1 files changed, 24 insertions, 0 deletions
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 204858e..d07fb1e 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -5507,6 +5507,30 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
         Attrs.addFnAttribute(getLLVMContext(), llvm::Attribute::AlwaysInline);
   }
 
+  // The await_suspend call performed by co_await is essentially asynchronous
+  // to the execution of the coroutine. Inlining it normally into an unsplit
+  // coroutine can cause miscompilation because the coroutine CFG misrepresents
+  // the true control flow of the program: things that happen in the
+  // await_suspend are not guaranteed to happen prior to the resumption of the
+  // coroutine, and things that happen after the resumption of the coroutine
+  // (including its exit and the potential deallocation of the coroutine frame)
+  // are not guaranteed to happen only after the end of await_suspend.
+  //
+  // The short-term solution to this problem is to mark the call as uninlinable.
+  // But we don't want to do this if the call is known to be trivial, which is
+  // very common.
+  //
+  // The long-term solution may introduce patterns like:
+  //
+  //  call @llvm.coro.await_suspend(ptr %awaiter, ptr %handle,
+  //                                ptr @awaitSuspendFn)
+  //
+  // Then it is much easier to perform the safety analysis in the middle end.
+  // If it is safe to inline the call to awaitSuspend, we can replace it in the
+  // CoroEarly pass. Otherwise we could replace it in the CoroSplit pass.
+  if (inSuspendBlock() && mayCoroHandleEscape())
+    Attrs = Attrs.addFnAttribute(getLLVMContext(), llvm::Attribute::NoInline);
+
   // Disable inlining inside SEH __try blocks.
   if (isSEHTryScope()) {
     Attrs = Attrs.addFnAttribute(getLLVMContext(), llvm::Attribute::NoInline);