cmd/compile: simplify exportsym flags and logic

We used to have three Sym flags for dealing with export/reexport:
Export, Package, and Exported.

Export and Package were used to distinguish whether a symbol is
exported or package-scope (i.e., mutually exclusive), except that for
local declarations Export served double-duty as tracking whether the
symbol had been added to exportlist.

Meanwhile, imported declarations that needed reexporting could be
added to exportlist multiple times, necessitating a flag to track
whether they'd already been written out by exporter.

Simplify all of these into a single OnExportList flag so that we can
ensure symbols on exportlist are present exactly once. Merge
reexportsym into exportsym so there's a single place where we append
to exportlist.

Code that used to set Exported to prevent a symbol from being exported
can now just set OnExportList before calling declare to prevent it
from even appearing on exportlist.

Lastly, drop the IsAlias check in exportsym: we call exportsym too
early for local symbols to detect if they're an alias, and we never
reexport aliases.

Passes toolstash-check.

Change-Id: Icdea3719105dc169fcd7651606589cd08b0a80ff
Reviewed-on: https://go-review.googlesource.com/103865
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -261,13 +261,6 @@ func export(out *bufio.Writer, trace bool) int {
 		p.marked = make(map[*types.Type]bool)
 		for _, n := range exportlist {
 			sym := n.Sym
-			if sym.Exported() {
-				// Closures are added to exportlist, but with Exported
-				// already set. The export code below skips over them, so
-				// we have to here as well.
-				// TODO(mdempsky): Investigate why. This seems suspicious.
-				continue
-			}
 			p.markType(asNode(sym.Def).Type)
 		}
 		p.marked = nil
@@ -278,11 +271,6 @@ func export(out *bufio.Writer, trace bool) int {
 	for _, n := range exportlist[:numglobals] {
 		sym := n.Sym
 
-		if sym.Exported() {
-			continue
-		}
-		sym.SetExported(true)
-
 		// TODO(gri) Closures have dots in their names;
 		// e.g., TestFloatZeroValue.func1 in math/big tests.
 		if strings.Contains(sym.Name, ".") {
@@ -337,11 +325,6 @@ func export(out *bufio.Writer, trace bool) int {
 		// are different optimization opportunities, but factor
 		// eventually.
 
-		if sym.Exported() {
-			continue
-		}
-		sym.SetExported(true)
-
 		// TODO(gri) Closures have dots in their names;
 		// e.g., TestFloatZeroValue.func1 in math/big tests.
 		if strings.Contains(sym.Name, ".") {

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

@@ -91,7 +91,7 @@ func typecheckclosure(clo *Node, top int) {
 	}
 
 	xfunc.Func.Nname.Sym = closurename(Curfn)
-	xfunc.Func.Nname.Sym.SetExported(true) // disable export
+	xfunc.Func.Nname.Sym.SetOnExportList(true) // disable export
 	declare(xfunc.Func.Nname, PFUNC)
 	xfunc = typecheck(xfunc, Etop)
 
@@ -496,7 +496,7 @@ func makepartialcall(fn *Node, t0 *types.Type, meth *types.Sym) *Node {
 
 	xfunc.Func.SetDupok(true)
 	xfunc.Func.Nname = newfuncname(sym)
-	xfunc.Func.Nname.Sym.SetExported(true) // disable export
+	xfunc.Func.Nname.Sym.SetOnExportList(true) // disable export
 	xfunc.Func.Nname.Name.Param.Ntype = xtype
 	xfunc.Func.Nname.Name.Defn = xfunc
 	declare(xfunc.Func.Nname, PFUNC)

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

@@ -28,40 +28,21 @@ func exportf(bout *bio.Writer, format string, args ...interface{}) {
 
 var asmlist []*Node
 
-// Mark n's symbol as exported
+// exportsym marks n for export (or reexport).
 func exportsym(n *Node) {
-	if n == nil || n.Sym == nil {
-		return
-	}
-	if n.Sym.Export() || n.Sym.Package() {
-		if n.Sym.Package() {
-			Fatalf("export/package mismatch: %v", n.Sym)
-		}
+	if n.Sym.OnExportList() {
 		return
 	}
+	n.Sym.SetOnExportList(true)
 
-	n.Sym.SetExport(true)
 	if Debug['E'] != 0 {
-		fmt.Printf("export symbol %v\n", n.Sym)
-	}
-
-	// Ensure original types are on exportlist before type aliases.
-	if IsAlias(n.Sym) {
-		exportlist = append(exportlist, asNode(n.Sym.Def))
-	}
-
-	exportlist = append(exportlist, n)
-}
-
-// reexportsym marks n for reexport.
-func reexportsym(n *Node) {
-	if exportedsym(n.Sym) {
-		return
+		if n.Sym.Pkg == localpkg {
+			fmt.Printf("export symbol %v\n", n.Sym)
+		} else {
+			fmt.Printf("reexport name %v\n", n.Sym)
+		}
 	}
 
-	if Debug['E'] != 0 {
-		fmt.Printf("reexport name %v\n", n.Sym)
-	}
 	exportlist = append(exportlist, n)
 }
 
@@ -77,19 +58,8 @@ func initname(s string) bool {
 	return s == "init"
 }
 
-// exportedsym reports whether a symbol will be visible
-// to files that import our package.
-func exportedsym(sym *types.Sym) bool {
-	// Builtins are visible everywhere.
-	if sym.Pkg == builtinpkg || sym.Origpkg == builtinpkg {
-		return true
-	}
-
-	return sym.Pkg == localpkg && exportname(sym.Name)
-}
-
 func autoexport(n *Node, ctxt Class) {
-	if n == nil || n.Sym == nil {
+	if n.Sym.Pkg != localpkg {
 		return
 	}
 	if (ctxt != PEXTERN && ctxt != PFUNC) || dclcontext != PEXTERN {
@@ -102,7 +72,7 @@ func autoexport(n *Node, ctxt Class) {
 	if exportname(n.Sym.Name) || initname(n.Sym.Name) {
 		exportsym(n)
 	}
-	if asmhdr != "" && n.Sym.Pkg == localpkg && !n.Sym.Asm() {
+	if asmhdr != "" && !n.Sym.Asm() {
 		n.Sym.SetAsm(true)
 		asmlist = append(asmlist, n)
 	}
@@ -160,15 +130,6 @@ func importsym(pkg *types.Pkg, s *types.Sym, op Op) {
 		pkgstr := fmt.Sprintf("during import %q", pkg.Path)
 		redeclare(s, pkgstr)
 	}
-
-	// mark the symbol so it is not reexported
-	if asNode(s.Def) == nil {
-		if exportname(s.Name) || initname(s.Name) {
-			s.SetExport(true)
-		} else {
-			s.SetPackage(true) // package scope
-		}
-	}
 }
 
 // pkgtype returns the named type declared by symbol s.

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

@@ -208,7 +208,7 @@ func inlFlood(n *Node) {
 			// because they're reexported alongside their
 			// receiver type.
 			if n.Class() == PEXTERN || n.Class() == PFUNC && !n.isMethodExpression() {
-				reexportsym(n)
+				exportsym(n)
 			}
 
 		case OCALLFUNC, OCALLMETH:

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

@@ -1689,9 +1689,9 @@ func genwrapper(rcvr *types.Type, method *types.Field, newnam *types.Sym, iface
 	t.List.Set(append(l, in...))
 	t.Rlist.Set(out)
 
+	newnam.SetOnExportList(true) // prevent export; see closure.go
 	fn := dclfunc(newnam, t)
 	fn.Func.SetDupok(true)
-	fn.Func.Nname.Sym.SetExported(true) // prevent export; see closure.go
 
 	// arg list
 	var args []*Node

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

@@ -35,30 +35,24 @@ type Sym struct {
 }
 
 const (
-	symExport = 1 << iota // added to exportlist (no need to add again)
-	symPackage
-	symExported // already written out by export
+	symOnExportList = 1 << iota // added to exportlist (no need to add again)
 	symUniq
 	symSiggen
 	symAsm
 	symAlgGen
 )
 
-func (sym *Sym) Export() bool   { return sym.flags&symExport != 0 }
-func (sym *Sym) Package() bool  { return sym.flags&symPackage != 0 }
-func (sym *Sym) Exported() bool { return sym.flags&symExported != 0 }
-func (sym *Sym) Uniq() bool     { return sym.flags&symUniq != 0 }
-func (sym *Sym) Siggen() bool   { return sym.flags&symSiggen != 0 }
-func (sym *Sym) Asm() bool      { return sym.flags&symAsm != 0 }
-func (sym *Sym) AlgGen() bool   { return sym.flags&symAlgGen != 0 }
+func (sym *Sym) OnExportList() bool { return sym.flags&symOnExportList != 0 }
+func (sym *Sym) Uniq() bool         { return sym.flags&symUniq != 0 }
+func (sym *Sym) Siggen() bool       { return sym.flags&symSiggen != 0 }
+func (sym *Sym) Asm() bool          { return sym.flags&symAsm != 0 }
+func (sym *Sym) AlgGen() bool       { return sym.flags&symAlgGen != 0 }
 
-func (sym *Sym) SetExport(b bool)   { sym.flags.set(symExport, b) }
-func (sym *Sym) SetPackage(b bool)  { sym.flags.set(symPackage, b) }
-func (sym *Sym) SetExported(b bool) { sym.flags.set(symExported, b) }
-func (sym *Sym) SetUniq(b bool)     { sym.flags.set(symUniq, b) }
-func (sym *Sym) SetSiggen(b bool)   { sym.flags.set(symSiggen, b) }
-func (sym *Sym) SetAsm(b bool)      { sym.flags.set(symAsm, b) }
-func (sym *Sym) SetAlgGen(b bool)   { sym.flags.set(symAlgGen, b) }
+func (sym *Sym) SetOnExportList(b bool) { sym.flags.set(symOnExportList, b) }
+func (sym *Sym) SetUniq(b bool)         { sym.flags.set(symUniq, b) }
+func (sym *Sym) SetSiggen(b bool)       { sym.flags.set(symSiggen, b) }
+func (sym *Sym) SetAsm(b bool)          { sym.flags.set(symAsm, b) }
+func (sym *Sym) SetAlgGen(b bool)       { sym.flags.set(symAlgGen, b) }
 
 func (sym *Sym) IsBlank() bool {
 	return sym != nil && sym.Name == "_"