diff options
Diffstat (limited to 'absl/base/attributes.h')
| -rw-r--r-- | absl/base/attributes.h | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/absl/base/attributes.h b/absl/base/attributes.h index acd1c5269829..8f77db77d23a 100644 --- a/absl/base/attributes.h +++ b/absl/base/attributes.h @@ -563,7 +563,19 @@ // ABSL_ATTRIBUTE_PACKED // -// Prevents the compiler from padding a structure to natural alignment +// Instructs the compiler not to use natural alignment for a tagged data +// structure, but instead to reduce its alignment to 1. This attribute can +// either be applied to members of a structure or to a structure in its +// entirety. Applying this attribute (judiciously) to a structure in its +// entirety to optimize the memory footprint of very commonly-used structs is +// fine. Do not apply this attribute to a structure in its entirety if the +// purpose is to control the offsets of the members in the structure. Instead, +// apply this attribute only to structure members that need it. +// +// When applying ABSL_ATTRIBUTE_PACKED only to specific structure members the +// natural alignment of structure members not annotated is preserved. Aligned +// member accesses are faster than non-aligned member accesses even if the +// targeted microprosessor supports non-aligned accesses. #if ABSL_HAVE_ATTRIBUTE(packed) || (defined(__GNUC__) && !defined(__clang__)) #define ABSL_ATTRIBUTE_PACKED __attribute__((__packed__)) #else |