[dev.regabi] cmd/compile: separate exportsym more cleanly

Clean up a TODO (and make the package gc split easier)
by moving the exportsym walk out of iexport proper.

Also move exportsym call out of fninit.

Change-Id: Ie5887a68d325f7154201f4a35b9b4be4bf4b48dd
Reviewed-on: https://go-review.googlesource.com/c/go/+/279298
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -60,6 +60,11 @@ func autoexport(n *ir.Name, ctxt ir.Class) {
 }
 
 func dumpexport(bout *bio.Writer) {
+	p := &exporter{marked: make(map[*types.Type]bool)}
+	for _, n := range Target.Exports {
+		p.markObject(n)
+	}
+
 	// The linker also looks for the $$ marker - use char after $$ to distinguish format.
 	exportf(bout, "\n$$B\n") // indicate binary export format
 	off := bout.Offset()

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

@@ -246,16 +246,6 @@ const (
 )
 
 func iexport(out *bufio.Writer) {
-	// Mark inline bodies that are reachable through exported objects.
-	// (Phase 0 of bexport.go.)
-	{
-		// TODO(mdempsky): Separate from bexport logic.
-		p := &exporter{marked: make(map[*types.Type]bool)}
-		for _, n := range Target.Exports {
-			p.markObject(n)
-		}
-	}
-
 	p := iexporter{
 		allPkgs:     map[*types.Pkg]bool{},
 		stringIndex: map[string]uint64{},

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

@@ -27,21 +27,21 @@ func renameinit() *types.Sym {
 	return s
 }
 
-// fninit makes an initialization record for the package.
+// fninit makes and returns an initialization record for the package.
 // See runtime/proc.go:initTask for its layout.
 // The 3 tasks for initialization are:
 //   1) Initialize all of the packages the current package depends on.
 //   2) Initialize all the variables that have initializers.
 //   3) Run any init functions.
-func fninit(n []ir.Node) {
-	nf := initOrder(n)
+func fninit() *ir.Name {
+	nf := initOrder(Target.Decls)
 
 	var deps []*obj.LSym // initTask records for packages the current package depends on
 	var fns []*obj.LSym  // functions to call for package initialization
 
 	// Find imported packages with init tasks.
 	for _, pkg := range Target.Imports {
-		n := resolve(oldname(pkg.Lookup(".inittask")))
+		n := resolve(ir.NewIdent(base.Pos, pkg.Lookup(".inittask")))
 		if n.Op() == ir.ONONAME {
 			continue
 		}
@@ -92,16 +92,15 @@ func fninit(n []ir.Node) {
 	}
 
 	if len(deps) == 0 && len(fns) == 0 && types.LocalPkg.Name != "main" && types.LocalPkg.Name != "runtime" {
-		return // nothing to initialize
+		return nil // nothing to initialize
 	}
 
 	// Make an .inittask structure.
 	sym := lookup(".inittask")
-	nn := NewName(sym)
-	nn.SetType(types.Types[types.TUINT8]) // fake type
-	nn.SetClass(ir.PEXTERN)
-	sym.Def = nn
-	exportsym(nn)
+	task := NewName(sym)
+	task.SetType(types.Types[types.TUINT8]) // fake type
+	task.SetClass(ir.PEXTERN)
+	sym.Def = task
 	lsym := sym.Linksym()
 	ot := 0
 	ot = duintptr(lsym, ot, 0) // state: not initialized yet
@@ -116,4 +115,5 @@ func fninit(n []ir.Node) {
 	// An initTask has pointers, but none into the Go heap.
 	// It's not quite read only, the state field must be modifiable.
 	ggloblsym(lsym, int32(ot), obj.NOPTR)
+	return task
 }

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

@@ -306,7 +306,9 @@ func Main(archInit func(*Arch)) {
 
 	timings.AddEvent(fcount, "funcs")
 
-	fninit(Target.Decls)
+	if initTask := fninit(); initTask != nil {
+		exportsym(initTask)
+	}
 
 	// Phase 4: Decide how to capture closed variables.
 	// This needs to run before escape analysis,