[WebAssembly] Use rethrow intrinsic in the rethrow block

[aheejin]

Summary

Because in wasm we merge all catch clauses into one big catchpad, in
case none of the types in catch handlers matches after we test against
each of them, we should unwind to the next EH enclosing scope. For this,
we should NOT use a call to __cxa_rethrow but rather a call to our own
rethrow intrinsic, because what we're trying to do here is just to
transfer the control flow into the next enclosing EH pad (or the
caller). Calls to __cxa_rethrow should only be used after a call to
__cxa_begin_catch.

include/clang/Basic/BuiltinsWebAssembly.def

 // Floating point min/max
 BUILTIN(__builtin_wasm_min_f32, "fff", "nc")
 BUILTIN(__builtin_wasm_max_f32, "fff", "nc")
 BUILTIN(__builtin_wasm_min_f64, "ddd", "nc")
 BUILTIN(__builtin_wasm_max_f64, "ddd", "nc")
 
 // Exception handling builtins.
 TARGET_BUILTIN(__builtin_wasm_throw, "vUiv*", "r", "exception-handling")
-TARGET_BUILTIN(__builtin_wasm_rethrow, "v", "r", "exception-handling")
+TARGET_BUILTIN(__builtin_wasm_rethrow_in_catch, "v", "r", "exception-handling")
 
 // Atomic wait and notify.
 BUILTIN(__builtin_wasm_atomic_wait_i32, "ii*iLLi", "n")
 BUILTIN(__builtin_wasm_atomic_wait_i64, "iLLi*LLiLLi", "n")
 BUILTIN(__builtin_wasm_atomic_notify, "Uii*Ui", "n")
 
 // Saturating fp-to-int conversions
 TARGET_BUILTIN(__builtin_wasm_trunc_saturate_s_i32_f32, "if", "nc", "nontrapping-fptoint")

lib/CodeGen/CGBuiltin.cpp

case WebAssembly::BI__builtin_wasm_data_drop: {
     return Builder.CreateCall(Callee, {Arg});
   }
   case WebAssembly::BI__builtin_wasm_throw: {
     Value *Tag = EmitScalarExpr(E->getArg(0));
     Value *Obj = EmitScalarExpr(E->getArg(1));
     Function *Callee = CGM.getIntrinsic(Intrinsic::wasm_throw);
     return Builder.CreateCall(Callee, {Tag, Obj});
   }
-  case WebAssembly::BI__builtin_wasm_rethrow: {
-    Function *Callee = CGM.getIntrinsic(Intrinsic::wasm_rethrow);
+  case WebAssembly::BI__builtin_wasm_rethrow_in_catch: {
+    Function *Callee = CGM.getIntrinsic(Intrinsic::wasm_rethrow_in_catch);
     return Builder.CreateCall(Callee);
   }
   case WebAssembly::BI__builtin_wasm_atomic_wait_i32: {
     Value *Addr = EmitScalarExpr(E->getArg(0));
     Value *Expected = EmitScalarExpr(E->getArg(1));
     Value *Timeout = EmitScalarExpr(E->getArg(2));
     Function *Callee = CGM.getIntrinsic(Intrinsic::wasm_atomic_wait_i32);
     return Builder.CreateCall(Callee, {Addr, Expected, Timeout});

lib/CodeGen/CGException.cpp

if (EHPersonality::get(*this).isWasmPersonality() && !HasCatchAll) {
     llvm::BasicBlock *RethrowBlock = WasmCatchStartBlock;
     while (llvm::Instruction *TI = RethrowBlock->getTerminator()) {
       auto *BI = cast<llvm::BranchInst>(TI);
       assert(BI->isConditional());
       RethrowBlock = BI->getSuccessor(1);
     }
     assert(RethrowBlock != WasmCatchStartBlock && RethrowBlock->empty());
     Builder.SetInsertPoint(RethrowBlock);
-    CGM.getCXXABI().emitRethrow(*this, /*isNoReturn=*/true);
+    llvm::Function *RethrowInCatchFn =
+        CGM.getIntrinsic(llvm::Intrinsic::wasm_rethrow_in_catch);
+    EmitNoreturnRuntimeCallOrInvoke(RethrowInCatchFn, {});
   }
 
   EmitBlock(ContBB);
   incrementProfileCounter(&S);
 }
 
 namespace {
   struct CallEndCatchForFinally final : EHScopeStack::Cleanup {

test/CodeGen/builtins-wasm.c

 }
 
 void throw(unsigned int tag, void *obj) {
   return __builtin_wasm_throw(tag, obj);
   // WEBASSEMBLY32: call void @llvm.wasm.throw(i32 %{{.*}}, i8* %{{.*}})
   // WEBASSEMBLY64: call void @llvm.wasm.throw(i32 %{{.*}}, i8* %{{.*}})
 }
 
-void rethrow(void) {
-  return __builtin_wasm_rethrow();
-  // WEBASSEMBLY32: call void @llvm.wasm.rethrow()
-  // WEBASSEMBLY64: call void @llvm.wasm.rethrow()
+void rethrow_in_catch(void) {
+  return __builtin_wasm_rethrow_in_catch();
+  // WEBASSEMBLY32: call void @llvm.wasm.rethrow.in.catch()
+  // WEBASSEMBLY64: call void @llvm.wasm.rethrow.in.catch()
 }
 
 int atomic_wait_i32(int *addr, int expected, long long timeout) {
   return __builtin_wasm_atomic_wait_i32(addr, expected, timeout);
   // WEBASSEMBLY32: call i32 @llvm.wasm.atomic.wait.i32(i32* %{{.*}}, i32 %{{.*}}, i64 %{{.*}})
   // WEBASSEMBLY64: call i32 @llvm.wasm.atomic.wait.i32(i32* %{{.*}}, i32 %{{.*}}, i64 %{{.*}})
 }
 

test/CodeGenCXX/wasm-eh.cpp

 
 // 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 @__cxa_rethrow() {{.*}} [ "funclet"(token %[[CATCHPAD]]) ]
+// CHECK-NEXT:   call void @llvm.wasm.rethrow.in.catch() {{.*}} [ "funclet"(token %[[CATCHPAD]]) ]
 // CHECK-NEXT:   unreachable
 
 // Single catch-all
 void test1() {
   try {
     may_throw();
   } catch (...) {
     dont_throw();

 // 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 @__cxa_rethrow() {{.*}} [ "funclet"(token %[[CATCHPAD]]) ]
+// CHECK-NEXT:   invoke void @llvm.wasm.rethrow.in.catch() {{.*}} [ "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 %struct.Cleanup* @_ZN7CleanupD1Ev(%struct.Cleanup* %{{.*}}) {{.*}} [ "funclet"(token %[[CLEANUPPAD2]]) ]
 // CHECK-NEXT:   cleanupret from %[[CLEANUPPAD2]] unwind label %[[EHCLEANUP_BB3:.*]]
 
 // CHECK: [[EHCLEANUP_BB3]]:

 // 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 @__cxa_rethrow() {{.*}} [ "funclet"(token %[[CATCHPAD0]]) ]
+// CHECK:   invoke void @llvm.wasm.rethrow.in.catch() {{.*}} [ "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:   %[[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 @__cxa_rethrow() {{.*}} [ "funclet"(token %[[CATCHPAD1]]) ]
+// CHECK:   invoke void @llvm.wasm.rethrow.in.catch() {{.*}} [ "funclet"(token %[[CATCHPAD1]]) ]
 
 // CHECK:   catchret from %[[CATCHPAD0]] to label
 
-// CHECK:   call void @__cxa_rethrow() {{.*}} [ "funclet"(token %[[CATCHPAD0]]) ]
+// CHECK:   call void @llvm.wasm.rethrow.in.catch() {{.*}} [ "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