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From: Sebastian Huber <sh@sourceware.org> To: newlib-cvs@sourceware.org Subject: [newlib-cygwin] Expose clang's alignment builtins and use them for roundup2/rounddown2 Date: Mon, 11 Jul 2022 09:53:37 +0000 (GMT) [thread overview] Message-ID: <20220711095338.016F93856DC6@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=68109f904bff0208e3e30e47adc4eb430d5d4c8c commit 68109f904bff0208e3e30e47adc4eb430d5d4c8c Author: Alex Richardson <arichardson@FreeBSD.org> Date: Wed Feb 3 15:27:17 2021 +0000 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 Diff: --- newlib/libc/include/sys/cdefs.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/newlib/libc/include/sys/cdefs.h b/newlib/libc/include/sys/cdefs.h index e6a31bd51..7dff2c8d8 100644 --- a/newlib/libc/include/sys/cdefs.h +++ b/newlib/libc/include/sys/cdefs.h @@ -716,4 +716,23 @@ #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) +#endif +#if !__has_builtin(__builtin_align_up) +#define __builtin_align_up(x, align) \ + ((__typeof__(x))(((__uintptr_t)(x)+((align)-1))&(~((align)-1)))) +#endif +#if !__has_builtin(__builtin_align_down) +#define __builtin_align_down(x, align) \ + ((__typeof__(x))((x)&(~((align)-1)))) +#endif + +#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_ */
next reply other threads:[~2022-07-11 9:53 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-07-11 9:53 Sebastian Huber [this message] 2022-07-11 11:53 Sebastian Huber
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