Re: Add returns_nonnull to infallible allocators

On Tue Sep 29, 2026 at 6:49 AM UTC, Peter Eisentraut wrote:
> On 06.07.26 20:11, Tristan Partin wrote:
>> On Mon Jul 6, 2026 at 6:10 PM UTC, Tristan Partin wrote:
>>> Postgres memory allocators, by default, ERROR out on memory allocation
>>> failures. An ERROR leads to a longjmp, which means that the caller of
>>> the allocator will never see a NULL return value. We can explicitly let
>>> the compiler know about this behavior by adding the returns_nonnull
>>> attribute to the allocators that follow this behavior. Postgres does
>>> support _extended versions of some of the allocators that take a flaks
>>> argument. The caller can provide the MCXT_ALLOC_NO_OOM flag to these
>>> allocators to request that they return NULL on allocation failure
>>> instead of ERROR-ing out. The _extended allocators cannot be marked as
>>> returns_nonnull because of that.
>>>
>>> By using returns_nonnull, we can help the compiler to optimize call
>>> sites.
>
> Your patch marks palloc_mul_extended() as pg_attribute_returns_nonnull,
> which seems incorrect per the above description.

Oops. Sorry about that. I must've not sent the most up to date version
of the patch because I definitely didn't have that locally.

> Also, per the discussion in the counted_by thread, lets put these new
> attributes in their more correct position in front of the declaration.
> (Note that several of these already use pg_nodiscard, which is also an
> attribute.) That way we can also use the MSVC annotation _Ret_notnull_.

Good points. See the revised attached patch. You definitely have a knack
for knowing MSVC attributes. I'll have to try to keep those in mind.

--
Tristan Partin
PostgreSQL Contributors Team
AWS (https://aws.amazon.com)