[dev.link] cmd/link: use new-style relocation accessors in LoadFull

This gives some small speedup:

(linking cmd/compile)
Loadlibfull     77.8ms ± 6%    68.6ms ± 5%  -11.88%  (p=0.008 n=5+5)

Also convert some Relocs.At to At2, which should have been done
earlier.

Change-Id: I2a66aeb5857234c6e645e1b23380149cffc8221f
Reviewed-on: https://go-review.googlesource.com/c/go/+/226363
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/deadcode2.go

@@ -272,7 +272,7 @@ func deadcode2(ctxt *Link) {
 			s := loader.Sym(i)
 			if ldr.IsItabLink(s) {
 				relocs := ldr.Relocs(s)
-				if relocs.Count > 0 && ldr.AttrReachable(relocs.At(0).Sym) {
+				if relocs.Count > 0 && ldr.AttrReachable(relocs.At2(0).Sym()) {
 					ldr.SetAttrReachable(s, true)
 				}
 			}

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

@@ -1480,9 +1480,9 @@ func addpersrc(ctxt *Link) {
 	// relocation
 	relocs := ctxt.loader.Relocs(rsrcsym)
 	for i := 0; i < relocs.Count; i++ {
-		r := relocs.At(i)
-		p := data[r.Off:]
-		val := uint32(int64(h.virtualAddress) + r.Add)
+		r := relocs.At2(i)
+		p := data[r.Off():]
+		val := uint32(int64(h.virtualAddress) + r.Add())
 
 		// 32-bit little-endian
 		p[0] = byte(val)

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

@@ -1865,7 +1865,8 @@ func (l *Loader) LoadFull(arch *sys.Arch, syms *sym.Symbols) {
 		batch := l.relocBatch
 		s.R = batch[:len(pp.relocs):len(pp.relocs)]
 		l.relocBatch = batch[len(pp.relocs):]
-		l.convertRelocations(pp.relocs, s, false)
+		relocs := l.Relocs(i)
+		l.convertRelocations(&relocs, s, false)
 
 		// Copy data
 		s.P = pp.data
@@ -1977,7 +1978,6 @@ func (l *Loader) PropagateLoaderChangesToSymbols(toconvert []Sym, anonVerReplace
 	// sym.Symbols are created.
 
 	// First pass, symbol creation and symbol data fixup.
-	rslice := []Reloc{}
 	for _, cand := range toconvert {
 
 		sn := l.SymName(cand)
@@ -2063,11 +2063,10 @@ func (l *Loader) PropagateLoaderChangesToSymbols(toconvert []Sym, anonVerReplace
 	for _, cand := range relocfixup {
 		s := l.Syms[cand]
 		relocs := l.Relocs(cand)
-		rslice = relocs.ReadAll(rslice)
-		if len(s.R) != len(rslice) {
-			s.R = make([]sym.Reloc, len(rslice))
+		if len(s.R) != relocs.Count {
+			s.R = make([]sym.Reloc, relocs.Count)
 		}
-		l.convertRelocations(rslice, s, true)
+		l.convertRelocations(&relocs, s, true)
 	}
 
 	return result
@@ -2426,7 +2425,6 @@ func loadObjFull(l *Loader, r *oReader) {
 	fdsyms := []*sym.Symbol{}
 	var funcAllocCounts funcAllocInfo
 	pcdataBase := r.PcdataBase()
-	rslice := []Reloc{}
 	for i, n := 0, r.NSym()+r.NNonpkgdef(); i < n; i++ {
 		// A symbol may be a dup or overwritten. In this case, its
 		// content will actually be provided by a different object
@@ -2471,11 +2469,10 @@ func loadObjFull(l *Loader, r *oReader) {
 
 		// Relocs
 		relocs := l.relocs(r, i)
-		rslice = relocs.ReadAll(rslice)
 		batch := l.relocBatch
 		s.R = batch[:relocs.Count:relocs.Count]
 		l.relocBatch = batch[relocs.Count:]
-		l.convertRelocations(rslice, s, false)
+		l.convertRelocations(&relocs, s, false)
 
 		// Aux symbol info
 		isym := -1
@@ -2645,12 +2642,12 @@ func loadObjFull(l *Loader, r *oReader) {
 // etc. It is assumed that the caller has pre-allocated the dst symbol
 // relocations slice. If 'strict' is set, then this method will
 // panic if it finds a relocation targeting a nil symbol.
-func (l *Loader) convertRelocations(src []Reloc, dst *sym.Symbol, strict bool) {
+func (l *Loader) convertRelocations(src *Relocs, dst *sym.Symbol, strict bool) {
 	for j := range dst.R {
-		r := src[j]
-		rs := r.Sym
-		sz := r.Size
-		rt := r.Type
+		r := src.At2(j)
+		rs := r.Sym()
+		sz := r.Siz()
+		rt := r.Type()
 		if rt == objabi.R_METHODOFF {
 			if l.attrReachable.Has(rs) {
 				rt = objabi.R_ADDROFF
@@ -2671,10 +2668,10 @@ func (l *Loader) convertRelocations(src []Reloc, dst *sym.Symbol, strict bool) {
 			panic("nil reloc target in convertRelocations")
 		}
 		dst.R[j] = sym.Reloc{
-			Off:  r.Off,
+			Off:  r.Off(),
 			Siz:  sz,
 			Type: rt,
-			Add:  r.Add,
+			Add:  r.Add(),
 			Sym:  l.Syms[rs],
 		}
 	}