cmd/compile/internal/devirtualize: improve debug logs

Change-Id: Ie8d74d0968c3dfa6fe3454f1d3fdf13d6a6a6944
Reviewed-on: https://go-review.googlesource.com/c/go/+/760162
Auto-Submit: Mateusz Poliwczak <mpoliwczak34@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/devirtualize/devirtualize.go b/src/cmd/compile/internal/devirtualize/devirtualize.go
index 59ddc2e536..08af63c39e 100644
--- a/src/cmd/compile/internal/devirtualize/devirtualize.go
+++ b/src/cmd/compile/internal/devirtualize/devirtualize.go
@@ -182,6 +182,17 @@ const concreteTypeDebug = false
 // Returns nil when the concrete type could not be determined, or when there are multiple
 // (different) types assigned to an interface.
 func concreteType(s *State, n ir.Node) (typ *types.Type) {
+	if concreteTypeDebug {
+		base.Warn("concreteType(%v) - analyzing", n)
+		defer func() {
+			t := typ.String()
+			if typ == nil {
+				t = "<nil> (unknown static type)"
+			}
+			base.Warn("concreteType(%v) -> %v", n, t)
+		}()
+	}
+
 	typ = concreteType1(s, n, make(map[*ir.Name]struct{}))
 	if typ == &noType {
 		return nil
@@ -207,6 +218,9 @@ func concreteType1(s *State, n ir.Node, seen map[*ir.Name]struct{}) (outT *types
 			if outT != &noType {
 				t = outT.String()
 			}
+			if outT == nil {
+				t = "<nil> (unknown static type)"
+			}
 			base.Warn("concreteType1(%v) -> %v", nn, t)
 		}()
 	}