update

Change-Id: I2bc464114e862a2a2d65f41a483bdeb12818a49e

Author: mateusz834

Diff for: src/cmd/compile/internal/ir/expr.go

@@ -682,7 +682,9 @@ type TypeAssertExpr struct {
 	// An internal/abi.TypeAssert descriptor to pass to the runtime.
 	Descriptor *obj.LSym
 
-	// Emit a nilcheck on the Itab of X.
+	// When set to true, then the ssagen package will emit a nilcheck on the itab, that
+	// will lead to a nil check panic in case the itab is nil at runtime.
+	// It must not be set for type asserts using the commaok form.
 	EmitItabNilCheck bool
 }
 

Diff for: src/cmd/compile/internal/ssagen/ssa.go

@@ -5627,6 +5627,9 @@ func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Val
 	}
 
 	if n.EmitItabNilCheck {
+		if commaok {
+			base.Fatalf("unexpected *ir.TypeAssertExpr with EmitItabNilCheck == true && commaok == true")
+		}
 		typs := s.f.Config.Types
 		iface = s.newValue2(
 			ssa.OpIMake,