[all-commits] [llvm/llvm-project] 0059fe: [LifetimeSafety] Add support for lifetime capture_...

[Kashika Akhouri via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0059fe6596aee0052f9ba40188ee2cef27b93af0
      https://github.com/llvm/llvm-project/commit/0059fe6596aee0052f9ba40188ee2cef27b93af0
  Author: Kashika Akhouri <akhourik at google.com>
  Date:   2026-06-01 (Mon, 01 Jun 2026)

  Changed paths:
    M clang/include/clang/Analysis/Analyses/LifetimeSafety/FactsGenerator.h
    M clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp
    M clang/test/Sema/warn-lifetime-safety.cpp

  Log Message:
  -----------
  [LifetimeSafety] Add support for lifetime capture_by (#196884)

This PR implements support for the `[[clang::lifetime_capture_by(X)]]`
attribute within the lifetime-safety analysis.

The PR introduces a new helper in `FactGenerator.cpp` called
`handleLifetimeCaptureBy` which detects
`[[clang::lifetime_capture_by(X)]]` on parameters. If detected, the
analyzer now generates an `OriginFlowFact` ensuring that captured
dependencies are added to the capturer's state. The PR supports
capture_by params and `this` and currently doesn't implement attributes
on function declarations.

Example:
Integrate `[[clang::lifetimebound]]`: This existing Clang annotation is
crucial for specifying that the lifetime of a function's output is tied
to one of its inputs.

```cpp
void setS(std::string_view& in, std::string_view out [[clang::lifetime_capture_by(X)]]);

std::string_view foo() {
  std::string a = "on stack";
  std::string_view res;
  setS(res, a);
  return res;  // warning: returning address of local variable 'a'.
}
```

Lifetime Facts:
```cpp
Function: foo
  Block B2:
  End of Block
  Block B1:
    OriginFlow: 
        Dest: 0 (Expr: ImplicitCastExpr, Type : const char *)
        Src:  1 (Expr: StringLiteral, Type : const char (&)[9])
    Use (0 (Expr: ImplicitCastExpr, Type : const char *), Read)
    Use (2 (Expr: CXXDefaultArgExpr, Type : const class std::allocator<char> &), Read)
    Expire (MaterializeTemporaryExpr at 0x562afa69fdb0)
    OriginFlow: 
        Dest: 3 (Decl: res, Type : std::string_view)
        Src:  4 (Expr: CXXConstructExpr, Type : std::string_view)
    Use (3 (Decl: res, Type : std::string_view), Read)
    Issue (0 (Path: res), ToOrigin: 7 (Expr: DeclRefExpr, Decl: res))
    Issue (1 (Path: a), ToOrigin: 8 (Expr: DeclRefExpr, Decl: a))
    OriginFlow: 
        Dest: 9 (Expr: ImplicitCastExpr, Type : const class std::basic_string<char> &)
        Src:  8 (Expr: DeclRefExpr, Decl: a)
    Use (9 (Expr: ImplicitCastExpr, Type : const class std::basic_string<char> &), Read)
    OriginFlow: 
        Dest: 10 (Expr: CXXMemberCallExpr, Type : __sv_type)
        Src:  9 (Expr: ImplicitCastExpr, Type : const class std::basic_string<char> &)
    OriginFlow: 
        Dest: 11 (Expr: ImplicitCastExpr, Type : __sv_type)
        Src:  10 (Expr: CXXMemberCallExpr, Type : __sv_type)
    Use (11 (Expr: ImplicitCastExpr, Type : __sv_type), Read)
// New Origin Flow fact added    
OriginFlow: 
        Dest: 3 (Decl: res, Type : std::string_view)
        Src:  11 (Expr: ImplicitCastExpr, Type : __sv_type), Merge
    Use (3 (Decl: res, Type : std::string_view), Read)
    Issue (2 (Path: res), ToOrigin: 12 (Expr: DeclRefExpr, Decl: res))
    OriginFlow: 
        Dest: 13 (Expr: ImplicitCastExpr, Type : const std::string_view &)
        Src:  12 (Expr: DeclRefExpr, Decl: res)
    OriginFlow: 
        Dest: 14 (Expr: ImplicitCastExpr, Type : std::string_view)
        Src:  3 (Decl: res, Type : std::string_view)
    OriginFlow: 
        Dest: 15 (Expr: CXXConstructExpr, Type : std::string_view)
        Src:  14 (Expr: ImplicitCastExpr, Type : std::string_view)
    Expire (a)
    Expire (res, Origin: 3 (Decl: res, Type : std::string_view))
    OriginEscapes (15 (Expr: CXXConstructExpr, Type : std::string_view), via Return)
  End of Block
  Block B0:
  End of Block
```



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