[Clang][Coroutines] Properly emit EH code for initial suspend await_resume

[yuxuanchen1997]

This change aims to fix an ICE in issue #63803

The crash happens in ExitCXXTryStmt because EmitAnyExpr() adds additional cleanup to the EHScopeStack. This messes up the assumption in ExitCXXTryStmt that the top of the stack should be a EHCatchScope.

However, since we never read a value returned from await_resume() of an init suspend, we can skip the part that builds this RValue.

The code here may not be in the best shape. There's another bug that memberCallExpressionCanThrow doesn't work on the current Expr due to type mismatch. I am preparing a separate PR to address it plus some refactoring might be beneficial.

[llvmbot]

@llvm/pr-subscribers-coroutines
@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-codegen

Author: Yuxuan Chen (yuxuanchen1997)

Changes

This change aims to fix an ICE in issue #63803

The crash happens in ExitCXXTryStmt because EmitAnyExpr() adds additional cleanup to the EHScopeStack. This messes up the assumption in ExitCXXTryStmt that the top of the stack should be a EHCatchScope.

However, since we never read a value returned from await_resume() of an init suspend, we can skip the part that builds this RValue.

---

Full diff: https://github.com/llvm/llvm-project/pull/73073.diff

2 Files Affected:

• (modified) clang/lib/CodeGen/CGCoroutine.cpp (+9-5)
• (added) clang/test/CodeGenCoroutines/coro-init-await-nontrivial-return.cpp (+49)

diff --git a/clang/lib/CodeGen/CGCoroutine.cpp b/clang/lib/CodeGen/CGCoroutine.cpp
index 7e449d5af3423cf..aaf122c0f83bc47 100644
--- a/clang/lib/CodeGen/CGCoroutine.cpp
+++ b/clang/lib/CodeGen/CGCoroutine.cpp
@@ -245,6 +245,15 @@ static LValueOrRValue emitSuspendExpression(CodeGenFunction &CGF, CGCoroData &Co
                                          FPOptionsOverride(), Loc, Loc);
     TryStmt = CXXTryStmt::Create(CGF.getContext(), Loc, TryBody, Catch);
     CGF.EnterCXXTryStmt(*TryStmt);
+    CGF.EmitStmt(TryBody);
+    // We don't use EmitCXXTryStmt here. We need to store to ResumeEHVar that
+    // doesn't exist in the body.
+    Builder.CreateFlagStore(false, Coro.ResumeEHVar);
+    CGF.ExitCXXTryStmt(*TryStmt);
+    LValueOrRValue Res;
+    // We are not supposed to obtain the value from init suspend await_resume().
+    Res.RV = RValue::getIgnored();
+    return Res;
   }
 
   LValueOrRValue Res;
@@ -253,11 +262,6 @@ static LValueOrRValue emitSuspendExpression(CodeGenFunction &CGF, CGCoroData &Co
   else
     Res.RV = CGF.EmitAnyExpr(S.getResumeExpr(), aggSlot, ignoreResult);
 
-  if (TryStmt) {
-    Builder.CreateFlagStore(false, Coro.ResumeEHVar);
-    CGF.ExitCXXTryStmt(*TryStmt);
-  }
-
   return Res;
 }
 
diff --git a/clang/test/CodeGenCoroutines/coro-init-await-nontrivial-return.cpp b/clang/test/CodeGenCoroutines/coro-init-await-nontrivial-return.cpp
new file mode 100644
index 000000000000000..78fc88a071d5c74
--- /dev/null
+++ b/clang/test/CodeGenCoroutines/coro-init-await-nontrivial-return.cpp
@@ -0,0 +1,49 @@
+// RUN: %clang_cc1 -std=c++20 -triple=x86_64-- -emit-llvm -fcxx-exceptions \
+// RUN:            -disable-llvm-passes %s -o - | FileCheck %s
+
+#include "Inputs/coroutine.h"
+
+struct NontrivialType {
+  ~NontrivialType() {}
+};
+
+struct Task {
+    struct promise_type;
+    using handle_type = std::coroutine_handle<promise_type>;
+
+    struct initial_suspend_awaiter {
+        bool await_ready() {
+            return false;
+        }
+
+        void await_suspend(handle_type h) {}
+
+        // Nontrivial type caused crash!
+        NontrivialType await_resume() noexcept {
+          return {};
+        }
+    };
+
+    struct promise_type {
+        void return_void() {}
+        void unhandled_exception() {}
+        initial_suspend_awaiter initial_suspend() { return {}; }
+        std::suspend_never final_suspend() noexcept { return {}; }
+        Task get_return_object() {
+            return Task{handle_type::from_promise(*this)};
+        }
+    };
+
+    handle_type handler;
+};
+
+Task coro_create() {
+    co_return;
+}
+
+// CHECK-LABEL: define{{.*}} ptr @_Z11coro_createv(
+// CHECK: init.ready:
+// CHECK-NEXT: store i1 true, ptr {{.*}}
+// CHECK-NEXT: call void @_ZN4Task23initial_suspend_awaiter12await_resumeEv(
+// CHECK-NEXT: call void @_ZN14NontrivialTypeD1Ev(
+// CHECK-NEXT: store i1 false, ptr {{.*}}

[ChuanqiXu9]

LGTM. Thanks.