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clang-p2996/clang/test/CodeGenCXX/eh.cpp
Fangrui Song c0a73918bf [ItaniumCXXABI] Add -fassume-nothrow-exception-dtor to assume that all exception objects' destructors are non-throwing 
Link: https://lists.llvm.org/pipermail/cfe-dev/2021-August/068740.html ("[Exception Handling] Could we mark __cxa_end_catch as nounwind conditionally?"
Link: https://github.com/llvm/llvm-project/issues/57375

A catch handler calls `__cxa_begin_catch` and `__cxa_end_catch`. For a catch-all
clause or a catch clause matching a record type, we:

* assume that the exception object may have a throwing destructor
* emit `invoke void @__cxa_end_catch` (as the call is not marked as the `nounwind` attribute).
* emit a landing pad to destroy local variables and call `_Unwind_Resume`

```
struct A { ~A(); };
struct B { int x; };
void opaque();
void foo() {
  A a;
  try { opaque(); } catch (...) { } // the exception object has an unknown type and may throw
  try { opaque(); } catch (B b) { } // B::~B is nothrow, but we do not utilize this
}
```

Per C++ [dcl.fct.def.coroutine], a coroutine's function body implies a `catch (...)`.
Our code generation pessimizes even simple code, like:
```
UserFacing foo() {
  A a;
  opaque();
  co_return;
  // For `invoke void @__cxa_end_catch()`, the landing pad destroys the
  // promise_type and deletes the coro frame.
}
```

Throwing destructors are typically discouraged. In many environments, the
destructors of exception objects are guaranteed to never throw, making our
conservative code generation approach seem wasteful.

Furthermore, throwing destructors tend not to work well in practice:

* GCC does not emit call site records for the region containing `__cxa_end_catch`. This has been a long time, since 2000.
* If a catch-all clause catches an exception object that throws, both GCC and Clang using libstdc++ leak the allocated exception object.

To avoid code generation pessimization, add an opt-in driver option
-fassume-nothrow-exception-dtor to assume that `__cxa_end_catch` calls have the
`nounwind` attribute. This implies that thrown exception objects' destructors
will never throw.

To detect misuses, diagnose throw expressions with a potentially-throwing
destructor. Technically, it is possible that a potentially-throwing destructor
never throws when called transitively by `__cxa_end_catch`, but these cases seem
rare enough to justify a relaxed mode.

Reviewed By: ChuanqiXu

Differential Revision: https://reviews.llvm.org/D108905
2023-11-05 00:39:38 -07:00

460 lines
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// RUN: %clang_cc1 -fcxx-exceptions -fexceptions -triple x86_64-apple-macosx10.13.99 -std=c++11 -emit-llvm -o - %s | FileCheck --check-prefixes=CHECK,UNALIGNED,THROWEND %s
// RUN: %clang_cc1 -fcxx-exceptions -fexceptions -triple x86_64-apple-macosx10.14 -std=c++11 -emit-llvm -o - %s | FileCheck --check-prefixes=CHECK,ALIGNED,THROWEND %s
// RUN: %clang_cc1 -fcxx-exceptions -fexceptions -triple x86_64-apple-macosx10.14 -std=c++11 -emit-llvm -o - %s -fassume-nothrow-exception-dtor -DNOTHROWEND | FileCheck --check-prefixes=CHECK,ALIGNED,NOTHROWEND %s
struct test1_D {
double d;
} d1;
void test1() {
throw d1;
}
// CHECK-LABEL: define{{.*}} void @_Z5test1v()
// CHECK: [[EXNOBJ:%.*]] = call ptr @__cxa_allocate_exception(i64 8)
// UNALIGNED-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 8 [[EXNOBJ]], ptr align 8 @d1, i64 8, i1 false)
// ALIGNED-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 16 [[EXNOBJ]], ptr align 8 @d1, i64 8, i1 false)
// CHECK-NEXT: call void @__cxa_throw(ptr [[EXNOBJ]], ptr @_ZTI7test1_D, ptr null) [[NR:#[0-9]+]]
// CHECK-NEXT: unreachable
struct test2_D {
test2_D(const test2_D&o);
test2_D();
virtual void bar() { }
int i; int j;
} d2;
void test2() {
throw d2;
}
// CHECK-LABEL: define{{.*}} void @_Z5test2v()
// CHECK: [[EXNVAR:%.*]] = alloca ptr
// CHECK-NEXT: [[SELECTORVAR:%.*]] = alloca i32
// CHECK-NEXT: [[EXNOBJ:%.*]] = call ptr @__cxa_allocate_exception(i64 16)
// CHECK-NEXT: invoke void @_ZN7test2_DC1ERKS_(ptr {{[^,]*}} [[EXNOBJ]], ptr noundef nonnull align {{[0-9]+}} dereferenceable({{[0-9]+}}) @d2)
// CHECK-NEXT: to label %[[CONT:.*]] unwind label %{{.*}}
// : [[CONT]]: (can't check this in Release-Asserts builds)
// CHECK: call void @__cxa_throw(ptr [[EXNOBJ]], ptr @_ZTI7test2_D, ptr null) [[NR]]
// CHECK-NEXT: unreachable
struct test3_D {
test3_D() { }
test3_D(volatile test3_D&o);
virtual void bar();
};
void test3() {
throw (volatile test3_D *)0;
}
// CHECK-LABEL: define{{.*}} void @_Z5test3v()
// CHECK: [[EXNOBJ:%.*]] = call ptr @__cxa_allocate_exception(i64 8)
// CHECK-NEXT: store ptr null, ptr [[EXNOBJ]]
// CHECK-NEXT: call void @__cxa_throw(ptr [[EXNOBJ]], ptr @_ZTIPV7test3_D, ptr null) [[NR]]
// CHECK-NEXT: unreachable
void test4() {
throw;
}
// CHECK-LABEL: define{{.*}} void @_Z5test4v()
// CHECK: call void @__cxa_rethrow() [[NR]]
// CHECK-NEXT: unreachable
namespace test5 {
struct A {
A();
A(const A&);
~A();
};
void test() {
try { throw A(); } catch (A &x) {}
}
// CHECK-LABEL: define{{.*}} void @_ZN5test54testEv()
// CHECK: [[EXNOBJ:%.*]] = call ptr @__cxa_allocate_exception(i64 1)
// CHECK: invoke void @_ZN5test51AC1Ev(ptr {{[^,]*}} [[EXNOBJ]])
// CHECK: invoke void @__cxa_throw(ptr [[EXNOBJ]], ptr @_ZTIN5test51AE, ptr @_ZN5test51AD1Ev) [[NR]]
// CHECK-NEXT: to label {{%.*}} unwind label %[[HANDLER:[^ ]*]]
// : [[HANDLER]]: (can't check this in Release-Asserts builds)
// CHECK: {{%.*}} = call i32 @llvm.eh.typeid.for(ptr @_ZTIN5test51AE)
}
namespace test6 {
template <class T> struct allocator {
~allocator() throw() { }
};
void foo() {
allocator<int> a;
}
}
// PR7127
namespace test7 {
// CHECK-LABEL: define{{.*}} i32 @_ZN5test73fooEv()
// CHECK-SAME: personality ptr @__gxx_personality_v0
int foo() {
// CHECK: [[CAUGHTEXNVAR:%.*]] = alloca ptr
// CHECK-NEXT: [[SELECTORVAR:%.*]] = alloca i32
// CHECK-NEXT: [[INTCATCHVAR:%.*]] = alloca i32
try {
try {
// CHECK-NEXT: [[EXNALLOC:%.*]] = call ptr @__cxa_allocate_exception
// CHECK-NEXT: store i32 1, ptr
// CHECK-NEXT: invoke void @__cxa_throw(ptr [[EXNALLOC]], ptr @_ZTIi, ptr null
throw 1;
}
// CHECK: [[CAUGHTVAL:%.*]] = landingpad { ptr, i32 }
// CHECK-NEXT: catch ptr @_ZTIi
// CHECK-NEXT: catch ptr null
// CHECK-NEXT: [[CAUGHTEXN:%.*]] = extractvalue { ptr, i32 } [[CAUGHTVAL]], 0
// CHECK-NEXT: store ptr [[CAUGHTEXN]], ptr [[CAUGHTEXNVAR]]
// CHECK-NEXT: [[SELECTOR:%.*]] = extractvalue { ptr, i32 } [[CAUGHTVAL]], 1
// CHECK-NEXT: store i32 [[SELECTOR]], ptr [[SELECTORVAR]]
// CHECK-NEXT: br label
// CHECK: [[SELECTOR:%.*]] = load i32, ptr [[SELECTORVAR]]
// CHECK-NEXT: [[T0:%.*]] = call i32 @llvm.eh.typeid.for(ptr @_ZTIi)
// CHECK-NEXT: icmp eq i32 [[SELECTOR]], [[T0]]
// CHECK-NEXT: br i1
// CHECK: [[T0:%.*]] = load ptr, ptr [[CAUGHTEXNVAR]]
// CHECK-NEXT: [[T1:%.*]] = call ptr @__cxa_begin_catch(ptr [[T0]])
// CHECK-NEXT: [[T3:%.*]] = load i32, ptr [[T1]]
// CHECK-NEXT: store i32 [[T3]], ptr {{%.*}}, align 4
// CHECK-NEXT: invoke void @__cxa_rethrow
catch (int) {
throw;
}
}
// CHECK: [[CAUGHTVAL:%.*]] = landingpad { ptr, i32 }
// CHECK-NEXT: catch ptr null
// CHECK-NEXT: [[CAUGHTEXN:%.*]] = extractvalue { ptr, i32 } [[CAUGHTVAL]], 0
// CHECK-NEXT: store ptr [[CAUGHTEXN]], ptr [[CAUGHTEXNVAR]]
// CHECK-NEXT: [[SELECTOR:%.*]] = extractvalue { ptr, i32 } [[CAUGHTVAL]], 1
// CHECK-NEXT: store i32 [[SELECTOR]], ptr [[SELECTORVAR]]
// CHECK-NEXT: call void @__cxa_end_catch()
// CHECK-NEXT: br label
// CHECK: load ptr, ptr [[CAUGHTEXNVAR]]
// CHECK-NEXT: call ptr @__cxa_begin_catch
// CHECK-NEXT: call void @__cxa_end_catch
catch (...) {
}
// CHECK: ret i32 0
return 0;
}
}
// Ordering of destructors in a catch handler.
namespace test8 {
struct A { A(const A&); ~A(); };
void bar();
// CHECK-LABEL: define{{.*}} void @_ZN5test83fooEv()
void foo() {
try {
// CHECK: invoke void @_ZN5test83barEv()
bar();
} catch (A a) {
// CHECK: call ptr @__cxa_get_exception_ptr
// CHECK-NEXT: invoke void @_ZN5test81AC1ERKS0_(
// CHECK: call ptr @__cxa_begin_catch
// CHECK-NEXT: call void @_ZN5test81AD1Ev(
// CHECK: call void @__cxa_end_catch()
// CHECK: ret void
}
}
}
// Constructor function-try-block must rethrow on fallthrough.
namespace test9 {
void opaque();
struct A { A(); };
// CHECK-LABEL: define{{.*}} void @_ZN5test91AC2Ev(ptr {{[^,]*}} %this) unnamed_addr
// CHECK-SAME: personality ptr @__gxx_personality_v0
A::A() try {
// CHECK: invoke void @_ZN5test96opaqueEv()
opaque();
} catch (int x) {
// CHECK: landingpad { ptr, i32 }
// CHECK-NEXT: catch ptr @_ZTIi
// CHECK: call ptr @__cxa_begin_catch
// CHECK: invoke void @_ZN5test96opaqueEv()
// CHECK: invoke void @__cxa_rethrow()
// CHECK-LABEL: define{{.*}} void @_ZN5test91AC1Ev(ptr {{[^,]*}} %this) unnamed_addr
// CHECK: call void @_ZN5test91AC2Ev
// CHECK-NEXT: ret void
opaque();
}
}
// __cxa_end_catch can throw for some kinds of caught exceptions.
namespace test10 {
void opaque();
struct A { ~A(); };
struct B { int x; };
// CHECK-LABEL: define{{.*}} void @_ZN6test103fooEv()
void foo() {
A a; // force a cleanup context
try {
// CHECK: invoke void @_ZN6test106opaqueEv()
opaque();
} catch (int i) {
// CHECK: call ptr @__cxa_begin_catch
// CHECK-NEXT: load i32, ptr
// CHECK-NEXT: store i32
// CHECK-NEXT: call void @__cxa_end_catch() [[NUW:#[0-9]+]]
} catch (B a) {
// CHECK: call ptr @__cxa_begin_catch
// CHECK-NEXT: call void @llvm.memcpy
// THROWEND-NEXT: invoke void @__cxa_end_catch()
// NOTHROWEND-NEXT: call void @__cxa_end_catch() [[NUW]]
} catch (...) {
// CHECK: call ptr @__cxa_begin_catch
// THROWEND-NEXT: invoke void @__cxa_end_catch()
// NOTHROWEND-NEXT: call void @__cxa_end_catch() [[NUW]]
}
// THROWEND: call void @_ZN6test101AD1Ev(
// NOTHROWEND-NOT: call void @_ZN6test101AD1Ev(
}
}
// __cxa_begin_catch returns pointers by value, even when catching by reference
namespace test11 {
void opaque();
// CHECK-LABEL: define{{.*}} void @_ZN6test113fooEv()
void foo() {
try {
// CHECK: invoke void @_ZN6test116opaqueEv()
opaque();
} catch (int**&p) {
// CHECK: [[EXN:%.*]] = load ptr, ptr
// CHECK-NEXT: call ptr @__cxa_begin_catch(ptr [[EXN]]) [[NUW]]
// CHECK-NEXT: [[ADJ1:%.*]] = getelementptr i8, ptr [[EXN]], i32 32
// CHECK-NEXT: store ptr [[ADJ1]], ptr [[P:%.*]]
// CHECK-NEXT: call void @__cxa_end_catch() [[NUW]]
}
}
struct A {};
// CHECK-LABEL: define{{.*}} void @_ZN6test113barEv()
void bar() {
try {
// CHECK: [[EXNSLOT:%.*]] = alloca ptr
// CHECK-NEXT: [[SELECTORSLOT:%.*]] = alloca i32
// CHECK-NEXT: [[P:%.*]] = alloca ptr,
// CHECK-NEXT: [[TMP:%.*]] = alloca ptr
// CHECK-NEXT: invoke void @_ZN6test116opaqueEv()
opaque();
} catch (A*&p) {
// CHECK: [[EXN:%.*]] = load ptr, ptr [[EXNSLOT]]
// CHECK-NEXT: [[ADJ1:%.*]] = call ptr @__cxa_begin_catch(ptr [[EXN]]) [[NUW]]
// CHECK-NEXT: store ptr [[ADJ1]], ptr [[TMP]]
// CHECK-NEXT: store ptr [[TMP]], ptr [[P]]
// CHECK-NEXT: call void @__cxa_end_catch() [[NUW]]
}
}
}
// PR7686
namespace test12 {
struct A { ~A() noexcept(false); };
bool opaque(const A&);
// CHECK-LABEL: define{{.*}} void @_ZN6test124testEv()
void test() {
// CHECK: [[X:%.*]] = alloca [[A:%.*]],
// CHECK: [[EHCLEANUPDEST:%.*]] = alloca i32
// CHECK: [[Y:%.*]] = alloca [[A:%.*]]
// CHECK: [[Z:%.*]] = alloca [[A]]
// CHECK: [[CLEANUPDEST:%.*]] = alloca i32
A x;
// CHECK: invoke noundef zeroext i1 @_ZN6test126opaqueERKNS_1AE(
if (opaque(x)) {
A y;
A z;
// CHECK: invoke void @_ZN6test121AD1Ev(ptr {{[^,]*}} [[Z]])
// CHECK: invoke void @_ZN6test121AD1Ev(ptr {{[^,]*}} [[Y]])
// CHECK-NOT: switch
goto success;
}
success:
bool _ = true;
// CHECK: call void @_ZN6test121AD1Ev(ptr {{[^,]*}} [[X]])
// CHECK-NEXT: ret void
}
}
// Reduced from some TableGen code that was causing a self-host crash.
namespace test13 {
struct A { ~A(); };
void test0(int x) {
try {
switch (x) {
case 0:
break;
case 1:{
A a;
break;
}
default:
return;
}
return;
} catch (int x) {
}
return;
}
void test1(int x) {
A y;
try {
switch (x) {
default: break;
}
} catch (int x) {}
}
}
namespace test14 {
struct A { ~A(); };
struct B { ~B(); };
B b();
void opaque();
void foo() {
A a;
try {
B str = b();
opaque();
} catch (int x) {
}
}
}
// JumpDests shouldn't get confused by scopes that aren't normal cleanups.
namespace test15 {
struct A { ~A(); };
bool opaque(int);
// CHECK-LABEL: define{{.*}} void @_ZN6test153fooEv()
void foo() {
A a;
try {
// CHECK: [[X:%.*]] = alloca i32
// CHECK: store i32 10, ptr [[X]]
// CHECK-NEXT: br label
// -> while.cond
int x = 10;
while (true) {
// CHECK: load i32, ptr [[X]]
// CHECK-NEXT: [[COND:%.*]] = invoke noundef zeroext i1 @_ZN6test156opaqueEi
// CHECK: br i1 [[COND]]
if (opaque(x))
// CHECK: br label
break;
// CHECK: br label
}
// CHECK: br label
} catch (int x) { }
// CHECK: call void @_ZN6test151AD1Ev
}
}
namespace test16 {
struct A { A(); ~A() noexcept(false); };
struct B { int x; B(const A &); ~B() noexcept(false); };
void foo();
bool cond();
// CHECK-LABEL: define{{.*}} void @_ZN6test163barEv()
void bar() {
// THROWEND: [[EXN_SAVE:%.*]] = alloca ptr
// THROWEND-NEXT: [[EXN_ACTIVE:%.*]] = alloca i1
// THROWEND-NEXT: [[TEMP:%.*]] = alloca [[A:%.*]],
// THROWEND-NEXT: [[EXNSLOT:%.*]] = alloca ptr
// THROWEND-NEXT: [[SELECTORSLOT:%.*]] = alloca i32
// THROWEND-NEXT: [[TEMP_ACTIVE:%.*]] = alloca i1
#ifndef NOTHROWEND
cond() ? throw B(A()) : foo();
#endif
// THROWEND-NEXT: [[COND:%.*]] = call noundef zeroext i1 @_ZN6test164condEv()
// THROWEND-NEXT: store i1 false, ptr [[EXN_ACTIVE]]
// THROWEND-NEXT: store i1 false, ptr [[TEMP_ACTIVE]]
// THROWEND-NEXT: br i1 [[COND]],
// THROWEND: [[EXN:%.*]] = call ptr @__cxa_allocate_exception(i64 4)
// THROWEND-NEXT: store ptr [[EXN]], ptr [[EXN_SAVE]]
// THROWEND-NEXT: store i1 true, ptr [[EXN_ACTIVE]]
// THROWEND-NEXT: invoke void @_ZN6test161AC1Ev(ptr {{[^,]*}} [[TEMP]])
// THROWEND: store i1 true, ptr [[TEMP_ACTIVE]]
// THROWEND-NEXT: invoke void @_ZN6test161BC1ERKNS_1AE(ptr {{[^,]*}} [[EXN]], ptr noundef nonnull align {{[0-9]+}} dereferenceable({{[0-9]+}}) [[TEMP]])
// THROWEND: store i1 false, ptr [[EXN_ACTIVE]]
// THROWEND-NEXT: invoke void @__cxa_throw(ptr [[EXN]],
// THROWEND: invoke void @_ZN6test163fooEv()
// THROWEND: br label
// THROWEND: invoke void @_ZN6test161AD1Ev(ptr {{[^,]*}} [[TEMP]])
// THROWEND: ret void
// THROWEND: [[T0:%.*]] = load i1, ptr [[EXN_ACTIVE]]
// THROWEND-NEXT: br i1 [[T0]]
// THROWEND: [[T1:%.*]] = load ptr, ptr [[EXN_SAVE]]
// THROWEND-NEXT: call void @__cxa_free_exception(ptr [[T1]])
// THROWEND-NEXT: br label
}
}
namespace test17 {
class BaseException {
private:
int a[4];
public:
BaseException() {};
};
class DerivedException: public BaseException {
};
int foo() {
throw DerivedException();
// The alignment passed to memset is 16 on Darwin.
// CHECK: [[T0:%.*]] = call ptr @__cxa_allocate_exception(i64 16)
// UNALIGNED-NEXT: call void @llvm.memset.p0.i64(ptr align 8 [[T0]], i8 0, i64 16, i1 false)
// ALIGNED-NEXT: call void @llvm.memset.p0.i64(ptr align 16 [[T0]], i8 0, i64 16, i1 false)
}
}
// CHECK: attributes [[NUW]] = { nounwind }
// CHECK: attributes [[NR]] = { noreturn }
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