[coroutines] Wrap the body of the coroutine in try-catch

Summary:
If unhandled_exception member function is present in the coroutine promise,
wrap the body of the coroutine in:

```
try {
  body
} catch(...) { promise.unhandled_exception(); }
```

Reviewers: EricWF, rnk, rsmith

Reviewed By: rsmith

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D31692

llvm-svn: 303583

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -8960,6 +8960,8 @@ def warn_coroutine_promise_unhandled_exception_required_with_exceptions : Warnin
   InGroup<CoroutineMissingUnhandledException>;
 def err_coroutine_promise_get_return_object_on_allocation_failure : Error<
   "%0: 'get_return_object_on_allocation_failure()' must be a static member function">;
+def err_seh_in_a_coroutine_with_cxx_exceptions : Error<
+  "cannot use SEH '__try' in a coroutine when C++ exceptions are enabled">;
 def err_coroutine_promise_new_requires_nothrow : Error<
   "%0 is required to have a non-throwing noexcept specification when the promise "
    "type declares 'get_return_object_on_allocation_failure()'">;

clang/lib/CodeGen/CGCoroutine.cpp

@@ -270,6 +270,15 @@ struct CallCoroDelete final : public EHScopeStack::Cleanup {
 };
 }
 
+static void emitBodyAndFallthrough(CodeGenFunction &CGF,
+                                   const CoroutineBodyStmt &S, Stmt *Body) {
+  CGF.EmitStmt(Body);
+  const bool CanFallthrough = CGF.Builder.GetInsertBlock();
+  if (CanFallthrough)
+    if (Stmt *OnFallthrough = S.getFallthroughHandler())
+      CGF.EmitStmt(OnFallthrough);
+}
+
 void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {
   auto *NullPtr = llvm::ConstantPointerNull::get(Builder.getInt8PtrTy());
   auto &TI = CGM.getContext().getTargetInfo();
@@ -318,7 +327,19 @@ void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {
     // FIXME: Emit initial suspend and more before the body.
 
     CurCoro.Data->CurrentAwaitKind = AwaitKind::Normal;
-    EmitStmt(S.getBody());
+
+    if (auto *OnException = S.getExceptionHandler()) {
+      auto Loc = S.getLocStart();
+      CXXCatchStmt Catch(Loc, /*exDecl=*/nullptr, OnException);
+      auto *TryStmt = CXXTryStmt::Create(getContext(), Loc, S.getBody(), &Catch);
+
+      EnterCXXTryStmt(*TryStmt);
+      emitBodyAndFallthrough(*this, S, TryStmt->getTryBlock());
+      ExitCXXTryStmt(*TryStmt);
+    }
+    else {
+      emitBodyAndFallthrough(*this, S, S.getBody());
+    }
 
     // See if we need to generate final suspend.
     const bool CanFallthrough = Builder.GetInsertBlock();

clang/lib/Sema/SemaCoroutine.cpp

@@ -1043,6 +1043,15 @@ bool CoroutineStmtBuilder::makeOnException() {
   if (UnhandledException.isInvalid())
     return false;
 
+  // Since the body of the coroutine will be wrapped in try-catch, it will
+  // be incompatible with SEH __try if present in a function.
+  if (!S.getLangOpts().Borland && Fn.FirstSEHTryLoc.isValid()) {
+    S.Diag(Fn.FirstSEHTryLoc, diag::err_seh_in_a_coroutine_with_cxx_exceptions);
+    S.Diag(Fn.FirstCoroutineStmtLoc, diag::note_declared_coroutine_here)
+        << Fn.getFirstCoroutineStmtKeyword();
+    return false;
+  }
+
   this->OnException = UnhandledException.get();
   return true;
 }

clang/test/CodeGenCoroutines/coro-cleanup.cpp

@@ -6,38 +6,38 @@ template <typename... T> struct coroutine_traits;
 
 template <class Promise = void> struct coroutine_handle {
   coroutine_handle() = default;
-  static coroutine_handle from_address(void *) { return {}; }
+  static coroutine_handle from_address(void *) noexcept;
 };
 template <> struct coroutine_handle<void> {
-  static coroutine_handle from_address(void *) { return {}; }
+  static coroutine_handle from_address(void *) noexcept;
   coroutine_handle() = default;
   template <class PromiseType>
-  coroutine_handle(coroutine_handle<PromiseType>) {}
+  coroutine_handle(coroutine_handle<PromiseType>) noexcept;
 };
 }
 
 struct suspend_always {
-  bool await_ready();
-  void await_suspend(std::experimental::coroutine_handle<>);
-  void await_resume();
+  bool await_ready() noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
+  void await_resume() noexcept;
 };
 
 template <> struct std::experimental::coroutine_traits<void> {
   struct promise_type {
-    void get_return_object();
-    suspend_always initial_suspend();
-    suspend_always final_suspend();
-    void return_void();
+    void get_return_object() noexcept;
+    suspend_always initial_suspend() noexcept;
+    suspend_always final_suspend() noexcept;
+    void return_void() noexcept;
     promise_type();
     ~promise_type();
-    void unhandled_exception();
+    void unhandled_exception() noexcept;
   };
 };
 
 struct Cleanup { ~Cleanup(); };
 void may_throw();
 
-// CHECK: define void @_Z1fv(
+// CHECK-LABEL: define void @_Z1fv(
 void f() {
   // CHECK: call i8* @_Znwm(i64
 
@@ -52,23 +52,46 @@ void f() {
   // if may_throw throws, check that we destroy the promise and free the memory.
 
   // CHECK: invoke void @_Z9may_throwv(
-  // CHECK-NEXT: to label %{{.+}} unwind label %[[PromDtorPad:.+]]
+  // CHECK-NEXT: to label %{{.+}} unwind label %[[CatchPad:.+]]
 
   // CHECK: [[DeallocPad]]:
   // CHECK-NEXT: landingpad
   // CHECK-NEXT:   cleanup
   // CHECK: br label %[[Dealloc:.+]]
 
-  // CHECK: [[PromDtorPad]]:
-  // CHECK-NEXT: landingpad
-  // CHECK-NEXT:   cleanup
-  // CHECK: call void @_ZN7CleanupD1Ev(%struct.Cleanup*
+  // CHECK: [[CatchPad]]:
+  // CHECK-NEXT:  landingpad
+  // CHECK-NEXT:       catch i8* null
+  // CHECK:  call void @_ZN7CleanupD1Ev(
+  // CHECK:  br label %[[Catch:.+]]
+
+  // CHECK: [[Catch]]:
+  // CHECK:    call i8* @__cxa_begin_catch(
+  // CHECK:    call void @_ZNSt12experimental16coroutine_traitsIJvEE12promise_type19unhandled_exceptionEv(
+  // CHECK:    invoke void @__cxa_end_catch()
+  // CHECK-NEXT:    to label %[[Cont:.+]] unwind
+
+  // CHECK: [[Cont]]:
+  // CHECK-NEXT: br label %[[Cont2:.+]]
+  // CHECK: [[Cont2]]:
+  // CHECK-NEXT: br label %[[Cleanup:.+]]
+
+  // CHECK: [[Cleanup]]:
   // CHECK: call void @_ZNSt12experimental16coroutine_traitsIJvEE12promise_typeD1Ev(
-  // CHECK: br label %[[Dealloc]]
+  // CHECK: %[[Mem0:.+]] = call i8* @llvm.coro.free(
+  // CHECK: call void @_ZdlPv(i8* %[[Mem0]]
 
   // CHECK: [[Dealloc]]:
   // CHECK:   %[[Mem:.+]] = call i8* @llvm.coro.free(
   // CHECK:   call void @_ZdlPv(i8* %[[Mem]])
 
   co_return;
 }
+
+// CHECK-LABEL: define void @_Z1gv(
+void g() {
+  for (;;)
+    co_await suspend_always{};
+  // Since this is the endless loop there should be no fallthrough handler (call to 'return_void').
+  // CHECK-NOT: call void @_ZNSt12experimental16coroutine_traitsIJvEE12promise_type11return_voidEv
+}

clang/test/CodeGenCoroutines/coro-eh-cleanup.cpp

@@ -51,7 +51,13 @@ coro_t f() {
 // CHECK: [[EHCLEANUP]]:
 // CHECK:   %[[INNERPAD:.+]] = cleanuppad within none []
 // CHECK:   call void @"\01??_DCleanup@@QEAAXXZ"(
-// CHECK:   cleanupret from %[[INNERPAD]] unwind label %[[COROENDBB:.+]]
+// CHECK:   cleanupret from %4 unwind label %[[CATCHDISPATCH:.+]]
+
+// CHECK: [[CATCHDISPATCH]]:
+// CHECK:   catchswitch within none [label %[[CATCHPAD:.+]]] unwind label %[[COROENDBB:.+]]
+// CHECK: [[CATCHPAD]]:
+// CHECK:   call void @"\01?unhandled_exception@promise_type@coro_t@@QEAAXXZ"
+
 // CHECK: [[COROENDBB]]:
 // CHECK-NEXT: %[[CLPAD:.+]] = cleanuppad within none
 // CHECK-NEXT: call i1 @llvm.coro.end(i8* null, i1 true) [ "funclet"(token %[[CLPAD]]) ]
@@ -62,8 +68,14 @@ coro_t f() {
 // CHECK-LPAD:       to label %[[CONT:.+]] unwind label %[[EHCLEANUP:.+]]
 // CHECK-LPAD: [[EHCLEANUP]]:
 // CHECK-LPAD:    landingpad { i8*, i32 }
-// CHECK-LPAD:          cleanup
+// CHECK-LPAD:          catch
 // CHECK-LPAD:   call void @_ZN7CleanupD1Ev(
+// CHECK-LPAD:   call i8* @__cxa_begin_catch
+// CHECK-LPAD:   call void @_ZN6coro_t12promise_type19unhandled_exceptionEv
+// CHECK-LPAD:   invoke void @__cxa_end_catch()
+// CHECK-LPAD:             to label %{{.+}} unwind label %[[UNWINDBB:.+]]
+
+// CHECK-LPAD: [[UNWINDBB]]:
 // CHECK-LPAD:   %[[I1RESUME:.+]] = call i1 @llvm.coro.end(i8* null, i1 true)
 // CHECK-LPAD:   br i1  %[[I1RESUME]], label %[[EHRESUME:.+]], label
 // CHECK-LPAD: [[EHRESUME]]:

clang/test/SemaCXX/coroutine-seh.cpp

@@ -0,0 +1,37 @@
+// RUN: %clang_cc1 -std=c++1z -fcoroutines-ts -verify %s -fcxx-exceptions -fexceptions -triple x86_64-windows-msvc -fms-extensions
+namespace std::experimental {
+template <typename... T> struct coroutine_traits;
+
+template <class Promise = void> struct coroutine_handle {
+  coroutine_handle() = default;
+  static coroutine_handle from_address(void *) noexcept;
+};
+template <> struct coroutine_handle<void> {
+  static coroutine_handle from_address(void *) noexcept;
+  coroutine_handle() = default;
+  template <class PromiseType>
+  coroutine_handle(coroutine_handle<PromiseType>) noexcept;
+};
+}
+
+struct suspend_always {
+  bool await_ready() noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
+  void await_resume() noexcept;
+};
+
+template <> struct std::experimental::coroutine_traits<void> {
+  struct promise_type {
+    void get_return_object() noexcept;
+    suspend_always initial_suspend() noexcept;
+    suspend_always final_suspend() noexcept;
+    void return_void() noexcept;
+    void unhandled_exception() noexcept;
+  };
+};
+
+void SEH_used() {
+  __try { // expected-error {{cannot use SEH '__try' in a coroutine when C++ exceptions are enabled}}
+    co_return; // expected-note {{function is a coroutine due to use of 'co_return' here}}
+  } __except(0) {}
+}