The following program:
"
cat -n main.c
1 #include <stdio.h>
2
3
4 int main()
5 {
6 __label__ lab3;
7 __label__ lab4;
8
9 int i = 0;
10
11 i++;
12 lab1: fprintf(stderr, "i=%d\n", i);
13
14 i++;
15 lab2: fprintf(stderr, "i=%d\n", i);
16
17 i++;
18 lab3: fprintf(stderr, "i=%d\n", i);
19
20 i++;
21 lab4: fprintf(stderr, "i=%d\n", i);
22
23 fprintf(stderr, "&&lab1=%08x\n", (unsigned)&&lab1);
24 fprintf(stderr, "&&lab2=%08x\n", (unsigned)&&lab2);
25 fprintf(stderr, "&&lab3=%08x\n", (unsigned)&&lab3);
26 fprintf(stderr, "&&lab4=%08x\n", (unsigned)&&lab4);
27
28 return 0;
29 }
"
after being compiled as
/mnt/sdb8/sergei/AFSWD_debug/install/gcc-4.3.3/binsh/gcc -O1 -Wall -Wextra
main.c -o main_-O1
produces:
"
./main_-O1
i=1
i=2
i=3
i=4
&&lab1=08048435
&&lab2=08048452
&&lab3=0804846f
&&lab4=0804848c
"
which is correct in a sense all the labels have different addresses.
When compiled as
/mnt/sdb8/sergei/AFSWD_debug/install/gcc-4.3.3/binsh/gcc -O2 -Wall -Wextra
main.c -c -o main_-O2.o
it produces
"
./main_-O2
i=1
i=2
i=3
i=4
&&lab1=08048430
&&lab2=08048430
&&lab3=08048430
&&lab4=08048430
",
which is wrong in the sense all the addresses are the same.
Please note that labels have intentionally been put against 'fprintf'
statements which are _not_ eliminated by optimization ('objdump' easily proves
this).
I have read pages ## 246 .. 248 in
http://gcc.gnu.org/onlinedocs/gcc-4.3.3/gcc.pdf
, they don't mention optimizations (or did I miss it ?).
The problem also exists with gcc-3.4.6.
--
Summary: -O2 and higher causes wrong label address calculation
Product: gcc
Version: 4.3.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: sergstesh at yahoo dot com
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40115
