[clang] [analyzer] Match dangling subobjects by their base region in DanglingPtrDeref (PR #211552)

[via cfe-commits]

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@@ -112,3 +112,105 @@ void inlined_callee_single_report() {
   // expected-note at -1 {{Calling 'deref_param'}}
   (void)r;
 }
+
+struct MyBuffer {
+  char buffer[8];
+};
+struct MyStruct { int x; };
+struct Inner { int x; };
+struct Outer { struct Inner inner; };
+
+char member_subregion_dangling_deref() {
+  const char *p = nullptr;
+  {
+    struct MyBuffer tmp_buffer = {};
+    p = tmp_buffer.buffer;
+  }
+  // expected-note at -1 {{'tmp_buffer.buffer[0]' is destroyed here}}
+  return *p; 
+  // expected-warning at -1 {{Use of 'tmp_buffer.buffer[0]' after its lifetime ended}}
+  // expected-note at -2    {{Use of 'tmp_buffer.buffer[0]' after its lifetime ended}}
+}
+
+void opaque(const char *);
+
+void passing_dangling_to_call() {
+  const char *p = nullptr;
+  {
+    struct MyBuffer tmp_buffer = {};
+    p = tmp_buffer.buffer;
+  }
+  // expected-note at -1 {{'tmp_buffer.buffer[0]' is destroyed here}}
+  opaque(p);
+  // expected-warning at -1 {{Use of 'tmp_buffer.buffer[0]' after its lifetime ended}}
+  // expected-note at -2    {{Use of 'tmp_buffer.buffer[0]' after its lifetime ended}}
+}
+
+char member_subregion_alive_deref() {
+  {
+    struct MyBuffer tmp_buffer = {};
+    const char *p = tmp_buffer.buffer;
+    opaque(p); //   no-warning
+    return *p; //   no-warning
+  }
+}
+
+void arr_elem_subreg_dangling_deref() {
+  int *ptr = nullptr;
+  {
+    int local_arr[5];
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isuckatcs wrote:

IIRC the magic number in the CSA is 4 by default, as that is the amount of times we allow the analyzer to execute the same statement in a row. After that it falls back to conservative evaluation.

It shouldn't cause an issue in this case, but with structured binding of arrays you might se different results. In general I recommend testing for `< 4` and `>= 4` cases.

https://github.com/llvm/llvm-project/pull/211552