https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95890
Bug ID: 95890
Summary: Probably wrong Line Information at Og
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: massarelli at diag dot uniroma1.it
Target Milestone: ---
$ cat a.c
int a;
void b() {
short l_196 = a = 0;
a+1;
}
int main() { b(); }
$ cat -n a.c
1 int a;
2 void b() {
3 short l_196 = a = 0;
4 a+1;
5 }
6 int main() { b(); }
7
When compiled with gcc trunk and flag -Og -g, gdb 9.2 shows a step over line 4,
while the add instruction does not exist in the assembly. When compiled with
-O0 it correctly jumps to line 5, never showing the step over line 4.
Even in the non optimized binary the add at line 4 is not translated in
assembly.
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/local/bin/../libexec/gcc/x86_64-pc-linux-gnu/11.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ./configure --prefix=/tmp/gcc_build --disable-multilib
--enable-languages=c,c++
Thread model: posix
Supported LTO compression algorithms: zlib
$ gcc -Og -g a.c -o a.out
$ gdb a.out
GNU gdb (GDB) 9.2
Reading symbols from a.out...
(gdb) b main
Breakpoint 1 at 0x400491: file a.c, line 6.
(gdb) r
Starting program: /home/stepping/output/a.out
Breakpoint 1, main () at a.c:6
6 int main() { b(); }
(gdb) s
b () at a.c:3
3 short l_196 = a = 0;
(gdb) s
4 a+1;
(gdb) disassemble
Dump of assembler code for function b:
0x0000000000400486 <+0>: movl $0x0,0x200b9c(%rip) # 0x60102c
=> 0x0000000000400490 <+10>: retq
End of assembler dump.
