[clang] [clang] Implement lifetime analysis for lifetime_capture_by(X) (PR #115921)

[Gábor Horváth via cfe-commits]

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@@ -793,3 +793,108 @@ void test13() {
 }
 
 } // namespace GH100526
+
+namespace lifetime_capture_by {
+struct S {
+  const int *x;
+  void captureInt(const int&x [[clang::lifetime_capture_by(this)]]) { this->x = &x; }
+  void captureSV(std::string_view sv [[clang::lifetime_capture_by(this)]]);
+};
+///////////////////////////
+// Detect dangling cases.
+///////////////////////////
+void captureInt(const int&x [[clang::lifetime_capture_by(s)]], S&s);
+void captureRValInt(int&&x [[clang::lifetime_capture_by(s)]], S&s);
+void noCaptureInt(int x [[clang::lifetime_capture_by(s)]], S&s);
+std::string_view substr(const std::string& s [[clang::lifetimebound]]);
+std::string_view strcopy(const std::string& s);
+void captureSV(std::string_view x [[clang::lifetime_capture_by(s)]], S&s);
+void captureRValSV(std::string_view&& x [[clang::lifetime_capture_by(s)]], S&s);
+void noCaptureSV(std::string_view x, S&s);
+void captureS(const std::string& x [[clang::lifetime_capture_by(s)]], S&s);
+void captureRValS(std::string&& x [[clang::lifetime_capture_by(s)]], S&s);
+const std::string* getPointerLB(const std::string& s[[clang::lifetimebound]]);
+const std::string* getPointerNoLB(const std::string& s);
+void capturePointer(const std::string* x [[clang::lifetime_capture_by(s)]], S&s);
+struct ThisIsCaptured {
+  void capture(S& s) [[clang::lifetime_capture_by(s)]];
+  void bar(S& s) [[clang::lifetime_capture_by(abcd)]]; // expected-error {{'lifetime_capture_by' attribute argument 'abcd' is not a known function parameter}}
+  void baz(S& s) [[clang::lifetime_capture_by(this)]]; // expected-error {{'lifetime_capture_by' argument references itself}}
+};
+void use() {
+  std::string_view local_sv;
+  std::string local_s;
+  S s;
+  // Capture an 'int'.
+  int local;
+  captureInt(1, // expected-warning {{object captured by 's' will be destroyed at the end of the full-expression}}
+            s);
+  captureRValInt(1, s); // expected-warning {{object captured by 's'}}
+  captureInt(local, s);
+  noCaptureInt(1, s);
+  noCaptureInt(local, s);
+
+  // Capture lifetimebound pointer.
+  capturePointer(getPointerLB(std::string()), s); // expected-warning {{object captured by 's'}}
+  capturePointer(getPointerLB(*getPointerLB(std::string())), s); // expected-warning {{object captured by 's'}}
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Xazax-hun wrote:

These are getting harder and harder to understand. I wonder if we should emit notes for each step (e.g., describing that the temporary object was lifetimebound in `getPointerLB`). 

https://github.com/llvm/llvm-project/pull/115921