[dev.regabi] cmd/compile: reshuffle type-checking code [generated]

This commit splits up typecheck.Package and moves the code
elsewhere. The type-checking code is moved into noder, so that it can
eventually be interleaved with the noding process. The
non-type-checking code is moved back into package gc, so that it can
be incorporated into appropriate compiler backend phases.

While here, deadcode removal is moved into its own package.

Passes toolstash -cmp.

[git-generate]
cd src/cmd/compile/internal/typecheck

: Split into two functions.
sed -i -e '/Phase 6/i}\n\nfunc postTypecheck() {' typecheck.go

rf '
	# Export needed identifiers.
	mv deadcode Deadcode
	mv loadsys InitRuntime
	mv declareUniverse DeclareUniverse
	mv dirtyAddrtaken DirtyAddrtaken
	mv computeAddrtaken ComputeAddrtaken
	mv incrementalAddrtaken IncrementalAddrtaken

	# Move into new package.
	mv Deadcode deadcodeslice deadcodeexpr deadcode.go
	mv deadcode.go cmd/compile/internal/deadcode

	# Move top-level type-checking code into noder.
	# Move DeclVars there too, now that nothing else uses it.
	mv DeclVars Package noder.go
	mv noder.go cmd/compile/internal/noder

	# Move non-type-checking code back into gc.
	mv postTypecheck main.go
	mv main.go cmd/compile/internal/gc
'

cd ../deadcode
rf '
	# Destutter names.
	mv Deadcode Func
	mv deadcodeslice stmts
	mv deadcodeexpr expr
'

cd ../noder
rf '
	# Move functions up, next to their related code.
	mv noder.go:/func Package/-1,$ \
		noder.go:/makeSrcPosBase translates/-1
	mv noder.go:/func DeclVars/-3,$ \
		noder.go:/constState tracks/-1
'

cd ../gc
rf '
	# Inline postTypecheck code back into gc.Main.
	mv main.go:/func postTypecheck/+0,/AllImportedBodies/+1 \
		main.go:/Build init task/-1
	rm postTypecheck
'

Change-Id: Ie5e992ece4a42204cce6aa98dd6eb52112d098c8
Reviewed-on: https://go-review.googlesource.com/c/go/+/280974
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/deadcode/deadcode.go

@@ -0,0 +1,150 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package deadcode
+
+import (
+	"go/constant"
+
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+)
+
+func Func(fn *ir.Func) {
+	stmts(&fn.Body)
+
+	if len(fn.Body) == 0 {
+		return
+	}
+
+	for _, n := range fn.Body {
+		if len(n.Init()) > 0 {
+			return
+		}
+		switch n.Op() {
+		case ir.OIF:
+			n := n.(*ir.IfStmt)
+			if !ir.IsConst(n.Cond, constant.Bool) || len(n.Body) > 0 || len(n.Else) > 0 {
+				return
+			}
+		case ir.OFOR:
+			n := n.(*ir.ForStmt)
+			if !ir.IsConst(n.Cond, constant.Bool) || ir.BoolVal(n.Cond) {
+				return
+			}
+		default:
+			return
+		}
+	}
+
+	fn.Body.Set([]ir.Node{ir.NewBlockStmt(base.Pos, nil)})
+}
+
+func stmts(nn *ir.Nodes) {
+	var lastLabel = -1
+	for i, n := range *nn {
+		if n != nil && n.Op() == ir.OLABEL {
+			lastLabel = i
+		}
+	}
+	for i, n := range *nn {
+		// Cut is set to true when all nodes after i'th position
+		// should be removed.
+		// In other words, it marks whole slice "tail" as dead.
+		cut := false
+		if n == nil {
+			continue
+		}
+		if n.Op() == ir.OIF {
+			n := n.(*ir.IfStmt)
+			n.Cond = expr(n.Cond)
+			if ir.IsConst(n.Cond, constant.Bool) {
+				var body ir.Nodes
+				if ir.BoolVal(n.Cond) {
+					n.Else = ir.Nodes{}
+					body = n.Body
+				} else {
+					n.Body = ir.Nodes{}
+					body = n.Else
+				}
+				// If "then" or "else" branch ends with panic or return statement,
+				// it is safe to remove all statements after this node.
+				// isterminating is not used to avoid goto-related complications.
+				// We must be careful not to deadcode-remove labels, as they
+				// might be the target of a goto. See issue 28616.
+				if body := body; len(body) != 0 {
+					switch body[(len(body) - 1)].Op() {
+					case ir.ORETURN, ir.ORETJMP, ir.OPANIC:
+						if i > lastLabel {
+							cut = true
+						}
+					}
+				}
+			}
+		}
+
+		stmts(n.PtrInit())
+		switch n.Op() {
+		case ir.OBLOCK:
+			n := n.(*ir.BlockStmt)
+			stmts(&n.List)
+		case ir.OFOR:
+			n := n.(*ir.ForStmt)
+			stmts(&n.Body)
+		case ir.OIF:
+			n := n.(*ir.IfStmt)
+			stmts(&n.Body)
+			stmts(&n.Else)
+		case ir.ORANGE:
+			n := n.(*ir.RangeStmt)
+			stmts(&n.Body)
+		case ir.OSELECT:
+			n := n.(*ir.SelectStmt)
+			for _, cas := range n.Cases {
+				stmts(&cas.Body)
+			}
+		case ir.OSWITCH:
+			n := n.(*ir.SwitchStmt)
+			for _, cas := range n.Cases {
+				stmts(&cas.Body)
+			}
+		}
+
+		if cut {
+			nn.Set((*nn)[:i+1])
+			break
+		}
+	}
+}
+
+func expr(n ir.Node) ir.Node {
+	// Perform dead-code elimination on short-circuited boolean
+	// expressions involving constants with the intent of
+	// producing a constant 'if' condition.
+	switch n.Op() {
+	case ir.OANDAND:
+		n := n.(*ir.LogicalExpr)
+		n.X = expr(n.X)
+		n.Y = expr(n.Y)
+		if ir.IsConst(n.X, constant.Bool) {
+			if ir.BoolVal(n.X) {
+				return n.Y // true && x => x
+			} else {
+				return n.X // false && x => false
+			}
+		}
+	case ir.OOROR:
+		n := n.(*ir.LogicalExpr)
+		n.X = expr(n.X)
+		n.Y = expr(n.Y)
+		if ir.IsConst(n.X, constant.Bool) {
+			if ir.BoolVal(n.X) {
+				return n.X // true || x => true
+			} else {
+				return n.Y // false || x => x
+			}
+		}
+	}
+	return n
+}

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

@@ -8,6 +8,7 @@ import (
 	"bufio"
 	"bytes"
 	"cmd/compile/internal/base"
+	"cmd/compile/internal/deadcode"
 	"cmd/compile/internal/devirtualize"
 	"cmd/compile/internal/dwarfgen"
 	"cmd/compile/internal/escape"
@@ -210,12 +211,51 @@ func Main(archInit func(*ssagen.ArchInfo)) {
 	dwarfgen.RecordPackageName()
 
 	// Typecheck.
-	typecheck.Package()
+	noder.Package()
 
 	// With all user code typechecked, it's now safe to verify unused dot imports.
 	noder.CheckDotImports()
 	base.ExitIfErrors()
+	// Phase 6: 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.
+	// We compute Addrtaken in bulk here.
+	// After this phase, we maintain Addrtaken incrementally.
+	if typecheck.DirtyAddrtaken {
+		typecheck.ComputeAddrtaken(typecheck.Target.Decls)
+		typecheck.DirtyAddrtaken = false
+	}
+	typecheck.IncrementalAddrtaken = true
 
+	// Phase 7: Eliminate some obviously dead code.
+	// Must happen after typechecking.
+	for _, n := range typecheck.Target.Decls {
+		if n.Op() == ir.ODCLFUNC {
+			deadcode.Func(n.(*ir.Func))
+		}
+	}
+
+	// Phase 8: Decide how to capture closed variables.
+	// This needs to run before escape analysis,
+	// because variables captured by value do not escape.
+	base.Timer.Start("fe", "capturevars")
+	for _, n := range typecheck.Target.Decls {
+		if n.Op() == ir.ODCLFUNC {
+			n := n.(*ir.Func)
+			if n.OClosure != nil {
+				ir.CurFunc = n
+				typecheck.CaptureVars(n)
+			}
+		}
+	}
+	typecheck.CaptureVarsComplete = true
+	ir.CurFunc = nil
+
+	if base.Debug.TypecheckInl != 0 {
+		// Typecheck imported function bodies if Debug.l > 1,
+		// otherwise lazily when used or re-exported.
+		typecheck.AllImportedBodies()
+	}
 	// Build init task.
 	if initTask := pkginit.Task(); initTask != nil {
 		typecheck.Export(initTask)

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

@@ -85,6 +85,69 @@ func ParseFiles(filenames []string) uint {
 	return lines
 }
 
+func Package() {
+	typecheck.DeclareUniverse()
+
+	typecheck.TypecheckAllowed = true
+
+	// Process top-level declarations in phases.
+
+	// Phase 1: const, type, and names and types of funcs.
+	//   This will gather all the information about types
+	//   and methods but doesn't depend on any of it.
+	//
+	//   We also defer type alias declarations until phase 2
+	//   to avoid cycles like #18640.
+	//   TODO(gri) Remove this again once we have a fix for #25838.
+
+	// Don't use range--typecheck can add closures to Target.Decls.
+	base.Timer.Start("fe", "typecheck", "top1")
+	for i := 0; i < len(typecheck.Target.Decls); i++ {
+		n := typecheck.Target.Decls[i]
+		if op := n.Op(); op != ir.ODCL && op != ir.OAS && op != ir.OAS2 && (op != ir.ODCLTYPE || !n.(*ir.Decl).X.Alias()) {
+			typecheck.Target.Decls[i] = typecheck.Stmt(n)
+		}
+	}
+
+	// Phase 2: Variable assignments.
+	//   To check interface assignments, depends on phase 1.
+
+	// Don't use range--typecheck can add closures to Target.Decls.
+	base.Timer.Start("fe", "typecheck", "top2")
+	for i := 0; i < len(typecheck.Target.Decls); i++ {
+		n := typecheck.Target.Decls[i]
+		if op := n.Op(); op == ir.ODCL || op == ir.OAS || op == ir.OAS2 || op == ir.ODCLTYPE && n.(*ir.Decl).X.Alias() {
+			typecheck.Target.Decls[i] = typecheck.Stmt(n)
+		}
+	}
+
+	// Phase 3: Type check function bodies.
+	// Don't use range--typecheck can add closures to Target.Decls.
+	base.Timer.Start("fe", "typecheck", "func")
+	var fcount int64
+	for i := 0; i < len(typecheck.Target.Decls); i++ {
+		n := typecheck.Target.Decls[i]
+		if n.Op() == ir.ODCLFUNC {
+			typecheck.FuncBody(n.(*ir.Func))
+			fcount++
+		}
+	}
+
+	// Phase 4: Check external declarations.
+	// TODO(mdempsky): This should be handled when type checking their
+	// corresponding ODCL nodes.
+	base.Timer.Start("fe", "typecheck", "externdcls")
+	for i, n := range typecheck.Target.Externs {
+		if n.Op() == ir.ONAME {
+			typecheck.Target.Externs[i] = typecheck.Expr(typecheck.Target.Externs[i])
+		}
+	}
+
+	// Phase 5: With all user code type-checked, it's now safe to verify map keys.
+	typecheck.CheckMapKeys()
+
+}
+
 // makeSrcPosBase translates from a *syntax.PosBase to a *src.PosBase.
 func (p *noder) makeSrcPosBase(b0 *syntax.PosBase) *src.PosBase {
 	// fast path: most likely PosBase hasn't changed
@@ -398,7 +461,61 @@ func (p *noder) varDecl(decl *syntax.VarDecl) []ir.Node {
 	}
 
 	p.setlineno(decl)
-	return typecheck.DeclVars(names, typ, exprs)
+	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
+
+	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 {
+			as2.Lhs.Append(v)
+			typecheck.Declare(v, typecheck.DeclContext)
+			v.Ntype = t
+			v.Defn = as2
+			if ir.CurFunc != nil {
+				init = append(init, ir.NewDecl(base.Pos, ir.ODCL, v))
+			}
+		}
+
+		return append(init, as2)
+	}
+
+	for i, v := range vl {
+		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]
+		}
+
+		typecheck.Declare(v, typecheck.DeclContext)
+		v.Ntype = t
+
+		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 len(el) > len(vl) {
+		base.Errorf("assignment mismatch: %d variables but %d values", len(vl), len(el))
+	}
+	return init
 }
 
 // constState tracks state between constant specifiers within a

src/cmd/compile/internal/typecheck/dcl.go

@@ -33,60 +33,6 @@ func DeclFunc(sym *types.Sym, tfn ir.Ntype) *ir.Func {
 	return fn
 }
 
-// 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
-
-	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 {
-			as2.Lhs.Append(v)
-			Declare(v, DeclContext)
-			v.Ntype = t
-			v.Defn = as2
-			if ir.CurFunc != nil {
-				init = append(init, ir.NewDecl(base.Pos, ir.ODCL, v))
-			}
-		}
-
-		return append(init, as2)
-	}
-
-	for i, v := range vl {
-		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]
-		}
-
-		Declare(v, DeclContext)
-		v.Ntype = t
-
-		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 len(el) > len(vl) {
-		base.Errorf("assignment mismatch: %d variables but %d values", len(vl), len(el))
-	}
-	return init
-}
-
 // Declare records that Node n declares symbol n.Sym in the specified
 // declaration context.
 func Declare(n *ir.Name, ctxt ir.Class) {

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

@@ -169,13 +169,13 @@ func ImportedBody(fn *ir.Func) {
 	// computeAddrtaken call below (after we typecheck the body).
 	// TODO: export/import types and addrtaken marks along with inlined bodies,
 	// so this will be unnecessary.
-	incrementalAddrtaken = false
+	IncrementalAddrtaken = false
 	defer func() {
-		if dirtyAddrtaken {
-			computeAddrtaken(fn.Inl.Body) // compute addrtaken marks once types are available
-			dirtyAddrtaken = false
+		if DirtyAddrtaken {
+			ComputeAddrtaken(fn.Inl.Body) // compute addrtaken marks once types are available
+			DirtyAddrtaken = false
 		}
-		incrementalAddrtaken = true
+		IncrementalAddrtaken = true
 	}()
 
 	ImportBody(fn)

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

@@ -72,7 +72,7 @@ func NodAddrAt(pos src.XPos, n ir.Node) *ir.AddrExpr {
 }
 
 func markAddrOf(n ir.Node) ir.Node {
-	if incrementalAddrtaken {
+	if IncrementalAddrtaken {
 		// We can only do incremental addrtaken computation when it is ok
 		// to typecheck the argument of the OADDR. That's only safe after the
 		// main typecheck has completed.
@@ -86,22 +86,22 @@ func markAddrOf(n ir.Node) ir.Node {
 	} else {
 		// Remember that we built an OADDR without computing the Addrtaken bit for
 		// its argument. We'll do that later in bulk using computeAddrtaken.
-		dirtyAddrtaken = true
+		DirtyAddrtaken = true
 	}
 	return n
 }
 
-// If incrementalAddrtaken is false, we do not compute Addrtaken for an OADDR Node
+// If IncrementalAddrtaken is false, we do not compute Addrtaken for an OADDR Node
 // when it is built. The Addrtaken bits are set in bulk by computeAddrtaken.
-// If incrementalAddrtaken is true, then when an OADDR Node is built the Addrtaken
+// If IncrementalAddrtaken is true, then when an OADDR Node is built the Addrtaken
 // field of its argument is updated immediately.
-var incrementalAddrtaken = false
+var IncrementalAddrtaken = false
 
-// If dirtyAddrtaken is true, then there are OADDR whose corresponding arguments
+// If DirtyAddrtaken is true, then there are OADDR whose corresponding arguments
 // have not yet been marked as Addrtaken.
-var dirtyAddrtaken = false
+var DirtyAddrtaken = false
 
-func computeAddrtaken(top []ir.Node) {
+func ComputeAddrtaken(top []ir.Node) {
 	for _, n := range top {
 		ir.Visit(n, func(n ir.Node) {
 			if n.Op() == ir.OADDR {

src/cmd/compile/internal/typecheck/syms.go

@@ -61,10 +61,10 @@ func Lookup(name string) *types.Sym {
 	return types.LocalPkg.Lookup(name)
 }
 
-// loadsys loads the definitions for the low-level runtime functions,
+// InitRuntime loads the definitions for the low-level runtime functions,
 // so that the compiler can generate calls to them,
 // but does not make them visible to user code.
-func loadsys() {
+func InitRuntime() {
 	types.Block = 1
 
 	inimport = true

src/cmd/compile/internal/typecheck/typecheck.go

@@ -35,110 +35,7 @@ func Init() {
 	initUniverse()
 	DeclContext = ir.PEXTERN
 	base.Timer.Start("fe", "loadsys")
-	loadsys()
-}
-
-func Package() {
-	declareUniverse()
-
-	TypecheckAllowed = true
-
-	// Process top-level declarations in phases.
-
-	// Phase 1: const, type, and names and types of funcs.
-	//   This will gather all the information about types
-	//   and methods but doesn't depend on any of it.
-	//
-	//   We also defer type alias declarations until phase 2
-	//   to avoid cycles like #18640.
-	//   TODO(gri) Remove this again once we have a fix for #25838.
-
-	// Don't use range--typecheck can add closures to Target.Decls.
-	base.Timer.Start("fe", "typecheck", "top1")
-	for i := 0; i < len(Target.Decls); i++ {
-		n := Target.Decls[i]
-		if op := n.Op(); op != ir.ODCL && op != ir.OAS && op != ir.OAS2 && (op != ir.ODCLTYPE || !n.(*ir.Decl).X.Alias()) {
-			Target.Decls[i] = Stmt(n)
-		}
-	}
-
-	// Phase 2: Variable assignments.
-	//   To check interface assignments, depends on phase 1.
-
-	// Don't use range--typecheck can add closures to Target.Decls.
-	base.Timer.Start("fe", "typecheck", "top2")
-	for i := 0; i < len(Target.Decls); i++ {
-		n := Target.Decls[i]
-		if op := n.Op(); op == ir.ODCL || op == ir.OAS || op == ir.OAS2 || op == ir.ODCLTYPE && n.(*ir.Decl).X.Alias() {
-			Target.Decls[i] = Stmt(n)
-		}
-	}
-
-	// Phase 3: Type check function bodies.
-	// Don't use range--typecheck can add closures to Target.Decls.
-	base.Timer.Start("fe", "typecheck", "func")
-	var fcount int64
-	for i := 0; i < len(Target.Decls); i++ {
-		n := Target.Decls[i]
-		if n.Op() == ir.ODCLFUNC {
-			FuncBody(n.(*ir.Func))
-			fcount++
-		}
-	}
-
-	// Phase 4: Check external declarations.
-	// TODO(mdempsky): This should be handled when type checking their
-	// corresponding ODCL nodes.
-	base.Timer.Start("fe", "typecheck", "externdcls")
-	for i, n := range Target.Externs {
-		if n.Op() == ir.ONAME {
-			Target.Externs[i] = Expr(Target.Externs[i])
-		}
-	}
-
-	// Phase 5: With all user code type-checked, it's now safe to verify map keys.
-	CheckMapKeys()
-
-	// Phase 6: 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.
-	// We compute Addrtaken in bulk here.
-	// After this phase, we maintain Addrtaken incrementally.
-	if dirtyAddrtaken {
-		computeAddrtaken(Target.Decls)
-		dirtyAddrtaken = false
-	}
-	incrementalAddrtaken = true
-
-	// Phase 7: Eliminate some obviously dead code.
-	// Must happen after typechecking.
-	for _, n := range Target.Decls {
-		if n.Op() == ir.ODCLFUNC {
-			deadcode(n.(*ir.Func))
-		}
-	}
-
-	// Phase 8: Decide how to capture closed variables.
-	// This needs to run before escape analysis,
-	// because variables captured by value do not escape.
-	base.Timer.Start("fe", "capturevars")
-	for _, n := range Target.Decls {
-		if n.Op() == ir.ODCLFUNC {
-			n := n.(*ir.Func)
-			if n.OClosure != nil {
-				ir.CurFunc = n
-				CaptureVars(n)
-			}
-		}
-	}
-	CaptureVarsComplete = true
-	ir.CurFunc = nil
-
-	if base.Debug.TypecheckInl != 0 {
-		// Typecheck imported function bodies if Debug.l > 1,
-		// otherwise lazily when used or re-exported.
-		AllImportedBodies()
-	}
+	InitRuntime()
 }
 
 func AssignExpr(n ir.Node) ir.Node { return typecheck(n, ctxExpr|ctxAssign) }
@@ -2247,144 +2144,6 @@ func CheckReturn(fn *ir.Func) {
 	}
 }
 
-func deadcode(fn *ir.Func) {
-	deadcodeslice(&fn.Body)
-
-	if len(fn.Body) == 0 {
-		return
-	}
-
-	for _, n := range fn.Body {
-		if len(n.Init()) > 0 {
-			return
-		}
-		switch n.Op() {
-		case ir.OIF:
-			n := n.(*ir.IfStmt)
-			if !ir.IsConst(n.Cond, constant.Bool) || len(n.Body) > 0 || len(n.Else) > 0 {
-				return
-			}
-		case ir.OFOR:
-			n := n.(*ir.ForStmt)
-			if !ir.IsConst(n.Cond, constant.Bool) || ir.BoolVal(n.Cond) {
-				return
-			}
-		default:
-			return
-		}
-	}
-
-	fn.Body.Set([]ir.Node{ir.NewBlockStmt(base.Pos, nil)})
-}
-
-func deadcodeslice(nn *ir.Nodes) {
-	var lastLabel = -1
-	for i, n := range *nn {
-		if n != nil && n.Op() == ir.OLABEL {
-			lastLabel = i
-		}
-	}
-	for i, n := range *nn {
-		// Cut is set to true when all nodes after i'th position
-		// should be removed.
-		// In other words, it marks whole slice "tail" as dead.
-		cut := false
-		if n == nil {
-			continue
-		}
-		if n.Op() == ir.OIF {
-			n := n.(*ir.IfStmt)
-			n.Cond = deadcodeexpr(n.Cond)
-			if ir.IsConst(n.Cond, constant.Bool) {
-				var body ir.Nodes
-				if ir.BoolVal(n.Cond) {
-					n.Else = ir.Nodes{}
-					body = n.Body
-				} else {
-					n.Body = ir.Nodes{}
-					body = n.Else
-				}
-				// If "then" or "else" branch ends with panic or return statement,
-				// it is safe to remove all statements after this node.
-				// isterminating is not used to avoid goto-related complications.
-				// We must be careful not to deadcode-remove labels, as they
-				// might be the target of a goto. See issue 28616.
-				if body := body; len(body) != 0 {
-					switch body[(len(body) - 1)].Op() {
-					case ir.ORETURN, ir.ORETJMP, ir.OPANIC:
-						if i > lastLabel {
-							cut = true
-						}
-					}
-				}
-			}
-		}
-
-		deadcodeslice(n.PtrInit())
-		switch n.Op() {
-		case ir.OBLOCK:
-			n := n.(*ir.BlockStmt)
-			deadcodeslice(&n.List)
-		case ir.OFOR:
-			n := n.(*ir.ForStmt)
-			deadcodeslice(&n.Body)
-		case ir.OIF:
-			n := n.(*ir.IfStmt)
-			deadcodeslice(&n.Body)
-			deadcodeslice(&n.Else)
-		case ir.ORANGE:
-			n := n.(*ir.RangeStmt)
-			deadcodeslice(&n.Body)
-		case ir.OSELECT:
-			n := n.(*ir.SelectStmt)
-			for _, cas := range n.Cases {
-				deadcodeslice(&cas.Body)
-			}
-		case ir.OSWITCH:
-			n := n.(*ir.SwitchStmt)
-			for _, cas := range n.Cases {
-				deadcodeslice(&cas.Body)
-			}
-		}
-
-		if cut {
-			nn.Set((*nn)[:i+1])
-			break
-		}
-	}
-}
-
-func deadcodeexpr(n ir.Node) ir.Node {
-	// Perform dead-code elimination on short-circuited boolean
-	// expressions involving constants with the intent of
-	// producing a constant 'if' condition.
-	switch n.Op() {
-	case ir.OANDAND:
-		n := n.(*ir.LogicalExpr)
-		n.X = deadcodeexpr(n.X)
-		n.Y = deadcodeexpr(n.Y)
-		if ir.IsConst(n.X, constant.Bool) {
-			if ir.BoolVal(n.X) {
-				return n.Y // true && x => x
-			} else {
-				return n.X // false && x => false
-			}
-		}
-	case ir.OOROR:
-		n := n.(*ir.LogicalExpr)
-		n.X = deadcodeexpr(n.X)
-		n.Y = deadcodeexpr(n.Y)
-		if ir.IsConst(n.X, constant.Bool) {
-			if ir.BoolVal(n.X) {
-				return n.X // true || x => true
-			} else {
-				return n.Y // false || x => x
-			}
-		}
-	}
-	return n
-}
-
 // getIotaValue returns the current value for "iota",
 // or -1 if not within a ConstSpec.
 func getIotaValue() int64 {

src/cmd/compile/internal/typecheck/universe.go

@@ -336,8 +336,8 @@ func makeErrorInterface() *types.Type {
 	return types.NewInterface(types.NoPkg, []*types.Field{method})
 }
 
-// declareUniverse makes the universe block visible within the current package.
-func declareUniverse() {
+// DeclareUniverse makes the universe block visible within the current package.
+func DeclareUniverse() {
 	// Operationally, this is similar to a dot import of builtinpkg, except
 	// that we silently skip symbols that are already declared in the
 	// package block rather than emitting a redeclared symbol error.