cmd/compile/internal/escape: change escapes and persists into bitset

This CL introduces a locAttr bitset type, which will make it easier to
add additional attributes in the near future.

Change-Id: I2689aa623097279dc1e7b7cf2adf5184d710c5a8
Reviewed-on: https://go-review.googlesource.com/c/go/+/520258
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

3 files changed, 34 insertions, 25 deletions

diff --git a/src/cmd/compile/internal/escape/escape.go b/src/cmd/compile/internal/escape/escape.go
index ea9287712c..5ad73bfc0d 100644
--- a/src/cmd/compile/internal/escape/escape.go
+++ b/src/cmd/compile/internal/escape/escape.go
@@ -129,8 +129,7 @@ func Batch(fns []*ir.Func, recursive bool) {
 	}
 
 	var b batch
-	b.heapLoc.escapes = true
-	b.heapLoc.persists = true
+	b.heapLoc.attrs = attrEscapes | attrPersists
 
 	// Construct data-flow graph from syntax trees.
 	for _, fn := range fns {
@@ -301,7 +300,7 @@ func (b *batch) finish(fns []*ir.Func) {
 		// TODO(mdempsky): Update tests to expect this.
 		goDeferWrapper := n.Op() == ir.OCLOSURE && n.(*ir.ClosureExpr).Func.Wrapper()
 
-		if loc.escapes {
+		if loc.hasAttr(attrEscapes) {
 			if n.Op() == ir.ONAME {
 				if base.Flag.CompilingRuntime {
 					base.ErrorfAt(n.Pos(), 0, "%v escapes to heap, not allowed in runtime", n)
@@ -324,7 +323,7 @@ func (b *batch) finish(fns []*ir.Func) {
 				base.WarnfAt(n.Pos(), "%v does not escape", n)
 			}
 			n.SetEsc(ir.EscNone)
-			if !loc.persists {
+			if !loc.hasAttr(attrPersists) {
 				switch n.Op() {
 				case ir.OCLOSURE:
 					n := n.(*ir.ClosureExpr)
@@ -453,7 +452,7 @@ func (b *batch) paramTag(fn *ir.Func, narg int, f *types.Field) string {
 	esc := loc.paramEsc
 	esc.Optimize()
 
-	if diagnose && !loc.escapes {
+	if diagnose && !loc.hasAttr(attrEscapes) {
 		if esc.Empty() {
 			base.WarnfAt(f.Pos, "%v does not escape", name())
 		}
diff --git a/src/cmd/compile/internal/escape/graph.go b/src/cmd/compile/internal/escape/graph.go
index ad97b7c28c..9b3a4558fb 100644
--- a/src/cmd/compile/internal/escape/graph.go
+++ b/src/cmd/compile/internal/escape/graph.go
@@ -66,15 +66,8 @@ type location struct {
 	// in the walk queue.
 	queued bool
 
-	// escapes reports whether the represented variable's address
-	// escapes; that is, whether the variable must be heap
-	// allocated.
-	escapes bool
-
-	// persists reports whether the represented expression's address
-	// outlives the statement; that is, whether its storage cannot be
-	// immediately reused.
-	persists bool
+	// attrs is a bitset of location attributes.
+	attrs locAttr
 
 	// paramEsc records the represented parameter's leak set.
 	paramEsc leaks
@@ -84,6 +77,21 @@ type location struct {
 	addrtaken  bool // has this variable's address been taken?
 }
 
+type locAttr uint8
+
+const (
+	// attrEscapes indicates whether the represented variable's address
+	// escapes; that is, whether the variable must be heap allocated.
+	attrEscapes locAttr = 1 << iota
+
+	// attrPersists indicates whether the represented expression's
+	// address outlives the statement; that is, whether its storage
+	// cannot be immediately reused.
+	attrPersists
+)
+
+func (l *location) hasAttr(attr locAttr) bool { return l.attrs&attr != 0 }
+
 // An edge represents an assignment edge between two Go variables.
 type edge struct {
 	src    *location
@@ -100,7 +108,7 @@ func (l *location) leakTo(sink *location, derefs int) {
 	// If sink is a result parameter that doesn't escape (#44614)
 	// and we can fit return bits into the escape analysis tag,
 	// then record as a result leak.
-	if !sink.escapes && sink.isName(ir.PPARAMOUT) && sink.curfn == l.curfn {
+	if !sink.hasAttr(attrEscapes) && sink.isName(ir.PPARAMOUT) && sink.curfn == l.curfn {
 		ri := sink.resultIndex - 1
 		if ri < numEscResults {
 			// Leak to result parameter.
@@ -182,7 +190,7 @@ func (b *batch) flow(k hole, src *location) {
 	if dst == src && k.derefs >= 0 { // dst = dst, dst = *dst, ...
 		return
 	}
-	if dst.escapes && k.derefs < 0 { // dst = &src
+	if dst.hasAttr(attrEscapes) && k.derefs < 0 { // dst = &src
 		if base.Flag.LowerM >= 2 || logopt.Enabled() {
 			pos := base.FmtPos(src.n.Pos())
 			if base.Flag.LowerM >= 2 {
@@ -195,7 +203,7 @@ func (b *batch) flow(k hole, src *location) {
 			}
 
 		}
-		src.escapes = true
+		src.attrs |= attrEscapes
 		return
 	}
 
@@ -230,7 +238,9 @@ func (e *escape) newLoc(n ir.Node, persists bool) *location {
 		n:         n,
 		curfn:     e.curfn,
 		loopDepth: e.loopDepth,
-		persists:  persists,
+	}
+	if persists {
+		loc.attrs |= attrPersists
 	}
 	e.allLocs = append(e.allLocs, loc)
 	if n != nil {
diff --git a/src/cmd/compile/internal/escape/solve.go b/src/cmd/compile/internal/escape/solve.go
index 2856c9c131..12866c0dc8 100644
--- a/src/cmd/compile/internal/escape/solve.go
+++ b/src/cmd/compile/internal/escape/solve.go
@@ -79,8 +79,8 @@ func (b *batch) walkOne(root *location, walkgen uint32, enqueue func(*location))
 
 			// If l's address flows to a persistent location, then l needs
 			// to persist too.
-			if root.persists && !l.persists {
-				l.persists = true
+			if root.hasAttr(attrPersists) && !l.hasAttr(attrPersists) {
+				l.attrs |= attrPersists
 				enqueue(l)
 			}
 		}
@@ -92,7 +92,7 @@ func (b *batch) walkOne(root *location, walkgen uint32, enqueue func(*location))
 			// that value flow for tagging the function
 			// later.
 			if l.isName(ir.PPARAM) {
-				if (logopt.Enabled() || base.Flag.LowerM >= 2) && !l.escapes {
+				if (logopt.Enabled() || base.Flag.LowerM >= 2) && !l.hasAttr(attrEscapes) {
 					if base.Flag.LowerM >= 2 {
 						fmt.Printf("%s: parameter %v leaks to %s with derefs=%d:\n", base.FmtPos(l.n.Pos()), l.n, b.explainLoc(root), derefs)
 					}
@@ -109,7 +109,7 @@ func (b *batch) walkOne(root *location, walkgen uint32, enqueue func(*location))
 			// If l's address flows somewhere that
 			// outlives it, then l needs to be heap
 			// allocated.
-			if addressOf && !l.escapes {
+			if addressOf && !l.hasAttr(attrEscapes) {
 				if logopt.Enabled() || base.Flag.LowerM >= 2 {
 					if base.Flag.LowerM >= 2 {
 						fmt.Printf("%s: %v escapes to heap:\n", base.FmtPos(l.n.Pos()), l.n)
@@ -120,14 +120,14 @@ func (b *batch) walkOne(root *location, walkgen uint32, enqueue func(*location))
 						logopt.LogOpt(l.n.Pos(), "escape", "escape", ir.FuncName(e_curfn), fmt.Sprintf("%v escapes to heap", l.n), explanation)
 					}
 				}
-				l.escapes = true
+				l.attrs |= attrEscapes
 				enqueue(l)
 				continue
 			}
 		}
 
 		for i, edge := range l.edges {
-			if edge.src.escapes {
+			if edge.src.hasAttr(attrEscapes) {
 				continue
 			}
 			d := derefs + edge.derefs
@@ -227,7 +227,7 @@ func (b *batch) explainLoc(l *location) string {
 // other's lifetime if stack allocated.
 func (b *batch) outlives(l, other *location) bool {
 	// The heap outlives everything.
-	if l.escapes {
+	if l.hasAttr(attrEscapes) {
 		return true
 	}