compiler: fix crash on type assert on interfaces with no methods

compiler/interface.go

@@ -684,8 +684,14 @@ func (b *builder) createTypeAssert(expr *ssa.TypeAssert) llvm.Value {
 
 	actualTypeNum := b.CreateExtractValue(itf, 0, "interface.type")
 	commaOk := llvm.Value{}
-	if _, ok := expr.AssertedType.Underlying().(*types.Interface); ok {
-		// Type assert on interface type.
+
+	if intf, ok := expr.AssertedType.Underlying().(*types.Interface); ok {
+		if intf.Empty() {
+			// intf is the empty interface => no methods
+			// This type assertion always succeeds, so we can just set commaOk to true.
+			commaOk = llvm.ConstInt(b.ctx.Int1Type(), 1, true)
+		} else {
+			// Type assert on interface type with methods.
 			// This is a call to an interface type assert function.
 			// The interface lowering pass will define this function by filling it
 			// with a type switch over all concrete types that implement this
@@ -696,7 +702,7 @@ func (b *builder) createTypeAssert(expr *ssa.TypeAssert) llvm.Value {
 			// https://research.swtch.com/interfaces
 			fn := b.getInterfaceImplementsFunc(expr.AssertedType)
 			commaOk = b.CreateCall(fn.GlobalValueType(), fn, []llvm.Value{actualTypeNum}, "")
-
+		}
 	} else {
 		name, _ := getTypeCodeName(expr.AssertedType)
 		globalName := "reflect/types.typeid:" + name

testdata/interface.go

@@ -116,6 +116,9 @@ func main() {
 
 	// check that pointer-to-pointer type switches work
 	ptrptrswitch()
+
+	// check that type asserts to interfaces with no methods work
+	emptyintfcrash()
 }
 
 func printItf(val interface{}) {
@@ -334,3 +337,9 @@ func identify(itf any) {
 		println("other type??")
 	}
 }
+
+func emptyintfcrash() {
+	if x, ok := any(5).(any); ok {
+		println("x is", x.(int))
+	}
+}

testdata/interface.txt

@@ -27,3 +27,4 @@ slept 1ms
 type is int
 type is *int
 type is **int
+x is 5