[dev.link] cmd/link: simplify named symbol resolution

Now that we have local-global index mappings, just use that for
symbol reference resolution.

Change-Id: I6bc5405853fe040ff21b624ccd8da7965d66ec8c
Reviewed-on: https://go-review.googlesource.com/c/go/+/217065
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>

src/cmd/link/internal/ld/lib.go

@@ -455,6 +455,9 @@ func (ctxt *Link) loadlib() {
 		}
 	}
 
+	// Add references of externally defined symbols.
+	ctxt.loader.LoadRefs(ctxt.Arch, ctxt.Syms)
+
 	// Process cgo directives (has to be done before host object loading).
 	ctxt.loadcgodirectives(ctxt.loaderSupport())
 
@@ -462,9 +465,6 @@ func (ctxt *Link) loadlib() {
 	hostobjs(ctxt)
 	hostlinksetup(ctxt)
 
-	// Add references of externally defined symbols.
-	ctxt.loader.LoadRefs(ctxt.Arch, ctxt.Syms)
-
 	if ctxt.LinkMode == LinkInternal && len(hostobj) != 0 {
 		// If we have any undefined symbols in external
 		// objects, try to read them from the libgcc file.

src/cmd/link/internal/loader/loader.go

@@ -61,7 +61,6 @@ type oReader struct {
 	version   int    // version of static symbol
 	flags     uint32 // read from object file
 	pkgprefix string
-	rcache    []Sym // cache mapping local PkgNone symbol to resolved Sym
 	syms      []Sym // Sym's global index, indexed by local index
 }
 
@@ -519,26 +518,6 @@ func (l *Loader) toLocal(i Sym) (*oReader, int) {
 	return l.objSyms[i].r, int(l.objSyms[i].s)
 }
 
-// rcacheGet checks for a valid entry for 's' in the readers cache,
-// where 's' is a local PkgIdxNone ref or def, or zero if
-// the cache is empty or doesn't contain a value for 's'.
-func (or *oReader) rcacheGet(symIdx uint32) Sym {
-	if len(or.rcache) > 0 {
-		return or.rcache[symIdx]
-	}
-	return 0
-}
-
-// rcacheSet installs a new entry in the oReader's PkgNone
-// resolver cache for the specified PkgIdxNone ref or def,
-// allocating a new cache if needed.
-func (or *oReader) rcacheSet(symIdx uint32, gsym Sym) {
-	if len(or.rcache) == 0 {
-		or.rcache = make([]Sym, or.NNonpkgdef()+or.NNonpkgref())
-	}
-	or.rcache[symIdx] = gsym
-}
-
 // Resolve a local symbol reference. Return global index.
 func (l *Loader) resolve(r *oReader, s goobj2.SymRef) Sym {
 	var rr *oReader
@@ -550,19 +529,7 @@ func (l *Loader) resolve(r *oReader, s goobj2.SymRef) Sym {
 		return 0
 	case goobj2.PkgIdxNone:
 		i := int(s.SymIdx) + r.NSym()
-		// Check for cached version first
+		return r.syms[i]
-		if cached := r.rcacheGet(s.SymIdx); cached != 0 {
-			return cached
-		}
-		// Resolve by name
-		osym := goobj2.Sym{}
-		osym.Read(r.Reader, r.SymOff(i))
-		name := strings.Replace(osym.Name, "\"\".", r.pkgprefix, -1)
-		v := abiToVer(osym.ABI, r.version)
-		gsym := l.Lookup(name, v)
-		// Add to cache, then return.
-		r.rcacheSet(s.SymIdx, gsym)
-		return gsym
 	case goobj2.PkgIdxBuiltin:
 		return l.builtinSyms[s.SymIdx]
 	case goobj2.PkgIdxSelf:
@@ -1596,7 +1563,7 @@ 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, nil, make([]Sym, ndef + nnonpkgdef + r.NNonpkgref())}
+	or := &oReader{r, unit, localSymVersion, r.Flags(), pkgprefix, make([]Sym, ndef + nnonpkgdef + r.NNonpkgref())}
 
 	// Autolib
 	lib.ImportStrings = append(lib.ImportStrings, r.Autolib()...)