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reflect, runtime: optimize Name method

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Several minor changes that remove a good chunk of the overhead added
to the reflect Name method over the 1.7 cycle, as seen from the
non-SSA architectures.

In particular, there are ~20 fewer instructions in reflect.name.name
on 386, and the method now qualifies for inlining.

The simple JSON decoding benchmark on darwin/386:

	name           old time/op    new time/op    delta
	CodeDecoder-8    49.2ms ± 0%    48.9ms ± 1%  -0.77%  (p=0.000 n=10+9)

	name           old speed      new speed      delta
	CodeDecoder-8  39.4MB/s ± 0%  39.7MB/s ± 1%  +0.77%  (p=0.000 n=10+9)

On darwin/amd64 the effect is less pronounced:

	name           old time/op    new time/op    delta
	CodeDecoder-8    38.9ms ± 0%    38.7ms ± 1%  -0.38%  (p=0.005 n=10+10)

	name           old speed      new speed      delta
	CodeDecoder-8  49.9MB/s ± 0%  50.1MB/s ± 1%  +0.38%  (p=0.006 n=10+10)

Counterintuitively, I get much more useful benchmark data out of my
MacBook Pro than a linux workstation with more expensive Intel chips.
While the laptop has fewer cores and an active GUI, the single-threaded
performance is significantly better (nearly 1.5x decoding throughput)
so the differences are more pronounced.

For #16117.

Change-Id: I4e0cc1cc2d271d47d5127b1ee1ca926faf34cabf
Reviewed-on: https://go-review.googlesource.com/24510
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
David Crawshaw 2016-06-27 21:37:19 -04:00
parent b75b0630fe
commit ed9362f769
2 changed files with 24 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
src/reflect/type.go
View File

@ -466,15 +466,13 @@ func (n name) tagLen() int {
func (n name) name() (s string) {
if n.bytes == nil {
return ""
}
nl := n.nameLen()
if nl == 0 {
return ""
return
}
b := (*[4]byte)(unsafe.Pointer(n.bytes))
hdr := (*stringHeader)(unsafe.Pointer(&s))
hdr.Data = unsafe.Pointer(n.data(3))
hdr.Len = nl
hdr.Data = unsafe.Pointer(&b[3])
hdr.Len = int(b[1])<<8 | int(b[2])
return s
}
@ -662,16 +660,10 @@ type typeOff int32 // offset to an *rtype
type textOff int32 // offset from top of text section
func (t *rtype) nameOff(off nameOff) name {
if off == 0 {
return name{}
}
return name{(*byte)(resolveNameOff(unsafe.Pointer(t), int32(off)))}
}
func (t *rtype) typeOff(off typeOff) *rtype {
if off == 0 {
return nil
}
return (*rtype)(resolveTypeOff(unsafe.Pointer(t), int32(off)))
}

23
src/runtime/type.go
View File

@ -170,14 +170,18 @@ func resolveNameOff(ptrInModule unsafe.Pointer, off nameOff) name {
return name{}
}
base := uintptr(ptrInModule)
var md *moduledata
for next := &firstmoduledata; next != nil; next = next.next {
if base >= next.types && base < next.etypes {
md = next
break
for md := &firstmoduledata; md != nil; md = md.next {
if base >= md.types && base < md.etypes {
res := md.types + uintptr(off)
if res > md.etypes {
println("runtime: nameOff", hex(off), "out of range", hex(md.types), "-", hex(md.etypes))
throw("runtime: name offset out of range")
}
return name{(*byte)(unsafe.Pointer(res))}
}
}
if md == nil {
// No module found. see if it is a run time name.
reflectOffsLock()
res, found := reflectOffs.m[int32(off)]
reflectOffsUnlock()
@ -189,13 +193,6 @@ func resolveNameOff(ptrInModule unsafe.Pointer, off nameOff) name {
throw("runtime: name offset base pointer out of range")
}
return name{(*byte)(res)}
}
res := md.types + uintptr(off)
if res > md.etypes {
println("runtime: nameOff", hex(off), "out of range", hex(md.types), "-", hex(md.etypes))
throw("runtime: name offset out of range")
}
return name{(*byte)(unsafe.Pointer(res))}
}
func (t *_type) nameOff(off nameOff) name {