This is not the same as bug 11751 as the variable used with ++ is not reused.
Here the simple code:
sadd.i:
# 1 "sadd.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "sadd.c"
typedef struct A A;
struct A {
int no;
A *sub;
};
void main()
{ A sub={0, ((void*)0)};
A root={0, &sub};
A *pos=&root;
pos=&pos->sub[pos->no++];
printf("%d %d %p %p %p\n", root.no, sub.no, &root, &sub, pos);
}
Here the compiler call:
<~/test> 82>/usr/local/gcc-4.1.0/bin/gcc -v -save-temps sadd.c
Using built-in specs.
Target: i586-suse-linux
Configured with: ../gcc-4.1.0/configure --prefix=/usr/local/gcc-4.1.0
--enable-java-awt=gtk --with-cpu=pentium4 --enable-threads=posix
--enable-languages=c,c++,java --disable-checking --host=i586-suse-linux
--disable-libjava-multilib --without-system-libunwind --with-sy
stem-zlib
Thread model: posix
gcc version 4.1.0
/usr/local/gcc-4.1.0/libexec/gcc/i586-suse-linux/4.1.0/cc1 -E -quiet -v sadd.c
-mtune=pentium4 -fpch-preprocess -o sadd.i
ignoring nonexistent directory
"/usr/local/gcc-4.1.0/lib/gcc/i586-suse-linux/4.1.0/../../../../i586-suse-linux/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/usr/local/gcc-4.1.0/include
/usr/local/gcc-4.1.0/lib/gcc/i586-suse-linux/4.1.0/include
/usr/include
End of search list.
/usr/local/gcc-4.1.0/libexec/gcc/i586-suse-linux/4.1.0/cc1 -fpreprocessed
sadd.i -quiet -dumpbase sadd.c -mtune=pentium4 -auxbase sadd
-version -o sadd.s
GNU C version 4.1.0 (i586-suse-linux)
compiled by GNU C version 4.1.0.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 9c3116972ab61a6d962b78330fe593eb
sadd.c: In function main:
sadd.c:15: warning: incompatible implicit declaration of built-in function
printf
sadd.c:10: warning: return type of main is not int
as -V -Qy -o sadd.o sadd.s
GNU assembler version 2.16.91.0.2 (i586-suse-linux) using BFD version
2.16.91.0.2 20050720 (SuSE Linux)
/usr/local/gcc-4.1.0/libexec/gcc/i586-suse-linux/4.1.0/collect2 --eh-frame-hdr
-m elf_i386 -dynamic-linker /lib/ld-linux.so.2 /usr/lib
/crt1.o /usr/lib/crti.o
/usr/local/gcc-4.1.0/lib/gcc/i586-suse-linux/4.1.0/crtbegin.o
-L/usr/local/gcc-4.1.0/lib/gcc/i586-suse-linux/4.
1.0 -L/usr/local/gcc-4.1.0/lib/gcc/i586-suse-linux/4.1.0/../../.. sadd.o -lgcc
--as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed
-lgcc_s --no-as-needed
/usr/local/gcc-4.1.0/lib/gcc/i586-suse-linux/4.1.0/crtend.o /usr/lib/crtn.o
Here the command execution.
<~/test> 85>sadd
0 1 0xbf995550 0xbf995558 0xbf995558
The problem is that the updated pos pointer is used to perform the ++ on the
field "no" while the assignment should be actually the last statement. Also
pos->no was needed and fetched before to actually calculate the new pos.
The problem is present even with -O0 on the gcc-4.0.2 (from SuSe 10.0) and
gcc-4.1.0 (see above)
The compilers gcc-3.4.6, gcc-3.3.1 don't have that problem on the same platform
and on Tru64 5.1. Also the Tru64 5.1 standard C compiler does not have the
problem.
<~/test> >gcc -o sadd sadd.c
sadd.c: In function `main':
sadd.c:10: warning: return type of `main' is not `int'
<~/test> >sadd
1 0 11fffbfe0 11fffbfd0 11fffbfd0
<~/test> >gcc -v
Reading specs from
/usr/local/gcc-3.3.1/lib/gcc-lib/alphaev68-dec-osf5.1/3.3.1/specs
Configured with: ../gcc-3.3.1/configure --prefix=/usr/local/gcc-3.3.1
--disable-shared
Thread model: single
gcc version 3.3.1
<~/test> >cc -o sadd sadd.c
<~/test> >sadd
1 0 11fffbfd8 11fffbfe8 11fffbfe8
<~/test> >cc -V
Compaq C V6.4-216 (dtk) on Compaq Tru64 UNIX V5.1A (Rev. 1885)
Compiler Driver V6.4-013 (dtk) cc Driver
<~/test> >
--
Summary: Pointer assignment used together with ++ leads to an
update of the wrong structure
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: SimonX200 at hotmail dot com
GCC build triplet: i586-suse-linux
GCC host triplet: i586-suse-linux
GCC target triplet: i586-suse-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26730
