1 //=== WebAssemblyLowerEmscriptenEHSjLj.cpp - Lower exceptions for Emscripten =//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
11 /// \brief This file lowers exception-related instructions and setjmp/longjmp
12 /// function calls in order to use Emscripten's JavaScript try and catch
15 /// To handle exceptions and setjmp/longjmps, this scheme relies on JavaScript's
16 /// try and catch syntax and relevant exception-related libraries implemented
17 /// in JavaScript glue code that will be produced by Emscripten. This is similar
18 /// to the current Emscripten asm.js exception handling in fastcomp. For
19 /// fastcomp's EH / SjLj scheme, see these files in fastcomp LLVM branch:
20 /// (Location: https://github.com/kripken/emscripten-fastcomp)
21 /// lib/Target/JSBackend/NaCl/LowerEmExceptionsPass.cpp
22 /// lib/Target/JSBackend/NaCl/LowerEmSetjmp.cpp
23 /// lib/Target/JSBackend/JSBackend.cpp
24 /// lib/Target/JSBackend/CallHandlers.h
26 /// * Exception handling
27 /// This pass lowers invokes and landingpads into library functions in JS glue
28 /// code. Invokes are lowered into function wrappers called invoke wrappers that
29 /// exist in JS side, which wraps the original function call with JS try-catch.
30 /// If an exception occurred, cxa_throw() function in JS side sets some
31 /// variables (see below) so we can check whether an exception occurred from
32 /// wasm code and handle it appropriately.
34 /// * Setjmp-longjmp handling
35 /// This pass lowers setjmp to a reasonably-performant approach for emscripten.
36 /// The idea is that each block with a setjmp is broken up into two parts: the
37 /// part containing setjmp and the part right after the setjmp. The latter part
38 /// is either reached from the setjmp, or later from a longjmp. To handle the
39 /// longjmp, all calls that might longjmp are also called using invoke wrappers
40 /// and thus JS / try-catch. JS longjmp() function also sets some variables so
41 /// we can check / whether a longjmp occurred from wasm code. Each block with a
42 /// function call that might longjmp is also split up after the longjmp call.
43 /// After the longjmp call, we check whether a longjmp occurred, and if it did,
44 /// which setjmp it corresponds to, and jump to the right post-setjmp block.
45 /// We assume setjmp-longjmp handling always run after EH handling, which means
46 /// we don't expect any exception-related instructions when SjLj runs.
47 /// FIXME Currently this scheme does not support indirect call of setjmp,
48 /// because of the limitation of the scheme itself. fastcomp does not support it
51 /// In detail, this pass does following things:
53 /// 1) Create three global variables: __THREW__, __threwValue, and __tempRet0.
54 /// __tempRet0 will be set within __cxa_find_matching_catch() function in
55 /// JS library, and __THREW__ and __threwValue will be set in invoke wrappers
56 /// in JS glue code. For what invoke wrappers are, refer to 3). These
57 /// variables are used for both exceptions and setjmp/longjmps.
58 /// __THREW__ indicates whether an exception or a longjmp occurred or not. 0
59 /// means nothing occurred, 1 means an exception occurred, and other numbers
60 /// mean a longjmp occurred. In the case of longjmp, __threwValue variable
61 /// indicates the corresponding setjmp buffer the longjmp corresponds to.
62 /// In exception handling, __tempRet0 indicates the type of an exception
63 /// caught, and in setjmp/longjmp, it means the second argument to longjmp
66 /// * Exception handling
68 /// 2) Create setThrew and setTempRet0 functions.
69 /// The global variables created in 1) will exist in wasm address space,
70 /// but their values should be set in JS code, so we provide these functions
71 /// as interfaces to JS glue code. These functions are equivalent to the
72 /// following JS functions, which actually exist in asm.js version of JS
75 /// function setThrew(threw, value) {
76 /// if (__THREW__ == 0) {
77 /// __THREW__ = threw;
78 /// __threwValue = value;
82 /// function setTempRet0(value) {
83 /// __tempRet0 = value;
87 /// invoke @func(arg1, arg2) to label %invoke.cont unwind label %lpad
90 /// call @__invoke_SIG(func, arg1, arg2)
91 /// %__THREW__.val = __THREW__;
93 /// if (%__THREW__.val == 1)
97 /// SIG is a mangled string generated based on the LLVM IR-level function
98 /// signature. After LLVM IR types are lowered to the target wasm types,
99 /// the names for these wrappers will change based on wasm types as well,
100 /// as in invoke_vi (function takes an int and returns void). The bodies of
101 /// these wrappers will be generated in JS glue code, and inside those
102 /// wrappers we use JS try-catch to generate actual exception effects. It
103 /// also calls the original callee function. An example wrapper in JS code
104 /// would look like this:
105 /// function invoke_vi(index,a1) {
107 /// Module["dynCall_vi"](index,a1); // This calls original callee
109 /// if (typeof e !== 'number' && e !== 'longjmp') throw e;
110 /// asm["setThrew"](1, 0); // setThrew is called here
113 /// If an exception is thrown, __THREW__ will be set to true in a wrapper,
114 /// so we can jump to the right BB based on this value.
117 /// %val = landingpad catch c1 catch c2 catch c3 ...
120 /// %fmc = call @__cxa_find_matching_catch_N(c1, c2, c3, ...)
121 /// %val = {%fmc, __tempRet0}
123 /// Here N is a number calculated based on the number of clauses.
124 /// Global variable __tempRet0 is set within __cxa_find_matching_catch() in
130 /// call @__resumeException(%a)
131 /// where __resumeException() is a function in JS glue code.
134 /// call @llvm.eh.typeid.for(type) (intrinsic)
136 /// call @llvm_eh_typeid_for(type)
137 /// llvm_eh_typeid_for function will be generated in JS glue code.
139 /// * Setjmp / Longjmp handling
141 /// 7) In the function entry that calls setjmp, initialize setjmpTable and
142 /// sejmpTableSize as follows:
143 /// setjmpTableSize = 4;
144 /// setjmpTable = (int *) malloc(40);
145 /// setjmpTable[0] = 0;
146 /// setjmpTable and setjmpTableSize are used in saveSetjmp() function in JS
152 /// setjmpTable = saveSetjmp(buf, label, setjmpTable, setjmpTableSize);
153 /// setjmpTableSize = __tempRet0;
154 /// For each dynamic setjmp call, setjmpTable stores its ID (a number which
155 /// is incrementally assigned from 0) and its label (a unique number that
156 /// represents each callsite of setjmp). When we need more entries in
157 /// setjmpTable, it is reallocated in saveSetjmp() in JS code and it will
158 /// return the new table address, and assign the new table size in
159 /// __tempRet0. saveSetjmp also stores the setjmp's ID into the buffer buf.
160 /// A BB with setjmp is split into two after setjmp call in order to make the
161 /// post-setjmp BB the possible destination of longjmp BB.
164 /// longjmp(buf, value)
166 /// emscripten_longjmp_jmpbuf(buf, value)
167 /// emscripten_longjmp_jmpbuf will be lowered to emscripten_longjmp later.
169 /// 10) Lower every call that might longjmp into
171 /// call @__invoke_SIG(func, arg1, arg2)
172 /// %__THREW__.val = __THREW__;
174 /// if (%__THREW__.val != 0 & __threwValue != 0) {
175 /// %label = testSetjmp(mem[%__THREW__.val], setjmpTable,
176 /// setjmpTableSize);
178 /// emscripten_longjmp(%__THREW__.val, __threwValue);
179 /// __tempRet0 = __threwValue;
183 /// longjmp_result = __tempRet0;
185 /// label 1: goto post-setjmp BB 1
186 /// label 2: goto post-setjmp BB 2
188 /// default: goto splitted next BB
190 /// testSetjmp examines setjmpTable to see if there is a matching setjmp
191 /// call. After calling an invoke wrapper, if a longjmp occurred, __THREW__
192 /// will be the address of matching jmp_buf buffer and __threwValue be the
193 /// second argument to longjmp. mem[__THREW__.val] is a setjmp ID that is
194 /// stored in saveSetjmp. testSetjmp returns a setjmp label, a unique ID to
195 /// each setjmp callsite. Label 0 means this longjmp buffer does not
196 /// correspond to one of the setjmp callsites in this function, so in this
197 /// case we just chain the longjmp to the caller. (Here we call
198 /// emscripten_longjmp, which is different from emscripten_longjmp_jmpbuf.
199 /// emscripten_longjmp_jmpbuf takes jmp_buf as its first argument, while
200 /// emscripten_longjmp takes an int. Both of them will eventually be lowered
201 /// to emscripten_longjmp in s2wasm, but here we need two signatures - we
202 /// can't translate an int value to a jmp_buf.)
203 /// Label -1 means no longjmp occurred. Otherwise we jump to the right
204 /// post-setjmp BB based on the label.
206 ///===----------------------------------------------------------------------===//
208 #include "WebAssembly.h"
209 #include "llvm/IR/CallSite.h"
210 #include "llvm/IR/Dominators.h"
211 #include "llvm/IR/IRBuilder.h"
212 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
213 #include "llvm/Transforms/Utils/SSAUpdater.h"
215 using namespace llvm;
217 #define DEBUG_TYPE "wasm-lower-em-ehsjlj"
219 static cl::list<std::string>
220 EHWhitelist("emscripten-cxx-exceptions-whitelist",
221 cl::desc("The list of function names in which Emscripten-style "
222 "exception handling is enabled (see emscripten "
223 "EMSCRIPTEN_CATCHING_WHITELIST options)"),
227 class WebAssemblyLowerEmscriptenEHSjLj final : public ModulePass {
228 static const char *ThrewGVName;
229 static const char *ThrewValueGVName;
230 static const char *TempRet0GVName;
231 static const char *ResumeFName;
232 static const char *EHTypeIDFName;
233 static const char *SetThrewFName;
234 static const char *SetTempRet0FName;
235 static const char *EmLongjmpFName;
236 static const char *EmLongjmpJmpbufFName;
237 static const char *SaveSetjmpFName;
238 static const char *TestSetjmpFName;
239 static const char *FindMatchingCatchPrefix;
240 static const char *InvokePrefix;
242 bool EnableEH; // Enable exception handling
243 bool EnableSjLj; // Enable setjmp/longjmp handling
245 GlobalVariable *ThrewGV;
246 GlobalVariable *ThrewValueGV;
247 GlobalVariable *TempRet0GV;
250 Function *EmLongjmpF;
251 Function *EmLongjmpJmpbufF;
252 Function *SaveSetjmpF;
253 Function *TestSetjmpF;
255 // __cxa_find_matching_catch_N functions.
256 // Indexed by the number of clauses in an original landingpad instruction.
257 DenseMap<int, Function *> FindMatchingCatches;
258 // Map of <function signature string, invoke_ wrappers>
259 StringMap<Function *> InvokeWrappers;
260 // Set of whitelisted function names for exception handling
261 std::set<std::string> EHWhitelistSet;
263 StringRef getPassName() const override {
264 return "WebAssembly Lower Emscripten Exceptions";
267 bool runEHOnFunction(Function &F);
268 bool runSjLjOnFunction(Function &F);
269 Function *getFindMatchingCatch(Module &M, unsigned NumClauses);
271 template <typename CallOrInvoke> Value *wrapInvoke(CallOrInvoke *CI);
272 void wrapTestSetjmp(BasicBlock *BB, Instruction *InsertPt, Value *Threw,
273 Value *SetjmpTable, Value *SetjmpTableSize, Value *&Label,
274 Value *&LongjmpResult, BasicBlock *&EndBB);
275 template <typename CallOrInvoke> Function *getInvokeWrapper(CallOrInvoke *CI);
277 bool areAllExceptionsAllowed() const { return EHWhitelistSet.empty(); }
278 bool canLongjmp(Module &M, const Value *Callee) const;
280 void createSetThrewFunction(Module &M);
281 void createSetTempRet0Function(Module &M);
283 void rebuildSSA(Function &F);
288 WebAssemblyLowerEmscriptenEHSjLj(bool EnableEH = true, bool EnableSjLj = true)
289 : ModulePass(ID), EnableEH(EnableEH), EnableSjLj(EnableSjLj),
290 ThrewGV(nullptr), ThrewValueGV(nullptr), TempRet0GV(nullptr),
291 ResumeF(nullptr), EHTypeIDF(nullptr), EmLongjmpF(nullptr),
292 EmLongjmpJmpbufF(nullptr), SaveSetjmpF(nullptr), TestSetjmpF(nullptr) {
293 EHWhitelistSet.insert(EHWhitelist.begin(), EHWhitelist.end());
295 bool runOnModule(Module &M) override;
297 void getAnalysisUsage(AnalysisUsage &AU) const override {
298 AU.addRequired<DominatorTreeWrapperPass>();
301 } // End anonymous namespace
303 const char *WebAssemblyLowerEmscriptenEHSjLj::ThrewGVName = "__THREW__";
304 const char *WebAssemblyLowerEmscriptenEHSjLj::ThrewValueGVName = "__threwValue";
305 const char *WebAssemblyLowerEmscriptenEHSjLj::TempRet0GVName = "__tempRet0";
306 const char *WebAssemblyLowerEmscriptenEHSjLj::ResumeFName = "__resumeException";
307 const char *WebAssemblyLowerEmscriptenEHSjLj::EHTypeIDFName =
308 "llvm_eh_typeid_for";
309 const char *WebAssemblyLowerEmscriptenEHSjLj::SetThrewFName = "setThrew";
310 const char *WebAssemblyLowerEmscriptenEHSjLj::SetTempRet0FName = "setTempRet0";
311 const char *WebAssemblyLowerEmscriptenEHSjLj::EmLongjmpFName =
312 "emscripten_longjmp";
313 const char *WebAssemblyLowerEmscriptenEHSjLj::EmLongjmpJmpbufFName =
314 "emscripten_longjmp_jmpbuf";
315 const char *WebAssemblyLowerEmscriptenEHSjLj::SaveSetjmpFName = "saveSetjmp";
316 const char *WebAssemblyLowerEmscriptenEHSjLj::TestSetjmpFName = "testSetjmp";
317 const char *WebAssemblyLowerEmscriptenEHSjLj::FindMatchingCatchPrefix =
318 "__cxa_find_matching_catch_";
319 const char *WebAssemblyLowerEmscriptenEHSjLj::InvokePrefix = "__invoke_";
321 char WebAssemblyLowerEmscriptenEHSjLj::ID = 0;
322 INITIALIZE_PASS(WebAssemblyLowerEmscriptenEHSjLj, DEBUG_TYPE,
323 "WebAssembly Lower Emscripten Exceptions / Setjmp / Longjmp",
326 ModulePass *llvm::createWebAssemblyLowerEmscriptenEHSjLj(bool EnableEH,
328 return new WebAssemblyLowerEmscriptenEHSjLj(EnableEH, EnableSjLj);
331 static bool canThrow(const Value *V) {
332 if (const auto *F = dyn_cast<const Function>(V)) {
333 // Intrinsics cannot throw
334 if (F->isIntrinsic())
336 StringRef Name = F->getName();
337 // leave setjmp and longjmp (mostly) alone, we process them properly later
338 if (Name == "setjmp" || Name == "longjmp")
340 return !F->doesNotThrow();
342 // not a function, so an indirect call - can throw, we can't tell
346 // Returns an available name for a global value.
347 // If the proposed name already exists in the module, adds '_' at the end of
348 // the name until the name is available.
349 static inline std::string createGlobalValueName(const Module &M,
350 const std::string &Propose) {
351 std::string Name = Propose;
352 while (M.getNamedGlobal(Name))
357 // Simple function name mangler.
358 // This function simply takes LLVM's string representation of parameter types
359 // and concatenate them with '_'. There are non-alphanumeric characters but llc
360 // is ok with it, and we need to postprocess these names after the lowering
362 static std::string getSignature(FunctionType *FTy) {
364 raw_string_ostream OS(Sig);
365 OS << *FTy->getReturnType();
366 for (Type *ParamTy : FTy->params())
367 OS << "_" << *ParamTy;
371 Sig.erase(remove_if(Sig, isspace), Sig.end());
372 // When s2wasm parses .s file, a comma means the end of an argument. So a
373 // mangled function name can contain any character but a comma.
374 std::replace(Sig.begin(), Sig.end(), ',', '.');
378 // Returns __cxa_find_matching_catch_N function, where N = NumClauses + 2.
379 // This is because a landingpad instruction contains two more arguments, a
380 // personality function and a cleanup bit, and __cxa_find_matching_catch_N
381 // functions are named after the number of arguments in the original landingpad
384 WebAssemblyLowerEmscriptenEHSjLj::getFindMatchingCatch(Module &M,
385 unsigned NumClauses) {
386 if (FindMatchingCatches.count(NumClauses))
387 return FindMatchingCatches[NumClauses];
388 PointerType *Int8PtrTy = Type::getInt8PtrTy(M.getContext());
389 SmallVector<Type *, 16> Args(NumClauses, Int8PtrTy);
390 FunctionType *FTy = FunctionType::get(Int8PtrTy, Args, false);
392 Function::Create(FTy, GlobalValue::ExternalLinkage,
393 FindMatchingCatchPrefix + Twine(NumClauses + 2), &M);
394 FindMatchingCatches[NumClauses] = F;
398 // Generate invoke wrapper seqence with preamble and postamble
402 // %__THREW__.val = __THREW__; __THREW__ = 0;
403 // Returns %__THREW__.val, which indicates whether an exception is thrown (or
404 // whether longjmp occurred), for future use.
405 template <typename CallOrInvoke>
406 Value *WebAssemblyLowerEmscriptenEHSjLj::wrapInvoke(CallOrInvoke *CI) {
407 LLVMContext &C = CI->getModule()->getContext();
409 // If we are calling a function that is noreturn, we must remove that
410 // attribute. The code we insert here does expect it to return, after we
411 // catch the exception.
412 if (CI->doesNotReturn()) {
413 if (auto *F = dyn_cast<Function>(CI->getCalledValue()))
414 F->removeFnAttr(Attribute::NoReturn);
415 CI->removeAttribute(AttributeSet::FunctionIndex, Attribute::NoReturn);
419 IRB.SetInsertPoint(CI);
423 IRB.CreateStore(IRB.getInt32(0), ThrewGV);
425 // Invoke function wrapper in JavaScript
426 SmallVector<Value *, 16> Args;
427 // Put the pointer to the callee as first argument, so it can be called
428 // within the invoke wrapper later
429 Args.push_back(CI->getCalledValue());
430 Args.append(CI->arg_begin(), CI->arg_end());
431 CallInst *NewCall = IRB.CreateCall(getInvokeWrapper(CI), Args);
432 NewCall->takeName(CI);
433 NewCall->setCallingConv(CI->getCallingConv());
434 NewCall->setDebugLoc(CI->getDebugLoc());
436 // Because we added the pointer to the callee as first argument, all
437 // argument attribute indices have to be incremented by one.
438 SmallVector<AttributeSet, 8> AttributesVec;
439 const AttributeSet &InvokePAL = CI->getAttributes();
440 CallSite::arg_iterator AI = CI->arg_begin();
441 unsigned i = 1; // Argument attribute index starts from 1
442 for (unsigned e = CI->getNumArgOperands(); i <= e; ++AI, ++i) {
443 if (InvokePAL.hasAttributes(i)) {
444 AttrBuilder B(InvokePAL, i);
445 AttributesVec.push_back(AttributeSet::get(C, i + 1, B));
448 // Add any return attributes.
449 if (InvokePAL.hasAttributes(AttributeSet::ReturnIndex))
450 AttributesVec.push_back(AttributeSet::get(C, InvokePAL.getRetAttributes()));
451 // Add any function attributes.
452 if (InvokePAL.hasAttributes(AttributeSet::FunctionIndex))
453 AttributesVec.push_back(AttributeSet::get(C, InvokePAL.getFnAttributes()));
454 // Reconstruct the AttributesList based on the vector we constructed.
455 AttributeSet NewCallPAL = AttributeSet::get(C, AttributesVec);
456 NewCall->setAttributes(NewCallPAL);
458 CI->replaceAllUsesWith(NewCall);
461 // %__THREW__.val = __THREW__; __THREW__ = 0;
462 Value *Threw = IRB.CreateLoad(ThrewGV, ThrewGV->getName() + ".val");
463 IRB.CreateStore(IRB.getInt32(0), ThrewGV);
467 // Get matching invoke wrapper based on callee signature
468 template <typename CallOrInvoke>
469 Function *WebAssemblyLowerEmscriptenEHSjLj::getInvokeWrapper(CallOrInvoke *CI) {
470 Module *M = CI->getModule();
471 SmallVector<Type *, 16> ArgTys;
472 Value *Callee = CI->getCalledValue();
473 FunctionType *CalleeFTy;
474 if (auto *F = dyn_cast<Function>(Callee))
475 CalleeFTy = F->getFunctionType();
477 auto *CalleeTy = cast<PointerType>(Callee->getType())->getElementType();
478 CalleeFTy = dyn_cast<FunctionType>(CalleeTy);
481 std::string Sig = getSignature(CalleeFTy);
482 if (InvokeWrappers.find(Sig) != InvokeWrappers.end())
483 return InvokeWrappers[Sig];
485 // Put the pointer to the callee as first argument
486 ArgTys.push_back(PointerType::getUnqual(CalleeFTy));
487 // Add argument types
488 ArgTys.append(CalleeFTy->param_begin(), CalleeFTy->param_end());
490 FunctionType *FTy = FunctionType::get(CalleeFTy->getReturnType(), ArgTys,
491 CalleeFTy->isVarArg());
492 Function *F = Function::Create(FTy, GlobalValue::ExternalLinkage,
493 InvokePrefix + Sig, M);
494 InvokeWrappers[Sig] = F;
498 bool WebAssemblyLowerEmscriptenEHSjLj::canLongjmp(Module &M,
499 const Value *Callee) const {
500 if (auto *CalleeF = dyn_cast<Function>(Callee))
501 if (CalleeF->isIntrinsic())
504 // The reason we include malloc/free here is to exclude the malloc/free
505 // calls generated in setjmp prep / cleanup routines.
506 Function *SetjmpF = M.getFunction("setjmp");
507 Function *MallocF = M.getFunction("malloc");
508 Function *FreeF = M.getFunction("free");
509 if (Callee == SetjmpF || Callee == MallocF || Callee == FreeF)
512 // There are functions in JS glue code
513 if (Callee == ResumeF || Callee == EHTypeIDF || Callee == SaveSetjmpF ||
514 Callee == TestSetjmpF)
517 // __cxa_find_matching_catch_N functions cannot longjmp
518 if (Callee->getName().startswith(FindMatchingCatchPrefix))
521 // Exception-catching related functions
522 Function *BeginCatchF = M.getFunction("__cxa_begin_catch");
523 Function *EndCatchF = M.getFunction("__cxa_end_catch");
524 Function *AllocExceptionF = M.getFunction("__cxa_allocate_exception");
525 Function *ThrowF = M.getFunction("__cxa_throw");
526 Function *TerminateF = M.getFunction("__clang_call_terminate");
527 if (Callee == BeginCatchF || Callee == EndCatchF ||
528 Callee == AllocExceptionF || Callee == ThrowF || Callee == TerminateF)
531 // Otherwise we don't know
535 // Generate testSetjmp function call seqence with preamble and postamble.
536 // The code this generates is equivalent to the following JavaScript code:
537 // if (%__THREW__.val != 0 & threwValue != 0) {
538 // %label = _testSetjmp(mem[%__THREW__.val], setjmpTable, setjmpTableSize);
540 // emscripten_longjmp(%__THREW__.val, threwValue);
541 // __tempRet0 = threwValue;
545 // %longjmp_result = __tempRet0;
547 // As output parameters. returns %label, %longjmp_result, and the BB the last
548 // instruction (%longjmp_result = ...) is in.
549 void WebAssemblyLowerEmscriptenEHSjLj::wrapTestSetjmp(
550 BasicBlock *BB, Instruction *InsertPt, Value *Threw, Value *SetjmpTable,
551 Value *SetjmpTableSize, Value *&Label, Value *&LongjmpResult,
552 BasicBlock *&EndBB) {
553 Function *F = BB->getParent();
554 LLVMContext &C = BB->getModule()->getContext();
556 IRB.SetInsertPoint(InsertPt);
558 // if (%__THREW__.val != 0 & threwValue != 0)
559 IRB.SetInsertPoint(BB);
560 BasicBlock *ThenBB1 = BasicBlock::Create(C, "if.then1", F);
561 BasicBlock *ElseBB1 = BasicBlock::Create(C, "if.else1", F);
562 BasicBlock *EndBB1 = BasicBlock::Create(C, "if.end", F);
563 Value *ThrewCmp = IRB.CreateICmpNE(Threw, IRB.getInt32(0));
565 IRB.CreateLoad(ThrewValueGV, ThrewValueGV->getName() + ".val");
566 Value *ThrewValueCmp = IRB.CreateICmpNE(ThrewValue, IRB.getInt32(0));
567 Value *Cmp1 = IRB.CreateAnd(ThrewCmp, ThrewValueCmp, "cmp1");
568 IRB.CreateCondBr(Cmp1, ThenBB1, ElseBB1);
570 // %label = _testSetjmp(mem[%__THREW__.val], _setjmpTable, _setjmpTableSize);
572 IRB.SetInsertPoint(ThenBB1);
573 BasicBlock *ThenBB2 = BasicBlock::Create(C, "if.then2", F);
574 BasicBlock *EndBB2 = BasicBlock::Create(C, "if.end2", F);
575 Value *ThrewInt = IRB.CreateIntToPtr(Threw, Type::getInt32PtrTy(C),
576 Threw->getName() + ".i32p");
578 IRB.CreateLoad(ThrewInt, ThrewInt->getName() + ".loaded");
579 Value *ThenLabel = IRB.CreateCall(
580 TestSetjmpF, {LoadedThrew, SetjmpTable, SetjmpTableSize}, "label");
581 Value *Cmp2 = IRB.CreateICmpEQ(ThenLabel, IRB.getInt32(0));
582 IRB.CreateCondBr(Cmp2, ThenBB2, EndBB2);
584 // emscripten_longjmp(%__THREW__.val, threwValue);
585 IRB.SetInsertPoint(ThenBB2);
586 IRB.CreateCall(EmLongjmpF, {Threw, ThrewValue});
587 IRB.CreateUnreachable();
589 // __tempRet0 = threwValue;
590 IRB.SetInsertPoint(EndBB2);
591 IRB.CreateStore(ThrewValue, TempRet0GV);
592 IRB.CreateBr(EndBB1);
594 IRB.SetInsertPoint(ElseBB1);
595 IRB.CreateBr(EndBB1);
597 // longjmp_result = __tempRet0;
598 IRB.SetInsertPoint(EndBB1);
599 PHINode *LabelPHI = IRB.CreatePHI(IRB.getInt32Ty(), 2, "label");
600 LabelPHI->addIncoming(ThenLabel, EndBB2);
602 LabelPHI->addIncoming(IRB.getInt32(-1), ElseBB1);
604 // Output parameter assignment
607 LongjmpResult = IRB.CreateLoad(TempRet0GV, "longjmp_result");
610 // Create setThrew function
611 // function setThrew(threw, value) {
612 // if (__THREW__ == 0) {
613 // __THREW__ = threw;
614 // __threwValue = value;
617 void WebAssemblyLowerEmscriptenEHSjLj::createSetThrewFunction(Module &M) {
618 LLVMContext &C = M.getContext();
621 assert(!M.getNamedGlobal(SetThrewFName) && "setThrew already exists");
622 Type *Params[] = {IRB.getInt32Ty(), IRB.getInt32Ty()};
623 FunctionType *FTy = FunctionType::get(IRB.getVoidTy(), Params, false);
625 Function::Create(FTy, GlobalValue::ExternalLinkage, SetThrewFName, &M);
626 Argument *Arg1 = &*(F->arg_begin());
627 Argument *Arg2 = &*(++F->arg_begin());
628 Arg1->setName("threw");
629 Arg2->setName("value");
630 BasicBlock *EntryBB = BasicBlock::Create(C, "entry", F);
631 BasicBlock *ThenBB = BasicBlock::Create(C, "if.then", F);
632 BasicBlock *EndBB = BasicBlock::Create(C, "if.end", F);
634 IRB.SetInsertPoint(EntryBB);
635 Value *Threw = IRB.CreateLoad(ThrewGV, ThrewGV->getName() + ".val");
636 Value *Cmp = IRB.CreateICmpEQ(Threw, IRB.getInt32(0), "cmp");
637 IRB.CreateCondBr(Cmp, ThenBB, EndBB);
639 IRB.SetInsertPoint(ThenBB);
640 IRB.CreateStore(Arg1, ThrewGV);
641 IRB.CreateStore(Arg2, ThrewValueGV);
644 IRB.SetInsertPoint(EndBB);
648 // Create setTempRet0 function
649 // function setTempRet0(value) {
650 // __tempRet0 = value;
652 void WebAssemblyLowerEmscriptenEHSjLj::createSetTempRet0Function(Module &M) {
653 LLVMContext &C = M.getContext();
656 assert(!M.getNamedGlobal(SetTempRet0FName) && "setTempRet0 already exists");
657 Type *Params[] = {IRB.getInt32Ty()};
658 FunctionType *FTy = FunctionType::get(IRB.getVoidTy(), Params, false);
660 Function::Create(FTy, GlobalValue::ExternalLinkage, SetTempRet0FName, &M);
661 F->arg_begin()->setName("value");
662 BasicBlock *EntryBB = BasicBlock::Create(C, "entry", F);
663 IRB.SetInsertPoint(EntryBB);
664 IRB.CreateStore(&*F->arg_begin(), TempRet0GV);
668 void WebAssemblyLowerEmscriptenEHSjLj::rebuildSSA(Function &F) {
669 DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(F).getDomTree();
670 DT.recalculate(F); // CFG has been changed
672 for (BasicBlock &BB : F) {
673 for (Instruction &I : BB) {
674 for (auto UI = I.use_begin(), UE = I.use_end(); UI != UE;) {
677 SSA.Initialize(I.getType(), I.getName());
678 SSA.AddAvailableValue(&BB, &I);
679 Instruction *User = cast<Instruction>(U.getUser());
680 if (User->getParent() == &BB)
683 if (PHINode *UserPN = dyn_cast<PHINode>(User))
684 if (UserPN->getIncomingBlock(U) == &BB)
687 if (DT.dominates(&I, User))
689 SSA.RewriteUseAfterInsertions(U);
695 bool WebAssemblyLowerEmscriptenEHSjLj::runOnModule(Module &M) {
696 LLVMContext &C = M.getContext();
699 Function *SetjmpF = M.getFunction("setjmp");
700 Function *LongjmpF = M.getFunction("longjmp");
701 bool SetjmpUsed = SetjmpF && !SetjmpF->use_empty();
702 bool LongjmpUsed = LongjmpF && !LongjmpF->use_empty();
703 bool DoSjLj = EnableSjLj && (SetjmpUsed || LongjmpUsed);
705 // Create global variables __THREW__, threwValue, and __tempRet0, which are
706 // used in common for both exception handling and setjmp/longjmp handling
707 ThrewGV = new GlobalVariable(M, IRB.getInt32Ty(), false,
708 GlobalValue::ExternalLinkage, IRB.getInt32(0),
709 createGlobalValueName(M, ThrewGVName));
710 ThrewValueGV = new GlobalVariable(
711 M, IRB.getInt32Ty(), false, GlobalValue::ExternalLinkage, IRB.getInt32(0),
712 createGlobalValueName(M, ThrewValueGVName));
713 TempRet0GV = new GlobalVariable(M, IRB.getInt32Ty(), false,
714 GlobalValue::ExternalLinkage, IRB.getInt32(0),
715 createGlobalValueName(M, TempRet0GVName));
717 bool Changed = false;
719 // Exception handling
721 // Register __resumeException function
722 FunctionType *ResumeFTy =
723 FunctionType::get(IRB.getVoidTy(), IRB.getInt8PtrTy(), false);
724 ResumeF = Function::Create(ResumeFTy, GlobalValue::ExternalLinkage,
727 // Register llvm_eh_typeid_for function
728 FunctionType *EHTypeIDTy =
729 FunctionType::get(IRB.getInt32Ty(), IRB.getInt8PtrTy(), false);
730 EHTypeIDF = Function::Create(EHTypeIDTy, GlobalValue::ExternalLinkage,
733 for (Function &F : M) {
734 if (F.isDeclaration())
736 Changed |= runEHOnFunction(F);
740 // Setjmp/longjmp handling
742 Changed = true; // We have setjmp or longjmp somewhere
744 Function *MallocF = M.getFunction("malloc");
745 Function *FreeF = M.getFunction("free");
746 if (!MallocF || !FreeF)
748 "malloc and free must be linked into the module if setjmp is used");
750 // Register saveSetjmp function
751 FunctionType *SetjmpFTy = SetjmpF->getFunctionType();
752 SmallVector<Type *, 4> Params = {SetjmpFTy->getParamType(0),
753 IRB.getInt32Ty(), Type::getInt32PtrTy(C),
756 FunctionType::get(Type::getInt32PtrTy(C), Params, false);
757 SaveSetjmpF = Function::Create(FTy, GlobalValue::ExternalLinkage,
758 SaveSetjmpFName, &M);
760 // Register testSetjmp function
761 Params = {IRB.getInt32Ty(), Type::getInt32PtrTy(C), IRB.getInt32Ty()};
762 FTy = FunctionType::get(IRB.getInt32Ty(), Params, false);
763 TestSetjmpF = Function::Create(FTy, GlobalValue::ExternalLinkage,
764 TestSetjmpFName, &M);
767 // Replace all uses of longjmp with emscripten_longjmp_jmpbuf, which is
768 // defined in JS code
769 EmLongjmpJmpbufF = Function::Create(LongjmpF->getFunctionType(),
770 GlobalValue::ExternalLinkage,
771 EmLongjmpJmpbufFName, &M);
773 LongjmpF->replaceAllUsesWith(EmLongjmpJmpbufF);
775 FTy = FunctionType::get(IRB.getVoidTy(),
776 {IRB.getInt32Ty(), IRB.getInt32Ty()}, false);
778 Function::Create(FTy, GlobalValue::ExternalLinkage, EmLongjmpFName, &M);
780 // Only traverse functions that uses setjmp in order not to insert
781 // unnecessary prep / cleanup code in every function
782 SmallPtrSet<Function *, 8> SetjmpUsers;
783 for (User *U : SetjmpF->users()) {
784 auto *UI = cast<Instruction>(U);
785 SetjmpUsers.insert(UI->getFunction());
787 for (Function *F : SetjmpUsers)
788 runSjLjOnFunction(*F);
792 // Delete unused global variables and functions
793 ThrewGV->eraseFromParent();
794 ThrewValueGV->eraseFromParent();
795 TempRet0GV->eraseFromParent();
797 ResumeF->eraseFromParent();
799 EHTypeIDF->eraseFromParent();
801 EmLongjmpF->eraseFromParent();
803 SaveSetjmpF->eraseFromParent();
805 TestSetjmpF->eraseFromParent();
809 // If we have made any changes while doing exception handling or
810 // setjmp/longjmp handling, we have to create these functions for JavaScript
812 createSetThrewFunction(M);
813 createSetTempRet0Function(M);
818 bool WebAssemblyLowerEmscriptenEHSjLj::runEHOnFunction(Function &F) {
819 Module &M = *F.getParent();
820 LLVMContext &C = F.getContext();
822 bool Changed = false;
823 SmallVector<Instruction *, 64> ToErase;
824 SmallPtrSet<LandingPadInst *, 32> LandingPads;
825 bool AllowExceptions =
826 areAllExceptionsAllowed() || EHWhitelistSet.count(F.getName());
828 for (BasicBlock &BB : F) {
829 auto *II = dyn_cast<InvokeInst>(BB.getTerminator());
833 LandingPads.insert(II->getLandingPadInst());
834 IRB.SetInsertPoint(II);
836 bool NeedInvoke = AllowExceptions && canThrow(II->getCalledValue());
838 // Wrap invoke with invoke wrapper and generate preamble/postamble
839 Value *Threw = wrapInvoke(II);
840 ToErase.push_back(II);
842 // Insert a branch based on __THREW__ variable
843 Value *Cmp = IRB.CreateICmpEQ(Threw, IRB.getInt32(1), "cmp");
844 IRB.CreateCondBr(Cmp, II->getUnwindDest(), II->getNormalDest());
847 // This can't throw, and we don't need this invoke, just replace it with a
849 SmallVector<Value *, 16> Args(II->arg_begin(), II->arg_end());
850 CallInst *NewCall = IRB.CreateCall(II->getCalledValue(), Args);
851 NewCall->takeName(II);
852 NewCall->setCallingConv(II->getCallingConv());
853 NewCall->setDebugLoc(II->getDebugLoc());
854 NewCall->setAttributes(II->getAttributes());
855 II->replaceAllUsesWith(NewCall);
856 ToErase.push_back(II);
858 IRB.CreateBr(II->getNormalDest());
860 // Remove any PHI node entries from the exception destination
861 II->getUnwindDest()->removePredecessor(&BB);
865 // Process resume instructions
866 for (BasicBlock &BB : F) {
867 // Scan the body of the basic block for resumes
868 for (Instruction &I : BB) {
869 auto *RI = dyn_cast<ResumeInst>(&I);
873 // Split the input into legal values
874 Value *Input = RI->getValue();
875 IRB.SetInsertPoint(RI);
876 Value *Low = IRB.CreateExtractValue(Input, 0, "low");
877 // Create a call to __resumeException function
878 IRB.CreateCall(ResumeF, {Low});
879 // Add a terminator to the block
880 IRB.CreateUnreachable();
881 ToErase.push_back(RI);
885 // Process llvm.eh.typeid.for intrinsics
886 for (BasicBlock &BB : F) {
887 for (Instruction &I : BB) {
888 auto *CI = dyn_cast<CallInst>(&I);
891 const Function *Callee = CI->getCalledFunction();
894 if (Callee->getIntrinsicID() != Intrinsic::eh_typeid_for)
897 IRB.SetInsertPoint(CI);
899 IRB.CreateCall(EHTypeIDF, CI->getArgOperand(0), "typeid");
900 CI->replaceAllUsesWith(NewCI);
901 ToErase.push_back(CI);
905 // Look for orphan landingpads, can occur in blocks with no predecesors
906 for (BasicBlock &BB : F) {
907 Instruction *I = BB.getFirstNonPHI();
908 if (auto *LPI = dyn_cast<LandingPadInst>(I))
909 LandingPads.insert(LPI);
912 // Handle all the landingpad for this function together, as multiple invokes
913 // may share a single lp
914 for (LandingPadInst *LPI : LandingPads) {
915 IRB.SetInsertPoint(LPI);
916 SmallVector<Value *, 16> FMCArgs;
917 for (unsigned i = 0, e = LPI->getNumClauses(); i < e; ++i) {
918 Constant *Clause = LPI->getClause(i);
919 // As a temporary workaround for the lack of aggregate varargs support
920 // in the interface between JS and wasm, break out filter operands into
921 // their component elements.
922 if (LPI->isFilter(i)) {
923 auto *ATy = cast<ArrayType>(Clause->getType());
924 for (unsigned j = 0, e = ATy->getNumElements(); j < e; ++j) {
925 Value *EV = IRB.CreateExtractValue(Clause, makeArrayRef(j), "filter");
926 FMCArgs.push_back(EV);
929 FMCArgs.push_back(Clause);
932 // Create a call to __cxa_find_matching_catch_N function
933 Function *FMCF = getFindMatchingCatch(M, FMCArgs.size());
934 CallInst *FMCI = IRB.CreateCall(FMCF, FMCArgs, "fmc");
935 Value *Undef = UndefValue::get(LPI->getType());
936 Value *Pair0 = IRB.CreateInsertValue(Undef, FMCI, 0, "pair0");
938 IRB.CreateLoad(TempRet0GV, TempRet0GV->getName() + ".val");
939 Value *Pair1 = IRB.CreateInsertValue(Pair0, TempRet0, 1, "pair1");
941 LPI->replaceAllUsesWith(Pair1);
942 ToErase.push_back(LPI);
945 // Erase everything we no longer need in this function
946 for (Instruction *I : ToErase)
947 I->eraseFromParent();
952 bool WebAssemblyLowerEmscriptenEHSjLj::runSjLjOnFunction(Function &F) {
953 Module &M = *F.getParent();
954 LLVMContext &C = F.getContext();
956 SmallVector<Instruction *, 64> ToErase;
957 // Vector of %setjmpTable values
958 std::vector<Instruction *> SetjmpTableInsts;
959 // Vector of %setjmpTableSize values
960 std::vector<Instruction *> SetjmpTableSizeInsts;
962 // Setjmp preparation
964 // This instruction effectively means %setjmpTableSize = 4.
965 // We create this as an instruction intentionally, and we don't want to fold
966 // this instruction to a constant 4, because this value will be used in
967 // SSAUpdater.AddAvailableValue(...) later.
968 BasicBlock &EntryBB = F.getEntryBlock();
969 BinaryOperator *SetjmpTableSize = BinaryOperator::Create(
970 Instruction::Add, IRB.getInt32(4), IRB.getInt32(0), "setjmpTableSize",
971 &*EntryBB.getFirstInsertionPt());
972 // setjmpTable = (int *) malloc(40);
973 Instruction *SetjmpTable = CallInst::CreateMalloc(
974 SetjmpTableSize, IRB.getInt32Ty(), IRB.getInt32Ty(), IRB.getInt32(40),
975 nullptr, nullptr, "setjmpTable");
976 // setjmpTable[0] = 0;
977 IRB.SetInsertPoint(SetjmpTableSize);
978 IRB.CreateStore(IRB.getInt32(0), SetjmpTable);
979 SetjmpTableInsts.push_back(SetjmpTable);
980 SetjmpTableSizeInsts.push_back(SetjmpTableSize);
982 // Setjmp transformation
983 std::vector<PHINode *> SetjmpRetPHIs;
984 Function *SetjmpF = M.getFunction("setjmp");
985 for (User *U : SetjmpF->users()) {
986 auto *CI = dyn_cast<CallInst>(U);
988 report_fatal_error("Does not support indirect calls to setjmp");
990 BasicBlock *BB = CI->getParent();
991 if (BB->getParent() != &F) // in other function
994 // The tail is everything right after the call, and will be reached once
995 // when setjmp is called, and later when longjmp returns to the setjmp
996 BasicBlock *Tail = SplitBlock(BB, CI->getNextNode());
997 // Add a phi to the tail, which will be the output of setjmp, which
998 // indicates if this is the first call or a longjmp back. The phi directly
999 // uses the right value based on where we arrive from
1000 IRB.SetInsertPoint(Tail->getFirstNonPHI());
1001 PHINode *SetjmpRet = IRB.CreatePHI(IRB.getInt32Ty(), 2, "setjmp.ret");
1003 // setjmp initial call returns 0
1004 SetjmpRet->addIncoming(IRB.getInt32(0), BB);
1005 // The proper output is now this, not the setjmp call itself
1006 CI->replaceAllUsesWith(SetjmpRet);
1007 // longjmp returns to the setjmp will add themselves to this phi
1008 SetjmpRetPHIs.push_back(SetjmpRet);
1011 // Our index in the function is our place in the array + 1 to avoid index
1012 // 0, because index 0 means the longjmp is not ours to handle.
1013 IRB.SetInsertPoint(CI);
1014 Value *Args[] = {CI->getArgOperand(0), IRB.getInt32(SetjmpRetPHIs.size()),
1015 SetjmpTable, SetjmpTableSize};
1016 Instruction *NewSetjmpTable =
1017 IRB.CreateCall(SaveSetjmpF, Args, "setjmpTable");
1018 Instruction *NewSetjmpTableSize =
1019 IRB.CreateLoad(TempRet0GV, "setjmpTableSize");
1020 SetjmpTableInsts.push_back(NewSetjmpTable);
1021 SetjmpTableSizeInsts.push_back(NewSetjmpTableSize);
1022 ToErase.push_back(CI);
1025 // Update each call that can longjmp so it can return to a setjmp where
1028 // Because we are creating new BBs while processing and don't want to make
1029 // all these newly created BBs candidates again for longjmp processing, we
1030 // first make the vector of candidate BBs.
1031 std::vector<BasicBlock *> BBs;
1032 for (BasicBlock &BB : F)
1035 // BBs.size() will change within the loop, so we query it every time
1036 for (unsigned i = 0; i < BBs.size(); i++) {
1037 BasicBlock *BB = BBs[i];
1038 for (Instruction &I : *BB) {
1039 assert(!isa<InvokeInst>(&I));
1040 auto *CI = dyn_cast<CallInst>(&I);
1044 const Value *Callee = CI->getCalledValue();
1045 if (!canLongjmp(M, Callee))
1048 Value *Threw = nullptr;
1050 if (Callee->getName().startswith(InvokePrefix)) {
1051 // If invoke wrapper has already been generated for this call in
1052 // previous EH phase, search for the load instruction
1053 // %__THREW__.val = __THREW__;
1054 // in postamble after the invoke wrapper call
1055 LoadInst *ThrewLI = nullptr;
1056 StoreInst *ThrewResetSI = nullptr;
1057 for (auto I = std::next(BasicBlock::iterator(CI)), IE = BB->end();
1059 if (auto *LI = dyn_cast<LoadInst>(I))
1060 if (auto *GV = dyn_cast<GlobalVariable>(LI->getPointerOperand()))
1061 if (GV == ThrewGV) {
1062 Threw = ThrewLI = LI;
1066 // Search for the store instruction after the load above
1068 for (auto I = std::next(BasicBlock::iterator(ThrewLI)), IE = BB->end();
1070 if (auto *SI = dyn_cast<StoreInst>(I))
1071 if (auto *GV = dyn_cast<GlobalVariable>(SI->getPointerOperand()))
1072 if (GV == ThrewGV && SI->getValueOperand() == IRB.getInt32(0)) {
1077 assert(Threw && ThrewLI && "Cannot find __THREW__ load after invoke");
1078 assert(ThrewResetSI && "Cannot find __THREW__ store after invoke");
1079 Tail = SplitBlock(BB, ThrewResetSI->getNextNode());
1082 // Wrap call with invoke wrapper and generate preamble/postamble
1083 Threw = wrapInvoke(CI);
1084 ToErase.push_back(CI);
1085 Tail = SplitBlock(BB, CI->getNextNode());
1088 // We need to replace the terminator in Tail - SplitBlock makes BB go
1089 // straight to Tail, we need to check if a longjmp occurred, and go to the
1090 // right setjmp-tail if so
1091 ToErase.push_back(BB->getTerminator());
1093 // Generate a function call to testSetjmp function and preamble/postamble
1094 // code to figure out (1) whether longjmp occurred (2) if longjmp
1095 // occurred, which setjmp it corresponds to
1096 Value *Label = nullptr;
1097 Value *LongjmpResult = nullptr;
1098 BasicBlock *EndBB = nullptr;
1099 wrapTestSetjmp(BB, CI, Threw, SetjmpTable, SetjmpTableSize, Label,
1100 LongjmpResult, EndBB);
1101 assert(Label && LongjmpResult && EndBB);
1103 // Create switch instruction
1104 IRB.SetInsertPoint(EndBB);
1105 SwitchInst *SI = IRB.CreateSwitch(Label, Tail, SetjmpRetPHIs.size());
1106 // -1 means no longjmp happened, continue normally (will hit the default
1107 // switch case). 0 means a longjmp that is not ours to handle, needs a
1108 // rethrow. Otherwise the index is the same as the index in P+1 (to avoid
1110 for (unsigned i = 0; i < SetjmpRetPHIs.size(); i++) {
1111 SI->addCase(IRB.getInt32(i + 1), SetjmpRetPHIs[i]->getParent());
1112 SetjmpRetPHIs[i]->addIncoming(LongjmpResult, EndBB);
1115 // We are splitting the block here, and must continue to find other calls
1116 // in the block - which is now split. so continue to traverse in the Tail
1117 BBs.push_back(Tail);
1121 // Erase everything we no longer need in this function
1122 for (Instruction *I : ToErase)
1123 I->eraseFromParent();
1125 // Free setjmpTable buffer before each return instruction
1126 for (BasicBlock &BB : F) {
1127 TerminatorInst *TI = BB.getTerminator();
1128 if (isa<ReturnInst>(TI))
1129 CallInst::CreateFree(SetjmpTable, TI);
1132 // Every call to saveSetjmp can change setjmpTable and setjmpTableSize
1133 // (when buffer reallocation occurs)
1135 // setjmpTableSize = 4;
1136 // setjmpTable = (int *) malloc(40);
1137 // setjmpTable[0] = 0;
1140 // setjmpTable = saveSetjmp(buf, label, setjmpTable, setjmpTableSize);
1141 // setjmpTableSize = __tempRet0;
1142 // So we need to make sure the SSA for these variables is valid so that every
1143 // saveSetjmp and testSetjmp calls have the correct arguments.
1144 SSAUpdater SetjmpTableSSA;
1145 SSAUpdater SetjmpTableSizeSSA;
1146 SetjmpTableSSA.Initialize(Type::getInt32PtrTy(C), "setjmpTable");
1147 SetjmpTableSizeSSA.Initialize(Type::getInt32Ty(C), "setjmpTableSize");
1148 for (Instruction *I : SetjmpTableInsts)
1149 SetjmpTableSSA.AddAvailableValue(I->getParent(), I);
1150 for (Instruction *I : SetjmpTableSizeInsts)
1151 SetjmpTableSizeSSA.AddAvailableValue(I->getParent(), I);
1153 for (auto UI = SetjmpTable->use_begin(), UE = SetjmpTable->use_end();
1155 // Grab the use before incrementing the iterator.
1157 // Increment the iterator before removing the use from the list.
1159 if (Instruction *I = dyn_cast<Instruction>(U.getUser()))
1160 if (I->getParent() != &EntryBB)
1161 SetjmpTableSSA.RewriteUse(U);
1163 for (auto UI = SetjmpTableSize->use_begin(), UE = SetjmpTableSize->use_end();
1167 if (Instruction *I = dyn_cast<Instruction>(U.getUser()))
1168 if (I->getParent() != &EntryBB)
1169 SetjmpTableSizeSSA.RewriteUse(U);
1172 // Finally, our modifications to the cfg can break dominance of SSA variables.
1173 // For example, in this code,
1174 // if (x()) { .. setjmp() .. }
1175 // if (y()) { .. longjmp() .. }
1176 // We must split the longjmp block, and it can jump into the block splitted
1177 // from setjmp one. But that means that when we split the setjmp block, it's
1178 // first part no longer dominates its second part - there is a theoretically
1179 // possible control flow path where x() is false, then y() is true and we
1180 // reach the second part of the setjmp block, without ever reaching the first
1181 // part. So, we rebuild SSA form here.