cmd/compile: retire "IsHiddenClosure" and "IsDeadcodeClosure"

Since CL 522318, all closures are now hidden. Thus this CL removes all
codes that worries about hidden vs non-hidden closures.

Change-Id: I1ea124168c76cedbfc4053d2f150937a382aa330
Reviewed-on: https://go-review.googlesource.com/c/go/+/523275
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Than McIntosh <thanm@google.com>

9 files changed, 34 insertions, 105 deletions

diff --git a/src/cmd/compile/internal/escape/escape.go b/src/cmd/compile/internal/escape/escape.go
index 7df367caf7..5997d8328a 100644
--- a/src/cmd/compile/internal/escape/escape.go
+++ b/src/cmd/compile/internal/escape/escape.go
@@ -139,7 +139,7 @@ func Batch(fns []*ir.Func, recursive bool) {
 		b.initFunc(fn)
 	}
 	for _, fn := range fns {
-		if !fn.IsHiddenClosure() {
+		if !fn.IsClosure() {
 			b.walkFunc(fn)
 		}
 	}
diff --git a/src/cmd/compile/internal/escape/expr.go b/src/cmd/compile/internal/escape/expr.go
index 6aa5ad7413..3c47bdf9e1 100644
--- a/src/cmd/compile/internal/escape/expr.go
+++ b/src/cmd/compile/internal/escape/expr.go
@@ -230,7 +230,7 @@ func (e *escape) exprSkipInit(k hole, n ir.Node) {
 		k = e.spill(k, n)
 		e.closures = append(e.closures, closure{k, n})
 
-		if fn := n.Func; fn.IsHiddenClosure() {
+		if fn := n.Func; fn.IsClosure() {
 			for _, cv := range fn.ClosureVars {
 				if loc := e.oldLoc(cv); !loc.captured {
 					loc.captured = true
diff --git a/src/cmd/compile/internal/gc/compile.go b/src/cmd/compile/internal/gc/compile.go
index 496daacb42..81a6023e47 100644
--- a/src/cmd/compile/internal/gc/compile.go
+++ b/src/cmd/compile/internal/gc/compile.go
@@ -39,12 +39,7 @@ func enqueueFunc(fn *ir.Func) {
 		return
 	}
 
-	// Don't try compiling dead hidden closure.
-	if fn.IsDeadcodeClosure() {
-		return
-	}
-
-	if clo := fn.OClosure; clo != nil && !ir.IsTrivialClosure(clo) {
+	if fn.IsClosure() {
 		return // we'll get this as part of its enclosing function
 	}
 
diff --git a/src/cmd/compile/internal/inline/inl.go b/src/cmd/compile/internal/inline/inl.go
index 31b3bdfa25..017bc25e46 100644
--- a/src/cmd/compile/internal/inline/inl.go
+++ b/src/cmd/compile/internal/inline/inl.go
@@ -186,57 +186,6 @@ func CanInlineFuncs(funcs []*ir.Func, profile *pgoir.Profile) {
 	})
 }
 
-// GarbageCollectUnreferencedHiddenClosures makes a pass over all the
-// top-level (non-hidden-closure) functions looking for nested closure
-// functions that are reachable, then sweeps through the Target.Decls
-// list and marks any non-reachable hidden closure function as dead.
-// See issues #59404 and #59638 for more context.
-func GarbageCollectUnreferencedHiddenClosures() {
-
-	liveFuncs := make(map[*ir.Func]bool)
-
-	var markLiveFuncs func(fn *ir.Func)
-	markLiveFuncs = func(fn *ir.Func) {
-		if liveFuncs[fn] {
-			return
-		}
-		liveFuncs[fn] = true
-		ir.Visit(fn, func(n ir.Node) {
-			if clo, ok := n.(*ir.ClosureExpr); ok {
-				markLiveFuncs(clo.Func)
-			}
-		})
-	}
-
-	for i := 0; i < len(typecheck.Target.Funcs); i++ {
-		fn := typecheck.Target.Funcs[i]
-		if fn.IsHiddenClosure() {
-			continue
-		}
-		markLiveFuncs(fn)
-	}
-
-	for i := 0; i < len(typecheck.Target.Funcs); i++ {
-		fn := typecheck.Target.Funcs[i]
-		if !fn.IsHiddenClosure() {
-			continue
-		}
-		if fn.IsDeadcodeClosure() {
-			continue
-		}
-		if liveFuncs[fn] {
-			continue
-		}
-		fn.SetIsDeadcodeClosure(true)
-		if base.Flag.LowerM > 2 {
-			fmt.Printf("%v: unreferenced closure %v marked as dead\n", ir.Line(fn), fn)
-		}
-		if fn.Inl != nil && fn.LSym == nil {
-			ir.InitLSym(fn, true)
-		}
-	}
-}
-
 // inlineBudget determines the max budget for function 'fn' prior to
 // analyzing the hairiness of the body of 'fn'. We pass in the pgo
 // profile if available (which can change the budget), also a
diff --git a/src/cmd/compile/internal/inline/interleaved/interleaved.go b/src/cmd/compile/internal/inline/interleaved/interleaved.go
index 9b2efd7f27..5b3fbf6be7 100644
--- a/src/cmd/compile/internal/inline/interleaved/interleaved.go
+++ b/src/cmd/compile/internal/inline/interleaved/interleaved.go
@@ -49,11 +49,6 @@ func DevirtualizeAndInlinePackage(pkg *ir.Package, profile *pgoir.Profile) {
 	}
 
 	if base.Flag.LowerL != 0 {
-		// Perform a garbage collection of hidden closures functions that
-		// are no longer reachable from top-level functions following
-		// inlining. See #59404 and #59638 for more context.
-		inline.GarbageCollectUnreferencedHiddenClosures()
-
 		if base.Debug.DumpInlFuncProps != "" {
 			inlheur.DumpFuncProps(nil, base.Debug.DumpInlFuncProps)
 		}
diff --git a/src/cmd/compile/internal/ir/func.go b/src/cmd/compile/internal/ir/func.go
index d0c8ee359b..3c4ec4a64f 100644
--- a/src/cmd/compile/internal/ir/func.go
+++ b/src/cmd/compile/internal/ir/func.go
@@ -222,21 +222,17 @@ type Mark struct {
 type ScopeID int32
 
 const (
-	funcDupok      = 1 << iota // duplicate definitions ok
-	funcWrapper                // hide frame from users (elide in tracebacks, don't count as a frame for recover())
-	funcABIWrapper             // is an ABI wrapper (also set flagWrapper)
-	funcNeedctxt               // function uses context register (has closure variables)
-	// true if closure inside a function; false if a simple function or a
-	// closure in a global variable initialization
-	funcIsHiddenClosure
-	funcIsDeadcodeClosure        // true if closure is deadcode
-	funcHasDefer                 // contains a defer statement
-	funcNilCheckDisabled         // disable nil checks when compiling this function
-	funcInlinabilityChecked      // inliner has already determined whether the function is inlinable
-	funcNeverReturns             // function never returns (in most cases calls panic(), os.Exit(), or equivalent)
-	funcOpenCodedDeferDisallowed // can't do open-coded defers
-	funcClosureResultsLost       // closure is called indirectly and we lost track of its results; used by escape analysis
-	funcPackageInit              // compiler emitted .init func for package
+	funcDupok                    = 1 << iota // duplicate definitions ok
+	funcWrapper                              // hide frame from users (elide in tracebacks, don't count as a frame for recover())
+	funcABIWrapper                           // is an ABI wrapper (also set flagWrapper)
+	funcNeedctxt                             // function uses context register (has closure variables)
+	funcHasDefer                             // contains a defer statement
+	funcNilCheckDisabled                     // disable nil checks when compiling this function
+	funcInlinabilityChecked                  // inliner has already determined whether the function is inlinable
+	funcNeverReturns                         // function never returns (in most cases calls panic(), os.Exit(), or equivalent)
+	funcOpenCodedDeferDisallowed             // can't do open-coded defers
+	funcClosureResultsLost                   // closure is called indirectly and we lost track of its results; used by escape analysis
+	funcPackageInit                          // compiler emitted .init func for package
 )
 
 type SymAndPos struct {
@@ -248,8 +244,6 @@ func (f *Func) Dupok() bool                    { return f.flags&funcDupok != 0 }
 func (f *Func) Wrapper() bool                  { return f.flags&funcWrapper != 0 }
 func (f *Func) ABIWrapper() bool               { return f.flags&funcABIWrapper != 0 }
 func (f *Func) Needctxt() bool                 { return f.flags&funcNeedctxt != 0 }
-func (f *Func) IsHiddenClosure() bool          { return f.flags&funcIsHiddenClosure != 0 }
-func (f *Func) IsDeadcodeClosure() bool        { return f.flags&funcIsDeadcodeClosure != 0 }
 func (f *Func) HasDefer() bool                 { return f.flags&funcHasDefer != 0 }
 func (f *Func) NilCheckDisabled() bool         { return f.flags&funcNilCheckDisabled != 0 }
 func (f *Func) InlinabilityChecked() bool      { return f.flags&funcInlinabilityChecked != 0 }
@@ -262,8 +256,6 @@ func (f *Func) SetDupok(b bool)                    { f.flags.set(funcDupok, b) }
 func (f *Func) SetWrapper(b bool)                  { f.flags.set(funcWrapper, b) }
 func (f *Func) SetABIWrapper(b bool)               { f.flags.set(funcABIWrapper, b) }
 func (f *Func) SetNeedctxt(b bool)                 { f.flags.set(funcNeedctxt, b) }
-func (f *Func) SetIsHiddenClosure(b bool)          { f.flags.set(funcIsHiddenClosure, b) }
-func (f *Func) SetIsDeadcodeClosure(b bool)        { f.flags.set(funcIsDeadcodeClosure, b) }
 func (f *Func) SetHasDefer(b bool)                 { f.flags.set(funcHasDefer, b) }
 func (f *Func) SetNilCheckDisabled(b bool)         { f.flags.set(funcNilCheckDisabled, b) }
 func (f *Func) SetInlinabilityChecked(b bool)      { f.flags.set(funcInlinabilityChecked, b) }
@@ -281,6 +273,14 @@ func (f *Func) SetWBPos(pos src.XPos) {
 	}
 }
 
+func (f *Func) IsClosure() bool {
+	if f.OClosure == nil {
+		return false
+	}
+	// Trivial closure will be converted to global.
+	return !IsTrivialClosure(f.OClosure)
+}
+
 // FuncName returns the name (without the package) of the function f.
 func FuncName(f *Func) string {
 	if f == nil || f.Nname == nil {
@@ -484,19 +484,20 @@ func closureName(outerfn *Func, pos src.XPos, why Op) *types.Sym {
 // should have an inline-adjusted position, whereas the ODCLFUNC and
 // ONAME must not.
 //
-// outerfn is the enclosing function, if any. The returned function is
+// outerfn is the enclosing function. The returned function is
 // appending to pkg.Funcs.
 //
 // why is the reason we're generating this Func. It can be OCLOSURE
 // (for a normal function literal) or OGO or ODEFER (for wrapping a
 // call expression that has parameters or results).
 func NewClosureFunc(fpos, cpos src.XPos, why Op, typ *types.Type, outerfn *Func, pkg *Package) *Func {
-	fn := NewFunc(fpos, fpos, closureName(outerfn, cpos, why), typ)
-	fn.SetIsHiddenClosure(outerfn != nil)
-	if outerfn != nil {
-		fn.SetDupok(outerfn.Dupok()) // if the outer function is dupok, so is the closure
+	if outerfn == nil {
+		base.FatalfAt(fpos, "outerfn is nil")
 	}
 
+	fn := NewFunc(fpos, fpos, closureName(outerfn, cpos, why), typ)
+	fn.SetDupok(outerfn.Dupok()) // if the outer function is dupok, so is the closure
+
 	clo := &ClosureExpr{Func: fn}
 	clo.op = OCLOSURE
 	clo.pos = cpos
diff --git a/src/cmd/compile/internal/ir/scc.go b/src/cmd/compile/internal/ir/scc.go
index a640f4fc16..265dce251e 100644
--- a/src/cmd/compile/internal/ir/scc.go
+++ b/src/cmd/compile/internal/ir/scc.go
@@ -14,10 +14,10 @@ package ir
 // The algorithm (known as Tarjan's algorithm) for doing that is taken from
 // Sedgewick, Algorithms, Second Edition, p. 482, with two adaptations.
 //
-// First, a hidden closure function (n.Func.IsHiddenClosure()) cannot be the
-// root of a connected component. Refusing to use it as a root
-// forces it into the component of the function in which it appears.
-// This is more convenient for escape analysis.
+// First, a non-trivial closure function (fn.OClosure != nil) cannot be
+// the root of a connected component. Refusing to use it as a root forces
+// it into the component of the function in which it appears.  This is
+// more convenient for escape analysis.
 //
 // Second, each function becomes two virtual nodes in the graph,
 // with numbers n and n+1. We record the function's node number as n
@@ -54,7 +54,7 @@ func VisitFuncsBottomUp(list []*Func, analyze func(list []*Func, recursive bool)
 	v.analyze = analyze
 	v.nodeID = make(map[*Func]uint32)
 	for _, n := range list {
-		if !n.IsHiddenClosure() {
+		if !n.IsClosure() {
 			v.visit(n)
 		}
 	}
@@ -97,7 +97,7 @@ func (v *bottomUpVisitor) visit(n *Func) uint32 {
 		}
 	})
 
-	if (min == id || min == id+1) && !n.IsHiddenClosure() {
+	if (min == id || min == id+1) && !n.IsClosure() {
 		// This node is the root of a strongly connected component.
 
 		// The original min was id+1. If the bottomUpVisitor found its way
diff --git a/src/cmd/compile/internal/noder/reader.go b/src/cmd/compile/internal/noder/reader.go
index 58fbb72f5d..ff44adedb4 100644
--- a/src/cmd/compile/internal/noder/reader.go
+++ b/src/cmd/compile/internal/noder/reader.go
@@ -3061,11 +3061,6 @@ func (r *reader) funcLit() ir.Node {
 
 	r.addBody(fn, nil)
 
-	// un-hide closures belong to init function.
-	if (r.curfn.IsPackageInit() || strings.HasPrefix(r.curfn.Sym().Name, "init.")) && ir.IsTrivialClosure(fn.OClosure) {
-		fn.SetIsHiddenClosure(false)
-	}
-
 	return fn.OClosure
 }
 
diff --git a/src/cmd/compile/internal/staticinit/sched.go b/src/cmd/compile/internal/staticinit/sched.go
index 91c0a27faf..56203120b2 100644
--- a/src/cmd/compile/internal/staticinit/sched.go
+++ b/src/cmd/compile/internal/staticinit/sched.go
@@ -393,12 +393,6 @@ func (s *Schedule) StaticAssign(l *ir.Name, loff int64, r ir.Node, typ *types.Ty
 			if base.Debug.Closure > 0 {
 				base.WarnfAt(r.Pos(), "closure converted to global")
 			}
-			// Issue 59680: if the closure we're looking at was produced
-			// by inlining, it could be marked as hidden, which we don't
-			// want (moving the func to a static init will effectively
-			// hide it from escape analysis). Mark as non-hidden here.
-			// so that it will participated in escape analysis.
-			r.Func.SetIsHiddenClosure(false)
 			// Closures with no captured variables are globals,
 			// so the assignment can be done at link time.
 			// TODO if roff != 0 { panic }