llvm-project/clang/test/CodeGenCXX/wasm-eh.cpp

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// REQUIRES: webassembly-registered-target
// RUN: %clang_cc1 -no-opaque-pointers %s -triple wasm32-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -mllvm -wasm-enable-eh -exception-model=wasm -target-feature +exception-handling -emit-llvm -o - -std=c++11 | FileCheck %s
// RUN: %clang_cc1 -no-opaque-pointers %s -triple wasm64-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -mllvm -wasm-enable-eh -exception-model=wasm -target-feature +exception-handling -emit-llvm -o - -std=c++11 | FileCheck %s
void may_throw();
void dont_throw() noexcept;
struct Cleanup {
~Cleanup() { dont_throw(); }
};
// Multiple catch clauses w/o catch-all
void test0() {
try {
may_throw();
} catch (int) {
dont_throw();
} catch (double) {
dont_throw();
}
}
// CHECK-LABEL: define void @_Z5test0v() {{.*}} personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*)
// CHECK: %[[INT_ALLOCA:.*]] = alloca i32
// CHECK: invoke void @_Z9may_throwv()
// CHECK-NEXT: to label %[[NORMAL_BB:.*]] unwind label %[[CATCHDISPATCH_BB:.*]]
// CHECK: [[CATCHDISPATCH_BB]]:
// CHECK-NEXT: %[[CATCHSWITCH:.*]] = catchswitch within none [label %[[CATCHSTART_BB:.*]]] unwind to caller
// CHECK: [[CATCHSTART_BB]]:
// CHECK-NEXT: %[[CATCHPAD:.*]] = catchpad within %[[CATCHSWITCH]] [i8* bitcast (i8** @_ZTIi to i8*), i8* bitcast (i8** @_ZTId to i8*)]
// CHECK-NEXT: %[[EXN:.*]] = call i8* @llvm.wasm.get.exception(token %[[CATCHPAD]])
// CHECK-NEXT: store i8* %[[EXN]], i8** %exn.slot
// CHECK-NEXT: %[[SELECTOR:.*]] = call i32 @llvm.wasm.get.ehselector(token %[[CATCHPAD]])
// CHECK-NEXT: %[[TYPEID:.*]] = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTIi to i8*)) #2
// CHECK-NEXT: %[[MATCHES:.*]] = icmp eq i32 %[[SELECTOR]], %[[TYPEID]]
// CHECK-NEXT: br i1 %[[MATCHES]], label %[[CATCH_INT_BB:.*]], label %[[CATCH_FALLTHROUGH_BB:.*]]
// CHECK: [[CATCH_INT_BB]]:
// CHECK-NEXT: %[[EXN:.*]] = load i8*, i8** %exn.slot
// CHECK-NEXT: %[[ADDR:.*]] = call i8* @__cxa_begin_catch(i8* %[[EXN]]) {{.*}} [ "funclet"(token %[[CATCHPAD]]) ]
// CHECK-NEXT: %[[ADDR_CAST:.*]] = bitcast i8* %[[ADDR]] to i32*
// CHECK-NEXT: %[[INT_VAL:.*]] = load i32, i32* %[[ADDR_CAST]]
// CHECK-NEXT: store i32 %[[INT_VAL]], i32* %[[INT_ALLOCA]]
// CHECK-NEXT: call void @_Z10dont_throwv() {{.*}} [ "funclet"(token %[[CATCHPAD]]) ]
// CHECK-NEXT: call void @__cxa_end_catch() {{.*}} [ "funclet"(token %[[CATCHPAD]]) ]
// CHECK-NEXT: catchret from %[[CATCHPAD]] to label %[[CATCHRET_DEST_BB0:.*]]
// CHECK: [[CATCHRET_DEST_BB0]]:
// CHECK-NEXT: br label %[[TRY_CONT_BB:.*]]
// CHECK: [[CATCH_FALLTHROUGH_BB]]
// CHECK-NEXT: %[[TYPEID:.*]] = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTId to i8*)) #2
// CHECK-NEXT: %[[MATCHES:.*]] = icmp eq i32 %[[SELECTOR]], %[[TYPEID]]
// CHECK-NEXT: br i1 %[[MATCHES]], label %[[CATCH_FLOAT_BB:.*]], label %[[RETHROW_BB:.*]]
// CHECK: [[CATCH_FLOAT_BB]]:
// CHECK: catchret from %[[CATCHPAD]] to label %[[CATCHRET_DEST_BB1:.*]]
// CHECK: [[CATCHRET_DEST_BB1]]:
// CHECK-NEXT: br label %[[TRY_CONT_BB]]
// CHECK: [[RETHROW_BB]]:
// CHECK-NEXT: call void @llvm.wasm.rethrow() {{.*}} [ "funclet"(token %[[CATCHPAD]]) ]
// CHECK-NEXT: unreachable
// Single catch-all
void test1() {
try {
may_throw();
} catch (...) {
dont_throw();
}
}
// CATCH-LABEL: @_Z5test1v()
// CHECK: %[[CATCHSWITCH:.*]] = catchswitch within none [label %[[CATCHSTART_BB:.*]]] unwind to caller
// CHECK: [[CATCHSTART_BB]]:
// CHECK-NEXT: %[[CATCHPAD:.*]] = catchpad within %[[CATCHSWITCH]] [i8* null]
// CHECK: br label %[[CATCH_ALL_BB:.*]]
// CHECK: [[CATCH_ALL_BB]]:
// CHECK: catchret from %[[CATCHPAD]] to label
// Multiple catch clauses w/ catch-all
void test2() {
try {
may_throw();
} catch (int) {
dont_throw();
} catch (...) {
dont_throw();
}
}
// CHECK-LABEL: @_Z5test2v()
// CHECK: %[[CATCHSWITCH:.*]] = catchswitch within none [label %[[CATCHSTART_BB:.*]]] unwind to caller
// CHECK: [[CATCHSTART_BB]]:
// CHECK-NEXT: %[[CATCHPAD:.*]] = catchpad within %[[CATCHSWITCH]] [i8* bitcast (i8** @_ZTIi to i8*), i8* null]
// CHECK: br i1 %{{.*}}, label %[[CATCH_INT_BB:.*]], label %[[CATCH_ALL_BB:.*]]
// CHECK: [[CATCH_INT_BB]]:
// CHECK: catchret from %[[CATCHPAD]] to label
// CHECK: [[CATCH_ALL_BB]]:
// CHECK: catchret from %[[CATCHPAD]] to label
// Cleanup
void test3() {
Cleanup c;
may_throw();
}
// CHECK-LABEL: @_Z5test3v()
// CHECK: invoke void @_Z9may_throwv()
// CHECK-NEXT: to label {{.*}} unwind label %[[EHCLEANUP_BB:.*]]
// CHECK: [[EHCLEANUP_BB]]:
// CHECK-NEXT: %[[CLEANUPPAD:.*]] = cleanuppad within none []
// CHECK-NEXT: call noundef %struct.Cleanup* @_ZN7CleanupD1Ev(%struct.Cleanup* {{[^,]*}} %{{.*}}) {{.*}} [ "funclet"(token %[[CLEANUPPAD]]) ]
// CHECK-NEXT: cleanupret from %[[CLEANUPPAD]] unwind to caller
// Possibly throwing function call within a catch
void test4() {
try {
may_throw();
} catch (int) {
may_throw();
}
}
// CHECK-LABEL: @_Z5test4v()
// CHECK: %[[CATCHSWITCH]] = catchswitch within none [label %[[CATCHSTART_BB]]] unwind to caller
// CHECK: [[CATCHSTART_BB]]:
// CHECK: %[[CATCHPAD:.*]] = catchpad within %[[CATCHSWITCH]] [i8* bitcast (i8** @_ZTIi to i8*)]
// CHECK: invoke void @_Z9may_throwv() [ "funclet"(token %[[CATCHPAD]]) ]
// CHECK-NEXT: to label %[[INVOKE_CONT_BB:.*]] unwind label %[[EHCLEANUP_BB:.*]]
// CHECK: [[INVOKE_CONT_BB]]:
// CHECK-NEXT: call void @__cxa_end_catch() {{.*}} [ "funclet"(token %[[CATCHPAD]]) ]
// CHECK-NEXT: catchret from %[[CATCHPAD]] to label
// CHECK: [[EHCLEANUP_BB]]:
// CHECK-NEXT: %[[CLEANUPPAD:.*]] = cleanuppad within %[[CATCHPAD]] []
// CHECK-NEXT: call void @__cxa_end_catch() {{.*}} [ "funclet"(token %[[CLEANUPPAD]]) ]
// CHECK-NEXT: cleanupret from %[[CLEANUPPAD]] unwind to caller
// Possibly throwing function call within a catch-all
void test5() {
try {
may_throw();
} catch (...) {
may_throw();
}
}
// CHECK-LABEL: @_Z5test5v()
// CHECK: %[[CATCHSWITCH:.*]] = catchswitch within none [label %[[CATCHSTART_BB]]] unwind to caller
// CHECK: [[CATCHSTART_BB]]:
// CHECK: %[[CATCHPAD:.*]] = catchpad within %[[CATCHSWITCH]] [i8* null]
// CHECK: invoke void @_Z9may_throwv() [ "funclet"(token %[[CATCHPAD]]) ]
// CHECK-NEXT: to label %[[INVOKE_CONT_BB0:.*]] unwind label %[[EHCLEANUP_BB:.*]]
// CHECK: [[INVOKE_CONT_BB0]]:
// CHECK-NEXT: call void @__cxa_end_catch() [ "funclet"(token %[[CATCHPAD]]) ]
// CHECK-NEXT: catchret from %[[CATCHPAD]] to label
// CHECK: [[EHCLEANUP_BB]]:
// CHECK-NEXT: %[[CLEANUPPAD0:.*]] = cleanuppad within %[[CATCHPAD]] []
// CHECK-NEXT: invoke void @__cxa_end_catch() [ "funclet"(token %[[CLEANUPPAD0]]) ]
// CHECK-NEXT: to label %[[INVOKE_CONT_BB1:.*]] unwind label %[[TERMINATE_BB:.*]]
// CHECK: [[INVOKE_CONT_BB1]]:
// CHECK-NEXT: cleanupret from %[[CLEANUPPAD0]] unwind to caller
// CHECK: [[TERMINATE_BB]]:
// CHECK-NEXT: %[[CLEANUPPAD1:.*]] = cleanuppad within %[[CLEANUPPAD0]] []
[WebAssembly] Disable uses of __clang_call_terminate Background: Wasm EH, while using Windows EH (catchpad/cleanuppad based) IR, uses Itanium-based libraries and ABIs with some modifications. `__clang_call_terminate` is a wrapper generated in Clang's Itanium C++ ABI implementation. It contains this code, in C-style pseudocode: ``` void __clang_call_terminate(void *exn) { __cxa_begin_catch(exn); std::terminate(); } ``` So this function is a wrapper to call `__cxa_begin_catch` on the exception pointer before termination. In Itanium ABI, this function is called when another exception is thrown while processing an exception. The pointer for this second, violating exception is passed as the argument of this `__clang_call_terminate`, which calls `__cxa_begin_catch` with that pointer and calls `std::terminate` to terminate the program. The spec (https://libcxxabi.llvm.org/spec.html) for `__cxa_begin_catch` says, ``` When the personality routine encounters a termination condition, it will call __cxa_begin_catch() to mark the exception as handled and then call terminate(), which shall not return to its caller. ``` In wasm EH's Clang implementation, this function is called from cleanuppads that terminates the program, which we also call terminate pads. Cleanuppads normally don't access the thrown exception and the wasm backend converts them to `catch_all` blocks. But because we need the exception pointer in this cleanuppad, we generate `wasm.get.exception` intrinsic (which will eventually be lowered to `catch` instruction) as we do in the catchpads. But because terminate pads are cleanup pads and should run even when a foreign exception is thrown, so what we have been doing is: 1. In `WebAssemblyLateEHPrepare::ensureSingleBBTermPads()`, we make sure terminate pads are in this simple shape: ``` %exn = catch call @__clang_call_terminate(%exn) unreachable ``` 2. In `WebAssemblyHandleEHTerminatePads` pass at the end of the pipeline, we attach a `catch_all` to terminate pads, so they will be in this form: ``` %exn = catch call @__clang_call_terminate(%exn) unreachable catch_all call @std::terminate() unreachable ``` In `catch_all` part, we don't have the exception pointer, so we call `std::terminate()` directly. The reason we ran HandleEHTerminatePads at the end of the pipeline, separate from LateEHPrepare, was it was convenient to assume there was only a single `catch` part per `try` during CFGSort and CFGStackify. --- Problem: While it thinks terminate pads could have been possibly split or calls to `__clang_call_terminate` could have been duplicated, `WebAssemblyLateEHPrepare::ensureSingleBBTermPads()` assumes terminate pads contain no more than calls to `__clang_call_terminate` and `unreachable` instruction. I assumed that because in LLVM very limited forms of transformations are done to catchpads and cleanuppads to maintain the scoping structure. But it turned out to be incorrect; passes can merge cleanuppads into one, including terminate pads, as long as the new code has a correct scoping structure. One pass that does this I observed was `SimplifyCFG`, but there can be more. After this transformation, a single cleanuppad can contain any number of other instructions with the call to `__clang_call_terminate` and can span many BBs. It wouldn't be practical to duplicate all these BBs within the cleanuppad to generate the equivalent `catch_all` blocks, only with calls to `__clang_call_terminate` replaced by calls to `std::terminate`. Unless we do more complicated transformation to split those calls to `__clang_call_terminate` into a separate cleanuppad, it is tricky to solve. --- Solution (?): This CL just disables the generation and use of `__clang_call_terminate` and calls `std::terminate()` directly in its place. The possible downside of this approach can be, because the Itanium ABI intended to "mark" the violating exception handled, we don't do that anymore. What `__cxa_begin_catch` actually does is increment the exception's handler count and decrement the uncaught exception count, which in my opinion do not matter much given that we are about to terminate the program anyway. Also it does not affect info like stack traces that can be possibly shown to developers. And while we use a variant of Itanium EH ABI, we can make some deviations if we choose to; we are already different in that in the current version of the EH spec we don't support two-phase unwinding. We can possibly consider a more complicated transformation later to reenable this, but I don't think that has high priority. Changes in this CL contains: - In Clang, we don't generate a call to `wasm.get.exception()` intrinsic and `__clang_call_terminate` function in terminate pads anymore; we simply generate calls to `std::terminate()`, which is the default implementation of `CGCXXABI::emitTerminateForUnexpectedException`. - Remove `WebAssembly::ensureSingleBBTermPads() function and `WebAssemblyHandleEHTerminatePads` pass, because terminate pads are already `catch_all` now (because they don't need the exception pointer) and we don't need these transformations anymore. - Change tests to use `std::terminate` directly. Also removes tests that tested `LateEHPrepare::ensureSingleBBTermPads` and `HandleEHTerminatePads` pass. - Drive-by fix: Add some function attributes to EH intrinsic declarations Fixes https://github.com/emscripten-core/emscripten/issues/13582. Reviewed By: dschuff, tlively Differential Revision: https://reviews.llvm.org/D97834
2021-03-03 07:05:30 +08:00
// CHECK-NEXT: call void @_ZSt9terminatev() {{.*}} [ "funclet"(token %[[CLEANUPPAD1]]) ]
// CHECK-NEXT: unreachable
// Try-catch with cleanups
void test6() {
Cleanup c1;
try {
Cleanup c2;
may_throw();
} catch (int) {
Cleanup c3;
may_throw();
}
}
// CHECK-LABEL: @_Z5test6v()
// CHECK: invoke void @_Z9may_throwv()
// CHECK-NEXT: to label %{{.*}} unwind label %[[EHCLEANUP_BB0:.*]]
// CHECK: [[EHCLEANUP_BB0]]:
// CHECK-NEXT: %[[CLEANUPPAD0:.*]] = cleanuppad within none []
// CHECK-NEXT: call noundef %struct.Cleanup* @_ZN7CleanupD1Ev(%struct.Cleanup* {{.*}}) {{.*}} [ "funclet"(token %[[CLEANUPPAD0]]) ]
// CHECK-NEXT: cleanupret from %[[CLEANUPPAD0]] unwind label %[[CATCH_DISPATCH_BB:.*]]
// CHECK: [[CATCH_DISPATCH_BB]]:
// CHECK-NEXT: %[[CATCHSWITCH:.*]] = catchswitch within none [label %[[CATCHSTART_BB:.*]]] unwind label %[[EHCLEANUP_BB1:.*]]
// CHECK: [[CATCHSTART_BB]]:
// CHECK-NEXT: %[[CATCHPAD:.*]] = catchpad within %[[CATCHSWITCH]] [i8* bitcast (i8** @_ZTIi to i8*)]
// CHECK: br i1 %{{.*}}, label %[[CATCH_INT_BB:.*]], label %[[RETHROW_BB:.*]]
// CHECK: [[CATCH_INT_BB]]:
// CHECK: invoke void @_Z9may_throwv() [ "funclet"(token %[[CATCHPAD]]) ]
// CHECK-NEXT: to label %[[INVOKE_CONT_BB:.*]] unwind label %[[EHCLEANUP_BB2:.*]]
// CHECK: [[INVOKE_CONT_BB]]:
// CHECK: catchret from %[[CATCHPAD]] to label %{{.*}}
// CHECK: [[RETHROW_BB]]:
// CHECK-NEXT: invoke void @llvm.wasm.rethrow() {{.*}} [ "funclet"(token %[[CATCHPAD]]) ]
// CHECK-NEXT: to label %[[UNREACHABLE_BB:.*]] unwind label %[[EHCLEANUP_BB1:.*]]
// CHECK: [[EHCLEANUP_BB2]]:
// CHECK-NEXT: %[[CLEANUPPAD2:.*]] = cleanuppad within %[[CATCHPAD]] []
// CHECK-NEXT: call noundef %struct.Cleanup* @_ZN7CleanupD1Ev(%struct.Cleanup* {{[^,]*}} %{{.*}}) {{.*}} [ "funclet"(token %[[CLEANUPPAD2]]) ]
// CHECK-NEXT: cleanupret from %[[CLEANUPPAD2]] unwind label %[[EHCLEANUP_BB3:.*]]
// CHECK: [[EHCLEANUP_BB3]]:
// CHECK-NEXT: %[[CLEANUPPAD3:.*]] = cleanuppad within %[[CATCHPAD]] []
// CHECK: cleanupret from %[[CLEANUPPAD3]] unwind label %[[EHCLEANUP_BB1:.*]]
// CHECK: [[EHCLEANUP_BB1]]:
// CHECK-NEXT: %[[CLEANUPPAD1:.*]] = cleanuppad within none []
// CHECK-NEXT: call noundef %struct.Cleanup* @_ZN7CleanupD1Ev(%struct.Cleanup* {{[^,]*}} %{{.*}}) {{.*}} [ "funclet"(token %[[CLEANUPPAD1]]) ]
// CHECK-NEXT: cleanupret from %[[CLEANUPPAD1]] unwind to caller
// CHECK: [[UNREACHABLE_BB]]:
// CHECK-NEXT: unreachable
// Nested try-catches within a try with cleanups
void test7() {
Cleanup c1;
may_throw();
try {
Cleanup c2;
may_throw();
try {
Cleanup c3;
may_throw();
} catch (int) {
may_throw();
} catch (double) {
may_throw();
}
} catch (int) {
may_throw();
} catch (...) {
may_throw();
}
}
// CHECK-LABEL: @_Z5test7v()
// CHECK: invoke void @_Z9may_throwv()
// CHECK: invoke void @_Z9may_throwv()
// CHECK: invoke void @_Z9may_throwv()
// CHECK: %[[CLEANUPPAD0:.*]] = cleanuppad within none []
// CHECK: cleanupret from %[[CLEANUPPAD0]] unwind label
// CHECK: %[[CATCHSWITCH0:.*]] = catchswitch within none
// CHECK: %[[CATCHPAD0:.*]] = catchpad within %[[CATCHSWITCH0]] [i8* bitcast (i8** @_ZTIi to i8*), i8* bitcast (i8** @_ZTId to i8*)]
// CHECK: invoke void @_Z9may_throwv() [ "funclet"(token %[[CATCHPAD0]]) ]
// CHECK: catchret from %[[CATCHPAD0]] to label
// CHECK: invoke void @_Z9may_throwv() [ "funclet"(token %[[CATCHPAD0]]) ]
// CHECK: catchret from %[[CATCHPAD0]] to label
// CHECK: invoke void @llvm.wasm.rethrow() {{.*}} [ "funclet"(token %[[CATCHPAD0]]) ]
// CHECK: %[[CLEANUPPAD1:.*]] = cleanuppad within %[[CATCHPAD0]] []
// CHECK: cleanupret from %[[CLEANUPPAD1]] unwind label
// CHECK: %[[CLEANUPPAD2:.*]] = cleanuppad within %[[CATCHPAD0]] []
// CHECK: cleanupret from %[[CLEANUPPAD2]] unwind label
// CHECK: %[[CLEANUPPAD3:.*]] = cleanuppad within none []
// CHECK: cleanupret from %[[CLEANUPPAD3]] unwind label
// CHECK: %[[CATCHSWITCH1:.*]] = catchswitch within none
// CHECK: %[[CATCHPAD1:.*]] = catchpad within %[[CATCHSWITCH1]] [i8* bitcast (i8** @_ZTIi to i8*), i8* null]
// CHECK: invoke void @_Z9may_throwv() [ "funclet"(token %[[CATCHPAD1]]) ]
// CHECK: catchret from %[[CATCHPAD1]] to label
// CHECK: invoke void @_Z9may_throwv() [ "funclet"(token %[[CATCHPAD1]]) ]
// CHECK: invoke void @__cxa_end_catch() [ "funclet"(token %[[CATCHPAD1]]) ]
// CHECK: catchret from %[[CATCHPAD1]] to label
// CHECK: %[[CLEANUPPAD4:.*]] = cleanuppad within %[[CATCHPAD1]] []
// CHECK: invoke void @__cxa_end_catch() [ "funclet"(token %[[CLEANUPPAD4]]) ]
// CHECK: cleanupret from %[[CLEANUPPAD4]] unwind label
// CHECK: %[[CLEANUPPAD5:.*]] = cleanuppad within %[[CATCHPAD1]] []
// CHECK: cleanupret from %[[CLEANUPPAD5]] unwind label
// CHECK: %[[CLEANUPPAD6:.*]] = cleanuppad within none []
// CHECK: cleanupret from %[[CLEANUPPAD6]] unwind to caller
// CHECK: unreachable
// CHECK: %[[CLEANUPPAD7:.*]] = cleanuppad within %[[CLEANUPPAD4]] []
[WebAssembly] Disable uses of __clang_call_terminate Background: Wasm EH, while using Windows EH (catchpad/cleanuppad based) IR, uses Itanium-based libraries and ABIs with some modifications. `__clang_call_terminate` is a wrapper generated in Clang's Itanium C++ ABI implementation. It contains this code, in C-style pseudocode: ``` void __clang_call_terminate(void *exn) { __cxa_begin_catch(exn); std::terminate(); } ``` So this function is a wrapper to call `__cxa_begin_catch` on the exception pointer before termination. In Itanium ABI, this function is called when another exception is thrown while processing an exception. The pointer for this second, violating exception is passed as the argument of this `__clang_call_terminate`, which calls `__cxa_begin_catch` with that pointer and calls `std::terminate` to terminate the program. The spec (https://libcxxabi.llvm.org/spec.html) for `__cxa_begin_catch` says, ``` When the personality routine encounters a termination condition, it will call __cxa_begin_catch() to mark the exception as handled and then call terminate(), which shall not return to its caller. ``` In wasm EH's Clang implementation, this function is called from cleanuppads that terminates the program, which we also call terminate pads. Cleanuppads normally don't access the thrown exception and the wasm backend converts them to `catch_all` blocks. But because we need the exception pointer in this cleanuppad, we generate `wasm.get.exception` intrinsic (which will eventually be lowered to `catch` instruction) as we do in the catchpads. But because terminate pads are cleanup pads and should run even when a foreign exception is thrown, so what we have been doing is: 1. In `WebAssemblyLateEHPrepare::ensureSingleBBTermPads()`, we make sure terminate pads are in this simple shape: ``` %exn = catch call @__clang_call_terminate(%exn) unreachable ``` 2. In `WebAssemblyHandleEHTerminatePads` pass at the end of the pipeline, we attach a `catch_all` to terminate pads, so they will be in this form: ``` %exn = catch call @__clang_call_terminate(%exn) unreachable catch_all call @std::terminate() unreachable ``` In `catch_all` part, we don't have the exception pointer, so we call `std::terminate()` directly. The reason we ran HandleEHTerminatePads at the end of the pipeline, separate from LateEHPrepare, was it was convenient to assume there was only a single `catch` part per `try` during CFGSort and CFGStackify. --- Problem: While it thinks terminate pads could have been possibly split or calls to `__clang_call_terminate` could have been duplicated, `WebAssemblyLateEHPrepare::ensureSingleBBTermPads()` assumes terminate pads contain no more than calls to `__clang_call_terminate` and `unreachable` instruction. I assumed that because in LLVM very limited forms of transformations are done to catchpads and cleanuppads to maintain the scoping structure. But it turned out to be incorrect; passes can merge cleanuppads into one, including terminate pads, as long as the new code has a correct scoping structure. One pass that does this I observed was `SimplifyCFG`, but there can be more. After this transformation, a single cleanuppad can contain any number of other instructions with the call to `__clang_call_terminate` and can span many BBs. It wouldn't be practical to duplicate all these BBs within the cleanuppad to generate the equivalent `catch_all` blocks, only with calls to `__clang_call_terminate` replaced by calls to `std::terminate`. Unless we do more complicated transformation to split those calls to `__clang_call_terminate` into a separate cleanuppad, it is tricky to solve. --- Solution (?): This CL just disables the generation and use of `__clang_call_terminate` and calls `std::terminate()` directly in its place. The possible downside of this approach can be, because the Itanium ABI intended to "mark" the violating exception handled, we don't do that anymore. What `__cxa_begin_catch` actually does is increment the exception's handler count and decrement the uncaught exception count, which in my opinion do not matter much given that we are about to terminate the program anyway. Also it does not affect info like stack traces that can be possibly shown to developers. And while we use a variant of Itanium EH ABI, we can make some deviations if we choose to; we are already different in that in the current version of the EH spec we don't support two-phase unwinding. We can possibly consider a more complicated transformation later to reenable this, but I don't think that has high priority. Changes in this CL contains: - In Clang, we don't generate a call to `wasm.get.exception()` intrinsic and `__clang_call_terminate` function in terminate pads anymore; we simply generate calls to `std::terminate()`, which is the default implementation of `CGCXXABI::emitTerminateForUnexpectedException`. - Remove `WebAssembly::ensureSingleBBTermPads() function and `WebAssemblyHandleEHTerminatePads` pass, because terminate pads are already `catch_all` now (because they don't need the exception pointer) and we don't need these transformations anymore. - Change tests to use `std::terminate` directly. Also removes tests that tested `LateEHPrepare::ensureSingleBBTermPads` and `HandleEHTerminatePads` pass. - Drive-by fix: Add some function attributes to EH intrinsic declarations Fixes https://github.com/emscripten-core/emscripten/issues/13582. Reviewed By: dschuff, tlively Differential Revision: https://reviews.llvm.org/D97834
2021-03-03 07:05:30 +08:00
// CHECK: call void @_ZSt9terminatev() {{.*}} [ "funclet"(token %[[CLEANUPPAD7]]) ]
// CHECK: unreachable
// Nested try-catches within a catch
void test8() {
try {
may_throw();
} catch (int) {
try {
may_throw();
} catch (int) {
may_throw();
}
}
}
// CHECK-LABEL: @_Z5test8v()
// CHECK: invoke void @_Z9may_throwv()
// CHECK: %[[CATCHSWITCH0:.*]] = catchswitch within none
// CHECK: %[[CATCHPAD0:.*]] = catchpad within %[[CATCHSWITCH0]] [i8* bitcast (i8** @_ZTIi to i8*)]
// CHECK: invoke void @_Z9may_throwv() [ "funclet"(token %[[CATCHPAD0]]) ]
// CHECK: %[[CATCHSWITCH1:.*]] = catchswitch within %[[CATCHPAD0]]
// CHECK: %[[CATCHPAD1:.*]] = catchpad within %[[CATCHSWITCH1]] [i8* bitcast (i8** @_ZTIi to i8*)]
// CHECK: invoke void @_Z9may_throwv() [ "funclet"(token %[[CATCHPAD1]]) ]
// CHECK: catchret from %[[CATCHPAD1]] to label
// CHECK: invoke void @llvm.wasm.rethrow() {{.*}} [ "funclet"(token %[[CATCHPAD1]]) ]
// CHECK: catchret from %[[CATCHPAD0]] to label
// CHECK: call void @llvm.wasm.rethrow() {{.*}} [ "funclet"(token %[[CATCHPAD0]]) ]
// CHECK: unreachable
// CHECK: %[[CLEANUPPAD0:.*]] = cleanuppad within %[[CATCHPAD1]] []
// CHECK: cleanupret from %[[CLEANUPPAD0]] unwind label
// CHECK: %[[CLEANUPPAD1:.*]] = cleanuppad within %[[CATCHPAD0]] []
// CHECK: cleanupret from %[[CLEANUPPAD1]] unwind to caller
// CHECK: unreachable
// RUN: %clang_cc1 -no-opaque-pointers %s -triple wasm32-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -exception-model=wasm -target-feature +exception-handling -emit-llvm -o - -std=c++11 2>&1 | FileCheck %s --check-prefix=WARNING-DEFAULT
// RUN: %clang_cc1 -no-opaque-pointers %s -triple wasm32-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -exception-model=wasm -target-feature +exception-handling -Wwasm-exception-spec -emit-llvm -o - -std=c++11 2>&1 | FileCheck %s --check-prefix=WARNING-ON
// RUN: %clang_cc1 -no-opaque-pointers %s -triple wasm32-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -exception-model=wasm -target-feature +exception-handling -Wno-wasm-exception-spec -emit-llvm -o - -std=c++11 2>&1 | FileCheck %s --check-prefix=WARNING-OFF
// RUN: %clang_cc1 -no-opaque-pointers %s -triple wasm32-unknown-unknown -fexceptions -fcxx-exceptions -emit-llvm -o - -std=c++11 2>&1 | FileCheck %s --check-prefix=EM-EH-WARNING
// Wasm EH ignores dynamic exception specifications with types at the moment.
// This is controlled by -Wwasm-exception-spec, which is on by default. This
// warning can be suppressed with -Wno-wasm-exception-spec. Checks if a warning
// message is correctly printed or not printed depending on the options.
void test9() throw(int) {
}
// WARNING-DEFAULT: warning: dynamic exception specifications with types are currently ignored in wasm
// WARNING-ON: warning: dynamic exception specifications with types are currently ignored in wasm
// WARNING-OFF-NOT: warning: dynamic exception specifications with types are currently ignored in wasm
// EM-EH-WARNING: warning: dynamic exception specifications with types are currently ignored in wasm
// Wasm curremtly treats 'throw()' in the same way as 'noexept'. Check if the
// same warning message is printed as if when a 'noexcept' function throws.
void test10() throw() {
throw 3;
}
// WARNING-DEFAULT: warning: 'test10' has a non-throwing exception specification but can still throw
// WARNING-DEFAULT: function declared non-throwing here
// Here we only check if the command enables wasm exception handling in the
// backend so that exception handling instructions can be generated in .s file.
// RUN: %clang_cc1 -no-opaque-pointers %s -triple wasm32-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -mllvm -wasm-enable-eh -exception-model=wasm -target-feature +exception-handling -S -o - -std=c++11 | FileCheck %s --check-prefix=ASSEMBLY
// ASSEMBLY: try
// ASSEMBLY: catch
// ASSEMBLY: rethrow
// ASSEMBLY: end_try