Pass GPU events instead of streams across async regions.

[csigg]

Summary

Lower !gpu.async.tokens returned from async.execute regions to events instead of streams.

Make !gpu.async.token returned from !async.execute single-use.
This allows creating one event per use and destroying them without leaking or ref-counting.
Technically we only need this for stream/event-based lowering. I kept the code separate
from the rest of the gpu-async-region pass so that we can make this optional or move
to a separate pass as needed.

[csigg]

Fix tests.

[csigg]

Remove debug printfs ;-)

[csigg]

Fix identifier naming.

[herhut]

mlir/lib/Conversion/GPUCommon/ConvertLaunchFuncToRuntimeCalls.cpp

483

The name is misleading. This is not done via types but rather by matching the defining op. Maybe reflect that in the name.

486

nit: Can you get that string from somewhere, so it is only defined in one place?

This will fall apart with control flow, but we do not support this currently, anyway.

mlir/lib/Dialect/GPU/Transforms/AsyncRegionRewriter.cpp

300

This is a bit confusing. Here results is the result operands and further down it is the actual result values of the updated op.

301

Can this be done without rewriting the op multiple times?

[csigg]

Address reviewer comments.

mlir/lib/Conversion/GPUCommon/ConvertLaunchFuncToRuntimeCalls.cpp

486

The idea is that we lower control flow to events, at least at the beginning.

mlir/lib/Dialect/GPU/Transforms/AsyncRegionRewriter.cpp

301

It's not worth the (quite significant) extra complexity, because in most cases there will be just one.

[herhut]

Thanks!

mlir/lib/Conversion/GPUCommon/ConvertLaunchFuncToRuntimeCalls.cpp

 //
 //===----------------------------------------------------------------------===//
 
 #include "mlir/Conversion/GPUCommon/GPUCommonPass.h"
 
 #include "../PassDetail.h"
 #include "mlir/Conversion/AsyncToLLVM/AsyncToLLVM.h"
 #include "mlir/Conversion/StandardToLLVM/ConvertStandardToLLVM.h"
+#include "mlir/Dialect/Async/IR/Async.h"
 #include "mlir/Dialect/GPU/GPUDialect.h"
 #include "mlir/Dialect/LLVMIR/LLVMDialect.h"
 #include "mlir/IR/Attributes.h"
 #include "mlir/IR/Builders.h"
 #include "mlir/IR/BuiltinOps.h"
 #include "mlir/IR/BuiltinTypes.h"
 
 #include "llvm/ADT/STLExtras.h"
ConvertDeallocOpToGpuRuntimeCallPattern(LLVMTypeConverter &typeConverter)
       : ConvertOpToGpuRuntimeCallPattern<gpu::DeallocOp>(typeConverter) {}
 
 private:
   LogicalResult
   matchAndRewrite(gpu::DeallocOp deallocOp, ArrayRef<Value> operands,
                   ConversionPatternRewriter &rewriter) const override;
 };
 
+class ConvertAsyncYieldToGpuRuntimeCallPattern
+    : public ConvertOpToGpuRuntimeCallPattern<async::YieldOp> {
+public:
+  ConvertAsyncYieldToGpuRuntimeCallPattern(LLVMTypeConverter &typeConverter)
+      : ConvertOpToGpuRuntimeCallPattern<async::YieldOp>(typeConverter) {}
+
+private:
+  LogicalResult
+  matchAndRewrite(async::YieldOp yieldOp, ArrayRef<Value> operands,
+                  ConversionPatternRewriter &rewriter) const override;
+};
+
 /// A rewrite pattern to convert gpu.wait operations into a GPU runtime
 /// call. Currently it supports CUDA and ROCm (HIP).
 class ConvertWaitOpToGpuRuntimeCallPattern
     : public ConvertOpToGpuRuntimeCallPattern<gpu::WaitOp> {
 public:
   ConvertWaitOpToGpuRuntimeCallPattern(LLVMTypeConverter &typeConverter)
       : ConvertOpToGpuRuntimeCallPattern<gpu::WaitOp>(typeConverter) {}
 
LogicalResult ConvertDeallocOpToGpuRuntimeCallPattern::matchAndRewrite(
   auto casted = rewriter.create<LLVM::BitcastOp>(loc, llvmPointerType, pointer);
   Value stream = adaptor.asyncDependencies().front();
   deallocCallBuilder.create(loc, rewriter, {casted, stream});
 
   rewriter.replaceOp(deallocOp, {stream});
   return success();
 }
 
-// Converts `gpu.wait` to runtime calls. The operands are all CUDA or ROCm
-// streams (i.e. void*). The converted op synchronizes the host with every
-// stream and then destroys it. That is, it assumes that the stream is not used
-// afterwards. In case this isn't correct, we will get a runtime error.
-// Eventually, we will have a pass that guarantees this property.
+static bool isGpuAsyncTokenType(Value value) {
+  return value.getType().isa<gpu::AsyncTokenType>();
+}
+
+// Converts !gpu.async.token operands of `async.yield` to runtime calls. The
+// !gpu.async.token are lowered to stream within the async.execute region, but
+// are passed as events between them. For each !gpu.async.token operand, we
+// create an event and record it on the stream.
+LogicalResult ConvertAsyncYieldToGpuRuntimeCallPattern::matchAndRewrite(
+    async::YieldOp yieldOp, ArrayRef<Value> operands,
+    ConversionPatternRewriter &rewriter) const {
+  if (llvm::none_of(yieldOp.operands(), isGpuAsyncTokenType))
+    return rewriter.notifyMatchFailure(yieldOp, "no gpu async token operand");
+
+  Location loc = yieldOp.getLoc();
+  SmallVector<Value, 4> newOperands(operands.begin(), operands.end());
+  llvm::SmallDenseSet<Value> streams;
+  for (auto &operand : yieldOp->getOpOperands()) {
+    if (!isGpuAsyncTokenType(operand.get()))
+      continue;
+    auto idx = operand.getOperandNumber();
+    auto stream = operands[idx];
+    auto event = eventCreateCallBuilder.create(loc, rewriter, {}).getResult(0);
+    eventRecordCallBuilder.create(loc, rewriter, {event, stream});
+    newOperands[idx] = event;
+    streams.insert(stream);
+  }
+  for (auto stream : streams)
+    streamDestroyCallBuilder.create(loc, rewriter, {stream});
+
+  rewriter.updateRootInPlace(yieldOp,
+                             [&] { yieldOp->setOperands(newOperands); });
+  return success();
+}
+
+// Returns whether `value` which was converted from a !gpu.async.token is a
+// stream (instead of an event). We use streams within a region, and events
+// for block arguments and to pass across async.execute ops.
+static bool isTypeStream(Value value) {
+  assert(value.getType().isa<LLVM::LLVMPointerType>());
+  if (auto defOp = value.getDefiningOp<LLVM::CallOp>())
+    return defOp.callee()->equals("mgpuStreamCreate");
+  return false;
+}
+
+// Converts `gpu.wait` to runtime calls. The converted op synchronizes the host
+// with the stream/event operands. The operands are destroyed. That is, it
+// assumes that it is not used afterwards or elsewhere. Otherwise we will get a
+// runtime error. Eventually, we should guarantee this property.
 LogicalResult ConvertWaitOpToGpuRuntimeCallPattern::matchAndRewrite(
     gpu::WaitOp waitOp, ArrayRef<Value> operands,
     ConversionPatternRewriter &rewriter) const {
   if (waitOp.asyncToken())
     return rewriter.notifyMatchFailure(waitOp, "Cannot convert async op.");
 
   Location loc = waitOp.getLoc();
 
-  for (auto asyncDependency : operands)
-    streamSynchronizeCallBuilder.create(loc, rewriter, {asyncDependency});
-  for (auto asyncDependency : operands)
-    streamDestroyCallBuilder.create(loc, rewriter, {asyncDependency});
+  for (auto operand : operands) {
+    if (isTypeStream(operand)) {
+      streamSynchronizeCallBuilder.create(loc, rewriter, {operand});
+      streamDestroyCallBuilder.create(loc, rewriter, {operand});
+    } else {
+      eventSynchronizeCallBuilder.create(loc, rewriter, {operand});
+      eventDestroyCallBuilder.create(loc, rewriter, {operand});
+    }
+  }
 
   rewriter.eraseOp(waitOp);
   return success();
 }
 
-// Converts `gpu.wait async` to runtime calls. The result is a new stream that
-// is synchronized with all operands, which are CUDA or ROCm streams (i.e.
-// void*). We create and record an event after the definition of the stream
-// and make the new stream wait on that event before destroying it again. This
-// assumes that there is no other use between the definition and this op, and
-// the plan is to have a pass that guarantees this property.
+// Converts `gpu.wait async` to runtime calls. The converted op creates a new
+// stream that is synchronized with stream/event operands. The operands are
+// destroyed. That is, it assumes that it is not used afterwards or elsewhere.
+// Otherwise we will get a runtime error. Eventually, we should guarantee this
+// property.
 LogicalResult ConvertWaitAsyncOpToGpuRuntimeCallPattern::matchAndRewrite(
     gpu::WaitOp waitOp, ArrayRef<Value> operands,
     ConversionPatternRewriter &rewriter) const {
   if (!waitOp.asyncToken())
     return rewriter.notifyMatchFailure(waitOp, "Can only convert async op.");
 
   Location loc = waitOp.getLoc();
 
   auto insertionPoint = rewriter.saveInsertionPoint();
   SmallVector<Value, 1> events;
   for (auto pair : llvm::zip(waitOp.asyncDependencies(), operands)) {
-    auto token = std::get<0>(pair);
-    if (auto *defOp = token.getDefiningOp()) {
+    auto operand = std::get<1>(pair);
+    if (isTypeStream(operand)) {
+      // The operand is a stream. Insert an event into the stream just after its
+      // last use (i.e. after the token-defining op, which always exists).
+      auto *defOp = std::get<0>(pair).getDefiningOp();
       rewriter.setInsertionPointAfter(defOp);
+      auto event =
+          eventCreateCallBuilder.create(loc, rewriter, {}).getResult(0);
+      eventRecordCallBuilder.create(loc, rewriter, {event, operand});
+      events.push_back(event);
     } else {
-      // If we can't find the defining op, we record the event at block start,
-      // which is late and therefore misses parallelism, but still valid.
-      rewriter.setInsertionPointToStart(waitOp->getBlock());
+      // The operand is an event.
+      events.push_back(operand);
     }
-    auto event = eventCreateCallBuilder.create(loc, rewriter, {}).getResult(0);
-    auto stream = std::get<1>(pair);
-    eventRecordCallBuilder.create(loc, rewriter, {event, stream});
-    events.push_back(event);
   }
   rewriter.restoreInsertionPoint(insertionPoint);
   auto stream = streamCreateCallBuilder.create(loc, rewriter, {}).getResult(0);
   for (auto event : events)
     streamWaitEventCallBuilder.create(loc, rewriter, {stream, event});
   for (auto event : events)
     eventDestroyCallBuilder.create(loc, rewriter, {event});
   rewriter.replaceOp(waitOp, {stream});
converter.addConversion(
       [context = &converter.getContext()](gpu::AsyncTokenType type) -> Type {
         return LLVM::LLVMPointerType::get(IntegerType::get(context, 8));
       });
   patterns.insert<ConvertAllocOpToGpuRuntimeCallPattern,
                   ConvertDeallocOpToGpuRuntimeCallPattern,
                   ConvertHostRegisterOpToGpuRuntimeCallPattern,
                   ConvertMemcpyOpToGpuRuntimeCallPattern,
                   ConvertWaitAsyncOpToGpuRuntimeCallPattern,
-                  ConvertWaitOpToGpuRuntimeCallPattern>(converter);
+                  ConvertWaitOpToGpuRuntimeCallPattern,
+                  ConvertAsyncYieldToGpuRuntimeCallPattern>(converter);
   patterns.insert<ConvertLaunchFuncOpToGpuRuntimeCallPattern>(
       converter, gpuBinaryAnnotation);
   patterns.insert<EraseGpuModuleOpPattern>(&converter.getContext());
 }

mlir/lib/Dialect/GPU/Transforms/AsyncRegionRewriter.cpp

 #include "mlir/Transforms/RegionUtils.h"
 #include "llvm/ADT/TypeSwitch.h"
 
 using namespace mlir;
 namespace {
 class GpuAsyncRegionPass : public GpuAsyncRegionPassBase<GpuAsyncRegionPass> {
   struct ThreadTokenCallback;
   struct DeferWaitCallback;
+  struct SingleTokenUseCallback;
   void runOnFunction() override;
 };
 } // namespace
 
 static bool isTerminator(Operation *op) {
   return op->mightHaveTrait<OpTrait::IsTerminator>();
 }
 static bool hasSideEffects(Operation *op) {
private:
 
   // The token that represents the current asynchronous dependency. It's valid
   // range starts with a `gpu.wait async` op, and ends with a `gpu.wait` op.
   // In between, each gpu::AsyncOpInterface depends on the current token and
   // produces the new one.
   Value currentToken = {};
 };
 
+/// Erases `executeOp` and returns a clone with additional `results`.
+async::ExecuteOp addExecuteResults(async::ExecuteOp executeOp,
+                                   ValueRange results) {
+  // Add values to async.yield op.
+  Operation *yieldOp = executeOp.getBody()->getTerminator();
+  yieldOp->insertOperands(yieldOp->getNumOperands(), results);
+
+  // Construct new result type list with additional types.
+  SmallVector<Type, 2> resultTypes;
+  resultTypes.reserve(executeOp.getNumResults() + results.size());
+  transform(executeOp.getResultTypes(), std::back_inserter(resultTypes),
+            [](Type type) {
+              // Extract value type from !async.value.
+              if (auto valueType = type.dyn_cast<async::ValueType>())
+                return valueType.getValueType();
+              assert(type.isa<async::TokenType>() && "expected token type");
+              return type;
+            });
+  transform(results, std::back_inserter(resultTypes),
+            [](Value value) { return value.getType(); });
+
+  // Clone executeOp with the extra results.
+  OpBuilder builder(executeOp);
+  auto newOp = builder.create<async::ExecuteOp>(
+      executeOp.getLoc(), TypeRange{resultTypes}.drop_front() /*drop token*/,
+      executeOp.dependencies(), executeOp.operands());
+  BlockAndValueMapping mapper;
+  newOp.getRegion().getBlocks().clear();
+  executeOp.getRegion().cloneInto(&newOp.getRegion(), mapper);
+
+  // Replace executeOp with cloned one.
+  executeOp.getOperation()->replaceAllUsesWith(
+      newOp.getResults().drop_back(results.size()));
+  executeOp.erase();
+
+  return newOp;
+}
+
 // Callback for `async.execute` ops which tries to push the contained
 // synchronous `gpu.wait` op to the dependencies of the `async.execute`.
 struct GpuAsyncRegionPass::DeferWaitCallback {
   // If the `executeOp`s token is used only in `async.execute` or `async.await`
   // ops, add the region's last `gpu.wait` op to the worklist if it is
   // synchronous and is the last op with side effects.
   void operator()(async::ExecuteOp executeOp) {
     if (!areAllUsersExecuteOrAwait(executeOp.token()))
void operator()(async::ExecuteOp executeOp) {
     }
   }
 
   // The destructor performs the actual rewrite work.
   ~DeferWaitCallback() {
     for (size_t i = 0; i < worklist.size(); ++i) {
       auto waitOp = worklist[i];
       auto executeOp = waitOp->getParentOfType<async::ExecuteOp>();
-      auto numDependencies = waitOp.asyncDependencies().size();
 
-      // Erase `gpu.wait` and return async dependencies from region instead.
-      auto &yieldOp = executeOp.getBody()->getOperations().back();
-      yieldOp.insertOperands(yieldOp.getNumOperands(),
-                             waitOp.asyncDependencies());
+      // Erase `gpu.wait` and return async dependencies from execute op instead.
+      SmallVector<Value, 4> dependencies = waitOp.asyncDependencies();
       waitOp.erase();
-      auto asyncTokens = addAsyncTokenResults(executeOp, numDependencies);
+      executeOp = addExecuteResults(executeOp, dependencies);
 
       // Add the async dependency to each user of the `async.execute` token.
+      auto asyncTokens = executeOp.getResults().take_back(dependencies.size());
       for (Operation *user : executeOp.token().getUsers())
         addAsyncDependencyAfter(asyncTokens, user);
     }
   }
 
 private:
-  // Append `count` `!async.value<!gpu.async.token>` results to `executeOp`.
-  static ValueRange addAsyncTokenResults(async::ExecuteOp &executeOp,
-                                         unsigned count) {
-    auto numResults = executeOp.getNumResults() + count;
-
-    // Construct new result type list with `count` additional types.
-    SmallVector<Type, 2> resultTypes;
-    resultTypes.reserve(numResults);
-    transform(executeOp.getResultTypes(), std::back_inserter(resultTypes),
-              [](Type type) {
-                // Extract value type from !async.value.
-                if (auto valueType = type.dyn_cast<async::ValueType>())
-                  return valueType.getValueType();
-                assert(type.isa<async::TokenType>() && "expected token type");
-                return type;
-              });
-    OpBuilder builder(executeOp);
-    auto tokenType = builder.getType<gpu::AsyncTokenType>();
-    resultTypes.resize(numResults, tokenType);
-
-    // Clone executeOp with the extra `!gpu.async.token` results.
-    auto newOp = builder.create<async::ExecuteOp>(
-        executeOp.getLoc(), TypeRange{resultTypes}.drop_front() /*drop token*/,
-        executeOp.dependencies(), executeOp.operands());
-    BlockAndValueMapping mapper;
-    newOp.getRegion().getBlocks().clear();
-    executeOp.getRegion().cloneInto(&newOp.getRegion(), mapper);
-
-    // Replace executeOp with cloned one.
-    executeOp.getOperation()->replaceAllUsesWith(
-        newOp.getResults().drop_back(count));
-    executeOp.erase();
-    executeOp = newOp;
-
-    // Return the new result values.
-    return executeOp.getResults().take_back(count);
-  }
-
   // Returns whether all token users are either 'async.execute' or 'async.await'
   // ops. This is used as a requirement for pushing 'gpu.wait' ops from a
   // 'async.execute' body to it's users. Specifically, we do not allow
   // terminator users, because it could mean that the `async.execute` is inside
   // control flow code.
   static bool areAllUsersExecuteOrAwait(Value token) {
-    return llvm::all_of(token.getUsers(), [](Operation *user) {
+    return !token.use_empty() &&
+           llvm::all_of(token.getUsers(), [](Operation *user) {
              return isa<async::ExecuteOp, async::AwaitOp>(user);
            });
   }
 
   // Add the `asyncToken` as dependency as needed after `op`.
   void addAsyncDependencyAfter(ValueRange asyncTokens, Operation *op) {
     OpBuilder builder(op->getContext());
     auto loc = op->getLoc();
 
     Block::iterator it;
void addAsyncDependencyAfter(ValueRange asyncTokens, Operation *op) {
     if (executeOp && areAllUsersExecuteOrAwait(executeOp.token()) &&
         !it->getNextNode())
       worklist.push_back(waitOp);
   }
 
   SmallVector<gpu::WaitOp, 8> worklist;
 };
 
+// Callback for `async.execute` ops which repeats !gpu.async.token results
+// so that each of them is only used once.
+struct GpuAsyncRegionPass::SingleTokenUseCallback {
+  void operator()(async::ExecuteOp executeOp) {
+    // !gpu.async.token results which have multiple uses.
+    auto multiUseResults =
+        llvm::make_filter_range(executeOp.results(), [](OpResult result) {
+          if (result.use_empty() || result.hasOneUse())
+            return false;
+          auto valueType = result.getType().dyn_cast<async::ValueType>();
+          return valueType &&
+                 valueType.getValueType().isa<gpu::AsyncTokenType>();
+        });
+    if (multiUseResults.empty())
+      return;
+
+    // Index within !async.execute results (that is, without the async.token).
+    SmallVector<int, 4> indices;
+    transform(multiUseResults, std::back_inserter(indices),
+              [](OpResult result) {
+                return result.getResultNumber() - 1; // Index witout token.
+              });
+
+    for (auto index : indices) {
+      assert(!executeOp.results()[index].getUses().empty());
+      // Repeat async.yield token result, one for each use after the first one.
+      auto uses = llvm::drop_begin(executeOp.results()[index].getUses());
+      auto count = std::distance(uses.begin(), uses.end());
+      auto yieldOp = cast<async::YieldOp>(executeOp.getBody()->getTerminator());
+      SmallVector<Value, 4> results(count, yieldOp.getOperand(index));
+      executeOp = addExecuteResults(executeOp, results);
+      // Update uses and results after replacing executeOp.
+      uses = llvm::drop_begin(executeOp.results()[index].getUses());
+      results = executeOp.results().take_back(count);
+      for (auto pair : llvm::zip(uses, results))
+        std::get<0>(pair).set(std::get<1>(pair));
+    }
+  }
+};
+
 // Replaces synchronous GPU ops in the op's region with asynchronous ones and
 // inserts the necessary synchronization (as gpu.wait ops). Assumes sequential
 // execution semantics and that no GPU ops are asynchronous yet.
 void GpuAsyncRegionPass::runOnFunction() {
   if (getFunction()
           .getRegion()
           .walk(ThreadTokenCallback(getContext()))
           .wasInterrupted())
     return signalPassFailure();
 
   // Collect gpu.wait ops that we can move out of async.execute regions.
   getFunction().getRegion().walk(DeferWaitCallback());
+  // Makes each !gpu.async.token returned from async.execute op have single use.
+  getFunction().getRegion().walk(SingleTokenUseCallback());
 }
 
 std::unique_ptr<OperationPass<FuncOp>> mlir::createGpuAsyncRegionPass() {
   return std::make_unique<GpuAsyncRegionPass>();
 }

mlir/test/Conversion/GPUCommon/lower-wait-to-gpu-runtime-calls.mlir

 // RUN: mlir-opt %s --gpu-to-llvm | FileCheck %s
 
 module attributes {gpu.container_module} {
 
   func @foo() {
     // CHECK: %[[t0:.*]] = llvm.call @mgpuStreamCreate
     // CHECK: %[[e0:.*]] = llvm.call @mgpuEventCreate
     // CHECK: llvm.call @mgpuEventRecord(%[[e0]], %[[t0]])
     %t0 = gpu.wait async
     // CHECK: %[[t1:.*]] = llvm.call @mgpuStreamCreate
     // CHECK: llvm.call @mgpuStreamWaitEvent(%[[t1]], %[[e0]])
     // CHECK: llvm.call @mgpuEventDestroy(%[[e0]])
     %t1 = gpu.wait async [%t0]
     // CHECK: llvm.call @mgpuStreamSynchronize(%[[t0]])
-    // CHECK: llvm.call @mgpuStreamSynchronize(%[[t1]])
     // CHECK: llvm.call @mgpuStreamDestroy(%[[t0]])
+    // CHECK: llvm.call @mgpuStreamSynchronize(%[[t1]])
     // CHECK: llvm.call @mgpuStreamDestroy(%[[t1]])
     gpu.wait [%t0, %t1]
     return
   }
 }

mlir/test/Dialect/GPU/async-region.mlir

func @async_execute_with_result(%sz : index) -> index {
     // CHECK: %[[t:.*]] = async.await %[[f0]]#1 : !async.value<!gpu.async.token>
     // CHECK: gpu.wait [%[[t]]]
     async.await %a0 : !async.token
     // CHECK: %[[x:.*]] = async.await %[[f0]]#0 : !async.value<index>
     %x = async.await %f0 : !async.value<index>
     // CHECK: return %[[x]] : index
     return %x : index
   }
+
+  // CHECK-LABEL:func @async_execute_no_use(%{{.*}}: index)
+  func @async_execute_no_use(%sz : index) {
+    // CHECK: async.execute {
+    %a0 = async.execute {
+      // CHECK: %[[t:.*]] = gpu.launch_func async
+      gpu.launch_func @kernels::@kernel
+          blocks in (%sz, %sz, %sz) threads in (%sz, %sz, %sz)
+      // CHECK: gpu.wait [%[[t]]]
+      async.yield
+    }
+    return
+  }
+
+  // CHECK-LABEL:func @async_execute_fork(%{{.*}}: index)
+  func @async_execute_fork(%sz : index) {
+    // CHECK: %[[a0:.*]], %[[f0:.*]]:2 = async.execute
+    // CHECK-SAME: -> (!async.value<!gpu.async.token>, !async.value<!gpu.async.token>)
+    %a0 = async.execute {
+      // CHECK: %[[t:.*]] = gpu.launch_func async
+      gpu.launch_func @kernels::@kernel
+          blocks in (%sz, %sz, %sz) threads in (%sz, %sz, %sz)
+      // CHECK-NOT: gpu.wait
+      // CHECK: async.yield %[[t]], %[[t]] : !gpu.async.token, !gpu.async.token
+      async.yield
+    }
+    // CHECK: async.execute [%[[a0]]] (%[[f0]]#0 as {{.*}}: !async.value<!gpu.async.token>)
+    %a1 = async.execute [%a0] {
+      // CHECK: %[[t:.*]] = gpu.launch_func async
+      gpu.launch_func @kernels::@kernel
+          blocks in (%sz, %sz, %sz) threads in (%sz, %sz, %sz)
+      // CHECK: gpu.wait [%[[t]]]
+      async.yield
+    }
+    // CHECK: async.execute [%[[a0]]] (%[[f0]]#1 as {{.*}}: !async.value<!gpu.async.token>)
+    %a2 = async.execute [%a0] {
+      // CHECK: %[[t:.*]] = gpu.launch_func async
+      gpu.launch_func @kernels::@kernel
+          blocks in (%sz, %sz, %sz) threads in (%sz, %sz, %sz)
+      // CHECK: gpu.wait [%[[t]]]
+      async.yield
+    }
+    return
+  }
 }