[clang] [Clang] CGCoroutines skip emitting try block for value returning `noexcept` init `await_resume` calls (PR #73160)
Yuxuan Chen via cfe-commits
cfe-commits at lists.llvm.org
Tue Nov 28 14:00:53 PST 2023
https://github.com/yuxuanchen1997 updated https://github.com/llvm/llvm-project/pull/73160
>From dbd06bc001c0e00436fcacac231d9d80b443edf4 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 1/2] add checks for nested noexcept in cxxtempexpr
---
clang/lib/CodeGen/CGCoroutine.cpp | 28 ++++++--
.../coro-init-await-nontrivial-return.cpp | 66 ++++++++++++++++++-
2 files changed, 88 insertions(+), 6 deletions(-)
diff --git a/clang/lib/CodeGen/CGCoroutine.cpp b/clang/lib/CodeGen/CGCoroutine.cpp
index aaf122c0f83bc47..37ac5bca38c7049 100644
--- a/clang/lib/CodeGen/CGCoroutine.cpp
+++ b/clang/lib/CodeGen/CGCoroutine.cpp
@@ -129,12 +129,32 @@ static SmallString<32> buildSuspendPrefixStr(CGCoroData &Coro, AwaitKind Kind) {
return Prefix;
}
-static bool memberCallExpressionCanThrow(const Expr *E) {
+static bool FunctionProtoNoexcept(const FunctionProtoType *Proto) {
+ return isNoexceptExceptionSpec(Proto->getExceptionSpecType()) &&
+ Proto->canThrow() == CT_Cannot;
+}
+
+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)) {
+ auto *Temporary = BindTempExpr->getTemporary();
+ const auto *DtorProto = Temporary->getDestructor()
+ ->getCanonicalDecl()
+ ->getType()
+ ->getAs<FunctionProtoType>();
+ bool DtorCanThrow = !FunctionProtoNoexcept(DtorProto);
+ if (DtorCanThrow) {
+ return true;
+ }
+ E = BindTempExpr->getSubExpr();
+ }
if (const auto *CE = dyn_cast<CXXMemberCallExpr>(E))
if (const auto *Proto =
CE->getMethodDecl()->getType()->getAs<FunctionProtoType>())
- if (isNoexceptExceptionSpec(Proto->getExceptionSpecType()) &&
- Proto->canThrow() == CT_Cannot)
+ if (FunctionProtoNoexcept(Proto))
return false;
return true;
}
@@ -233,7 +253,7 @@ 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..052b4e235e739fe 100644
--- a/clang/test/CodeGenCoroutines/coro-init-await-nontrivial-return.cpp
+++ b/clang/test/CodeGenCoroutines/coro-init-await-nontrivial-return.cpp
@@ -7,6 +7,11 @@ struct NontrivialType {
~NontrivialType() {}
};
+struct NontrivialTypeWithThrowingDtor {
+ ~NontrivialTypeWithThrowingDtor() noexcept(false) {}
+};
+
+namespace can_throw {
struct Task {
struct promise_type;
using handle_type = std::coroutine_handle<promise_type>;
@@ -38,9 +43,66 @@ 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 @_ZN9can_throw4Task23initial_suspend_awaiter12await_resumeEv(
// CHECK-NEXT: call void @_ZN14NontrivialTypeD1Ev(
// CHECK-NEXT: store i1 false, ptr {{.*}}
+}
+
+template <typename R>
+struct NoexceptResumeTask {
+ 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) {}
+
+ R 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 {}; }
+ NoexceptResumeTask get_return_object() {
+ return NoexceptResumeTask{handle_type::from_promise(*this)};
+ }
+ };
+
+ handle_type handler;
+};
+
+namespace no_throw {
+using InitNoThrowTask = NoexceptResumeTask<NontrivialType>;
+
+InitNoThrowTask coro_create() {
+ co_return;
+}
+
+// CHECK-LABEL: define{{.*}} ptr @_ZN8no_throw11coro_createEv(
+// CHECK: init.ready:
+// CHECK-NEXT: call void @_ZN18NoexceptResumeTaskI14NontrivialTypeE23initial_suspend_awaiter12await_resumeEv(
+// CHECK-NEXT: call void @_ZN14NontrivialTypeD1Ev(
+}
+
+namespace throwing_dtor {
+using InitTaskWithThrowingDtor = NoexceptResumeTask<NontrivialTypeWithThrowingDtor>;
+
+InitTaskWithThrowingDtor coro_create() {
+ co_return;
+}
+
+// CHECK-LABEL: define{{.*}} ptr @_ZN13throwing_dtor11coro_createEv(
+// CHECK: init.ready:
+// CHECK-NEXT: store i1 true, ptr {{.*}}
+// CHECK-NEXT: call void @_ZN18NoexceptResumeTaskI30NontrivialTypeWithThrowingDtorE23initial_suspend_awaiter12await_resumeEv(
+// CHECK-NEXT: call void @_ZN30NontrivialTypeWithThrowingDtorD1Ev(
+// CHECK-NEXT: store i1 false, ptr {{.*}}
+}
>From eebbffba771f14c92c90cd023aaeed491f51819f Mon Sep 17 00:00:00 2001
From: Yuxuan Chen <ych at meta.com>
Date: Tue, 28 Nov 2023 14:00:40 -0800
Subject: [PATCH 2/2] new way to (conservatively) check stmt no throw
---
clang/lib/CodeGen/CGCoroutine.cpp | 63 +++++++++++++++++++------------
1 file changed, 39 insertions(+), 24 deletions(-)
diff --git a/clang/lib/CodeGen/CGCoroutine.cpp b/clang/lib/CodeGen/CGCoroutine.cpp
index 37ac5bca38c7049..eb9dc3f357eea44 100644
--- a/clang/lib/CodeGen/CGCoroutine.cpp
+++ b/clang/lib/CodeGen/CGCoroutine.cpp
@@ -129,34 +129,49 @@ static SmallString<32> buildSuspendPrefixStr(CGCoroData &Coro, AwaitKind Kind) {
return Prefix;
}
-static bool FunctionProtoNoexcept(const FunctionProtoType *Proto) {
- return isNoexceptExceptionSpec(Proto->getExceptionSpecType()) &&
- Proto->canThrow() == CT_Cannot;
+// Check if function can throw based on prototype noexcept, also works for
+// destructors which are implicitly noexcept but can be marked noexcept(false).
+static bool FunctionCanThrow(const FunctionDecl *D) {
+ const auto *Proto = D->getType()->getAs<FunctionProtoType>();
+ if (!Proto) {
+ // Function proto is not found, we conservatively assume throwing.
+ return true;
+ }
+ return !isNoexceptExceptionSpec(Proto->getExceptionSpecType()) ||
+ Proto->canThrow() != CT_Cannot;
}
-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)) {
- auto *Temporary = BindTempExpr->getTemporary();
- const auto *DtorProto = Temporary->getDestructor()
- ->getCanonicalDecl()
- ->getType()
- ->getAs<FunctionProtoType>();
- bool DtorCanThrow = !FunctionProtoNoexcept(DtorProto);
- if (DtorCanThrow) {
+static bool ResumeStmtCanThrow(const Stmt *S) {
+ if (const auto *CE = dyn_cast<CallExpr>(S)) {
+ const auto *Callee = CE->getDirectCallee();
+ if (!Callee)
+ // We don't have direct callee. Conservatively assume throwing.
+ return true;
+
+ if (FunctionCanThrow(Callee))
+ return true;
+
+ // Fall through to visit the children.
+ }
+
+ if (const auto *TE = dyn_cast<CXXBindTemporaryExpr>(S)) {
+ // Special handling of CXXBindTemporaryExpr here as calling of Dtor of the
+ // temporary is not part of `children()` as covered in the fall through.
+ // We need to mark entire statement as throwing if the destructor of the
+ // temporary throws.
+ const auto *Dtor = TE->getTemporary()->getDestructor();
+ if (FunctionCanThrow(Dtor))
+ return true;
+
+ // Fall through to visit the children.
+ }
+
+ for (const auto *child : S->children()) {
+ if (ResumeStmtCanThrow(child)) {
return true;
}
- E = BindTempExpr->getSubExpr();
}
- if (const auto *CE = dyn_cast<CXXMemberCallExpr>(E))
- if (const auto *Proto =
- CE->getMethodDecl()->getType()->getAs<FunctionProtoType>())
- if (FunctionProtoNoexcept(Proto))
- return false;
- return true;
+ return false;
}
// Emit suspend expression which roughly looks like:
@@ -253,7 +268,7 @@ 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 &&
- ResumeExprCanThrow(S)) {
+ ResumeStmtCanThrow(S.getResumeExpr())) {
Coro.ResumeEHVar =
CGF.CreateTempAlloca(Builder.getInt1Ty(), Prefix + Twine("resume.eh"));
Builder.CreateFlagStore(true, Coro.ResumeEHVar);
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