[Draft] Summary Based Analysis Prototype

[isuckatcs]

This is the initial implementation of how I imagine summaries used in clang and the CSA. There are still rooms for improvement and the patch still serves as an RFC to discuss which direction to go further.

1.) Compile each TU to generate the summaries

// main.cpp
int *x;

void foo();

int main() {
  x = nullptr;
  foo();
  return *x;
}

// foo.cpp
void foo() {}

clang++ main.cpp foo.cpp --emit-summaries

2.) Give the path to the directory containing the summaries to a clang tool to use them

clang++ --analyze main.cpp --summaries-dir=.

main.cpp:8:10: warning: Dereference of null pointer (loaded from variable 'x') [core.NullDereference]
    8 |   return *x;
      |          ^~

The summaries for main.cpp and foo.cpp look like this:

[
  {
    "id": "c:@F@main#",
    "attrs": {
      "function": []
    },
    "calls": [
      {
        "id": "c:@F@foo#"
      }
    ]
  }
]

[
  {
    "id": "c:@F@foo#",
    "attrs": {
      "function": [
        "no_write_global"
      ]
    },
    "calls": []
  }
]

[github-actions]

⚠️ We detected that you are using a GitHub private e-mail address to contribute to the repo.
Please turn off Keep my email addresses private setting in your account.
See LLVM Developer Policy and LLVM Discourse for more information.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[Xazax-hun]

I did not have time to look at it properly, just some small drive by comments.

[Xazax-hun]

Should we assert here that we don't have a summary context yet?

[isuckatcs]

I'm not sure tbh. I just mirrored what other create functions such as CompilerInstance::createSema() do. Those don't assert the existence, so maybe the consumers of the class expect this kind of behaviour.

[Xazax-hun]

Why SmallVector instead of a string type?

[isuckatcs]

This is just an artifact from index::generateUSRForDecl() expecting a SmallVectorImpl<char> & as it's buffer. In the very beginning, the constructor of this class took a FunctionDecl and generated the USR into this field.

This and every other data structure used needs to be revisited throught these source files once again before the patch is finalized.

[Xazax-hun]

Did you want to return a StringRef/ArrayRef instead?

[Xazax-hun]

Nit: missing new line.