[clang-tools-extra] [clang-tidy] Added Conflicting Global Accesses checker (PR #130421)

[Baranov Victor via cfe-commits]

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+.. title:: clang-tidy - bugprone-conflicting-global-accesses
+
+bugprone-conflicting-global-accesses
+====================================
+
+Finds conflicting accesses on global variables.
+
+Modifying twice or reading and modifying a memory location without a
+defined sequence of the operations is either undefined behavior or has
+unspecified order. This checker is similar to the -Wunsequenced clang warning,
+however it only looks at global variables and therefore can find conflicting
+actions recursively inside functions as well.
+
+For example::
+
+    int a = 0;
+    int b = (a++) - a; // This is flagged by -Wunsequenced.
+
+However global variables allow for more complex scenarios that
+-Wunsequenced doesn't detect. E.g. ::
+
+    int globalVar = 0;
+
+    int incFun() {
+      globalVar++;
+      return globalVar;
+    }
+
+    int main() {
+      return globalVar + incFun(); // This is not detected by -Wunsequenced.
+    }
+
+This checker attempts to detect such cases. It recurses into functions that are
+inside the same translation unit. It also attempts not to flag cases that are
+already covered by -Wunsequenced. Global unions and structs are also handled.
+For example::
+    
+    typedef struct {
+        int A;
+        float B;
+    } IntAndFloat;
+
+    IntAndFloat GlobalIF;
+
+    int globalIFGetSum() {
+        int sum = GlobalIF.A + (int)GlobalIF.B;
+        GlobalIF = (IntAndFloat){};
+        return sum;
+    }
+
+    int main() {
+        // The following printf could give different results on different
+        // compilers.
+        printf("sum: %i, int: %i", globalIFGetSum(), GlobalIF.A);
+    }
+
+Options
+-------
+
+.. option:: HandleMutableFunctionParametersAsWrites
+
+    It's possible to enable handling mutable reference and pointer function
+    parameters as writes using the HandleMutableFunctionParametersAsWrites
+    option. For example:
+
+    void func(int& a);
----------------
vbvictor wrote:

ditto code-block

https://github.com/llvm/llvm-project/pull/130421