path: root/sys
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authorAlex Richardson <arichardson@FreeBSD.org>2021-02-03 15:27:17 +0000
committerAlex Richardson <arichardson@FreeBSD.org>2021-02-03 16:02:54 +0000
commit8fa6abb6f4f64f4f23e2920e2aea7996566851a4 (patch)
tree5b452808841a951012e806113d513b60b2773b5c /sys
parent7791ecf04b48a0c365b003447f479ec890115dfc (diff)
Expose clang's alignment builtins and use them for roundup2/rounddown2
This makes roundup2/rounddown2 type- and const-preserving and allows using it on pointer types without casting to uintptr_t first. Not performing pointer-to-integer conversions also helps the compiler's optimization passes and can therefore result in better code generation. When using it with integer values there should be no change other than the compiler checking that the alignment value is a valid power-of-two. I originally implemented these builtins for CHERI a few years ago and they have been very useful for CheriBSD. However, they are also useful for non-CHERI code so I was able to upstream them for Clang 10.0. Rationale from the clang documentation: Clang provides builtins to support checking and adjusting alignment of pointers and integers. These builtins can be used to avoid relying on implementation-defined behavior of arithmetic on integers derived from pointers. Additionally, these builtins retain type information and, unlike bitwise arithmetic, they can perform semantic checking on the alignment value. There is also a feature request for GCC, so GCC may also support it in the future: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98641 Reviewed By: brooks, jhb, imp Differential Revision: https://reviews.freebsd.org/D28332
Diffstat (limited to 'sys')
2 files changed, 21 insertions, 2 deletions
diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
index 75bedd4b8128..72ef942084f2 100644
--- a/sys/sys/cdefs.h
+++ b/sys/sys/cdefs.h
@@ -884,4 +884,23 @@
#define __guarded_by(x) __lock_annotate(guarded_by(x))
#define __pt_guarded_by(x) __lock_annotate(pt_guarded_by(x))
+/* Alignment builtins for better type checking and improved code generation. */
+/* Provide fallback versions for other compilers (GCC/Clang < 10): */
+#if !__has_builtin(__builtin_is_aligned)
+#define __builtin_is_aligned(x, align) \
+ (((__uintptr_t)x & ((align) - 1)) == 0)
+#if !__has_builtin(__builtin_align_up)
+#define __builtin_align_up(x, align) \
+ ((__typeof__(x))(((__uintptr_t)(x)+((align)-1))&(~((align)-1))))
+#if !__has_builtin(__builtin_align_down)
+#define __builtin_align_down(x, align) \
+ ((__typeof__(x))((x)&(~((align)-1))))
+#define __align_up(x, y) __builtin_align_up(x, y)
+#define __align_down(x, y) __builtin_align_down(x, y)
+#define __is_aligned(x, y) __builtin_is_aligned(x, y)
#endif /* !_SYS_CDEFS_H_ */
diff --git a/sys/sys/param.h b/sys/sys/param.h
index 079357a19d47..d6f1eb21dcd2 100644
--- a/sys/sys/param.h
+++ b/sys/sys/param.h
@@ -305,9 +305,9 @@
#define nitems(x) (sizeof((x)) / sizeof((x)[0]))
#define rounddown(x, y) (((x)/(y))*(y))
-#define rounddown2(x, y) ((x)&(~((y)-1))) /* if y is power of two */
+#define rounddown2(x, y) __align_down(x, y) /* if y is power of two */
#define roundup(x, y) ((((x)+((y)-1))/(y))*(y)) /* to any y */
-#define roundup2(x, y) (((x)+((y)-1))&(~((y)-1))) /* if y is powers of two */
+#define roundup2(x, y) __align_up(x, y) /* if y is powers of two */
#define powerof2(x) ((((x)-1)&(x))==0)
/* Macros for min/max. */