[clang] Fixed issue #128882: don't warn if 1st argument to 'getcwd' is NULL (PR #135720)

[Balázs Kéri via cfe-commits]

================
@@ -105,9 +105,6 @@ void errno_getcwd(char *Buf, size_t Sz) {
     clang_analyzer_eval(errno != 0);   // expected-warning{{TRUE}}
     clang_analyzer_eval(Path == NULL); // expected-warning{{TRUE}}
     if (errno) {}                      // no warning
-  } else if (Path == NULL) {
-    clang_analyzer_eval(errno != 0);   // expected-warning{{TRUE}}
-    if (errno) {}                      // no warning
----------------
balazske wrote:

I think the following tests would be good in the llvm main branch:
```c
void errno_getcwd_buf_nonnull(char *Buf, size_t Sz) {
  if (Buf == NULL)
    return;
  char *Path = getcwd(Buf, Sz);
  if (Sz == 0) {
    clang_analyzer_eval(errno != 0);   // expected-warning{{TRUE}}
    clang_analyzer_eval(Path == NULL); // expected-warning{{TRUE}}
    if (errno) {}                      // no warning
  } else if (Path == NULL) {
    clang_analyzer_eval(errno != 0);   // expected-warning{{TRUE}}
    if (errno) {}                      // no warning
  } else {
    clang_analyzer_eval(Path == Buf);  // expected-warning{{TRUE}}
    if (errno) {}                      // expected-warning{{An undefined value may be read from 'errno'}}
  }
}

void errno_getcwd_buf_null() {
  // POSIX does not mention this case but many implementations (Linux, FreeBSD) work this way.
  char *Path = getcwd(NULL, 1);
  if (Path == NULL) {
    clang_analyzer_eval(errno != 0);   // expected-warning{{TRUE}}
    if (errno) {}                      // no warning
  } else {
    if (errno) {}                      // expected-warning{{An undefined value may be read from 'errno'}}
  }
}
```
I can add the patch for this in the next few days.

https://github.com/llvm/llvm-project/pull/135720