# HG changeset patch
# User Taylor R Campbell <riastradh@NetBSD.org>
# Date 1778943563 0
#      Sat May 16 14:59:23 2026 +0000
# Branch trunk
# Node ID a4a4770864657061ca9abe602fdacaecf659b561
# Parent  4b096084d48b7231fbaeef6fbb718731f7e43289
# EXP-Topic riastradh-pr60272-atomicstackspill
WIP: sys/atomic.h: Avoid needless stack spillage with typeof_unqual.

Using typeof_unqual strips the volatile qualifier on the local
temporaries, so the compiler doesn't issue store/load cycles for
access to them.

PR kern/60272: sys/atomic.h: unnecessary stack spillage

diff -r 4b096084d48b -r a4a477086465 sys/sys/atomic.h
--- a/sys/sys/atomic.h	Wed May 13 02:40:08 2026 +0000
+++ b/sys/sys/atomic.h	Sat May 16 14:59:23 2026 +0000
@@ -406,6 +406,12 @@ void		membar_datadep_consumer(void);
 #define	__ATOMIC_SIZE_MAX		4
 #endif
 
+#if __GNUC_PREREQ__(14, 0) && !defined(__clang__)
+#define	__atomic_typeof_unqual		__typeof_unqual__
+#else
+#define	__atomic_typeof_unqual		__typeof__
+#endif
+
 /*
  * We assume that access to an aligned pointer to a volatile object of
  * at most __ATOMIC_SIZE_MAX bytes is guaranteed to be atomic.  This is
@@ -422,7 +428,7 @@ void		membar_datadep_consumer(void);
 void kcsan_atomic_load(const volatile void *, void *, int);
 void kcsan_atomic_store(volatile void *, const void *, int);
 #define __BEGIN_ATOMIC_LOAD(p, v) \
-	union { __typeof__(*(p)) __al_val; char __al_buf[1]; } v; \
+	union { __atomic_typeof_unqual(*(p)) __al_val; char __al_buf[1]; } v; \
 	kcsan_atomic_load(p, v.__al_buf, sizeof(v.__al_val))
 #define __END_ATOMIC_LOAD(v) \
 	(v).__al_val
@@ -430,7 +436,7 @@ void kcsan_atomic_store(volatile void *,
 	kcsan_atomic_store(p, __UNVOLATILE(&v), sizeof(v))
 #else
 #define __BEGIN_ATOMIC_LOAD(p, v) \
-	__typeof__(*(p)) v = *(p)
+	const __atomic_typeof_unqual(*(p)) v = *(p)
 #define __END_ATOMIC_LOAD(v) \
 	v
 #ifdef __HAVE_HASHLOCKED_ATOMICS
@@ -471,7 +477,7 @@ void kcsan_atomic_store(volatile void *,
 #define	atomic_store_relaxed(p,v)					      \
 ({									      \
 	volatile __typeof__(*(p)) *__as_ptr = (p);			      \
-	__typeof__(*(p)) __as_val = (v);				      \
+	const __atomic_typeof_unqual(*(p)) __as_val = (v);		      \
 	__ATOMIC_PTR_CHECK(__as_ptr);					      \
 	__DO_ATOMIC_STORE(__as_ptr, __as_val);				      \
 })
@@ -479,7 +485,7 @@ void kcsan_atomic_store(volatile void *,
 #define	atomic_store_release(p,v)					      \
 ({									      \
 	volatile __typeof__(*(p)) *__as_ptr = (p);			      \
-	__typeof__(*(p)) __as_val = (v);				      \
+	const __atomic_typeof_unqual(*(p)) __as_val = (v);		      \
 	__ATOMIC_PTR_CHECK(__as_ptr);					      \
 	membar_release();						      \
 	__DO_ATOMIC_STORE(__as_ptr, __as_val);				      \
@@ -549,7 +555,7 @@ static __inline __always_inline void
 #else
 #define	atomic_load_consume(p)						      \
 ({									      \
-	const __typeof__(*(p)) __al_val = atomic_load_relaxed(p);	      \
+	const __atomic_typeof_unqual(*(p)) __al_val = atomic_load_relaxed(p); \
 	membar_datadep_consumer();					      \
 	__al_val;							      \
 })