[all-commits] [llvm/llvm-project] 9eeafc: Implement `-dump-minimization-hints` flag. (#133910)

[Viktoriia Bakalova via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 9eeafc63d2f06f7aa216ddcf2370b20fbb1d9015
      https://github.com/llvm/llvm-project/commit/9eeafc63d2f06f7aa216ddcf2370b20fbb1d9015
  Author: Viktoriia Bakalova <115406782+VitaNuo at users.noreply.github.com>
  Date:   2025-04-11 (Fri, 11 Apr 2025)

  Changed paths:
    M clang/include/clang/Driver/Options.td
    M clang/include/clang/Frontend/FrontendOptions.h
    M clang/lib/Frontend/FrontendAction.cpp
    A clang/test/Frontend/dump-minimization-hints.cpp

  Log Message:
  -----------
  Implement `-dump-minimization-hints` flag.  (#133910)

This PR implements a CC1 flag `-dump-minimization-hints`.
The flag allows to specify a file path to dump ranges of deserialized
declarations in `ASTReader`. Example usage:

```
clang -Xclang=-dump-minimization-hints=/tmp/decls -c file.cc -o file.o
```

Example output:
```
// /tmp/decls
{
  "required_ranges": [
    {
      "file": "foo.h",
      "range": [
        {
          "from": {
            "line": 26,
            "column": 1
          },
          "to": {
            "line": 27,
            "column": 77
          }
        }
      ]
    },
    {
      "file": "bar.h",
      "range": [
        {
          "from": {
            "line": 30,
            "column": 1
          },
          "to": {
            "line": 35,
            "column": 1
          }
        },
        {
          "from": {
            "line": 92,
            "column": 1
          },
          "to": {
            "line": 95,
            "column": 1
          }
        }
      ]
    }
  ]
}

```
Specifying the flag creates an instance of
`DeserializedDeclsSourceRangePrinter`, which dumps ranges of deserialized
declarations to aid debugging and bug minimization (we use is as input to [C-Vise](https://github.com/emaxx-google/cvise/tree/multifile-hints).

Required ranges are computed from source ranges of Decls.
`TranslationUnitDecl`, `LinkageSpecDecl` and `NamespaceDecl` are ignored
for the sake of this PR.

Technical details:
* `DeserializedDeclsSourceRangePrinter` implements `ASTConsumer` and
`ASTDeserializationListener`, so that an object of
`DeserializedDeclsSourceRangePrinter` registers as its own listener.
* `ASTDeserializationListener` interface provides the `DeclRead`
callback that we use to collect the deserialized Decls.
Printing or otherwise processing them as this point is dangerous, since
that could trigger additional deserialization and crash compilation.
* The collected Decls are processed in `HandleTranslationUnit` method of
`ASTConsumer`. This is a safe point, since we know that by this point
all the Decls needed by the compiler frontend have been deserialized.
* In case our processing causes further deserialization, `DeclRead` from
the listener might be called again. However, at that point we don't
accept any more Decls for processing.



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