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runtime: speed up stack copying a little 

Remove a branch and a stack spill.

name                old time/op  new time/op  delta
StackCopy-8         79.2ms ± 1%  79.1ms ± 2%    ~     (p=0.063 n=96+95)
StackCopyNoCache-8   121ms ± 1%   120ms ± 2%  -0.46%  (p=0.000 n=97+88)

Change-Id: Ifcbbb05d773178fad84cb11a9a6768ace69fcf24
Reviewed-on: https://go-review.googlesource.com/94029
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Josh Bleecher Snyder 2017-09-30 23:06:49 -07:00
parent 910d232a28
commit 605c9feeb1
1 changed files with 2 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
src/runtime/symtab.go
View File

@ -853,13 +853,9 @@ func step(p []byte, pc *uintptr, val *int32, first bool) (newp []byte, ok bool)
if uvdelta&0x80 != 0 {
n, uvdelta = readvarint(p)
}
*val += int32(-(uvdelta & 1) ^ (uvdelta >> 1))
p = p[n:]
if uvdelta&1 != 0 {
uvdelta = ^(uvdelta >> 1)
} else {
uvdelta >>= 1
}
vdelta := int32(uvdelta)
pcdelta := uint32(p[0])
n = 1
if pcdelta&0x80 != 0 {
@ -867,7 +863,6 @@ func step(p []byte, pc *uintptr, val *int32, first bool) (newp []byte, ok bool)
}
p = p[n:]
*pc += uintptr(pcdelta * sys.PCQuantum)
*val += vdelta
return p, true
}