[dev.link] cmd/link: delete ctxt.Reachparent

It is no longer needed as we have converted the fieldtrack pass
to using the loader.

Also free loader.Reachparent after we are done with it.

Change-Id: Ibc4b29f282e1e4aea363a1b549755e31f84b0295
Reviewed-on: https://go-review.googlesource.com/c/go/+/229322
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>

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

@@ -45,7 +45,7 @@ type deadcodePass struct {
 func (d *deadcodePass) init() {
 	d.ldr.InitReachable()
 	d.ifaceMethod = make(map[methodsig]bool)
-	if d.ctxt.Reachparent != nil {
+	if objabi.Fieldtrack_enabled != 0 {
 		d.ldr.Reachparent = make([]loader.Sym, d.ldr.NSym())
 	}
 	heap.Init(&d.wq)
@@ -190,7 +190,7 @@ func (d *deadcodePass) mark(symIdx, parent loader.Sym) {
 	if symIdx != 0 && !d.ldr.AttrReachable(symIdx) {
 		d.wq.push(symIdx)
 		d.ldr.SetAttrReachable(symIdx, true)
-		if d.ctxt.Reachparent != nil {
+		if objabi.Fieldtrack_enabled != 0 {
 			d.ldr.Reachparent[symIdx] = parent
 		}
 		if *flagDumpDep {

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

@@ -383,6 +383,7 @@ func fieldtrack(arch *sys.Arch, l *loader.Loader) {
 			}
 		}
 	}
+	l.Reachparent = nil // we are done with it
 	if *flagFieldTrack == "" {
 		return
 	}

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

@@ -2812,7 +2812,7 @@ func (ctxt *Link) loadlibfull() {
 	}
 
 	// Pull the symbols out.
-	ctxt.loader.ExtractSymbols(ctxt.Syms, ctxt.Reachparent)
+	ctxt.loader.ExtractSymbols(ctxt.Syms)
 	ctxt.lookup = ctxt.Syms.ROLookup
 
 	// Recreate dynexp using *sym.Symbol instead of loader.Sym

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

@@ -82,9 +82,6 @@ type Link struct {
 
 	tramps []loader.Sym // trampolines
 
-	// Used to implement field tracking.
-	Reachparent map[*sym.Symbol]*sym.Symbol
-
 	compUnits []*sym.CompilationUnit // DWARF compilation units
 	runtimeCU *sym.CompilationUnit   // One of the runtime CUs, the last one seen.
 

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

@@ -35,7 +35,6 @@ import (
 	"cmd/internal/objabi"
 	"cmd/internal/sys"
 	"cmd/link/internal/benchmark"
-	"cmd/link/internal/sym"
 	"flag"
 	"log"
 	"os"
@@ -156,9 +155,6 @@ func Main(arch *sys.Arch, theArch Arch) {
 		}
 	}
 
-	if objabi.Fieldtrack_enabled != 0 {
-		ctxt.Reachparent = make(map[*sym.Symbol]*sym.Symbol)
-	}
 	checkStrictDups = *FlagStrictDups
 
 	startProfile()

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

@@ -2128,7 +2128,7 @@ func (l *Loader) PropagateLoaderChangesToSymbols(toconvert []Sym, anonVerReplace
 
 // ExtractSymbols grabs the symbols out of the loader for work that hasn't been
 // ported to the new symbol type.
-func (l *Loader) ExtractSymbols(syms *sym.Symbols, rp map[*sym.Symbol]*sym.Symbol) {
+func (l *Loader) ExtractSymbols(syms *sym.Symbols) {
 	// Add symbols to the ctxt.Syms lookup table. This explicitly skips things
 	// created via loader.Create (marked with versions less than zero), since
 	// if we tried to add these we'd wind up with collisions. We do, however,
@@ -2148,13 +2148,6 @@ func (l *Loader) ExtractSymbols(syms *sym.Symbols, rp map[*sym.Symbol]*sym.Symbo
 		}
 	}
 
-	for i, s := range l.Reachparent {
-		if i == 0 {
-			continue
-		}
-		rp[l.Syms[i]] = l.Syms[s]
-	}
-
 	// Provide lookup functions for sym.Symbols.
 	l.SymLookup = func(name string, ver int) *sym.Symbol {
 		i := l.LookupOrCreateSym(name, ver)