[clang] Make [[clang::lifetimebound]] work for expressions coming from default arguments (PR #112047)

[via cfe-commits]

================
@@ -107,6 +107,39 @@ namespace std {
 using std::operator""s;
 using std::operator""sv;
 
+namespace default_args {
+  using IntArray = int[];
+  const int *defaultparam1(const int &def1 [[clang::lifetimebound]] = 0); // #def1
+  const int &defaultparam_array([[clang::lifetimebound]] const int *p = IntArray{1, 2, 3}); // #def2
+  struct A {
+    A(const char*, const int& def3 [[clang::lifetimebound]] = 0); // #def3
+  };
+  const int &defaultparam2(const int &def4 [[clang::lifetimebound]] = 0); // #def4
+  const int &defaultparam3(const int &def5 [[clang::lifetimebound]] = defaultparam2()); // #def5
+  std::string_view defaultparam4(std::string_view s [[clang::lifetimebound]] = std::string()); // #def6
+
+  const int*test_default_args() {
+    const int *c = defaultparam1(); // expected-warning {{temporary whose address is used as value of local variable 'c' will be destroyed at the end of the full-expression}} expected-note@#def1 {{initializing parameter 'def1' with default argument}}
+    A a = A(""); // expected-warning {{temporary whose address is used as value of local variable 'a' will be destroyed at the end of the full-expression}} expected-note@#def3 {{initializing parameter 'def3' with default argument}}
+    const int &s = defaultparam2(); // expected-warning {{temporary bound to local reference 's' will be destroyed at the end of the full-expression}} expected-note@#def4 {{initializing parameter 'def4' with default argument}}
+    const int &t = defaultparam3(); // expected-warning {{temporary bound to local reference 't' will be destroyed at the end of the full-expression}} expected-note@#def4 {{initializing parameter 'def4' with default argument}} expected-note@#def5 {{initializing parameter 'def5' with default argument}}
+    const int &u = defaultparam_array(); // expected-warning {{temporary bound to local reference 'u' will be destroyed at the end of the full-expression}} expected-note@#def2 {{initializing parameter 'p' with default argument}}
+    int local;
+    const int &v = defaultparam2(local); // no warning
+    const int &w = defaultparam2(1); // expected-warning {{temporary bound to local reference 'w' will be destroyed at the end of the full-expression}}
+    int x = defaultparam2(1); // FIXME: This should warn
+    x = defaultparam2(1); // FIXME: This should warn
+    if (false) {
+      return &defaultparam2();  // expected-warning {{returning address of local temporary object}}
+    }
+    if (false) {
+      return &defaultparam2(0);  // expected-warning {{returning address of local temporary object}} expected-note@#def4 {{initializing parameter 'def4' with default argument}}
+    }
+    std::string_view sv = defaultparam4(); // expected-warning {{temporary whose address is used as value of local variable 'sv' will be destroyed at the end of the full-expression}} expected-note@#def6 {{initializing parameter 's' with default argument}}
+    return nullptr;
+  }
+}
----------------
higher-performance wrote:

Done.

https://github.com/llvm/llvm-project/pull/112047