[clang] [analyzer] Discard non-live source frames from the current stack (PR #213779)

[via cfe-commits]

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@@ -52,9 +52,15 @@ static bool isDanglingStackSource(const MemRegion *Source,
         })) {
       return false;
     }
-
-    if (SF == CurrentSF || !SF->isParentOf(CurrentSF))
-      return true;
+    // Only a source whose frame is still live on the current stack can
+    // dangle. If that frame is not on the stack then the source outlives
+    // the returned value. The source is still alive when the returned value
+    // is used, so it does not dangle.
+    if (llvm::any_of(C.stackframes(),
+                     [&](const StackFrame &Frame) { return &Frame == SF; }))
+
+      if (SF == CurrentSF || !SF->isParentOf(CurrentSF))
+        return true;
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isuckatcs wrote:

Are these `if` statements supposed to be nested? If so you could try to merge the conditions, or surround the outer if with `{}` to make it more reabable.

https://github.com/llvm/llvm-project/pull/213779