From bc276c585b24a5e3adb9c6cdfebc4d69d910cc2e Mon Sep 17 00:00:00 2001 From: isharipo Date: Thu, 17 May 2018 19:47:52 +0300 Subject: [PATCH] cmd/link/internal/ld: avoid Reloc copies in range loops MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Copying sym.Reloc in loops hurts performance as it has 48 byte size (on 64-bit platforms). There are quite many symbols and each of them has more than 1 relocation (so, it's possible to have more than 1kk relocs). The're also traversed more than once in some code paths. By using pointers to them, copies are avoided. For linking "hello world" example from net/http: name old time/op new time/op delta Linker-4 530ms ± 2% 521ms ± 3% -1.80% (p=0.000 n=17+20) Change-Id: I6518aec69d6adcd137f84b5c089ceab4cb4ea2dd Reviewed-on: https://go-review.googlesource.com/113636 Run-TryBot: Iskander Sharipov TryBot-Result: Gobot Gobot Reviewed-by: Brad Fitzpatrick --- src/cmd/link/internal/ld/ar.go | 3 ++- src/cmd/link/internal/ld/data.go | 3 ++- src/cmd/link/internal/ld/deadcode.go | 4 ++-- src/cmd/link/internal/ld/dwarf.go | 9 ++++++--- src/cmd/link/internal/ld/lib.go | 3 ++- 5 files changed, 14 insertions(+), 8 deletions(-) diff --git a/src/cmd/link/internal/ld/ar.go b/src/cmd/link/internal/ld/ar.go index ae7554c929..779f3565f9 100644 --- a/src/cmd/link/internal/ld/ar.go +++ b/src/cmd/link/internal/ld/ar.go @@ -105,7 +105,8 @@ func hostArchive(ctxt *Link, name string) { for any { var load []uint64 for _, s := range ctxt.Syms.Allsym { - for _, r := range s.R { + for i := range s.R { + r := &s.R[i] // Copying sym.Reloc has measurable impact on peformance if r.Sym != nil && r.Sym.Type == sym.SXREF { if off := armap[r.Sym.Name]; off != 0 && !loaded[off] { load = append(load, off) diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go index d71b8b6ac7..5dd4aac03e 100644 --- a/src/cmd/link/internal/ld/data.go +++ b/src/cmd/link/internal/ld/data.go @@ -772,7 +772,8 @@ func Datblk(ctxt *Link, addr int64, size int64) { if ctxt.LinkMode != LinkExternal { continue } - for _, r := range sym.R { + for i := range sym.R { + r := &sym.R[i] // Copying sym.Reloc has measurable impact on peformance rsname := "" if r.Sym != nil { rsname = r.Sym.Name diff --git a/src/cmd/link/internal/ld/deadcode.go b/src/cmd/link/internal/ld/deadcode.go index 540f4068cb..df989cc944 100644 --- a/src/cmd/link/internal/ld/deadcode.go +++ b/src/cmd/link/internal/ld/deadcode.go @@ -245,8 +245,8 @@ func (d *deadcodepass) init() { // but we do keep the symbols it refers to. exports := d.ctxt.Syms.ROLookup("go.plugin.exports", 0) if exports != nil { - for _, r := range exports.R { - d.mark(r.Sym, nil) + for i := range exports.R { + d.mark(exports.R[i].Sym, nil) } } } diff --git a/src/cmd/link/internal/ld/dwarf.go b/src/cmd/link/internal/ld/dwarf.go index ae6f90b079..c803180cad 100644 --- a/src/cmd/link/internal/ld/dwarf.go +++ b/src/cmd/link/internal/ld/dwarf.go @@ -1061,7 +1061,8 @@ func getCompilationDir() string { func importInfoSymbol(ctxt *Link, dsym *sym.Symbol) { dsym.Attr |= sym.AttrNotInSymbolTable | sym.AttrReachable dsym.Type = sym.SDWARFINFO - for _, r := range dsym.R { + for i := range dsym.R { + r := &dsym.R[i] // Copying sym.Reloc has measurable impact on peformance if r.Type == objabi.R_DWARFSECREF && r.Sym.Size == 0 { if ctxt.BuildMode == BuildModeShared { // These type symbols may not be present in BuildModeShared. Skip. @@ -1090,7 +1091,8 @@ func collectAbstractFunctions(ctxt *Link, fn *sym.Symbol, dsym *sym.Symbol, absf // Walk the relocations on the primary subprogram DIE and look for // references to abstract funcs. - for _, reloc := range dsym.R { + for i := range dsym.R { + reloc := &dsym.R[i] // Copying sym.Reloc has measurable impact on peformance candsym := reloc.Sym if reloc.Type != objabi.R_DWARFSECREF { continue @@ -1801,7 +1803,8 @@ func collectlocs(ctxt *Link, syms []*sym.Symbol, units []*compilationUnit) []*sy empty := true for _, u := range units { for _, fn := range u.funcDIEs { - for _, reloc := range fn.R { + for i := range fn.R { + reloc := &fn.R[i] // Copying sym.Reloc has measurable impact on peformance if reloc.Type == objabi.R_DWARFSECREF && strings.HasPrefix(reloc.Sym.Name, dwarf.LocPrefix) { reloc.Sym.Attr |= sym.AttrReachable | sym.AttrNotInSymbolTable syms = append(syms, reloc.Sym) diff --git a/src/cmd/link/internal/ld/lib.go b/src/cmd/link/internal/ld/lib.go index 9f89457753..d86b2aa544 100644 --- a/src/cmd/link/internal/ld/lib.go +++ b/src/cmd/link/internal/ld/lib.go @@ -503,7 +503,8 @@ func (ctxt *Link) loadlib() { // objects, try to read them from the libgcc file. any := false for _, s := range ctxt.Syms.Allsym { - for _, r := range s.R { + for i := range s.R { + r := &s.R[i] // Copying sym.Reloc has measurable impact on peformance if r.Sym != nil && r.Sym.Type == sym.SXREF && r.Sym.Name != ".got" { any = true break -- 2.50.0