This patch may be too ugly to live, it suppresses a lot of
sparse warnings in the libata build and produces slightly
tighter code. (4 instructions vs 5 and a few bytes saved).
include/linux/libata.h:1214:13: warning: potentially expensive pointer subtraction
Original:
if (++link - ap->pmp_link < ap->nr_pmp_links)
return link;
52b: 89 d8 mov %ebx,%eax
52d: 2b 82 60 26 00 00 sub 0x2660(%edx),%eax
533: c1 f8 02 sar $0x2,%eax
536: 69 c0 dd 3d c8 44 imul $0x44c83ddd,%eax,%eax
53c: 3b 82 5c 26 00 00 cmp 0x265c(%edx),%eax
542: 7d 04 jge 548 <sata_pmp_detach+0xbe>
Next:
if ((char*)++link - (char *)ap->pmp_link < ap->nr_pmp_links * sizeof(*link))
return link;
52b: 69 81 5c 26 00 00 d4 imul $0x9d4,0x265c(%ecx),%eax
532: 09 00 00
535: 89 da mov %ebx,%edx
537: 2b 91 60 26 00 00 sub 0x2660(%ecx),%edx
53d: 39 c2 cmp %eax,%edx
53f: 73 04 jae 545 <sata_pmp_detach+0xbb>
Signed-off-by: Harvey Harrison <harvey.harrison@xxxxxxxxx>
---
I know it's ugly, but I had it done anyways. The one real problem I have
with it is that if link and ap->pmp_link ever get changed to different types
the compiler will not even warn as we cast away to (char *). To make it
a bit more robust, a BUILD_BUG_ON checking the pointer types may be a
good idea.
include/linux/libata.h | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 2845983..f0e1178 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -1211,7 +1211,7 @@ static inline struct ata_link *ata_port_next_link(struct ata_link *link)
return ap->pmp_link;
}
- if (++link - ap->pmp_link < ap->nr_pmp_links)
+ if ((char*)++link - (char *)ap->pmp_link < ap->nr_pmp_links * sizeof(*link))
return link;
return NULL;
}
--
1.5.4.1.1278.gc75be
-
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