cmd/compile/internal/devirtualize: use CallExpr.GoDefer for PGO

CL 543657 dedup'd the go/defer statement recognition between the
inliner and static devirtualizer. This CL extends that for PGO-based
devirtualization too.

Change-Id: I998753132af1ef17329676f4e17515f16e0acb03
Reviewed-on: https://go-review.googlesource.com/c/go/+/543775
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

Author: mdempsky

src/cmd/compile/internal/devirtualize/pgo.go

@@ -107,9 +107,6 @@ func ProfileGuided(fn *ir.Func, p *pgo.Profile) {
 
 	name := ir.LinkFuncName(fn)
 
-	// Can't devirtualize go/defer calls. See comment in Static.
-	goDeferCall := make(map[*ir.CallExpr]bool)
-
 	var jsonW *json.Encoder
 	if base.Debug.PGODebug >= 3 {
 		jsonW = json.NewEncoder(os.Stdout)
@@ -121,12 +118,6 @@ func ProfileGuided(fn *ir.Func, p *pgo.Profile) {
 			return n
 		}
 
-		if gds, ok := n.(*ir.GoDeferStmt); ok {
-			if call, ok := gds.Call.(*ir.CallExpr); ok {
-				goDeferCall[call] = true
-			}
-		}
-
 		ir.EditChildren(n, edit)
 
 		call, ok := n.(*ir.CallExpr)
@@ -156,7 +147,7 @@ func ProfileGuided(fn *ir.Func, p *pgo.Profile) {
 			fmt.Printf("%v: PGO devirtualize considering call %v\n", ir.Line(call), call)
 		}
 
-		if goDeferCall[call] {
+		if call.GoDefer {
 			if base.Debug.PGODebug >= 2 {
 				fmt.Printf("%v: can't PGO devirtualize go/defer call %v\n", ir.Line(call), call)
 			}