[dev.regabi] cmd/compile: fix package-initialization order

This CL fixes package initialization order by creating the init task
before the general deadcode-removal pass.

It also changes noder to emit zero-initialization assignments (i.e.,
OAS with nil RHS) for package-block variables, so that initOrder can
tell the variables still need initialization. To allow this, we need
to also extend the static-init code to recognize zero-initialization
assignments.

This doesn't pass toolstash -cmp, because it reorders some package
initialization routines.

Fixes #43444.

Change-Id: I0da7996a62c85e15e97ce965298127e075390a7e
Reviewed-on: https://go-review.googlesource.com/c/go/+/280976
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/main.go

@@ -208,6 +208,11 @@ func Main(archInit func(*ssagen.ArchInfo)) {
 	dwarfgen.RecordPackageName()
 	ssagen.CgoSymABIs()
 
+	// Build init task.
+	if initTask := pkginit.Task(); initTask != nil {
+		typecheck.Export(initTask)
+	}
+
 	// Compute Addrtaken for names.
 	// We need to wait until typechecking is done so that when we see &x[i]
 	// we know that x has its address taken if x is an array, but not if x is a slice.
@@ -249,11 +254,6 @@ func Main(archInit func(*ssagen.ArchInfo)) {
 		typecheck.AllImportedBodies()
 	}
 
-	// Build init task.
-	if initTask := pkginit.Task(); initTask != nil {
-		typecheck.Export(initTask)
-	}
-
 	// Inlining
 	base.Timer.Start("fe", "inlining")
 	if base.Flag.LowerL != 0 {

src/cmd/compile/internal/noder/noder.go

@@ -474,24 +474,15 @@ func (p *noder) varDecl(decl *syntax.VarDecl) []ir.Node {
 		p.checkUnused(pragma)
 	}
 
-	p.setlineno(decl)
-	return DeclVars(names, typ, exprs)
-}
-
-// declare variables from grammar
-// new_name_list (type | [type] = expr_list)
-func DeclVars(vl []*ir.Name, t ir.Ntype, el []ir.Node) []ir.Node {
 	var init []ir.Node
-	doexpr := len(el) > 0
+	p.setlineno(decl)
 
-	if len(el) == 1 && len(vl) > 1 {
-		e := el[0]
-		as2 := ir.NewAssignListStmt(base.Pos, ir.OAS2, nil, nil)
-		as2.Rhs = []ir.Node{e}
-		for _, v := range vl {
+	if len(names) > 1 && len(exprs) == 1 {
+		as2 := ir.NewAssignListStmt(base.Pos, ir.OAS2, nil, exprs)
+		for _, v := range names {
 			as2.Lhs.Append(v)
 			typecheck.Declare(v, typecheck.DeclContext)
-			v.Ntype = t
+			v.Ntype = typ
 			v.Defn = as2
 			if ir.CurFunc != nil {
 				init = append(init, ir.NewDecl(base.Pos, ir.ODCL, v))
@@ -501,34 +492,29 @@ func DeclVars(vl []*ir.Name, t ir.Ntype, el []ir.Node) []ir.Node {
 		return append(init, as2)
 	}
 
-	for i, v := range vl {
+	for i, v := range names {
 		var e ir.Node
-		if doexpr {
-			if i >= len(el) {
-				base.Errorf("assignment mismatch: %d variables but %d values", len(vl), len(el))
-				break
-			}
-			e = el[i]
+		if i < len(exprs) {
+			e = exprs[i]
 		}
 
 		typecheck.Declare(v, typecheck.DeclContext)
-		v.Ntype = t
+		v.Ntype = typ
 
-		if e != nil || ir.CurFunc != nil || ir.IsBlank(v) {
-			if ir.CurFunc != nil {
-				init = append(init, ir.NewDecl(base.Pos, ir.ODCL, v))
-			}
-			as := ir.NewAssignStmt(base.Pos, v, e)
-			init = append(init, as)
-			if e != nil {
-				v.Defn = as
-			}
+		if ir.CurFunc != nil {
+			init = append(init, ir.NewDecl(base.Pos, ir.ODCL, v))
+		}
+		as := ir.NewAssignStmt(base.Pos, v, e)
+		init = append(init, as)
+		if e != nil || ir.CurFunc == nil {
+			v.Defn = as
 		}
 	}
 
-	if len(el) > len(vl) {
-		base.Errorf("assignment mismatch: %d variables but %d values", len(vl), len(el))
+	if len(exprs) != 0 && len(names) != len(exprs) {
+		base.Errorf("assignment mismatch: %d variables but %d values", len(names), len(exprs))
 	}
+
 	return init
 }
 

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

@@ -6,6 +6,7 @@ package pkginit
 
 import (
 	"cmd/compile/internal/base"
+	"cmd/compile/internal/deadcode"
 	"cmd/compile/internal/ir"
 	"cmd/compile/internal/objw"
 	"cmd/compile/internal/typecheck"
@@ -68,6 +69,9 @@ func Task() *ir.Name {
 
 	// Record user init functions.
 	for _, fn := range typecheck.Target.Inits {
+		// Must happen after initOrder; see #43444.
+		deadcode.Func(fn)
+
 		// Skip init functions with empty bodies.
 		if len(fn.Body) == 1 {
 			if stmt := fn.Body[0]; stmt.Op() == ir.OBLOCK && len(stmt.(*ir.BlockStmt).List) == 0 {

src/cmd/compile/internal/staticinit/sched.go

@@ -86,17 +86,22 @@ func (s *Schedule) staticcopy(l *ir.Name, loff int64, rn *ir.Name, typ *types.Ty
 	if rn.Class_ != ir.PEXTERN || rn.Sym().Pkg != types.LocalPkg {
 		return false
 	}
-	if rn.Defn == nil { // probably zeroed but perhaps supplied externally and of unknown value
-		return false
-	}
 	if rn.Defn.Op() != ir.OAS {
 		return false
 	}
 	if rn.Type().IsString() { // perhaps overwritten by cmd/link -X (#34675)
 		return false
 	}
+	if rn.Embed != nil {
+		return false
+	}
 	orig := rn
 	r := rn.Defn.(*ir.AssignStmt).Y
+	if r == nil {
+		// No explicit initialization value. Probably zeroed but perhaps
+		// supplied externally and of unknown value.
+		return false
+	}
 
 	for r.Op() == ir.OCONVNOP && !types.Identical(r.Type(), typ) {
 		r = r.(*ir.ConvExpr).X
@@ -185,6 +190,11 @@ func (s *Schedule) staticcopy(l *ir.Name, loff int64, rn *ir.Name, typ *types.Ty
 }
 
 func (s *Schedule) StaticAssign(l *ir.Name, loff int64, r ir.Node, typ *types.Type) bool {
+	if r == nil {
+		// No explicit initialization value. Either zero or supplied
+		// externally.
+		return true
+	}
 	for r.Op() == ir.OCONVNOP {
 		r = r.(*ir.ConvExpr).X
 	}

test/fixedbugs/issue43444.go

@@ -0,0 +1,28 @@
+// run
+
+package main
+
+var sp = ""
+
+func f(name string, _ ...interface{}) int {
+	print(sp, name)
+	sp = " "
+	return 0
+}
+
+var a = f("a", x)
+var b = f("b", y)
+var c = f("c", z)
+var d = func() int {
+	if false {
+		_ = z
+	}
+	return f("d")
+}()
+var e = f("e")
+
+var x int
+var y int = 42
+var z int = func() int { return 42 }()
+
+func main() { println() }

test/fixedbugs/issue43444.out

@@ -0,0 +1 @@
+e a b c d