$ clang-trunk -v
clang version 14.0.0 (https://github.com/llvm/llvm-project.git 82fc4cc60bec6d0eacad7e8575f404dcdf5144c5)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/cnsun/usr/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$ cat program0_preprocessed.c
int a, e;
int volatile b;
int *c;
short d;
void main() {
int f;
for (;;) {
int g, h;
int i[6];
c = i;
d ^= 4;
f = d > i[5] ? 0 : d + i[5];
g = h = f - a;
int j = 2;
e = 2 - h;
b = e;
}
}
$ clang-trunk -w -flto -O2 program0_preprocessed.c -o a.out; objdump --disassemble --section=.text a.out > no_g.txt
$ clang-trunk -w -flto -O2 -g program0_preprocessed.c -o a.out; objdump --disassemble --section=.text a.out > g.txt
$ diff no_g.txt g.txt
98,106c98,105
< 401144: ba 02 00 00 00 mov $0x2,%edx
< 401149: 29 f2 sub %esi,%edx
< 40114b: 29 fa sub %edi,%edx
< 40114d: 39 fe cmp %edi,%esi
< 40114f: 41 0f 4c d1 cmovl %r9d,%edx
< 401153: 89 15 e3 2e 00 00 mov %edx,0x2ee3(%rip) # 40403c <b>
< 401159: 8b 74 24 fc mov -0x4(%rsp),%esi
< 40115d: eb d1 jmp 401130 <main+0x20>
< 40115f: 90 nop
---
> 401144: 8d 0c 3e lea (%rsi,%rdi,1),%ecx
> 401147: ba 02 00 00 00 mov $0x2,%edx
> 40114c: 29 ca sub %ecx,%edx
> 40114e: 39 fe cmp %edi,%esi
> 401150: 41 0f 4c d1 cmovl %r9d,%edx
> 401154: 89 15 e2 2e 00 00 mov %edx,0x2ee2(%rip) # 40403c <b>
> 40115a: 8b 74 24 fc mov -0x4(%rsp),%esi
> 40115e: eb d0 jmp 401130 <main+0x20>
$
Extended Description
The .text section for the following program (program0_preprocessed.c
) changes after toggling the -g flag.