diff --git a/coroutine_test.go b/coroutine_test.go
new file mode 100644
index 0000000..1cff30a
--- /dev/null
+++ b/coroutine_test.go
@@ -0,0 +1,289 @@
+//===- coroutine_test.go - Tests for coroutine lowering ------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+package llvm
+
+import (
+	"strconv"
+	"strings"
+	"testing"
+)
+
+func TestSwitchedResumeCoroutinePassPipelines(t *testing.T) {
+	majorVersion, err := strconv.Atoi(strings.SplitN(Version, ".", 2)[0])
+	if err != nil {
+		t.Fatalf("could not parse LLVM version %q: %v", Version, err)
+	}
+
+	InitializeAllTargetInfos()
+	InitializeAllTargets()
+	InitializeAllTargetMCs()
+	InitializeAllAsmPrinters()
+	triple := DefaultTargetTriple()
+	target, err := GetTargetFromTriple(triple)
+	if err != nil {
+		t.Fatal(err)
+	}
+	tm := target.CreateTargetMachine(
+		triple, "", "", CodeGenLevelDefault, RelocDefault, CodeModelDefault,
+	)
+	defer tm.Dispose()
+
+	explicitPipeline := "coro-early,cgscc(coro-split),coro-cleanup"
+	if majorVersion == 14 {
+		// In LLVM 14, coro-early and coro-cleanup are function passes. Newer
+		// releases expose them as module passes and accept the unnested form.
+		explicitPipeline = "function(coro-early),cgscc(coro-split),function(coro-cleanup)"
+	}
+	for _, test := range []struct {
+		name     string
+		pipeline string
+	}{
+		{name: "explicit coroutine pipeline", pipeline: explicitPipeline},
+		{name: "production O0 pipeline", pipeline: "default<O0>"},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			ctx := NewContext()
+			defer ctx.Dispose()
+			mod := buildSwitchedResumeCoroutine(t, ctx, tm, majorVersion)
+			defer mod.Dispose()
+			assertSwitchedResumeCoroutineFrontendState(t, mod, majorVersion)
+
+			if err := VerifyModule(mod, ReturnStatusAction); err != nil {
+				t.Fatalf("coroutine module did not verify before %s: %v\n%s", test.pipeline, err, mod.String())
+			}
+
+			options := NewPassBuilderOptions()
+			defer options.Dispose()
+			options.SetVerifyEach(true)
+			if err := mod.RunPasses(test.pipeline, tm, options); err != nil {
+				t.Fatalf("could not run %s: %v\n%s", test.pipeline, err, mod.String())
+			}
+
+			if err := VerifyModule(mod, ReturnStatusAction); err != nil {
+				t.Fatalf("coroutine module did not verify after %s: %v\n%s", test.pipeline, err, mod.String())
+			}
+			assertSwitchedResumeCoroutineLowered(t, mod, test.pipeline)
+		})
+	}
+}
+
+func buildSwitchedResumeCoroutine(t *testing.T, ctx Context, tm TargetMachine, majorVersion int) Module {
+	t.Helper()
+
+	mod := ctx.NewModule("switched-resume-coroutine")
+	returned := false
+	defer func() {
+		if !returned {
+			mod.Dispose()
+		}
+	}()
+	mod.SetTarget(tm.Triple())
+	targetData := tm.CreateTargetData()
+	mod.SetDataLayout(targetData.String())
+	pointerSize := targetData.PointerSize()
+	targetData.Dispose()
+
+	i1 := ctx.Int1Type()
+	i8 := ctx.Int8Type()
+	i32 := ctx.Int32Type()
+	ptr := PointerType(i8, 0)
+	void := ctx.VoidType()
+	falseValue := ConstInt(i1, 0, false)
+	nullPointer := ConstPointerNull(ptr)
+	var sizeType Type
+	switch pointerSize {
+	case 4:
+		sizeType = i32
+	case 8:
+		sizeType = ctx.Int64Type()
+	default:
+		t.Fatalf("unsupported target pointer size %d", pointerSize)
+	}
+
+	fn := AddFunction(mod, "stackless", FunctionType(ptr, nil, false))
+	if majorVersion == 14 {
+		// LLVM 14 models this as a frontend-to-CoroEarly state machine: "0"
+		// means unprepared input, while "1" is reserved for prepared IR.
+		fn.AddFunctionAttr(ctx.CreateStringAttribute("coroutine.presplit", "0"))
+	} else {
+		kind := AttributeKindID("presplitcoroutine")
+		if kind == 0 {
+			t.Fatal("could not look up presplitcoroutine attribute")
+		}
+		fn.AddFunctionAttr(ctx.CreateEnumAttribute(kind, 0))
+	}
+
+	frameAllocType := FunctionType(ptr, []Type{sizeType, sizeType}, false)
+	frameAlloc := AddFunction(mod, "coro_frame_alloc", frameAllocType)
+	freeType := FunctionType(void, []Type{ptr}, false)
+	free := AddFunction(mod, "coro_frame_free", freeType)
+
+	entry := AddBasicBlock(fn, "entry")
+	allocate := AddBasicBlock(fn, "allocate")
+	begin := AddBasicBlock(fn, "begin")
+	initialSuspend := AddBasicBlock(fn, "initial.suspend")
+	body := AddBasicBlock(fn, "body")
+	finalSuspend := AddBasicBlock(fn, "final.suspend")
+	finalResumeUnreachable := AddBasicBlock(fn, "final.resume.unreachable")
+	cleanup := AddBasicBlock(fn, "cleanup")
+	deallocate := AddBasicBlock(fn, "deallocate")
+	end := AddBasicBlock(fn, "end")
+
+	ids := make(map[string]int)
+	for _, name := range []string{
+		"llvm.coro.id",
+		"llvm.coro.alloc",
+		"llvm.coro.size",
+		"llvm.coro.align",
+		"llvm.coro.begin",
+		"llvm.coro.save",
+		"llvm.coro.suspend",
+		"llvm.coro.free",
+		"llvm.coro.end",
+	} {
+		ids[name] = LookupIntrinsicID(name)
+		if ids[name] == 0 {
+			t.Fatalf("could not look up %s intrinsic", name)
+		}
+	}
+
+	builder := ctx.NewBuilder()
+	defer builder.Dispose()
+
+	createIntrinsic := func(ret Type, name string, args []Value, resultName string) Value {
+		value := builder.CreateIntrinsic(ret, ids[name], args, resultName)
+		if value.IsNil() {
+			t.Fatalf("could not construct %s intrinsic", name)
+		}
+		return value
+	}
+	createSuspend := func(block BasicBlock, handle Value, final bool, resume, destroy BasicBlock) {
+		builder.SetInsertPointAtEnd(block)
+		saved := createIntrinsic(ctx.TokenType(), "llvm.coro.save", []Value{handle}, "save")
+		finalValue := ConstInt(i1, 0, false)
+		if final {
+			finalValue = ConstInt(i1, 1, false)
+		}
+		suspended := createIntrinsic(i8, "llvm.coro.suspend", []Value{saved, finalValue}, "suspend")
+		dispatch := builder.CreateSwitch(suspended, end, 2)
+		dispatch.AddCase(ConstInt(i8, 0, false), resume)
+		dispatch.AddCase(ConstInt(i8, 1, false), destroy)
+	}
+
+	builder.SetInsertPointAtEnd(entry)
+	// Zero requests LLVM's default allocation memory alignment guarantee of
+	// twice the target pointer size.
+	allocationAlignmentGuarantee := ConstInt(i32, 0, false)
+	id := createIntrinsic(ctx.TokenType(), "llvm.coro.id", []Value{
+		allocationAlignmentGuarantee,
+		nullPointer,
+		nullPointer,
+		nullPointer,
+	}, "id")
+	needsAllocation := createIntrinsic(i1, "llvm.coro.alloc", []Value{id}, "needs.alloc")
+	builder.CreateCondBr(needsAllocation, allocate, begin)
+
+	builder.SetInsertPointAtEnd(allocate)
+	frameSize := createIntrinsic(sizeType, "llvm.coro.size", nil, "frame.size")
+	frameAlignment := createIntrinsic(sizeType, "llvm.coro.align", nil, "frame.align")
+	minimumAlignment := ConstInt(sizeType, uint64(2*pointerSize), false)
+	belowMinimum := builder.CreateICmp(IntULT, frameAlignment, minimumAlignment, "below.minimum.alignment")
+	allocationAlignment := builder.CreateSelect(
+		belowMinimum, minimumAlignment, frameAlignment, "allocation.alignment",
+	)
+	allocatedMemory := builder.CreateCall(
+		frameAllocType, frameAlloc, []Value{frameSize, allocationAlignment}, "allocated.memory",
+	)
+	builder.CreateBr(begin)
+
+	builder.SetInsertPointAtEnd(begin)
+	frameMemory := builder.CreatePHI(ptr, "frame.memory")
+	frameMemory.AddIncoming(
+		[]Value{nullPointer, allocatedMemory},
+		[]BasicBlock{entry, allocate},
+	)
+	handle := createIntrinsic(ptr, "llvm.coro.begin", []Value{id, frameMemory}, "handle")
+	builder.CreateBr(initialSuspend)
+
+	createSuspend(initialSuspend, handle, false, body, cleanup)
+	createSuspend(body, handle, false, finalSuspend, cleanup)
+	createSuspend(finalSuspend, handle, true, finalResumeUnreachable, cleanup)
+
+	builder.SetInsertPointAtEnd(finalResumeUnreachable)
+	builder.CreateUnreachable()
+
+	builder.SetInsertPointAtEnd(cleanup)
+	frameToFree := createIntrinsic(ptr, "llvm.coro.free", []Value{id, handle}, "frame.to.free")
+	hasFrameToFree := builder.CreateIsNotNull(frameToFree, "has.frame.to.free")
+	builder.CreateCondBr(hasFrameToFree, deallocate, end)
+
+	builder.SetInsertPointAtEnd(deallocate)
+	builder.CreateCall(freeType, free, []Value{frameToFree}, "")
+	builder.CreateBr(end)
+
+	builder.SetInsertPointAtEnd(end)
+	endArgs := []Value{handle, falseValue}
+	endType := i1
+	endName := "ended"
+	if majorVersion >= 18 {
+		endArgs = append(endArgs, ctx.ConstTokenNone())
+	}
+	if majorVersion >= 22 {
+		endType = void
+		endName = ""
+	}
+	createIntrinsic(endType, "llvm.coro.end", endArgs, endName)
+	builder.CreateRet(handle)
+
+	returned = true
+	return mod
+}
+
+func assertSwitchedResumeCoroutineFrontendState(t *testing.T, mod Module, majorVersion int) {
+	t.Helper()
+
+	text := mod.String()
+	if majorVersion == 14 {
+		if !strings.Contains(text, `"coroutine.presplit"="0"`) {
+			t.Fatalf("LLVM 14 frontend coroutine is not marked unprepared for CoroEarly:\n%s", text)
+		}
+	} else if !strings.Contains(text, "presplitcoroutine") {
+		t.Fatalf("frontend coroutine lacks presplitcoroutine attribute:\n%s", text)
+	}
+	if !strings.Contains(text, "%allocation.alignment = select i1") {
+		t.Fatalf("frame allocator does not normalize coro.align to the coro.id guarantee:\n%s", text)
+	}
+	for _, line := range strings.Split(text, "\n") {
+		if strings.Contains(line, "call") && strings.Contains(line, "@coro_frame_alloc") {
+			if !strings.Contains(line, "%allocation.alignment") {
+				t.Fatalf("frame allocator does not receive the normalized alignment: %s\n%s", line, text)
+			}
+			return
+		}
+	}
+	t.Fatalf("frontend coroutine does not call the frame allocator:\n%s", text)
+}
+
+func assertSwitchedResumeCoroutineLowered(t *testing.T, mod Module, pipeline string) {
+	t.Helper()
+
+	for _, name := range []string{"stackless", "stackless.resume", "stackless.destroy"} {
+		fn := mod.NamedFunction(name)
+		if fn.IsNil() || fn.BasicBlocksCount() == 0 {
+			t.Fatalf("%s did not produce coroutine function %q:\n%s", pipeline, name, mod.String())
+		}
+	}
+
+	text := mod.String()
+	for _, line := range strings.Split(text, "\n") {
+		if strings.Contains(line, " call ") && strings.Contains(line, "@llvm.coro.") {
+			t.Fatalf("%s left coroutine intrinsic call after lowering: %s\n%s", pipeline, line, text)
+		}
+	}
+}