[dev.regabi] cmd/compile: add Linksym helpers

Syms are meant to be just interned (pkg, name) tuples, and are a
purely abstract, Go-language concept. As such, associating them with
linker symbols (a low-level, implementation-oriented detail) is
inappropriate.

There's still work to be done before linker symbols can be directly
attached to their appropriate, higher-level objects instead. But in
the mean-time, we can at least add helper functions and discourage
folks from using Sym.Linksym directly. The next CL will mechanically
rewrite code to use these helpers where possible.

Passes toolstash -cmp.

Change-Id: I413bd1c80bce056304f9a7343526bd153f2b9c7d
Reviewed-on: https://go-review.googlesource.com/c/go/+/280639
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

src/cmd/compile/internal/gc/obj.go

@@ -260,7 +260,7 @@ func addGCLocals() {
 	}
 }
 
-func ggloblnod(nam ir.Node) {
+func ggloblnod(nam *ir.Name) {
 	s := nam.Sym().Linksym()
 	s.Gotype = reflectdata.TypeSym(nam.Type()).Linksym()
 	flags := 0

src/cmd/compile/internal/ir/func.go

@@ -78,7 +78,7 @@ type Func struct {
 	// Marks records scope boundary changes.
 	Marks []Mark
 
-	FieldTrack map[*types.Sym]struct{}
+	FieldTrack map[*obj.LSym]struct{}
 	DebugInfo  interface{}
 	LSym       *obj.LSym
 
@@ -119,12 +119,8 @@ func (f *Func) isStmt() {}
 func (f *Func) Type() *types.Type     { return f.typ }
 func (f *Func) SetType(x *types.Type) { f.typ = x }
 
-func (f *Func) Sym() *types.Sym {
-	if f.Nname != nil {
-		return f.Nname.Sym()
-	}
-	return nil
-}
+func (f *Func) Sym() *types.Sym    { return f.Nname.Sym() }
+func (f *Func) Linksym() *obj.LSym { return f.Nname.Linksym() }
 
 // An Inline holds fields used for function bodies that can be inlined.
 type Inline struct {

src/cmd/compile/internal/ir/name.go

@@ -7,6 +7,7 @@ package ir
 import (
 	"cmd/compile/internal/base"
 	"cmd/compile/internal/types"
+	"cmd/internal/obj"
 	"cmd/internal/objabi"
 	"cmd/internal/src"
 
@@ -238,6 +239,8 @@ func (n *Name) SetFrameOffset(x int64) { n.Offset_ = x }
 func (n *Name) Iota() int64            { return n.Offset_ }
 func (n *Name) SetIota(x int64)        { n.Offset_ = x }
 
+func (n *Name) Linksym() *obj.LSym { return n.sym.Linksym() }
+
 func (*Name) CanBeNtype()    {}
 func (*Name) CanBeAnSSASym() {}
 func (*Name) CanBeAnSSAAux() {}

src/cmd/compile/internal/reflectdata/reflect.go

@@ -812,8 +812,8 @@ func dcommontype(lsym *obj.LSym, t *types.Type) int {
 
 // TrackSym returns the symbol for tracking use of field/method f, assumed
 // to be a member of struct/interface type t.
-func TrackSym(t *types.Type, f *types.Field) *types.Sym {
-	return ir.Pkgs.Track.Lookup(t.ShortString() + "." + f.Sym.Name)
+func TrackSym(t *types.Type, f *types.Field) *obj.LSym {
+	return ir.Pkgs.Track.Lookup(t.ShortString() + "." + f.Sym.Name).Linksym()
 }
 
 func TypeSymPrefix(prefix string, t *types.Type) *types.Sym {
@@ -845,6 +845,18 @@ func TypeSym(t *types.Type) *types.Sym {
 	return s
 }
 
+func TypeLinksymPrefix(prefix string, t *types.Type) *obj.LSym {
+	return TypeSymPrefix(prefix, t).Linksym()
+}
+
+func TypeLinksymLookup(name string) *obj.LSym {
+	return types.TypeSymLookup(name).Linksym()
+}
+
+func TypeLinksym(t *types.Type) *obj.LSym {
+	return TypeSym(t).Linksym()
+}
+
 func TypePtr(t *types.Type) *ir.AddrExpr {
 	s := TypeSym(t)
 	if s.Def == nil {

src/cmd/compile/internal/ssagen/pgen.go

@@ -225,7 +225,7 @@ func StackOffset(slot ssa.LocalSlot) int32 {
 
 // fieldtrack adds R_USEFIELD relocations to fnsym to record any
 // struct fields that it used.
-func fieldtrack(fnsym *obj.LSym, tracked map[*types.Sym]struct{}) {
+func fieldtrack(fnsym *obj.LSym, tracked map[*obj.LSym]struct{}) {
 	if fnsym == nil {
 		return
 	}
@@ -233,24 +233,18 @@ func fieldtrack(fnsym *obj.LSym, tracked map[*types.Sym]struct{}) {
 		return
 	}
 
-	trackSyms := make([]*types.Sym, 0, len(tracked))
+	trackSyms := make([]*obj.LSym, 0, len(tracked))
 	for sym := range tracked {
 		trackSyms = append(trackSyms, sym)
 	}
-	sort.Sort(symByName(trackSyms))
+	sort.Slice(trackSyms, func(i, j int) bool { return trackSyms[i].Name < trackSyms[j].Name })
 	for _, sym := range trackSyms {
 		r := obj.Addrel(fnsym)
-		r.Sym = sym.Linksym()
+		r.Sym = sym
 		r.Type = objabi.R_USEFIELD
 	}
 }
 
-type symByName []*types.Sym
-
-func (a symByName) Len() int           { return len(a) }
-func (a symByName) Less(i, j int) bool { return a[i].Name < a[j].Name }
-func (a symByName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
-
 // largeStack is info about a function whose stack frame is too large (rare).
 type largeStack struct {
 	locals int64

src/cmd/compile/internal/ssagen/ssa.go

@@ -2106,7 +2106,7 @@ func (s *state) expr(n ir.Node) *ssa.Value {
 		return s.newValue3(ssa.OpSliceMake, n.Type(), ptr, len, len)
 	case ir.OCFUNC:
 		n := n.(*ir.UnaryExpr)
-		aux := n.X.Sym().Linksym()
+		aux := n.X.(*ir.Name).Linksym()
 		return s.entryNewValue1A(ssa.OpAddr, n.Type(), aux, s.sb)
 	case ir.ONAME:
 		n := n.(*ir.Name)
@@ -6826,7 +6826,7 @@ func AddAux2(a *obj.Addr, v *ssa.Value, offset int64) {
 	case *ir.Name:
 		if n.Class_ == ir.PPARAM || n.Class_ == ir.PPARAMOUT {
 			a.Name = obj.NAME_PARAM
-			a.Sym = ir.Orig(n).Sym().Linksym()
+			a.Sym = ir.Orig(n).(*ir.Name).Linksym()
 			a.Offset += n.FrameOffset()
 			break
 		}

src/cmd/compile/internal/staticdata/data.go

@@ -258,6 +258,13 @@ func FuncSym(s *types.Sym) *types.Sym {
 	return sf
 }
 
+func FuncLinksym(n *ir.Name) *obj.LSym {
+	if n.Op() != ir.ONAME || n.Class_ != ir.PFUNC {
+		base.Fatalf("expected func name: %v", n)
+	}
+	return FuncSym(n.Sym()).Linksym()
+}
+
 // NeedFuncSym ensures that s·f is exported.
 // It is only used with -dynlink.
 // When not compiling for dynamic linking,

src/cmd/compile/internal/types/sym.go

@@ -74,6 +74,10 @@ func (sym *Sym) LinksymName() string {
 	return sym.Pkg.Prefix + "." + sym.Name
 }
 
+// Deprecated: This method should not be used directly. Instead, use a
+// higher-level abstraction that directly returns the linker symbol
+// for a named object. For example, reflectdata.TypeLinksym(t) instead
+// of reflectdata.TypeSym(t).Linksym().
 func (sym *Sym) Linksym() *obj.LSym {
 	if sym == nil {
 		return nil

src/cmd/compile/internal/walk/expr.go

@@ -975,7 +975,7 @@ func usefield(n *ir.SelectorExpr) {
 
 	sym := reflectdata.TrackSym(outer, field)
 	if ir.CurFunc.FieldTrack == nil {
-		ir.CurFunc.FieldTrack = make(map[*types.Sym]struct{})
+		ir.CurFunc.FieldTrack = make(map[*obj.LSym]struct{})
 	}
 	ir.CurFunc.FieldTrack[sym] = struct{}{}
 }