[coroutines] Add coro.end handling

[GorNishanov]

Summary

For WinEH, We add a funclet bundle to a coro.end call, so that CoroSplit in LLVM can replace it with cleanup ret and cut the rest out.
For landing pad, we add a branch to resume block if coro.end returns true.

LLVM Part: https://reviews.llvm.org/D25445

[majnemer]

Can we have a test for this?

lib/CodeGen/CGCoroutine.cpp

436 ↗

(On Diff #74158)

auto *

440 ↗

(On Diff #74158)

You could just do CGF.Builder.getTrue()

[GorNishanov]

Added a dedicated test, addressed comments in CGCoroutine.cpp

(This does not go into clang branch yet, there are many more patches to filter through @rsmith :) .)

[mehdi_amini]

LLVM-commits wasn't added on creation of this revision.

[GorNishanov]

In D25444#568531, @mehdi_amini wrote:

LLVM-commits wasn't added on creation of this revision.

I was mostly looking for a sanity check of the this direction. Over the weekend, David and I discussed several alternatives how we can handle the exceptional cleanup paths and trim unneeded ones with coro.end.

This CR is an attempt to show how a particular way of solving the problem might look. This is not meant to be checked-in to clang trunk yet, hence, no llvm-commit tag. When the time comes, I will create a dedicated commit for it with llvm-commits added during creation.

[mehdi_amini]

OK, all is well then :)

[GorNishanov]

In D25444#568551, @mehdi_amini wrote:

OK, all is well then :)

:)

The problem was that one approach (bundles) worked really well for WinEH, another, explicit control flow and bool returning coro.end with explicit control flow doing a jump to ehresume block worked great for landingpad EH model.

After a few unsuccessful attempts to have a grand unified model, I ended up with aesthetically unsatisfying, but, codewise quite simple hybrid approach where I do bundles for WinEH and explicit control flow for landing pad model.

[majnemer]

LGTM

[GorNishanov]

Preparing to land

cfe/trunk/lib/CodeGen/CGCoroutine.cpp

 }
 
 void CodeGenFunction::EmitCoreturnStmt(CoreturnStmt const &S) {
   ++CurCoro.Data->CoreturnCount;
   EmitStmt(S.getPromiseCall());
   EmitBranchThroughCleanup(CurCoro.Data->FinalJD);
 }
 
+// For WinEH exception representation backend need to know what funclet coro.end
+// belongs to. That information is passed in a funclet bundle.
+static SmallVector<llvm::OperandBundleDef, 1>
+getBundlesForCoroEnd(CodeGenFunction &CGF) {
+  SmallVector<llvm::OperandBundleDef, 1> BundleList;
+
+  if (llvm::Instruction *EHPad = CGF.CurrentFuncletPad)
+    BundleList.emplace_back("funclet", EHPad);
+
+  return BundleList;
+}
+
+namespace {
+// We will insert coro.end to cut any of the destructors for objects that
+// do not need to be destroyed once the coroutine is resumed.
+// See llvm/docs/Coroutines.rst for more details about coro.end.
+struct CallCoroEnd final : public EHScopeStack::Cleanup {
+  void Emit(CodeGenFunction &CGF, Flags flags) override {
+    auto &CGM = CGF.CGM;
+    auto *NullPtr = llvm::ConstantPointerNull::get(CGF.Int8PtrTy);
+    llvm::Function *CoroEndFn = CGM.getIntrinsic(llvm::Intrinsic::coro_end);
+    // See if we have a funclet bundle to associate coro.end with. (WinEH)
+    auto Bundles = getBundlesForCoroEnd(CGF);
+    auto *CoroEnd = CGF.Builder.CreateCall(
+        CoroEndFn, {NullPtr, CGF.Builder.getTrue()}, Bundles);
+    if (Bundles.empty()) {
+      // Otherwise, (landingpad model), create a conditional branch that leads
+      // either to a cleanup block or a block with EH resume instruction.
+      auto *ResumeBB = CGF.getEHResumeBlock(/*cleanup=*/true);
+      auto *CleanupContBB = CGF.createBasicBlock("cleanup.cont");
+      CGF.Builder.CreateCondBr(CoroEnd, ResumeBB, CleanupContBB);
+      CGF.EmitBlock(CleanupContBB);
+    }
+  }
+};
+}
+
 namespace {
 // Make sure to call coro.delete on scope exit.
 struct CallCoroDelete final : public EHScopeStack::Cleanup {
   Stmt *Deallocate;
 
   // TODO: Wrap deallocate in if(coro.free(...)) Deallocate.
   void Emit(CodeGenFunction &CGF, Flags) override {
     // Note: That deallocation will be emitted twice: once for a normal exit and
void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {
 
   CurCoro.Data->CleanupJD = getJumpDestInCurrentScope(RetBB);
   {
     CodeGenFunction::RunCleanupsScope ResumeScope(*this);
     EHStack.pushCleanup<CallCoroDelete>(NormalAndEHCleanup, S.getDeallocate());
 
     EmitStmt(S.getPromiseDeclStmt());
 
+    EHStack.pushCleanup<CallCoroEnd>(EHCleanup);
+
     CurCoro.Data->FinalJD = getJumpDestInCurrentScope(FinalBB);
 
     // FIXME: Emit initial suspend and more before the body.
 
     CurCoro.Data->CurrentAwaitKind = AwaitKind::Normal;
     EmitStmt(S.getBody());
 
     // See if we need to generate final suspend.
     const bool CanFallthrough = Builder.GetInsertBlock();
     const bool HasCoreturns = CurCoro.Data->CoreturnCount > 0;
     if (CanFallthrough || HasCoreturns) {
       EmitBlock(FinalBB);
       // FIXME: Emit final suspend.
     }
   }
 
   EmitBlock(RetBB);
+  llvm::Function *CoroEnd = CGM.getIntrinsic(llvm::Intrinsic::coro_end);
+  Builder.CreateCall(CoroEnd, {NullPtr, Builder.getFalse()});
 
   // FIXME: Emit return for the coroutine return object.
 }
 
 // Emit coroutine intrinsic and patch up arguments of the token type.
 RValue CodeGenFunction::EmitCoroutineIntrinsic(const CallExpr *E,
                                                unsigned int IID) {
   SmallVector<llvm::Value *, 8> Args;

cfe/trunk/test/CodeGenCoroutines/coro-eh-cleanup.cpp

+// RUN: %clang_cc1 -std=c++1z -fcoroutines-ts -triple=x86_64-pc-windows-msvc18.0.0 -emit-llvm %s -o - -fexceptions -fcxx-exceptions -disable-llvm-passes | FileCheck %s
+// RUN: %clang_cc1 -std=c++1z -fcoroutines-ts -triple=x86_64-unknown-linux-gnu -emit-llvm -o - %s -fexceptions -fcxx-exceptions -disable-llvm-passes | FileCheck --check-prefix=CHECK-LPAD %s
+
+namespace std::experimental {
+template <typename R, typename... T> struct coroutine_traits {
+  using promise_type = typename R::promise_type;
+};
+
+template <class Promise = void> struct coroutine_handle;
+
+template <> struct coroutine_handle<void> {
+  static coroutine_handle from_address(void *) noexcept;
+  coroutine_handle() = default;
+  template <class PromiseType>
+  coroutine_handle(coroutine_handle<PromiseType>) noexcept;
+};
+template <class Promise> struct coroutine_handle: coroutine_handle<void> {
+  coroutine_handle() = default;
+  static coroutine_handle from_address(void *) noexcept;
+};
+}
+
+struct suspend_always {
+  bool await_ready() noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
+  void await_resume() noexcept;
+};
+
+struct coro_t {
+  struct promise_type {
+    coro_t get_return_object() noexcept;
+    suspend_always initial_suspend() noexcept;
+    suspend_always final_suspend() noexcept;
+    void return_void() noexcept;
+    void unhandled_exception() noexcept;
+  };
+};
+
+struct Cleanup { ~Cleanup(); };
+void may_throw();
+
+coro_t f() {
+  Cleanup x;
+  may_throw();
+  co_return;
+}
+
+// CHECK: @"\01?f@@YA?AUcoro_t@@XZ"(
+// CHECK:   invoke void @"\01?may_throw@@YAXXZ"()
+// CHECK:       to label %[[CONT:.+]] unwind label %[[EHCLEANUP:.+]]
+// CHECK: [[EHCLEANUP]]:
+// CHECK:   %[[INNERPAD:.+]] = cleanuppad within none []
+// CHECK:   call void @"\01??_DCleanup@@QEAAXXZ"(
+// CHECK:   cleanupret from %[[INNERPAD]] unwind label %[[COROENDBB:.+]]
+// CHECK: [[COROENDBB]]:
+// CHECK-NEXT: %[[CLPAD:.+]] = cleanuppad within none
+// CHECK-NEXT: call i1 @llvm.coro.end(i8* null, i1 true) [ "funclet"(token %[[CLPAD]]) ]
+// CHECK-NEXT: cleanupret from %[[CLPAD]] unwind label
+
+// CHECK-LPAD: @_Z1fv(
+// CHECK-LPAD:   invoke void @_Z9may_throwv()
+// CHECK-LPAD:       to label %[[CONT:.+]] unwind label %[[EHCLEANUP:.+]]
+// CHECK-LPAD: [[EHCLEANUP]]:
+// CHECK-LPAD:    landingpad { i8*, i32 }
+// CHECK-LPAD:          cleanup
+// CHECK-LPAD:   call void @_ZN7CleanupD1Ev(
+// CHECK-LPAD:   %[[I1RESUME:.+]] = call i1 @llvm.coro.end(i8* null, i1 true)
+// CHECK-LPAD:   br i1  %[[I1RESUME]], label %[[EHRESUME:.+]], label
+// CHECK-LPAD: [[EHRESUME]]:
+// CHECK-LPAD-NEXT:  %[[exn:.+]] = load i8*, i8** %exn.slot, align 8
+// CHECK-LPAD-NEXT:  %[[sel:.+]] = load i32, i32* %ehselector.slot, align 4
+// CHECK-LPAD-NEXT:  %[[val1:.+]] = insertvalue { i8*, i32 } undef, i8* %[[exn]], 0
+// CHECK-LPAD-NEXT:  %[[val2:.+]] = insertvalue { i8*, i32 } %[[val1]], i32 %[[sel]], 1
+// CHECK-LPAD-NEXT:  resume { i8*, i32 } %[[val2]]