From fe4916093d0ce036e7b70595b39351b4ecf93798 Mon Sep 17 00:00:00 2001 From: Tristan Partin Date: Tue, 19 Dec 2023 14:39:03 -0600 Subject: [PATCH v2 1/2] Add support for __attribute__((returns_nonnull)) Allows for marking functions that can't possibly return NULL, like those that always elog(ERROR) for instance in the case of failures. While not only being good documentation, annotating functions which can't return NULL can lead to better code generation since the optimizer can more easily analyze a function. Quoting the LLVM documentation: > The returns_nonnull attribute implies that returning a null pointer is > undefined behavior, which the optimizer may take advantage of. The more we mark, the better the analysis can become. --- src/include/c.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/src/include/c.h b/src/include/c.h index 26bf7ec16e..e3a127f954 100644 --- a/src/include/c.h +++ b/src/include/c.h @@ -285,6 +285,18 @@ #define pg_unreachable() abort() #endif +/* + * Place on functions which return a pointer but can't return NULL. When used, + * it can allow the compiler to warn if a NULL check occurs in the parent + * function because that NULL check would always fail. It is also an opportunity + * to help the compiler with optimizations. + */ +#if __has_attribute (returns_nonnull) +#define pg_returns_nonnull __attribute__((returns_nonnull)) +#else +#define pg_returns_nonnull +#endif + /* * Hints to the compiler about the likelihood of a branch. Both likely() and * unlikely() return the boolean value of the contained expression. -- Tristan Partin Neon (https://neon.tech)