[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

2 files changed, 31 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGCoroutine.cpp b/clang/lib/CodeGen/CGCoroutine.cpp
index f01237205f0..c09c63f04b8 100644
--- a/clang/lib/CodeGen/CGCoroutine.cpp
+++ b/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();
diff --git a/clang/lib/Sema/SemaCoroutine.cpp b/clang/lib/Sema/SemaCoroutine.cpp
index be89cd16deb..857dcda4e6e 100644
--- a/clang/lib/Sema/SemaCoroutine.cpp
+++ b/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;
 }