cmd/compile: improve interface type switches

For type switches where the targets are interface types,
call into the runtime once instead of doing a sequence
of assert* calls.

name                                 old time/op  new time/op  delta
SwitchInterfaceTypePredictable-24    26.6ns ± 1%  25.8ns ± 2%  -2.86%  (p=0.000 n=10+10)
SwitchInterfaceTypeUnpredictable-24  39.3ns ± 1%  37.5ns ± 2%  -4.57%  (p=0.000 n=10+10)

Not super helpful by itself, but this code organization allows
followon CLs that add caching to the lookups.

Change-Id: I7967f85a99171faa6c2550690e311bea8b54b01c
Reviewed-on: https://go-review.googlesource.com/c/go/+/526657
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/test/codegen/switch.go b/test/codegen/switch.go
index 556d02a162..63b0dce8a6 100644
--- a/test/codegen/switch.go
+++ b/test/codegen/switch.go
@@ -118,3 +118,24 @@ func typeSwitch(x any) int {
 	}
 	return 7
 }
+
+type I interface {
+	foo()
+}
+type J interface {
+	bar()
+}
+
+// use a runtime call for type switches to interface types.
+func interfaceSwitch(x any) int {
+	// amd64:`CALL\truntime.interfaceSwitch`
+	// arm64:`CALL\truntime.interfaceSwitch`
+	switch x.(type) {
+	case I:
+		return 1
+	case J:
+		return 2
+	default:
+		return 3
+	}
+}