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[dev.link] cmd/link: only read necessary fields in deadcode pass

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Reading unnecessary fields from object file take time, even from
memory mapping. In deadcode, we do this a alot, so only read
necessary ones. In particular, for relocations, for non-type
symbols, we only need their target symbols and reloc types to
build the dependency graph, so don't read other fields. This
should speed up the deadcode pass.

Also cache an object's number of defined package symbols, as it
is accessed a lot in resolve.

This is a bit ugly from an API point of view. It would be nice if
the compiler could figure out some fields are not used so don't
fill them.

Change-Id: I5c4e9526b8a3b0aead9fa71901a51fb214f013a7
Reviewed-on: https://go-review.googlesource.com/c/go/+/218479
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>
This commit is contained in:
Cherry Zhang 2020-02-07 10:26:06 -05:00
parent 06e2339dfe
commit 38437ce118
3 changed files with 58 additions and 13 deletions
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38
src/cmd/link/internal/loader/loader.go
View file

@ -60,6 +60,7 @@ type oReader struct {
flags uint32 // read from object file
pkgprefix string
syms []Sym // Sym's global index, indexed by local index
ndef int // cache goobj2.Reader.NSym()
}
type objIdx struct {
@ -169,7 +170,7 @@ type Loader struct {
symsByName [2]map[string]Sym // map symbol name to index, two maps are for ABI0 and ABIInternal
extStaticSyms map[nameVer]Sym // externally defined static symbols, keyed by name
extReader *oReader // a dummy oReader, for external symbols
extReader *oReader // a dummy oReader, for external symbols
payloadBatch []extSymPayload
payloads []*extSymPayload // contents of linker-materialized external syms
values []int64 // symbol values, indexed by global sym index
@ -510,7 +511,7 @@ func (l *Loader) resolve(r *oReader, s goobj2.SymRef) Sym {
}
return 0
case goobj2.PkgIdxNone:
i := int(s.SymIdx) + r.NSym()
i := int(s.SymIdx) + r.ndef
return r.syms[i]
case goobj2.PkgIdxBuiltin:
return l.builtinSyms[s.SymIdx]
@ -641,7 +642,7 @@ func (l *Loader) SymAttr(i Sym) uint8 {
}
r, li := l.toLocal(i)
osym := goobj2.Sym{}
osym.Read(r.Reader, r.SymOff(li))
osym.ReadFlag(r.Reader, r.SymOff(li))
return osym.Flag
}
@ -745,7 +746,7 @@ func (l *Loader) AttrDuplicateOK(i Sym) bool {
// into a larger bitmap during preload.
r, li := l.toLocal(i)
osym := goobj2.Sym{}
osym.Read(r.Reader, r.SymOff(li))
osym.ReadFlag(r.Reader, r.SymOff(li))
return osym.Dupok()
}
return l.attrDuplicateOK.has(l.extIndex(i))
@ -1252,9 +1253,9 @@ func (l *Loader) ReadAuxSyms(symIdx Sym, dst []Sym) []Sym {
dst = dst[:0]
r, li := l.toLocal(symIdx)
a := goobj2.Aux{}
for i := 0; i < naux; i++ {
a := goobj2.Aux{}
a.Read(r.Reader, r.AuxOff(li, i))
a.ReadSym(r.Reader, r.AuxOff(li, i))
dst = append(dst, l.resolve(r, a.Sym))
}
@ -1386,6 +1387,17 @@ func (relocs *Relocs) At(j int) Reloc {
// specified slice. If the slice capacity is not large enough, a new
// larger slice will be allocated. Final slice is returned.
func (relocs *Relocs) ReadAll(dst []Reloc) []Reloc {
return relocs.readAll(dst, false)
}
// ReadSyms method reads all relocation target symbols and reloc types
// for a symbol into the specified slice. It is like ReadAll but only
// fill in the Sym and Type fields.
func (relocs *Relocs) ReadSyms(dst []Reloc) []Reloc {
return relocs.readAll(dst, true)
}
func (relocs *Relocs) readAll(dst []Reloc, onlySymType bool) []Reloc {
if relocs.Count == 0 {
return dst[:0]
}
@ -1402,9 +1414,13 @@ func (relocs *Relocs) ReadAll(dst []Reloc) []Reloc {
}
off := relocs.r.RelocOff(relocs.li, 0)
rel := goobj2.Reloc{}
for i := 0; i < relocs.Count; i++ {
rel := goobj2.Reloc{}
rel.Read(relocs.r.Reader, off)
if onlySymType {
rel.ReadSymType(relocs.r.Reader, off)
} else {
rel.Read(relocs.r.Reader, off)
}
off += uint32(rel.Size())
target := relocs.l.resolve(relocs.r, rel.Sym)
dst = append(dst, Reloc{
@ -1467,7 +1483,7 @@ func (l *Loader) Preload(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, lib *
pkgprefix := objabi.PathToPrefix(lib.Pkg) + "."
ndef := r.NSym()
nnonpkgdef := r.NNonpkgdef()
or := &oReader{r, unit, localSymVersion, r.Flags(), pkgprefix, make([]Sym, ndef + nnonpkgdef + r.NNonpkgref())}
or := &oReader{r, unit, localSymVersion, r.Flags(), pkgprefix, make([]Sym, ndef+nnonpkgdef+r.NNonpkgref()), ndef}
// Autolib
lib.ImportStrings = append(lib.ImportStrings, r.Autolib()...)
@ -1740,7 +1756,7 @@ func loadObjSyms(l *Loader, syms *sym.Symbols, r *oReader) int {
nr := 0
for i, n := 0, r.NSym()+r.NNonpkgdef(); i < n; i++ {
gi := r.syms[i]
if r2, i2 := l.toLocal(gi); r2 != r || i2 != i{
if r2, i2 := l.toLocal(gi); r2 != r || i2 != i {
continue // come from a different object
}
osym := goobj2.Sym{}
@ -2278,7 +2294,7 @@ func (l *Loader) UndefinedRelocTargets(limit int) []Sym {
rslice := []Reloc{}
for si := Sym(1); si < Sym(len(l.objSyms)); si++ {
relocs := l.Relocs(si)
rslice = relocs.ReadAll(rslice)
rslice = relocs.ReadSyms(rslice)
for ri := 0; ri < relocs.Count; ri++ {
r := &rslice[ri]
if r.Sym != 0 && l.SymType(r.Sym) == sym.SXREF && l.RawSymName(r.Sym) != ".got" {