[dev.typeparams] cmd/compile: implement generic type switches

Add a new dynamicType node, which is used as a case entry when
the type being switched to is generic.

Change-Id: Ice77c6f224b8fdd3ff574fdf4a8ea5f6c7ddbe75
Reviewed-on: https://go-review.googlesource.com/c/go/+/339429
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/ir/type.go b/src/cmd/compile/internal/ir/type.go
index 431468375a..63dd673dcd 100644
--- a/src/cmd/compile/internal/ir/type.go
+++ b/src/cmd/compile/internal/ir/type.go
@@ -319,3 +319,17 @@ func TypeNodeAt(pos src.XPos, t *types.Type) Ntype {
 	}
 	return newTypeNode(pos, t)
 }
+
+// A DynamicType represents the target type in a type switch.
+type DynamicType struct {
+	miniExpr
+	X    Node // a *runtime._type for the targeted type
+	ITab Node // for type switches from nonempty interfaces to non-interfaces, this is the itab for that pair.
+}
+
+func NewDynamicType(pos src.XPos, x Node) *DynamicType {
+	n := &DynamicType{X: x}
+	n.pos = pos
+	n.op = ODYNAMICTYPE
+	return n
+}