Unnecessary `mov eax, eax` generated only if there is a conditional branch.

https://godbolt.org/z/48scbhEKo

Code
```c++
int eax();

unsigned long long x(int in) {
in |= eax();

if (in < 0) {
while (true) {}
}

return (unsigned long long)(unsigned)in;
}

unsigned long long y(int in) {
in |= eax();

return (unsigned long long)(unsigned)in;
}
```
Assembly
```asm
x(int):
push rbx
mov ebx, edi
call eax()@PLT
or eax, ebx
js .LBB0_1
mov eax, eax ; <---
pop rbx
ret
.LBB0_1:
jmp .LBB0_1

y(int):
push rbx
mov ebx, edi
call eax()@PLT
or eax, ebx
pop rbx
ret```

Start by reproducing the example at https://godbolt.org/z/48scbhEKo and compare the generated assembly for x and y. Trace the LLVM code-generation path responsible for the conditional branch and integer conversion; done means the unnecessary mov eax, eax is no longer emitted while the branch behavior remains correct.

Written by the indexing model from the issue text.