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 <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>

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) }