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authorDenys Vlasenko <vda.linux@googlemail.com>2015-02-10 18:30:56 +0100
committerRich Felker <dalias@aerifal.cx>2015-02-10 18:53:31 -0500
commitbf2071eda32528ee8b0bb89544152646684a2cf3 (patch)
treed2d826f84c6a2d23be25019208bf80b6dee3f071 /src/string
parent6a5242e4cb2f9c695f613dc312ed5e1bb8008912 (diff)
downloadmusl-bf2071eda32528ee8b0bb89544152646684a2cf3.tar.gz
x86_64/memset: simple optimizations
"and $0xff,%esi" is a six-byte insn (81 e6 ff 00 00 00), can use 4-byte "movzbl %sil,%esi" (40 0f b6 f6) instead. 64-bit imul is slow, move it as far up as possible so that the result (rax) has more time to be ready by the time we start using it in mem stores. There is no need to shuffle registers in preparation to "rep movs" if we are not going to take that code path. Thus, patch moves "jump if len < 16" instructions up, and changes alternate code path to use rdx and rdi instead of rcx and r8. Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'src/string')
-rw-r--r--src/string/x86_64/memset.s30
1 files changed, 16 insertions, 14 deletions
diff --git a/src/string/x86_64/memset.s b/src/string/x86_64/memset.s
index fc06eef8..263336b5 100644
--- a/src/string/x86_64/memset.s
+++ b/src/string/x86_64/memset.s
@@ -1,41 +1,43 @@
.global memset
.type memset,@function
memset:
- and $0xff,%esi
+ movzbl %sil,%esi
mov $0x101010101010101,%rax
- mov %rdx,%rcx
- mov %rdi,%r8
+ # 64-bit imul has 3-7 cycles latency, launch early
imul %rsi,%rax
- cmp $16,%rcx
+
+ cmp $16,%rdx
jb 1f
- mov %rax,-8(%rdi,%rcx)
+ mov %rdx,%rcx
+ mov %rdi,%r8
shr $3,%rcx
+ mov %rax,-8(%rdi,%rdx)
rep
stosq
mov %r8,%rax
ret
-1: test %ecx,%ecx
+1: test %edx,%edx
jz 1f
mov %al,(%rdi)
- mov %al,-1(%rdi,%rcx)
- cmp $2,%ecx
+ mov %al,-1(%rdi,%rdx)
+ cmp $2,%edx
jbe 1f
mov %al,1(%rdi)
- mov %al,-2(%rdi,%rcx)
- cmp $4,%ecx
+ mov %al,-2(%rdi,%rdx)
+ cmp $4,%edx
jbe 1f
mov %eax,(%rdi)
- mov %eax,-4(%rdi,%rcx)
- cmp $8,%ecx
+ mov %eax,-4(%rdi,%rdx)
+ cmp $8,%edx
jbe 1f
mov %eax,4(%rdi)
- mov %eax,-8(%rdi,%rcx)
+ mov %eax,-8(%rdi,%rdx)
-1: mov %r8,%rax
+1: mov %rdi,%rax
ret