================
@@ -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
----------------
erichkeane wrote:
Does the 'must be non-null' create an optimization opportunity here too? I
guess that is kind of what 'dereferenceable' means, but should we better point
out that:
```
int foo(int * x) {
__builtin_assume_dereferenceable(x, 1);
if (x) {
return 1;
}
return 0;
}
```
Can be optimized to just: `return 1`?
https://github.com/llvm/llvm-project/pull/121789
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