Author: delphij
Date: Thu Oct 2 00:13:08 2014
New Revision: 272389
URL: https://svnweb.freebsd.org/changeset/base/272389
Log:
Diff reduction with kernel code: instruct the compiler that the data of
these types may be unaligned to their "normal" alignment and exercise
caution when accessing them.
PR: 194071
MFC after: 3 days
Modified:
head/sys/cddl/boot/zfs/lz4.c
Modified: head/sys/cddl/boot/zfs/lz4.c
==============================================================================
--- head/sys/cddl/boot/zfs/lz4.c Wed Oct 1 23:15:23 2014
(r272388)
+++ head/sys/cddl/boot/zfs/lz4.c Thu Oct 2 00:13:08 2014
(r272389)
@@ -83,6 +83,17 @@ lz4_decompress(void *s_start, void *d_st
#endif
/*
+ * Unaligned memory access is automatically enabled for "common" CPU,
+ * such as x86. For others CPU, the compiler will be more cautious, and
+ * insert extra code to ensure aligned access is respected. If you know
+ * your target CPU supports unaligned memory access, you may want to
+ * force this option manually to improve performance
+ */
+#if defined(__ARM_FEATURE_UNALIGNED)
+#define LZ4_FORCE_UNALIGNED_ACCESS 1
+#endif
+
+/*
* Compiler Options
*/
#if __STDC_VERSION__ >= 199901L /* C99 */
@@ -113,6 +124,10 @@ lz4_decompress(void *s_start, void *d_st
#define S32 int32_t
#define U64 uint64_t
+#ifndef LZ4_FORCE_UNALIGNED_ACCESS
+#pragma pack(1)
+#endif
+
typedef struct _U16_S {
U16 v;
} U16_S;
@@ -123,6 +138,10 @@ typedef struct _U64_S {
U64 v;
} U64_S;
+#ifndef LZ4_FORCE_UNALIGNED_ACCESS
+#pragma pack()
+#endif
+
#define A64(x) (((U64_S *)(x))->v)
#define A32(x) (((U32_S *)(x))->v)
#define A16(x) (((U16_S *)(x))->v)
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