================
@@ -0,0 +1,100 @@
+.. title:: clang-tidy - bugprone-unsequenced-global-accesses
+
+bugprone-unsequenced-global-accesses
+====================================
+
+Finds unsequenced actions (i.e. unsequenced write and read/write)
+on global variables nested in functions in the same translation unit.
+
+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 check is similar to the ``-Wunsequenced`` Clang
warning,
+however it only looks at global variables and therefore can find unsequenced
+actions recursively inside function calls as well. For example:
+
+.. code-block:: c++
+
+ int a = 0;
+ int b = (a++) - a; // This is flagged by -Wunsequenced.
+
+Because there is no sequencing defined for the ``-`` operator, ``a`` and
``a++``
+could be evaluated in any order. The compiler can even interleave the
evaluation
+of the sides as this is undefined behavior. The above code would generate a
+warning when ``-Wunsequenced`` (or ``-Wsequence-point`` in GCC) is enabled.
+
+However, global variables allow for more complex scenarios that
+``-Wunsequenced`` doesn't detect. E.g.
+
+.. code-block:: c++
+
+ int globalVar = 0;
+
+ int incFun() {
+ globalVar++;
+ return globalVar;
+ }
+
+ int main() {
+ return globalVar + incFun(); // This is not detected by -Wunsequenced.
+ }
+
+This clang-tidy check attempts to detect such cases. It recurses into functions
+that are inside the same translation unit. Global unions and structs are also
+handled. For example:
+
+.. code-block:: c++
+
+ 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);
+ }
+
+In the above example, the struct fields ``A`` and ``B`` are treated as
+separate global variables, while an access (i.e. read or write) to the struct
+itself is treated as an access to both ``A`` and ``B``.
+
+Options
+~~~~~~~
+
+.. option:: HandleMutableFunctionParametersAsWrites
+
+ When ``true``, treat function calls with mutable reference or pointer
+ parameters as writes to the parameter.
+
+ The default value is ``false``.
+
+ For example, the following code block will get flagged if
+ ``HandleMutableFunctionParametersAsWrites`` is ``true``:
----------------
EugeneZelenko wrote:
```suggestion
:option:`HandleMutableFunctionParametersAsWrites` is `true`:
```
https://github.com/llvm/llvm-project/pull/130421
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