[clang] [LifetimeSafety] Detect use-after-return (PR #165370)

[Utkarsh Saxena via cfe-commits]

================
@@ -1202,5 +1202,242 @@ TEST_F(LifetimeAnalysisTest, LivenessOutsideLoop) {
   EXPECT_THAT(Origins({"p"}), MaybeLiveAt("p1"));
 }
 
+TEST_F(LifetimeAnalysisTest, SimpleReturnStackAddress) {
+  SetupTest(R"(
+    MyObj* target() {
+      MyObj s;
+      MyObj* p = &s;
+      POINT(p1);
+      return p;
----------------
usx95 wrote:

Could you also try to test the point after return.
```cpp
POINT(p1);
return p;
POINT(p2);
```
(Not sure whether we have the point p2 in the CFG as it is dead code so feel free to ignore if p2 is not available.)

https://github.com/llvm/llvm-project/pull/165370