[clang] [Clang] Coroutines code gen check for member call noexcept nested in a temp expr (PR #73160)

[Yuxuan Chen via cfe-commits]

https://github.com/yuxuanchen1997 created https://github.com/llvm/llvm-project/pull/73160

Previously we were not properly skipping the generation of the `try { }` block around the `init_suspend.await_resume()` if the `await_resume` is not returning void. The reason being that the resume expression was wrapped in a `CXXBindTemporaryExpr` and the first dyn_cast failed, silently ignoring the noexcept. This only mattered for `init_suspend` because it had its own try block.

This patch changes that to extract the sub expression when we see a `CXXBindTemporaryExpr`. Another version of this patch also wanted to assert by `cast<CXXMemberCallExpr>` and as far as I understand it should be a valid assumption. I can change to that if upstream prefers. 


>From c17522689ef4449d0c8c464dcdd3092c081c07e6 Mon Sep 17 00:00:00 2001
From: Yuxuan Chen <ych at meta.com>
Date: Tue, 21 Nov 2023 21:38:12 -0800
Subject: [PATCH] add checks for nested noexcept in cxxtempexpr

---
 clang/lib/CodeGen/CGCoroutine.cpp             | 14 ++++--
 .../coro-init-await-nontrivial-return.cpp     | 50 +++++++++++++++++--
 2 files changed, 58 insertions(+), 6 deletions(-)

diff --git a/clang/lib/CodeGen/CGCoroutine.cpp b/clang/lib/CodeGen/CGCoroutine.cpp
index aaf122c0f83bc47..724d471cc9d78b6 100644
--- a/clang/lib/CodeGen/CGCoroutine.cpp
+++ b/clang/lib/CodeGen/CGCoroutine.cpp
@@ -12,9 +12,10 @@
 
 #include "CGCleanup.h"
 #include "CodeGenFunction.h"
-#include "llvm/ADT/ScopeExit.h"
+#include "clang/AST/ExprCXX.h"
 #include "clang/AST/StmtCXX.h"
 #include "clang/AST/StmtVisitor.h"
+#include "llvm/ADT/ScopeExit.h"
 
 using namespace clang;
 using namespace CodeGen;
@@ -129,7 +130,14 @@ static SmallString<32> buildSuspendPrefixStr(CGCoroData &Coro, AwaitKind Kind) {
   return Prefix;
 }
 
-static bool memberCallExpressionCanThrow(const Expr *E) {
+static bool ResumeExprCanThrow(const CoroutineSuspendExpr &S) {
+  const Expr *E = S.getResumeExpr();
+
+  // If the return type of await_resume is not void, get the CXXMemberCallExpr
+  // from its subexpr.
+  if (const auto *BindTempExpr = dyn_cast<CXXBindTemporaryExpr>(E)) {
+    E = BindTempExpr->getSubExpr();
+  }
   if (const auto *CE = dyn_cast<CXXMemberCallExpr>(E))
     if (const auto *Proto =
             CE->getMethodDecl()->getType()->getAs<FunctionProtoType>())
@@ -233,7 +241,7 @@ static LValueOrRValue emitSuspendExpression(CodeGenFunction &CGF, CGCoroData &Co
   // is marked as 'noexcept', we avoid generating this additional IR.
   CXXTryStmt *TryStmt = nullptr;
   if (Coro.ExceptionHandler && Kind == AwaitKind::Init &&
-      memberCallExpressionCanThrow(S.getResumeExpr())) {
+      ResumeExprCanThrow(S)) {
     Coro.ResumeEHVar =
         CGF.CreateTempAlloca(Builder.getInt1Ty(), Prefix + Twine("resume.eh"));
     Builder.CreateFlagStore(true, Coro.ResumeEHVar);
diff --git a/clang/test/CodeGenCoroutines/coro-init-await-nontrivial-return.cpp b/clang/test/CodeGenCoroutines/coro-init-await-nontrivial-return.cpp
index c4b8da327f5c140..0e50a616d6ef7c2 100644
--- a/clang/test/CodeGenCoroutines/coro-init-await-nontrivial-return.cpp
+++ b/clang/test/CodeGenCoroutines/coro-init-await-nontrivial-return.cpp
@@ -3,6 +3,7 @@
 
 #include "Inputs/coroutine.h"
 
+namespace can_throw {
 struct NontrivialType {
   ~NontrivialType() {}
 };
@@ -38,9 +39,52 @@ Task coro_create() {
     co_return;
 }
 
-// CHECK-LABEL: define{{.*}} ptr @_Z11coro_createv(
+// CHECK-LABEL: define{{.*}} ptr @_ZN9can_throw11coro_createEv(
 // CHECK: init.ready:
 // CHECK-NEXT: store i1 true, ptr {{.*}}
-// CHECK-NEXT: call void @_ZN4Task23initial_suspend_awaiter12await_resumeEv(
-// CHECK-NEXT: call void @_ZN14NontrivialTypeD1Ev(
+// CHECK-NEXT: call void @_ZN9can_throw4Task23initial_suspend_awaiter12await_resumeEv(
+// CHECK-NEXT: call void @_ZN9can_throw14NontrivialTypeD1Ev(
 // CHECK-NEXT: store i1 false, ptr {{.*}}
+}
+
+namespace no_throw {
+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) {}
+
+        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 @_ZN8no_throw11coro_createEv(
+// CHECK: init.ready:
+// CHECK-NEXT: call void @_ZN8no_throw4Task23initial_suspend_awaiter12await_resumeEv(
+// CHECK-NEXT: call void @_ZN8no_throw14NontrivialTypeD1Ev(
+}