[dev.link] cmd/link: record go.itablink symbols during object file read

Change the new loader to keep a note of the set of "go.itablink.*"
symbols (using a small map), and add a method that clients can use to
query whether a given global index corresponds to a "go.itablink.*"
sym. This eliminates one instance of raw symbol name reading/matching
during new deadcode, which should produce a minor speedup.

Change-Id: I5915773a3f33c16099ccd68592dbba783d909bc9
Reviewed-on: https://go-review.googlesource.com/c/go/+/201400
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

diff --git a/src/cmd/link/internal/ld/deadcode2.go b/src/cmd/link/internal/ld/deadcode2.go
index 818024069e89e04fb529cfe33beed6673d2911fd..82626c7a289f0a6beeca71d01947f76a440c0308 100644 (file)
--- a/src/cmd/link/internal/ld/deadcode2.go
+++ b/src/cmd/link/internal/ld/deadcode2.go
@@ -11,7 +11,6 @@ import (
        "cmd/link/internal/loader"
        "cmd/link/internal/sym"
        "fmt"
-       "strings"
        "unicode"
 )
 
@@ -226,7 +225,7 @@ func deadcode2(ctxt *Link) {
                // (When BuildModeShared, always keep itablinks.)
                for i := 1; i < n; i++ {
                        s := loader.Sym(i)
-                       if strings.HasPrefix(ldr.RawSymName(s), "go.itablink.") { // TODO: use an attribute instread of checking name
+                       if ldr.IsItabLink(s) {
                                relocs := ldr.Relocs(s)
                                if relocs.Count > 0 && ldr.Reachable.Has(relocs.At(0).Sym) {
                                        ldr.Reachable.Set(s)

diff --git a/src/cmd/link/internal/loader/loader.go b/src/cmd/link/internal/loader/loader.go
index 708e8d0d3ec07d538f45a382542c42cb3c5bf03a..5f631f16256d2227c2fd70f8c0aaceaf572e8032 100644 (file)
--- a/src/cmd/link/internal/loader/loader.go
+++ b/src/cmd/link/internal/loader/loader.go
@@ -100,6 +100,8 @@ type Loader struct {
        symsByName map[nameVer]Sym // map symbol name to index
        overwrite  map[Sym]Sym     // overwrite[i]=j if symbol j overwrites symbol i
 
+       itablink map[Sym]struct{} // itablink[j] defined if j is go.itablink.*
+
        objByPkg map[string]*oReader // map package path to its Go object reader
 
        Syms []*sym.Symbol // indexed symbols. XXX we still make sym.Symbol for now.
@@ -114,6 +116,7 @@ func NewLoader() *Loader {
                symsByName: make(map[nameVer]Sym),
                objByPkg:   make(map[string]*oReader),
                overwrite:  make(map[Sym]Sym),
+               itablink:   make(map[Sym]struct{}),
        }
 }
 
@@ -369,6 +372,14 @@ func (l *Loader) IsGoType(i Sym) bool {
        return l.SymAttr(i)&goobj2.SymFlagGoType != 0
 }
 
+// Returns whether this is a "go.itablink.*" symbol.
+func (l *Loader) IsItabLink(i Sym) bool {
+       if _, ok := l.itablink[i]; ok {
+               return true
+       }
+       return false
+}
+
 // Returns the symbol content of the i-th symbol. i is global index.
 func (l *Loader) Data(i Sym) []byte {
        if l.isExternal(i) {
@@ -491,7 +502,10 @@ func (l *Loader) Preload(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, lib *
                }
                v := abiToVer(osym.ABI, localSymVersion)
                dupok := osym.Dupok()
-               l.AddSym(name, v, istart+Sym(i), or, dupok, sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type)])
+               added := l.AddSym(name, v, istart+Sym(i), or, dupok, sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type)])
+               if added && strings.HasPrefix(name, "go.itablink.") {
+                       l.itablink[istart+Sym(i)] = struct{}{}
+               }
        }
 
        // The caller expects us consuming all the data