[WebAssembly] Make Emscripten EH work with Emscripten SjLj

[aheejin]

Summary

When Emscripten EH mixes with Emscripten SjLj, we are not currently
handling some of them correctly. There are three cases:

1. The current function calls setjmp and there is an invoke to a function that can either throw or longjmp. In this case, we have to check both for exception and longjmp. We are currently handling this case correctly: https://github.com/llvm/llvm-project/blob/0c0eb76782d5224b8d81a5afbb9a152bcf7c94c7/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp#L1058-L1090 When inserting routines for functions that can longjmp, which we do only for setjmp-calling functions, we check if the function was previously an invoke and handle it correctly.

2. The current function does NOT call setjmp and there is an invoke to a function that can either throw or longjmp. Because there is no setjmp call, we haven't been doing any check for functions that can longjmp. But in that case, for invoke, we only check for an exception and if it is not an exception we reset __THREW__ to 0, which can silently swallow the longjmp: https://github.com/llvm/llvm-project/blob/0c0eb76782d5224b8d81a5afbb9a152bcf7c94c7/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp#L70-L80 This CL fixes this.

3. The current function calls setjmp and there is no invoke. Because it is not an invoke, we haven't been doing any check for functions that can throw, and only insert longjmp-checking routines for functions that can longjmp. But in that case, if a longjmpable function throws, we only check for a longjmp so if it is not a longjmp we reset __THREW__ to 0, which can silently swallow the exception: https://github.com/llvm/llvm-project/blob/0c0eb76782d5224b8d81a5afbb9a152bcf7c94c7/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp#L156-L169 This CL fixes this.

To do that, this moves around some code, so we register necessary
functions for both EH and SjLj and precompute some data (the set of
functions that contains setjmp) before doing actual EH or SjLj
transformation.

[aheejin]

llvm/lib/Target/WebAssembly/WebAssembly.h

28–30

We are using DoSjLj and EnableSjLj for different meanings in the pass. EnableSjLj is true by default in Emscripten setting, but DoSjLj is true only when setjmp or longjmp is really used. This was confusing so I changed it to Enable.

llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp

219

This was a local variable; I needed to access this from multiple functions so I hoisted it here.

238–239

This was a local variable too. It was computed right before we run runSjLjOnFunction, but now we precompute this because we need to access this also within runEHOnFunction.

[aheejin]

Remove a newline

llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll

104

This test has been moved to lower-em-ehsjlj.ll

[aheejin]

typo

[aheejin]

Some more tests need fixing.

[aheejin]

Tests fix

[aheejin]

llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll

248–250

This file is only for testing sjlj, so I made this nounwind. Mixed exceptions and sjlj cases are tested in lower-em-ehsjlj.ll.

[dschuff]

llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp

238

786

834

I think this first sentence would be clearer as "the thrown value can be either an exception or a longjmp", or "could be a longjmp instead of an exception". Likewise in the comment below.

[aheejin]

This CL makes 2nd and 3rd tests in https://github.com/emscripten-core/emscripten/pull/14732 work.

llvm/lib/Target/WebAssembly/WebAssembly.h

 
 namespace llvm {
 
 class WebAssemblyTargetMachine;
 class ModulePass;
 class FunctionPass;
 
 // LLVM IR passes.
-ModulePass *createWebAssemblyLowerEmscriptenEHSjLj(bool DoEH, bool DoSjLj);
+ModulePass *createWebAssemblyLowerEmscriptenEHSjLj(bool EnableEH,
+                                                   bool EnableSjLj);
 ModulePass *createWebAssemblyLowerGlobalDtors();
 ModulePass *createWebAssemblyAddMissingPrototypes();
 ModulePass *createWebAssemblyFixFunctionBitcasts();
 FunctionPass *createWebAssemblyOptimizeReturned();
 
 // ISel and immediate followup passes.
 FunctionPass *createWebAssemblyISelDag(WebAssemblyTargetMachine &TM,
                                        CodeGenOpt::Level OptLevel);
 FunctionPass *createWebAssemblyArgumentMove();

llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp

EHAllowlist("emscripten-cxx-exceptions-allowed",
                          "exception handling is enabled (see emscripten "
                          "EMSCRIPTEN_CATCHING_ALLOWED options)"),
                 cl::CommaSeparated);
 
 namespace {
 class WebAssemblyLowerEmscriptenEHSjLj final : public ModulePass {
   bool EnableEH;   // Enable exception handling
   bool EnableSjLj; // Enable setjmp/longjmp handling
+  bool DoSjLj;     // Whether we actually perform setjmp/longjmp handling
 
   GlobalVariable *ThrewGV = nullptr;
   GlobalVariable *ThrewValueGV = nullptr;
   Function *GetTempRet0Func = nullptr;
   Function *SetTempRet0Func = nullptr;
   Function *ResumeF = nullptr;
   Function *EHTypeIDF = nullptr;
   Function *EmLongjmpF = nullptr;
   Function *SaveSetjmpF = nullptr;
   Function *TestSetjmpF = nullptr;
 
   // __cxa_find_matching_catch_N functions.
   // Indexed by the number of clauses in an original landingpad instruction.
   DenseMap<int, Function *> FindMatchingCatches;
   // Map of <function signature string, invoke_ wrappers>
   StringMap<Function *> InvokeWrappers;
   // Set of allowed function names for exception handling
   std::set<std::string> EHAllowlistSet;
+  // Functions that contains calls to setjmp
+  SmallPtrSet<Function *, 8> SetjmpUsers;
 
   StringRef getPassName() const override {
     return "WebAssembly Lower Emscripten Exceptions";
   }
 
   bool runEHOnFunction(Function &F);
   bool runSjLjOnFunction(Function &F);
   Function *getFindMatchingCatch(Module &M, unsigned NumClauses);
 
   Value *wrapInvoke(CallBase *CI);
   void wrapTestSetjmp(BasicBlock *BB, DebugLoc DL, Value *Threw,
                       Value *SetjmpTable, Value *SetjmpTableSize, Value *&Label,
                       Value *&LongjmpResult, BasicBlock *&EndBB);
   Function *getInvokeWrapper(CallBase *CI);
 
   bool areAllExceptionsAllowed() const { return EHAllowlistSet.empty(); }
   bool canLongjmp(Module &M, const Value *Callee) const;
   bool isEmAsmCall(Module &M, const Value *Callee) const;
+  bool supportsException(const Function *F) const {
+    return EnableEH && (areAllExceptionsAllowed() ||
+                        EHAllowlistSet.count(std::string(F->getName())));
+  }
 
   void rebuildSSA(Function &F);
 
 public:
   static char ID;
 
   WebAssemblyLowerEmscriptenEHSjLj(bool EnableEH = true, bool EnableSjLj = true)
       : ModulePass(ID), EnableEH(EnableEH), EnableSjLj(EnableSjLj) {

 
 static bool canThrow(const Value *V) {
   if (const auto *F = dyn_cast<const Function>(V)) {
     // Intrinsics cannot throw
     if (F->isIntrinsic())
       return false;
     StringRef Name = F->getName();
     // leave setjmp and longjmp (mostly) alone, we process them properly later
-    if (Name == "setjmp" || Name == "longjmp")
+    if (Name == "setjmp" || Name == "longjmp" || Name == "emscripten_longjmp")
       return false;
     return !F->doesNotThrow();
   }
   // not a function, so an indirect call - can throw, we can't tell
   return true;
 }
 
 // Get a global variable with the given name. If it doesn't exist declare it,
bool WebAssemblyLowerEmscriptenEHSjLj::runOnModule(Module &M) {
 
   LLVMContext &C = M.getContext();
   IRBuilder<> IRB(C);
 
   Function *SetjmpF = M.getFunction("setjmp");
   Function *LongjmpF = M.getFunction("longjmp");
   bool SetjmpUsed = SetjmpF && !SetjmpF->use_empty();
   bool LongjmpUsed = LongjmpF && !LongjmpF->use_empty();
-  bool DoSjLj = EnableSjLj && (SetjmpUsed || LongjmpUsed);
+  DoSjLj = EnableSjLj && (SetjmpUsed || LongjmpUsed);
 
   auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
   assert(TPC && "Expected a TargetPassConfig");
   auto &TM = TPC->getTM<WebAssemblyTargetMachine>();
 
   if (EnableEH && TM.Options.ExceptionModel == ExceptionHandling::Wasm)
     report_fatal_error("-exception-model=wasm not allowed with "
                        "-enable-emscripten-cxx-exceptions");
 
   // Declare (or get) global variables __THREW__, __threwValue, and
   // getTempRet0/setTempRet0 function which are used in common for both
   // exception handling and setjmp/longjmp handling
   ThrewGV = getGlobalVariable(M, getAddrIntType(&M), TM, "__THREW__");
   ThrewValueGV = getGlobalVariable(M, IRB.getInt32Ty(), TM, "__threwValue");
   GetTempRet0Func = getEmscriptenFunction(
       FunctionType::get(IRB.getInt32Ty(), false), "getTempRet0", &M);
   SetTempRet0Func = getEmscriptenFunction(
       FunctionType::get(IRB.getVoidTy(), IRB.getInt32Ty(), false),
       "setTempRet0", &M);
   GetTempRet0Func->setDoesNotThrow();
   SetTempRet0Func->setDoesNotThrow();
 
   bool Changed = false;
 
-  // Exception handling
+  // Function registration for exception handling
   if (EnableEH) {
     // Register __resumeException function
     FunctionType *ResumeFTy =
         FunctionType::get(IRB.getVoidTy(), IRB.getInt8PtrTy(), false);
     ResumeF = getEmscriptenFunction(ResumeFTy, "__resumeException", &M);
 
     // Register llvm_eh_typeid_for function
     FunctionType *EHTypeIDTy =
         FunctionType::get(IRB.getInt32Ty(), IRB.getInt8PtrTy(), false);
     EHTypeIDF = getEmscriptenFunction(EHTypeIDTy, "llvm_eh_typeid_for", &M);
-
-    for (Function &F : M) {
-      if (F.isDeclaration())
-        continue;
-      Changed |= runEHOnFunction(F);
-    }
   }
 
-  // Setjmp/longjmp handling
+  // Function registration and data pre-gathering for setjmp/longjmp handling
   if (DoSjLj) {
-    Changed = true; // We have setjmp or longjmp somewhere
-
     // Register emscripten_longjmp function
     FunctionType *FTy = FunctionType::get(
         IRB.getVoidTy(), {getAddrIntType(&M), IRB.getInt32Ty()}, false);
     EmLongjmpF = getEmscriptenFunction(FTy, "emscripten_longjmp", &M);
 
-    if (LongjmpF)
-      replaceLongjmpWithEmscriptenLongjmp(LongjmpF, EmLongjmpF);
-
     if (SetjmpF) {
       // Register saveSetjmp function
       FunctionType *SetjmpFTy = SetjmpF->getFunctionType();
       FTy = FunctionType::get(Type::getInt32PtrTy(C),
                               {SetjmpFTy->getParamType(0), IRB.getInt32Ty(),
                                Type::getInt32PtrTy(C), IRB.getInt32Ty()},
                               false);
       SaveSetjmpF = getEmscriptenFunction(FTy, "saveSetjmp", &M);
 
       // Register testSetjmp function
       FTy = FunctionType::get(
           IRB.getInt32Ty(),
           {getAddrIntType(&M), Type::getInt32PtrTy(C), IRB.getInt32Ty()},
           false);
       TestSetjmpF = getEmscriptenFunction(FTy, "testSetjmp", &M);
 
-      // Only traverse functions that uses setjmp in order not to insert
-      // unnecessary prep / cleanup code in every function
-      SmallPtrSet<Function *, 8> SetjmpUsers;
+      // Precompute setjmp users
       for (User *U : SetjmpF->users()) {
         auto *UI = cast<Instruction>(U);
         SetjmpUsers.insert(UI->getFunction());
       }
+    }
+  }
+
+  // Exception handling transformation
+  if (EnableEH) {
+    for (Function &F : M) {
+      if (F.isDeclaration())
+        continue;
+      Changed |= runEHOnFunction(F);
+    }
+  }
+
+  // Setjmp/longjmp handling transformation
+  if (DoSjLj) {
+    Changed = true; // We have setjmp or longjmp somewhere
+    if (LongjmpF)
+      replaceLongjmpWithEmscriptenLongjmp(LongjmpF, EmLongjmpF);
+    // Only traverse functions that uses setjmp in order not to insert
+    // unnecessary prep / cleanup code in every function
+    if (SetjmpF)
       for (Function *F : SetjmpUsers)
         runSjLjOnFunction(*F);
-    }
-  }
 
   if (!Changed) {
     // Delete unused global variables and functions
     if (ResumeF)
       ResumeF->eraseFromParent();
     if (EHTypeIDF)
       EHTypeIDF->eraseFromParent();
     if (EmLongjmpF)

 
 bool WebAssemblyLowerEmscriptenEHSjLj::runEHOnFunction(Function &F) {
   Module &M = *F.getParent();
   LLVMContext &C = F.getContext();
   IRBuilder<> IRB(C);
   bool Changed = false;
   SmallVector<Instruction *, 64> ToErase;
   SmallPtrSet<LandingPadInst *, 32> LandingPads;
-  bool AllowExceptions = areAllExceptionsAllowed() ||
-                         EHAllowlistSet.count(std::string(F.getName()));
 
   for (BasicBlock &BB : F) {
     auto *II = dyn_cast<InvokeInst>(BB.getTerminator());
     if (!II)
       continue;
     Changed = true;
     LandingPads.insert(II->getLandingPadInst());
     IRB.SetInsertPoint(II);
 
-    bool NeedInvoke = AllowExceptions && canThrow(II->getCalledOperand());
+    const Value *Callee = II->getCalledOperand();
+    bool NeedInvoke = supportsException(&F) && canThrow(Callee);
     if (NeedInvoke) {
       // Wrap invoke with invoke wrapper and generate preamble/postamble
       Value *Threw = wrapInvoke(II);
       ToErase.push_back(II);
 
+      // If setjmp/longjmp handling is enabled, the thrown value can be not an
+      // exception but a longjmp. If the current function contains calls to
+      // setjmp, it will be appropriately handled in runSjLjOnFunction. But even
+      // if the function does not contain setjmp calls, we shouldn't silently
+      // ignore longjmps; we should rethrow them so they can be correctly
+      // handled in somewhere up the call chain where setjmp is.
+      // __THREW__'s value is 0 when nothing happened, 1 when an exception is
+      // thrown, other values when longjmp is thrown.
+      //
+      // if (%__THREW__.val == 0 || %__THREW__.val == 1)
+      //   goto %tail
+      // else
+      //   goto %longjmp.rethrow
+      //
+      // longjmp.rethrow: ;; This is longjmp. Rethrow it
+      //   %__threwValue.val = __threwValue
+      //   emscripten_longjmp(%__THREW__.val, %__threwValue.val);
+      //
+      // tail: ;; Nothing happened or an exception is thrown
+      //   ... Continue exception handling ...
+      if (DoSjLj && !SetjmpUsers.count(&F) && canLongjmp(M, Callee)) {
+        BasicBlock *Tail = BasicBlock::Create(C, "tail", &F);
+        BasicBlock *RethrowBB = BasicBlock::Create(C, "longjmp.rethrow", &F);
+        Value *CmpEqOne =
+            IRB.CreateICmpEQ(Threw, getAddrSizeInt(&M, 1), "cmp.eq.one");
+        Value *CmpEqZero =
+            IRB.CreateICmpEQ(Threw, getAddrSizeInt(&M, 0), "cmp.eq.zero");
+        Value *Or = IRB.CreateOr(CmpEqZero, CmpEqOne, "or");
+        IRB.CreateCondBr(Or, Tail, RethrowBB);
+        IRB.SetInsertPoint(RethrowBB);
+        Value *ThrewValue = IRB.CreateLoad(IRB.getInt32Ty(), ThrewValueGV,
+                                           ThrewValueGV->getName() + ".val");
+        IRB.CreateCall(EmLongjmpF, {Threw, ThrewValue});
+
+        IRB.CreateUnreachable();
+        IRB.SetInsertPoint(Tail);
+      }
+
       // Insert a branch based on __THREW__ variable
       Value *Cmp = IRB.CreateICmpEQ(Threw, getAddrSizeInt(&M, 1), "cmp");
       IRB.CreateCondBr(Cmp, II->getUnwindDest(), II->getNormalDest());
 
     } else {
       // This can't throw, and we don't need this invoke, just replace it with a
       // call+branch
       SmallVector<Value *, 16> Args(II->args());
for (Instruction &I : *BB) {
         assert(ThrewResetSI && "Cannot find __THREW__ store after invoke");
         Tail = SplitBlock(BB, ThrewResetSI->getNextNode());
 
       } else {
         // Wrap call with invoke wrapper and generate preamble/postamble
         Threw = wrapInvoke(CI);
         ToErase.push_back(CI);
         Tail = SplitBlock(BB, CI->getNextNode());
+
+        // If exception handling is enabled, the thrown value can be not a
+        // longjmp but an exception, in which case we shouldn't silently ignore
+        // exceptions; we should rethrow them.
+        // __THREW__'s value is 0 when nothing happened, 1 when an exception is
+        // thrown, other values when longjmp is thrown.
+        //
+        // if (%__THREW__.val == 1)
+        //   goto %eh.rethrow
+        // else
+        //   goto %normal
+        //
+        // eh.rethrow: ;; Rethrow exception
+        //   %exn = call @__cxa_find_matching_catch_2() ;; Retrieve thrown ptr
+        //   __resumeException(%exn)
+        //
+        // normal:
+        //   <-- Insertion point. Will insert sjlj handling code from here
+        //   goto %tail
+        //
+        // tail:
+        //   ...
+        if (supportsException(&F) && canThrow(Callee)) {
+          IRB.SetInsertPoint(CI);
+          // We will add a new conditional branch. So remove the branch created
+          // when we split the BB
+          ToErase.push_back(BB->getTerminator());
+          BasicBlock *NormalBB = BasicBlock::Create(C, "normal", &F);
+          BasicBlock *RethrowBB = BasicBlock::Create(C, "eh.rethrow", &F);
+          Value *CmpEqOne =
+              IRB.CreateICmpEQ(Threw, getAddrSizeInt(&M, 1), "cmp.eq.one");
+          IRB.CreateCondBr(CmpEqOne, RethrowBB, NormalBB);
+          IRB.SetInsertPoint(RethrowBB);
+          CallInst *Exn = IRB.CreateCall(getFindMatchingCatch(M, 0), {}, "exn");
+          IRB.CreateCall(ResumeF, {Exn});
+          IRB.CreateUnreachable();
+          IRB.SetInsertPoint(NormalBB);
+          IRB.CreateBr(Tail);
+          BB = NormalBB; // New insertion point to insert testSetjmp()
+        }
       }
 
       // We need to replace the terminator in Tail - SplitBlock makes BB go
       // straight to Tail, we need to check if a longjmp occurred, and go to the
       // right setjmp-tail if so
       ToErase.push_back(BB->getTerminator());
 
       // Generate a function call to testSetjmp function and preamble/postamble

llvm/test/CodeGen/WebAssembly/lower-em-ehsjlj.ll

+; RUN: opt < %s -wasm-lower-em-ehsjlj -S | FileCheck %s
+; RUN: llc < %s
+
+; Tests for cases when exception handling and setjmp/longjmp handling are mixed.
+
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown"
+
+%struct.__jmp_buf_tag = type { [6 x i32], i32, [32 x i32] }
+
+; There is a function call (@foo) that can either throw an exception or longjmp
+; and there is also a setjmp call. When @foo throws, we have to check both for
+; exception and longjmp and jump to exception or longjmp handling BB depending
+; on the result.
+define void @setjmp_longjmp_exception() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+; CHECK-LABEL: @setjmp_longjmp_exception
+entry:
+  %buf = alloca [1 x %struct.__jmp_buf_tag], align 16
+  %arraydecay = getelementptr inbounds [1 x %struct.__jmp_buf_tag], [1 x %struct.__jmp_buf_tag]* %buf, i32 0, i32 0
+  %call = call i32 @setjmp(%struct.__jmp_buf_tag* %arraydecay) #0
+  invoke void @foo()
+          to label %try.cont unwind label %lpad
+
+; CHECK:    entry.split:
+; CHECK:      %[[CMP0:.*]] = icmp ne i32 %__THREW__.val, 0
+; CHECK-NEXT: %__threwValue.val = load i32, i32* @__threwValue
+; CHECK-NEXT: %[[CMP1:.*]] = icmp ne i32 %__threwValue.val, 0
+; CHECK-NEXT: %[[CMP:.*]] = and i1 %[[CMP0]], %[[CMP1]]
+; CHECK-NEXT: br i1 %[[CMP]], label %if.then1, label %if.else1
+
+; This is exception checking part. %if.else1 leads here
+; CHECK:    entry.split.split:
+; CHECK-NEXT: %[[CMP:.*]] = icmp eq i32 %__THREW__.val, 1
+; CHECK-NEXT: br i1 %[[CMP]], label %lpad, label %try.cont
+
+; longjmp checking part
+; CHECK:    if.then1:
+; CHECK:      call i32 @testSetjmp
+
+lpad:                                             ; preds = %entry
+  %0 = landingpad { i8*, i32 }
+          catch i8* null
+  %1 = extractvalue { i8*, i32 } %0, 0
+  %2 = extractvalue { i8*, i32 } %0, 1
+  %3 = call i8* @__cxa_begin_catch(i8* %1) #2
+  call void @__cxa_end_catch()
+  br label %try.cont
+
+try.cont:                                         ; preds = %entry, %lpad
+  ret void
+}
+
+; @foo can either throw an exception or longjmp. Because this function doesn't
+; have any setjmp calls, we only handle exceptions in this function. But because
+; sjlj is enabled, we check if the thrown value is longjmp and if so rethrow it
+; by calling @emscripten_longjmp.
+define void @rethrow_longjmp() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+; CHECK-LABEL: @rethrow_longjmp
+entry:
+  invoke void @foo()
+          to label %try.cont unwind label %lpad
+; CHECK:    entry:
+; CHECK:      %cmp.eq.one = icmp eq i32 %__THREW__.val, 1
+; CHECK-NEXT: %cmp.eq.zero = icmp eq i32 %__THREW__.val, 0
+; CHECK-NEXT: %or = or i1 %cmp.eq.zero, %cmp.eq.one
+; CHECK-NEXT: br i1 %or, label %tail, label %longjmp.rethrow
+
+; CHECK:    tail:
+; CHECK-NEXT: %cmp = icmp eq i32 %__THREW__.val, 1
+; CHECK-NEXT: br i1 %cmp, label %lpad, label %try.cont
+
+; CHECK:    longjmp.rethrow:
+; CHECK-NEXT: %__threwValue.val = load i32, i32* @__threwValue, align 4
+; CHECK-NEXT: call void @emscripten_longjmp(i32 %__THREW__.val, i32 %__threwValue.val)
+; CHECK-NEXT: unreachable
+
+lpad:                                             ; preds = %entry
+  %0 = landingpad { i8*, i32 }
+          catch i8* null
+  %1 = extractvalue { i8*, i32 } %0, 0
+  %2 = extractvalue { i8*, i32 } %0, 1
+  %3 = call i8* @__cxa_begin_catch(i8* %1) #5
+  call void @__cxa_end_catch()
+  br label %try.cont
+
+try.cont:                                         ; preds = %entry, %lpad
+  ret void
+}
+
+; This function contains a setjmp call and no invoke, so we only handle longjmp
+; here. But @foo can also throw an exception, so we check if an exception is
+; thrown and if so rethrow it by calling @__resumeException.
+define void @rethrow_exception() {
+; CHECK-LABEL: @rethrow_exception
+entry:
+  %buf = alloca [1 x %struct.__jmp_buf_tag], align 16
+  %arraydecay = getelementptr inbounds [1 x %struct.__jmp_buf_tag], [1 x %struct.__jmp_buf_tag]* %buf, i32 0, i32 0
+  %call = call i32 @setjmp(%struct.__jmp_buf_tag* %arraydecay) #0
+  %cmp = icmp ne i32 %call, 0
+  br i1 %cmp, label %return, label %if.end
+
+if.end:                                           ; preds = %entry
+  call void @foo()
+  br label %return
+
+; CHECK:    if.end:
+; CHECK:      %cmp.eq.one = icmp eq i32 %__THREW__.val, 1
+; CHECK-NEXT: br i1 %cmp.eq.one, label %eh.rethrow, label %normal
+
+; CHECK:    normal:
+; CHECK-NEXT: icmp ne i32 %__THREW__.val, 0
+
+; CHECK:    eh.rethrow:
+; CHECK-NEXT: %exn = call i8* @__cxa_find_matching_catch_2()
+; CHECK-NEXT: call void @__resumeException(i8* %exn)
+; CHECK-NEXT: unreachable
+
+return:                                           ; preds = %entry, %if.end
+  ret void
+}
+
+declare void @foo()
+; Function Attrs: returns_twice
+declare i32 @setjmp(%struct.__jmp_buf_tag*)
+; Function Attrs: noreturn
+declare void @longjmp(%struct.__jmp_buf_tag*, i32)
+declare i32 @__gxx_personality_v0(...)
+declare i8* @__cxa_begin_catch(i8*)
+declare void @__cxa_end_catch()
+
+attributes #0 = { returns_twice }
+attributes #1 = { noreturn }

llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll

 ; CHECK: @__invoke_void(void ()* @foo)
 
 ; CHECK: entry.split.split:
 ; CHECK-NEXT: %[[BUF:.*]] = bitcast i32* %[[SETJMP_TABLE]] to i8*
 ; CHECK-NEXT: tail call void @free(i8* %[[BUF]])
 ; CHECK-NEXT: ret void
 }
 
-; Test a case when a function call is within try-catch, after a setjmp
-define void @exception_and_longjmp() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
-; CHECK-LABEL: @exception_and_longjmp
-entry:
-  %buf = alloca [1 x %struct.__jmp_buf_tag], align 16
-  %arraydecay = getelementptr inbounds [1 x %struct.__jmp_buf_tag], [1 x %struct.__jmp_buf_tag]* %buf, i32 0, i32 0
-  %call = call i32 @setjmp(%struct.__jmp_buf_tag* %arraydecay) #0
-  invoke void @foo()
-          to label %try.cont unwind label %lpad
-
-; CHECK: entry.split:
-; CHECK: store [[PTR]] 0, [[PTR]]* @__THREW__
-; CHECK-NEXT: call cc{{.*}} void @__invoke_void(void ()* @foo)
-; CHECK-NEXT: %[[__THREW__VAL:.*]] = load [[PTR]], [[PTR]]* @__THREW__
-; CHECK-NEXT: store [[PTR]] 0, [[PTR]]* @__THREW__
-; CHECK-NEXT: %[[CMP0:.*]] = icmp ne [[PTR]] %[[__THREW__VAL]], 0
-; CHECK-NEXT: %[[THREWVALUE_VAL:.*]] = load i32, i32* @__threwValue
-; CHECK-NEXT: %[[CMP1:.*]] = icmp ne i32 %[[THREWVALUE_VAL]], 0
-; CHECK-NEXT: %[[CMP:.*]] = and i1 %[[CMP0]], %[[CMP1]]
-; CHECK-NEXT: br i1 %[[CMP]], label %if.then1, label %if.else1
-
-; CHECK: entry.split.split:
-; CHECK-NEXT: %[[CMP:.*]] = icmp eq [[PTR]] %[[__THREW__VAL]], 1
-; CHECK-NEXT: br i1 %[[CMP]], label %lpad, label %try.cont
-
-lpad:                                             ; preds = %entry
-  %0 = landingpad { i8*, i32 }
-          catch i8* null
-  %1 = extractvalue { i8*, i32 } %0, 0
-  %2 = extractvalue { i8*, i32 } %0, 1
-  %3 = call i8* @__cxa_begin_catch(i8* %1) #2
-  call void @__cxa_end_catch()
-  br label %try.cont
-
-try.cont:                                         ; preds = %entry, %lpad
-  ret void
-}
-
 ; Test SSA validity
 define void @ssa(i32 %n) {
 ; CHECK-LABEL: @ssa
 entry:
   %buf = alloca [1 x %struct.__jmp_buf_tag], align 16
   %cmp = icmp sgt i32 %n, 5
   br i1 %cmp, label %if.then, label %if.end
 ; CHECK: entry:
entry:
 
   ; Pass longjmp as a function argument. This is a call but longjmp is not a
   ; callee but an argument.
   call void @take_longjmp(void (%struct.__jmp_buf_tag*, i32)* @longjmp)
   ; CHECK: call void @take_longjmp(void (%struct.__jmp_buf_tag*, i32)* bitcast (void ([[PTR]], i32)* @emscripten_longjmp to void (%struct.__jmp_buf_tag*, i32)*))
   ret void
 }
 
-declare void @foo()
+; Function Attrs: nounwind
+declare void @foo() #2
 ; Function Attrs: returns_twice
 declare i32 @setjmp(%struct.__jmp_buf_tag*) #0
 ; Function Attrs: noreturn
 declare void @longjmp(%struct.__jmp_buf_tag*, i32) #1
 declare i32 @__gxx_personality_v0(...)
 declare i8* @__cxa_begin_catch(i8*)
 declare void @__cxa_end_catch()
 declare i8* @malloc(i32)
 declare void @free(i8*)

 attributes #1 = { noreturn }
 attributes #2 = { nounwind }
 attributes #3 = { allocsize(0) }
 ; CHECK-DAG: attributes #{{[0-9]+}} = { nounwind "wasm-import-module"="env" "wasm-import-name"="getTempRet0" }
 ; CHECK-DAG: attributes #{{[0-9]+}} = { nounwind "wasm-import-module"="env" "wasm-import-name"="setTempRet0" }
 ; CHECK-DAG: attributes #{{[0-9]+}} = { "wasm-import-module"="env" "wasm-import-name"="__resumeException" }
 ; CHECK-DAG: attributes #{{[0-9]+}} = { "wasm-import-module"="env" "wasm-import-name"="llvm_eh_typeid_for" }
 ; CHECK-DAG: attributes #{{[0-9]+}} = { "wasm-import-module"="env" "wasm-import-name"="__invoke_void" }
-; CHECK-DAG: attributes #{{[0-9]+}} = { "wasm-import-module"="env" "wasm-import-name"="__cxa_find_matching_catch_3" }
+; CHECK-DAG: attributes #{{[0-9]+}} = { "wasm-import-module"="env" "wasm-import-name"="__cxa_find_matching_catch_2" }
 ; CHECK-DAG: attributes #{{[0-9]+}} = { "wasm-import-module"="env" "wasm-import-name"="saveSetjmp" }
 ; CHECK-DAG: attributes #{{[0-9]+}} = { "wasm-import-module"="env" "wasm-import-name"="testSetjmp" }
 ; CHECK-DAG: attributes #{{[0-9]+}} = { "wasm-import-module"="env" "wasm-import-name"="emscripten_longjmp" }
 ; CHECK-DAG: attributes #{{[0-9]+}} = { "wasm-import-module"="env" "wasm-import-name"="__invoke_i8*_i32_%struct.__jmp_buf_tag*" }
 ; CHECK-DAG: attributes #[[ALLOCSIZE_ATTR]] = { allocsize(1) }
 
 !llvm.dbg.cu = !{!2}
 !llvm.module.flags = !{!0}