http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55559
Bug #: 55559
Summary: Marshalling double through union with inlines,
incorrect behavior with -O2
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: mpr...@gmail.com
Created attachment 28848
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28848
.ii preprocessed source
The following simple program returns different results depending on being
compiled with / without -O2.
The expected result is (unsigned)-1, but the observed result with -O2 is 0.
//----------
union V {
long long v;
double dbl;
};
inline long long VAL_NUM(double d) { return V{dbl: d}.v; }
inline double GET_NUM(long long val) { return V{v: val}.dbl; }
int main() {
return (unsigned) GET_NUM(VAL_NUM(-1));
}
//---------
gcc -v -save-temps -std=c++11 -Wall bug.cpp
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.7/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.7.2-2ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs
--enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.7 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object
--enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i686
--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 4.7.2 (Ubuntu/Linaro 4.7.2-2ubuntu1)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c++11' '-Wall' '-mtune=generic'
'-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/4.7/cc1plus -E -quiet -v -imultiarch
x86_64-linux-gnu -D_GNU_SOURCE bug.cpp -mtune=generic -march=x86-64 -std=c++11
-Wall -fpch-preprocess -fstack-protector -o bug.ii
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/include/c++/4.7
/usr/include/c++/4.7/x86_64-linux-gnu
/usr/include/c++/4.7/backward
/usr/lib/gcc/x86_64-linux-gnu/4.7/include
/usr/local/include
/usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c++11' '-Wall' '-mtune=generic'
'-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/4.7/cc1plus -fpreprocessed bug.ii -quiet
-dumpbase bug.cpp -mtune=generic -march=x86-64 -auxbase bug -Wall -std=c++11
-version -fstack-protector -o bug.s
GNU C++ (Ubuntu/Linaro 4.7.2-2ubuntu1) version 4.7.2 (x86_64-linux-gnu)
compiled by GNU C version 4.7.2, GMP version 5.0.2, MPFR version 3.1.0-p3,
MPC version 0.9
warning: GMP header version 5.0.2 differs from library version 5.0.5.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++ (Ubuntu/Linaro 4.7.2-2ubuntu1) version 4.7.2 (x86_64-linux-gnu)
compiled by GNU C version 4.7.2, GMP version 5.0.2, MPFR version 3.1.0-p3,
MPC version 0.9
warning: GMP header version 5.0.2 differs from library version 5.0.5.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 521527ea42f0901bf839bcaad0cb13e6
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c++11' '-Wall' '-mtune=generic'
'-march=x86-64'
as -v --64 -o bug.o bug.s
GNU assembler version 2.22.90 (x86_64-linux-gnu) using BFD version (GNU
Binutils for Ubuntu) 2.22.90.20120924
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c++11' '-Wall' '-mtune=generic'
'-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/4.7/collect2 --sysroot=/ --build-id
--no-add-needed --as-needed --eh-frame-hdr -m elf_x86_64 --hash-style=gnu
-dynamic-linker /lib64/ld-linux-x86-64.so.2 -z relro
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crt1.o
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crti.o
/usr/lib/gcc/x86_64-linux-gnu/4.7/crtbegin.o
-L/usr/lib/gcc/x86_64-linux-gnu/4.7
-L/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu
-L/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../lib -L/lib/x86_64-linux-gnu
-L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib
-L/usr/lib/gcc/x86_64-linux-gnu/4.7/../../.. bug.o -lgcc --as-needed -lgcc_s
--no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed
/usr/lib/gcc/x86_64-linux-gnu/4.7/crtend.o
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crtn.o
