/build/arm-none-eabi/work/arm-none-eabi/buildtools
--with-isl=/home/niels/workspace/toolchains/build/arm-none-eabi/work/arm-none-eabi/buildtools
--enable-lto --with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++ -lm'
--enable-target-optspace --disable-nls --disable-multilib
--enable-languages=c,c++
Thread model: single
gcc version 5.3.0 (crosstool-NG crosstool-ng-1.22.0-134-ge1d494a)
$ ${CROSS_COMPILE}g++ -###
Using built-in specs.
COLLECT_GCC=/opt/OSELAS.Toolchain-2012.12.1/arm-v5te-linux-gnueabi/gcc-4.7.2-glibc-2.16.0-binutils-2.22-kernel-3.6-sanitized/bin/arm-v5te-linux-gnueabi-g++
COLLECT_LTO_WRAPPER=/opt/OSELAS.Toolchain-2012.12.1/arm-v5te-linux-gnueabi/gcc-4.7.2-glibc-2.16.0-binutils-2.22-kernel-3.6-sanitized/bin/../libexec/gcc/arm-v5te-linux-gnueabi/4.7.2/lto-wrapper
Target: arm-v5te-linux-gnueabi
Configured with:
/home/mol/dude/tmp/OSELAS.Toolchain-2012.12.1/platform-arm-v5te-linux-gnueabi-gcc-4.7.2-glibc-2.16.0-binutils-2.22-kernel-3.6-sanitized/build-cross/gcc-4.7.2/configure
--build=x86_64-host-linux-gnu --host=x86_64-host-linux-gnu
--target=arm-v5te-linux-gnueabi
--with-sysroot=/home/mol/dude/tmp/OSELAS.Toolchain-2012.12.1/inst/opt/OSELAS.Toolchain-2012.12.1/arm-v5te-linux-gnueabi/gcc-4.7.2-glibc-2.16.0-binutils-2.22-kernel-3.6-sanitized/sysroot-arm-v5te-linux-gnueabi
--disable-multilib --with-float=soft --with-fpu=vfp --with-cpu=arm926ej-s
--enable-__cxa_atexit --disable-sjlj-exceptions --disable-nls
--disable-decimal-float --disable-fixed-point --disable-win32-registry
--enable-symvers=gnu --with-pkgversion=OSELAS.Toolchain-2012.12.1
--enable-threads=posix --with-system-zlib
--with-gmp=/home/mol/dude/tmp/OSELAS.Toolchain-2012.12.1/platform-arm-v5te-linux-gnueabi-gcc-4.7.2-glibc-2.16.0-binutils-2.22-kernel-3.6-sanitized/sysroot-host
--with-mpfr=/home/mol/dude/tmp/OSELAS.Toolchain-2012.12.1/platform-arm-v5te-linux-gnueabi-gcc-4.7.2-glibc-2.16.0-binutils-2.22-kernel-3.6-sanitized/sysroot-host
--prefix=/home/mol/dude/tmp/OSELAS.Toolchain-2012.12.1/inst/opt/OSELAS.Toolchain-2012.12.1/arm-v5te-linux-gnueabi/gcc-4.7.2-glibc-2.16.0-binutils-2.22-kernel-3.6-sanitized
--enable-languages=c,c++ --enable-c99 --enable-long-long
--enable-libstdcxx-debug --enable-profile --enable-shared --disable-libssp
--enable-checking=release
Thread model: posix
gcc version 4.7.2 (OSELAS.Toolchain-2012.12.1)
