cmd/compile: split n.Noescape() into separate uses

n.Noescape() was overloaded for two uses: (1) to indicate a function
was annotated with //go:noescape, and (2) to indicate that certain
temporary allocations don't outlive the current statement.

The first use case is redundant with n.Func.Pragma&Noescape!=0, which
is the convention we use for checking other function-level pragmas.

The second use case is better served by renaming "Noescape" to
"Transient".

Passes toolstash-check.

Change-Id: I0f09d2d5767513894b7bf49da9cdabd04aa4a05e
Reviewed-on: https://go-review.googlesource.com/c/go/+/199822
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

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

@@ -369,7 +369,7 @@ func (e *Escape) paramTag(fn *Node, narg int, f *types.Field) string {
 
 		// External functions are assumed unsafe, unless
 		// //go:noescape is given before the declaration.
-		if fn.Noescape() {
+		if fn.Func.Pragma&Noescape != 0 {
 			if Debug['m'] != 0 && f.Sym != nil {
 				Warnl(f.Pos, "%v does not escape", name())
 			}

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

@@ -1293,7 +1293,7 @@ func (e *Escape) finish(fns []*Node) {
 			}
 			n.Esc = EscNone
 			if loc.transient {
-				n.SetNoescape(true)
+				n.SetTransient(true)
 			}
 		}
 	}

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

@@ -495,7 +495,6 @@ func (p *noder) funcDecl(fun *syntax.FuncDecl) *Node {
 
 	pragma := fun.Pragma
 	f.Func.Pragma = fun.Pragma
-	f.SetNoescape(pragma&Noescape != 0)
 	if pragma&Systemstack != 0 && pragma&Nosplit != 0 {
 		yyerrorl(f.Pos, "go:nosplit and go:systemstack cannot be combined")
 	}
@@ -507,7 +506,7 @@ func (p *noder) funcDecl(fun *syntax.FuncDecl) *Node {
 	p.funcBody(f, fun.Body)
 
 	if fun.Body != nil {
-		if f.Noescape() {
+		if f.Func.Pragma&Noescape != 0 {
 			yyerrorl(f.Pos, "can only use //go:noescape with external func implementations")
 		}
 	} else {

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

@@ -1174,7 +1174,7 @@ func (o *Order) expr(n, lhs *Node) *Node {
 		}
 
 	case OCLOSURE:
-		if n.Noescape() && n.Func.Closure.Func.Cvars.Len() > 0 {
+		if n.Transient() && n.Func.Closure.Func.Cvars.Len() > 0 {
 			prealloc[n] = o.newTemp(closureType(n), false)
 		}
 
@@ -1183,7 +1183,7 @@ func (o *Order) expr(n, lhs *Node) *Node {
 		n.Right = o.expr(n.Right, nil)
 		o.exprList(n.List)
 		o.exprList(n.Rlist)
-		if n.Noescape() {
+		if n.Transient() {
 			var t *types.Type
 			switch n.Op {
 			case OSLICELIT:
@@ -1195,7 +1195,7 @@ func (o *Order) expr(n, lhs *Node) *Node {
 		}
 
 	case ODDDARG:
-		if n.Noescape() {
+		if n.Transient() {
 			// The ddd argument does not live beyond the call it is created for.
 			// Allocate a temporary that will be cleaned up when this statement
 			// completes. We could be more aggressive and try to arrange for it

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

@@ -151,7 +151,7 @@ const (
 	_, nodeDiag      // already printed error about this
 	_, nodeColas     // OAS resulting from :=
 	_, nodeNonNil    // guaranteed to be non-nil
-	_, nodeNoescape  // func arguments do not escape; TODO(rsc): move Noescape to Func struct (see CL 7360)
+	_, nodeTransient // storage can be reused immediately after this statement
 	_, nodeBounded   // bounds check unnecessary
 	_, nodeAddable   // addressable
 	_, nodeHasCall   // expression contains a function call
@@ -179,7 +179,7 @@ func (n *Node) IsDDD() bool                 { return n.flags&nodeIsDDD != 0 }
 func (n *Node) Diag() bool                  { return n.flags&nodeDiag != 0 }
 func (n *Node) Colas() bool                 { return n.flags&nodeColas != 0 }
 func (n *Node) NonNil() bool                { return n.flags&nodeNonNil != 0 }
-func (n *Node) Noescape() bool              { return n.flags&nodeNoescape != 0 }
+func (n *Node) Transient() bool             { return n.flags&nodeTransient != 0 }
 func (n *Node) Bounded() bool               { return n.flags&nodeBounded != 0 }
 func (n *Node) Addable() bool               { return n.flags&nodeAddable != 0 }
 func (n *Node) HasCall() bool               { return n.flags&nodeHasCall != 0 }
@@ -206,7 +206,7 @@ func (n *Node) SetIsDDD(b bool)                 { n.flags.set(nodeIsDDD, b) }
 func (n *Node) SetDiag(b bool)                  { n.flags.set(nodeDiag, b) }
 func (n *Node) SetColas(b bool)                 { n.flags.set(nodeColas, b) }
 func (n *Node) SetNonNil(b bool)                { n.flags.set(nodeNonNil, b) }
-func (n *Node) SetNoescape(b bool)              { n.flags.set(nodeNoescape, b) }
+func (n *Node) SetTransient(b bool)             { n.flags.set(nodeTransient, b) }
 func (n *Node) SetBounded(b bool)               { n.flags.set(nodeBounded, b) }
 func (n *Node) SetAddable(b bool)               { n.flags.set(nodeAddable, b) }
 func (n *Node) SetHasCall(b bool)               { n.flags.set(nodeHasCall, b) }