================
@@ -293,6 +293,48 @@ To silence reports from unsigned integer overflow, you can
set
``-fsanitize-recover=unsigned-integer-overflow``, is particularly useful for
providing fuzzing signal without blowing up logs.
+Disabling instrumentation for common overflow patterns
+------------------------------------------------------
+
+There are certain overflow-dependent or overflow-prone code patterns which
+produce a lot of noise for integer overflow/truncation sanitizers. Negated
+unsigned constants, post-decrements in a while loop condition and simple
+overflow checks are accepted and pervasive code patterns. However, the signal
+received from sanitizers instrumenting these code patterns may be too noisy for
+some projects. To disable instrumentation for these common patterns one should
+use ``-fsanitize-undefined-ignore-overflow-pattern=``.
+
+Currently, this option supports three overflow-dependent code idioms:
+
+``negated-unsigned-const``
+
+.. code-block:: c++
+
+ /// -fsanitize-undefined-ignore-overflow-pattern=negated-unsigned-const
+ unsigned long foo = -1UL; // No longer causes a negation overflow warning
+ unsigned long bar = -2UL; // and so on...
+
+``post-decr-while``
+
+.. code-block:: c++
+
+ /// -fsanitize-undefined-ignore-overflow-pattern=post-decr-while
+ unsigned char count = 16;
+ while (count--) { /* ... */ } // No longer causes
unsigned-integer-overflow sanitizer to trip
+
+``add-overflow-test``
+
+.. code-block:: c++
+
+ /// -fsanitize-undefined-ignore-overflow-pattern=add-overflow-test
+ if (base + offset < base) { /* ... */ } // The pattern of `a + b < a`, and
other re-orderings,
----------------
JustinStitt wrote:
Since the overflow checks are never inserted with `add-overflow-test` in that
case the optimizer would be free to do whatever it wants. One should consider
`-fwrapv`. These pattern exclusions should not try to do too much (i.e; try to
prevent the optimizer from doing its thing).
https://github.com/llvm/llvm-project/pull/104889
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