[clang] [rtsan][NFC] Documentation of suppression flag (PR #112727)

[via cfe-commits]

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@@ -194,12 +198,43 @@ Some issues with flags can be debugged using the ``verbosity=$NUM`` flag:
    misspelled_flag
    ...
 
-Disabling
----------
+Disabling and suppressing
+-------------------------
 
-In some circumstances, you may want to suppress error reporting in a specific scope.
+There are multiple ways to suppress error reporting when using RealtimeSanitizer.
 
-In C++, this is achieved via  ``__rtsan::ScopedDisabler``. Within the scope where the ``ScopedDisabler`` object is instantiated, all sanitizer error reports are suppressed. This suppression applies to the current scope as well as all invoked functions, including any functions called transitively.
+In general, ``ScopedDisabler`` should be preferred, as it is the most performant.
+
+.. list-table:: Suppression methods
+   :widths: 30 15 15 10 70
+   :header-rows: 1
+
+   * - Suppression method
+     - Specified at?
+     - Scope
+     - Run-time cost
+     - Description
+   * - ``ScopedDisabler``
+     - Compile-time
+     - Stack
+     - Very low
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davidtrevelyan wrote:

I appreciate that we might want something really concise and snappy here, but if that's not a massive motivation, I think we could quantify these costs a bit, rather than just saying low, medium and high. Maybe something like "Very low: single bool check" could work?

https://github.com/llvm/llvm-project/pull/112727