compiler,transform: fix for pointer-to-pointer type switches from @aykevl

Author: dgryski

compiler/interface.go

@@ -683,11 +683,8 @@ func (b *builder) createTypeAssert(expr *ssa.TypeAssert) llvm.Value {
 		commaOk = b.CreateCall(fn.GlobalValueType(), fn, []llvm.Value{actualTypeNum}, "")
 
 	} else {
-		assertedTypeGlobal := b.getTypeCode(expr.AssertedType)
-		if !assertedTypeGlobal.IsAConstantExpr().IsNil() {
-			assertedTypeGlobal = assertedTypeGlobal.Operand(0) // resolve the GEP operation
-		}
-		globalName := "reflect/types.typeid:" + strings.TrimPrefix(assertedTypeGlobal.Name(), "reflect/types.type:")
+		name, _ := getTypeCodeName(expr.AssertedType)
+		globalName := "reflect/types.typeid:" + name
 		assertedTypeCodeGlobal := b.mod.NamedGlobal(globalName)
 		if assertedTypeCodeGlobal.IsNil() {
 			// Create a new typecode global.

testdata/interface.go

@@ -113,6 +113,9 @@ func main() {
 	println("slept 1ms")
 	blockStatic(SleepBlocker(time.Millisecond))
 	println("slept 1ms")
+
+	// check that pointer-to-pointer type switches work
+	ptrptrswitch()
 }
 
 func printItf(val interface{}) {
@@ -312,3 +315,22 @@ func namedptr2() interface{} {
 	type Test byte
 	return (*Test)(nil)
 }
+
+func ptrptrswitch() {
+	identify(0)
+	identify(new(int))
+	identify(new(*int))
+}
+
+func identify(itf any) {
+	switch itf.(type) {
+	case int:
+		println("type is int")
+	case *int:
+		println("type is *int")
+	case **int:
+		println("type is **int")
+	default:
+		println("other type??")
+	}
+}

testdata/interface.txt

@@ -24,3 +24,6 @@ Byte():  3
 non-blocking call on sometimes-blocking interface
 slept 1ms
 slept 1ms
+type is int
+type is *int
+type is **int

transform/interface-lowering.go

@@ -285,11 +285,27 @@ func (p *lowerInterfacesPass) run() error {
 	for _, use := range getUses(p.mod.NamedFunction("runtime.typeAssert")) {
 		actualType := use.Operand(0)
 		name := strings.TrimPrefix(use.Operand(1).Name(), "reflect/types.typeid:")
+		gepOffset := uint64(0)
+		for strings.HasPrefix(name, "pointer:pointer:") {
+			// This is a type like **int, which has the name pointer:pointer:int
+			// but is encoded using pointer tagging.
+			// Calculate the pointer tag, which is emitted as a GEP instruction.
+			name = name[len("pointer:"):]
+			gepOffset++
+		}
+
 		if t, ok := p.types[name]; ok {
 			// The type exists in the program, so lower to a regular pointer
 			// comparison.
 			p.builder.SetInsertPointBefore(use)
-			commaOk := p.builder.CreateICmp(llvm.IntEQ, t.typecodeGEP, actualType, "typeassert.ok")
+			typecodeGEP := t.typecodeGEP
+			if gepOffset != 0 {
+				// This is a tagged pointer.
+				typecodeGEP = llvm.ConstInBoundsGEP(p.ctx.Int8Type(), typecodeGEP, []llvm.Value{
+					llvm.ConstInt(p.ctx.Int64Type(), gepOffset, false),
+				})
+			}
+			commaOk := p.builder.CreateICmp(llvm.IntEQ, typecodeGEP, actualType, "typeassert.ok")
 			use.ReplaceAllUsesWith(commaOk)
 		} else {
 			// The type does not exist in the program, so lower to a constant