[llvm] [X86] Recognize POP/ADD/SUB modifying rsp in getSPAdjust. (PR #114265)

[via llvm-commits]

dyung wrote:

@daniel-zabawa sorry for the delay, but here is a reduced C++ program which demonstrates the issue we were seeing on our internal tests.
```c++
extern "C" {
void printf(char *);
void snprintf(char *, long...);
void atexit(void());
}
void a() { printf("{PASS}\n{END}\n\x1a\n"); }
__attribute__((constructor)) void b() { atexit(a); }
void c(char *, int, char *fmt...) {
  __builtin_va_list args;
  __builtin_va_start(args, fmt);
}
char d[1];
long e;
int main() {
  struct f {
    f() {
      struct m {
        m() {
          for (long g = -10; g; ++g)
            for (long h = -10; h != 10; ++h)
              struct i {
                long j;
                i(long initial) {
                  char *k;
                  long l = initial, actual = __sync_lock_test_and_set_8(&l, j);
                  k = "";
                  snprintf(d, sizeof(d),
                           "%%s %%s0 expected %s/%s but got %s/%s", 0, 0, 0, 0,
                           0, "");
                  c("", 0, d, 0, "__sync_lock_test_and_set_8", initial, j,
                    actual, l);
                }
              } i(g);
          struct i {
            long j;
            i(long initial) {
              long actual = __sync_lock_test_and_set_8(&e, j);
              c("", 0, "", j, 0, initial, actual, initial);
            }
          } i(0);
        }
      } m;
    }
  } f;
}
```
Compile with `clang -O2 -g -mavx repro.cpp` and run the resulting binary. A compiler built from the commit preceeding yours (a8a1e9033a902d961ad050a139b97ac0319b9e25) generates a binary that finishes quickly when run. When using a compiler built from your change (6fb7cdff3d90c565b87a253ff7dbd36319879111), the resulting binary gets stuck in an infinite loop. Like @bjope's example, debug info generation is required to hit the problem. Hope this helps.

https://github.com/llvm/llvm-project/pull/114265