[dev.link] cmd/link: only do name expansion when needed
Most Go objects are compiled with known package path, so the
symbol name is already fully expanded. Nevertheless, currently
in the linker strings.Replace is called unconditionally, and most
of the time it doesn't do anything.
This CL records a per-object flag in the object file, and do the
name expansion only when the name is not expanded at compile time.
This gives small speedups for the linker. Linking cmd/compile:
name old time/op new time/op delta
Loadlib 35.1ms ± 2% 32.8ms ± 4% -6.43% (p=0.008 n=5+5)
Symtab 15.8ms ± 2% 14.0ms ± 8% -11.45% (p=0.008 n=5+5)
TotalTime 399ms ± 1% 385ms ± 2% -3.63% (p=0.008 n=5+5)
Change-Id: I735084971a051cd9be4284ad294c284cd5b545f4
Reviewed-on: https://go-review.googlesource.com/c/go/+/234490
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/src/cmd/internal/goobj2/objfile.go b/src/cmd/internal/goobj2/objfile.go
index fde482e..dc5174f 100644
--- a/src/cmd/internal/goobj2/objfile.go
+++ b/src/cmd/internal/goobj2/objfile.go
@@ -228,7 +228,8 @@
const SymABIstatic = ^uint16(0)
const (
- ObjFlagShared = 1 << iota
+ ObjFlagShared = 1 << iota // this object is built with -shared
+ ObjFlagNeedNameExpansion // the linker needs to expand `"".` to package path in symbol names
)
const (
@@ -675,3 +676,6 @@
func (r *Reader) Flags() uint32 {
return r.h.Flags
}
+
+func (r *Reader) Shared() bool { return r.Flags()&ObjFlagShared != 0 }
+func (r *Reader) NeedNameExpansion() bool { return r.Flags()&ObjFlagNeedNameExpansion != 0 }
diff --git a/src/cmd/internal/obj/objfile2.go b/src/cmd/internal/obj/objfile2.go
index 0b3b2be..c28ae56 100644
--- a/src/cmd/internal/obj/objfile2.go
+++ b/src/cmd/internal/obj/objfile2.go
@@ -38,6 +38,9 @@
if ctxt.Flag_shared {
flags |= goobj2.ObjFlagShared
}
+ if pkgpath == "" {
+ flags |= goobj2.ObjFlagNeedNameExpansion
+ }
h := goobj2.Header{
Magic: goobj2.Magic,
Fingerprint: ctxt.Fingerprint,
diff --git a/src/cmd/link/internal/loader/loader.go b/src/cmd/link/internal/loader/loader.go
index 5696c51..26b17ce 100644
--- a/src/cmd/link/internal/loader/loader.go
+++ b/src/cmd/link/internal/loader/loader.go
@@ -661,7 +661,11 @@
return pp.name
}
r, li := l.toLocal(i)
- return strings.Replace(r.Sym(li).Name(r.Reader), "\"\".", r.pkgprefix, -1)
+ name := r.Sym(li).Name(r.Reader)
+ if !r.NeedNameExpansion() {
+ return name
+ }
+ return strings.Replace(name, "\"\".", r.pkgprefix, -1)
}
// Returns the version of the i-th symbol.
@@ -843,7 +847,7 @@
// might make more sense to copy the flag value out of the
// object into a larger bitmap during preload.
r, _ := l.toLocal(i)
- return (r.Flags() & goobj2.ObjFlagShared) != 0
+ return r.Shared()
}
return l.attrShared.Has(l.extIndex(i))
}
@@ -1948,9 +1952,13 @@
panic("preloadSyms: bad kind")
}
l.growAttrBitmaps(len(l.objSyms) + int(end-start))
+ needNameExpansion := r.NeedNameExpansion()
for i := start; i < end; i++ {
osym := r.Sym(i)
- name := strings.Replace(osym.Name(r.Reader), "\"\".", r.pkgprefix, -1)
+ name := osym.Name(r.Reader)
+ if needNameExpansion {
+ name = strings.Replace(name, "\"\".", r.pkgprefix, -1)
+ }
v := abiToVer(osym.ABI(), r.version)
dupok := osym.Dupok()
gi, added := l.AddSym(name, v, r, i, kind, dupok, sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type())])
@@ -1998,9 +2006,13 @@
func loadObjRefs(l *Loader, r *oReader, arch *sys.Arch) {
ndef := uint32(r.NSym() + r.NNonpkgdef())
+ needNameExpansion := r.NeedNameExpansion()
for i, n := uint32(0), uint32(r.NNonpkgref()); i < n; i++ {
osym := r.Sym(ndef + i)
- name := strings.Replace(osym.Name(r.Reader), "\"\".", r.pkgprefix, -1)
+ name := osym.Name(r.Reader)
+ if needNameExpansion {
+ name = strings.Replace(name, "\"\".", r.pkgprefix, -1)
+ }
v := abiToVer(osym.ABI(), r.version)
r.syms[ndef+i] = l.LookupOrCreateSym(name, v)
gi := r.syms[ndef+i]
@@ -2109,7 +2121,10 @@
// Read the particulars from object.
r, li := l.toLocal(symIdx)
osym := r.Sym(li)
- sname := strings.Replace(osym.Name(r.Reader), "\"\".", r.pkgprefix, -1)
+ sname := osym.Name(r.Reader)
+ if r.NeedNameExpansion() {
+ sname = strings.Replace(sname, "\"\".", r.pkgprefix, -1)
+ }
sver := abiToVer(osym.ABI(), r.version)
skind := sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type())]
