[coroutines] Build fallthrough and set_exception statements.

Summary:
This patch adds semantic checking and building of the fall-through `co_return;` statement as well as the `p.set_exception(std::current_exception())` call for handling uncaught exceptions.

The fall-through statement is built and checked according to:
> [dcl.fct.def.coroutine]/4
> The unqualified-ids return_void and return_value are looked up in the scope of class P. If
> both are found, the program is ill-formed. If the unqualified-id return_void is found, flowing
> off the end of a coroutine is equivalent to a co_return with no operand. Otherwise, flowing off
> the end of a coroutine results in undefined behavior.

Similarly the `set_exception` call is only built when that unqualified-id is found in the scope of class P.

Additionally this patch adds fall-through warnings for non-void returning coroutines. Since it's surprising undefined behavior I thought it would be important to add the warning right away. 


Reviewers: majnemer, GorNishanov, rsmith

Subscribers: mehdi_amini, cfe-commits

Differential Revision: https://reviews.llvm.org/D25349

llvm-svn: 285271

1 files changed, 81 insertions, 5 deletions

diff --git a/clang/lib/Sema/SemaCoroutine.cpp b/clang/lib/Sema/SemaCoroutine.cpp
index 323878e2d57..5231e23c1c1 100644
--- a/clang/lib/Sema/SemaCoroutine.cpp
+++ b/clang/lib/Sema/SemaCoroutine.cpp
@@ -378,6 +378,34 @@ StmtResult Sema::BuildCoreturnStmt(SourceLocation Loc, Expr *E) {
   return Res;
 }
 
+static ExprResult buildStdCurrentExceptionCall(Sema &S, SourceLocation Loc) {
+  NamespaceDecl *Std = S.getStdNamespace();
+  if (!Std) {
+    S.Diag(Loc, diag::err_implied_std_current_exception_not_found);
+    return ExprError();
+  }
+  LookupResult Result(S, &S.PP.getIdentifierTable().get("current_exception"),
+                      Loc, Sema::LookupOrdinaryName);
+  if (!S.LookupQualifiedName(Result, Std)) {
+    S.Diag(Loc, diag::err_implied_std_current_exception_not_found);
+    return ExprError();
+  }
+
+  // FIXME The STL is free to provide more than one overload.
+  FunctionDecl *FD = Result.getAsSingle<FunctionDecl>();
+  if (!FD) {
+    S.Diag(Loc, diag::err_malformed_std_current_exception);
+    return ExprError();
+  }
+  ExprResult Res = S.BuildDeclRefExpr(FD, FD->getType(), VK_LValue, Loc);
+  Res = S.ActOnCallExpr(/*Scope*/ nullptr, Res.get(), Loc, None, Loc);
+  if (Res.isInvalid()) {
+    S.Diag(Loc, diag::err_malformed_std_current_exception);
+    return ExprError();
+  }
+  return Res;
+}
+
 void Sema::CheckCompletedCoroutineBody(FunctionDecl *FD, Stmt *&Body) {
   FunctionScopeInfo *Fn = getCurFunction();
   assert(Fn && !Fn->CoroutineStmts.empty() && "not a coroutine");
@@ -432,10 +460,59 @@ void Sema::CheckCompletedCoroutineBody(FunctionDecl *FD, Stmt *&Body) {
   if (FinalSuspend.isInvalid())
     return FD->setInvalidDecl();
 
-  // FIXME: Perform analysis of set_exception call.
-
-  // FIXME: Try to form 'p.return_void();' expression statement to handle
+  // Try to form 'p.return_void();' expression statement to handle
   // control flowing off the end of the coroutine.
+  // Also try to form 'p.set_exception(std::current_exception());' to handle
+  // uncaught exceptions.
+  ExprResult SetException;
+  StmtResult Fallthrough;
+  if (Fn->CoroutinePromise &&
+      !Fn->CoroutinePromise->getType()->isDependentType()) {
+    CXXRecordDecl *RD = Fn->CoroutinePromise->getType()->getAsCXXRecordDecl();
+    assert(RD && "Type should have already been checked");
+    // [dcl.fct.def.coroutine]/4
+    // The unqualified-ids 'return_void' and 'return_value' are looked up in
+    // the scope of class P. If both are found, the program is ill-formed.
+    DeclarationName RVoidDN = PP.getIdentifierInfo("return_void");
+    LookupResult RVoidResult(*this, RVoidDN, Loc, Sema::LookupMemberName);
+    const bool HasRVoid = LookupQualifiedName(RVoidResult, RD);
+
+    DeclarationName RValueDN = PP.getIdentifierInfo("return_value");
+    LookupResult RValueResult(*this, RValueDN, Loc, Sema::LookupMemberName);
+    const bool HasRValue = LookupQualifiedName(RValueResult, RD);
+
+    if (HasRVoid && HasRValue) {
+      // FIXME Improve this diagnostic
+      Diag(FD->getLocation(), diag::err_coroutine_promise_return_ill_formed)
+          << RD;
+      return FD->setInvalidDecl();
+    } else if (HasRVoid) {
+      // If the unqualified-id return_void is found, flowing off the end of a
+      // coroutine is equivalent to a co_return with no operand. Otherwise,
+      // flowing off the end of a coroutine results in undefined behavior.
+      Fallthrough = BuildCoreturnStmt(FD->getLocation(), nullptr);
+      Fallthrough = ActOnFinishFullStmt(Fallthrough.get());
+      if (Fallthrough.isInvalid())
+        return FD->setInvalidDecl();
+    }
+
+    // [dcl.fct.def.coroutine]/3
+    // The unqualified-id set_exception is found in the scope of P by class
+    // member access lookup (3.4.5).
+    DeclarationName SetExDN = PP.getIdentifierInfo("set_exception");
+    LookupResult SetExResult(*this, SetExDN, Loc, Sema::LookupMemberName);
+    if (LookupQualifiedName(SetExResult, RD)) {
+      // Form the call 'p.set_exception(std::current_exception())'
+      SetException = buildStdCurrentExceptionCall(*this, Loc);
+      if (SetException.isInvalid())
+        return FD->setInvalidDecl();
+      Expr *E = SetException.get();
+      SetException = buildPromiseCall(*this, Fn, Loc, "set_exception", E);
+      SetException = ActOnFinishFullExpr(SetException.get(), Loc);
+      if (SetException.isInvalid())
+        return FD->setInvalidDecl();
+    }
+  }
 
   // Build implicit 'p.get_return_object()' expression and form initialization
   // of return type from it.
@@ -462,6 +539,5 @@ void Sema::CheckCompletedCoroutineBody(FunctionDecl *FD, Stmt *&Body) {
   // Build body for the coroutine wrapper statement.
   Body = new (Context) CoroutineBodyStmt(
       Body, PromiseStmt.get(), InitialSuspend.get(), FinalSuspend.get(),
-      /*SetException*/nullptr, /*Fallthrough*/nullptr,
-      ReturnObject.get(), ParamMoves);
+      SetException.get(), Fallthrough.get(), ReturnObject.get(), ParamMoves);
 }