================
@@ -2761,6 +2761,41 @@ etc.).
Query for this feature with
``__has_builtin(__builtin_assume_separate_storage)``.
+``__builtin_assume_dereferenceable``
+-------------------------------------
+
+``__builtin_assume_derefernceable`` is used to provide the optimizer with the
+knowledge that the pointer argument P is dereferenceable up to the specified
+number of bytes.
+
+**Syntax**:
+
+.. code-block:: c++
+
+ __builtin_assume_dereferenceable(const void *, size_t)
+
+**Example of Use**:
+
+.. code-block:: c++
+
+ int foo(int *x, int y) {
+ __builtin_assume_dereferenceable(x, 4);
+ int z = 0;
+ if (y == 1) {
+ // The optimizer may execute the load of x unconditionally.
+ z = *x;
+ }
+ return z;
+ }
+
+**Description**:
+
+The arguments to this function provide a start pointer ``P`` and a size ``S``.
+``P`` must be non-null and ``S`` at least 1. The optimizer may assume that
----------------
jdoerfert wrote:
> dereferenceable implies nonnull if the null pointer is not dereferenceable
> (duh).
>
> Unless `-fno-delete-null-pointer-checks` is used, the null pointer is known
> to not be dereferenceable.
It depends on the address space/target, e.g., AS(3) on AMD GPUs has a
dereferenceable NULL.
You need to use the helper that takes the function and the AS tells you if NULL
is dereferenceable.
https://github.com/llvm/llvm-project/pull/121789
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