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Date: Mon, 12 Oct 2015 20:30:33 +0200
From: Denys Vlasenko <vda.linux@...glemail.com>
To: Rich Felker <dalias@...c.org>
Cc: Denys Vlasenko <vda.linux@...glemail.com>, musl@...ts.openwall.com
Subject: [PATCH 2/3] i386/memset: do not fetch fill char from memory again
shl $16,%edx
mov 8(%esp),%dl
mov 8(%esp),%dh
The above code has two register merge stalls, and it goes to load unit
to fetch the data. I don't know what's worse. Both are not pleasant.
Replace them with IMUL. It has ~3 cycle latency, but no stalls.
Move it a bit up to hide its latency.
text data bss dec hex filename
182 0 0 182 b6 memset1.o
177 0 0 177 b1 memset2.o
Signed-off-by: Denys Vlasenko <vda.linux@...glemail.com>
CC: Rich Felker <dalias@...c.org>
CC: musl@...ts.openwall.com
---
src/string/i386/memset.s | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/src/string/i386/memset.s b/src/string/i386/memset.s
index d6118c7..cd13f41 100644
--- a/src/string/i386/memset.s
+++ b/src/string/i386/memset.s
@@ -19,13 +19,10 @@ memset:
mov %dx,1(%eax)
mov %dx,(-1-2)(%eax,%ecx)
+ imul $0x10001,%edx
cmp $6,%ecx
jbe 1f
- shl $16,%edx
- mov 8(%esp),%dl
- mov 8(%esp),%dh
-
mov %edx,(1+2)(%eax)
mov %edx,(-1-2-4)(%eax,%ecx)
cmp $14,%ecx
--
1.8.1.4
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