cmd/compile: adjust PGO devirtualization diagnostic message

Make it more consistent with the static devirtualization
diagnostic message. Keep the print of concrete callee's method
name, as it is clearer.

Change-Id: Ibe9b40253eaff2c0071353a2b388177213488822
Reviewed-on: https://go-review.googlesource.com/c/go/+/500960
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>

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

@@ -265,7 +265,7 @@ func constructCallStat(p *pgo.Profile, fn *ir.Func, name string, call *ir.CallEx
 // concretetyp.
 func rewriteCondCall(call *ir.CallExpr, curfn, callee *ir.Func, concretetyp *types.Type) ir.Node {
 	if base.Flag.LowerM != 0 {
-		fmt.Printf("%v: PGO devirtualizing call to %v\n", ir.Line(call), callee)
+		fmt.Printf("%v: PGO devirtualizing %v to %v\n", ir.Line(call), call.X, callee)
 	}
 
 	// We generate an OINCALL of:

src/cmd/compile/internal/test/pgo_devirtualize_test.go

@@ -68,7 +68,7 @@ go 1.19
 
 	got := make(map[devirtualization]struct{})
 
-	devirtualizedLine := regexp.MustCompile(`(.*): PGO devirtualizing call to (.*)`)
+	devirtualizedLine := regexp.MustCompile(`(.*): PGO devirtualizing .* to (.*)`)
 
 	scanner := bufio.NewScanner(pr)
 	for scanner.Scan() {