http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54558
Bug #: 54558
Summary: get wrong answer in {static int a; a = 4; a += (a++);}
Classification: Unclassified
Product: gcc
Version: 4.7.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: soar...@foxmail.com
1. Code below should output "a=9", however it output "a=5"
#include <stdio.h>
int main()
{
static int a;
a = 4;
a += (a++);
printf("a=%d\n", a);
return 0;
}
2. If omit "static" in "static int a", compile and re-run, it output expected
result "a=9"
3. If omit "++" in "a += (a++)", compile and re-run, it output expected result
"a=8"
4. Using gcc -S code in 1, below is a segment of assembly code, hope that helps
movl $4, a.1817
movl a.1817, %eax
movl a.1817, %edx
addl %eax, %edx // %edx equals to 8
movl %edx, a.1817
addl $1, %eax // %eax equals to 5
movl %eax, a.1817
movl a.1817, %eax
movl %eax, 4(%esp)
movl $.LC0, (%esp)
call printf
movl $0, %eax
leave
5. information obtained by "gcc -v -save-temps all-your-options source-file"
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: /build/src/gcc-4.7-20120721/configure --prefix=/usr
--libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared
--enable-threads=posix --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch
--enable-libstdcxx-time --enable-gnu-unique-object --enable-linker-build-id
--with-ppl --enable-cloog-backend=isl --disable-ppl-version-check
--disable-cloog-version-check --enable-lto --enable-gold --enable-ld=default
--enable-plugin --with-plugin-ld=ld.gold --with-linker-hash-style=gnu
--disable-multilib --disable-libssp --disable-build-with-cxx
--disable-build-poststage1-with-cxx --enable-checking=release
Thread model: posix
gcc version 4.7.1 20120721 (prerelease) (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-mtune=generic' '-march=pentiumpro'
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/cc1 -E -quiet -v app.c -mtune=generic
-march=pentiumpro -fpch-preprocess -o app.i
ignoring nonexistent directory
"/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/../../../../i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/include
/usr/local/include
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/include-fixed
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-mtune=generic' '-march=pentiumpro'
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/cc1 -fpreprocessed app.i -quiet -dumpbase
app.c -mtune=generic -march=pentiumpro -auxbase app -version -o app.s
GNU C (GCC) version 4.7.1 20120721 (prerelease) (i686-pc-linux-gnu)
compiled by GNU C version 4.7.1 20120721 (prerelease), GMP version 5.0.5,
MPFR version 3.1.1, MPC version 1.0
warning: MPC header version 1.0 differs from library version 1.0.1.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C (GCC) version 4.7.1 20120721 (prerelease) (i686-pc-linux-gnu)
compiled by GNU C version 4.7.1 20120721 (prerelease), GMP version 5.0.5,
MPFR version 3.1.1, MPC version 1.0
warning: MPC header version 1.0 differs from library version 1.0.1.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: b205659ec6a57a28c245e2c9c58a01b0
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-mtune=generic' '-march=pentiumpro'
as -v --32 -o app.o app.s
GNU assembler version 2.22.0 (i686-pc-linux-gnu) using BFD version (GNU
Binutils) 2.22.0.20120323
COMPILER_PATH=/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/:/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/:/usr/lib/gcc/i686-pc-linux-gnu/:/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/:/usr/lib/gcc/i686-pc-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/:/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-mtune=generic' '-march=pentiumpro'
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/collect2 --build-id --eh-frame-hdr
--hash-style=gnu -m elf_i386 -dynamic-linker /lib/ld-linux.so.2
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/../../../crt1.o
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/../../../crti.o
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/crtbegin.o
-L/usr/lib/gcc/i686-pc-linux-gnu/4.7.1
-L/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/../../.. app.o -lgcc --as-needed -lgcc_s
--no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/crtend.o
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/../../../crtn.o
