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//=== WebAssemblyLowerEmscriptenEHSjLj.cpp - Lower exceptions for Emscripten =//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file lowers exception-related instructions and setjmp/longjmp
/// function calls in order to use Emscripten's JavaScript try and catch
/// mechanism.
///
/// To handle exceptions and setjmp/longjmps, this scheme relies on JavaScript's
/// try and catch syntax and relevant exception-related libraries implemented
/// in JavaScript glue code that will be produced by Emscripten.
///
/// * Exception handling
/// This pass lowers invokes and landingpads into library functions in JS glue
/// code. Invokes are lowered into function wrappers called invoke wrappers that
/// exist in JS side, which wraps the original function call with JS try-catch.
/// If an exception occurred, cxa_throw() function in JS side sets some
/// variables (see below) so we can check whether an exception occurred from
/// wasm code and handle it appropriately.
///
/// * Setjmp-longjmp handling
/// This pass lowers setjmp to a reasonably-performant approach for emscripten.
/// The idea is that each block with a setjmp is broken up into two parts: the
/// part containing setjmp and the part right after the setjmp. The latter part
/// is either reached from the setjmp, or later from a longjmp. To handle the
/// longjmp, all calls that might longjmp are also called using invoke wrappers
/// and thus JS / try-catch. JS longjmp() function also sets some variables so
/// we can check / whether a longjmp occurred from wasm code. Each block with a
/// function call that might longjmp is also split up after the longjmp call.
/// After the longjmp call, we check whether a longjmp occurred, and if it did,
/// which setjmp it corresponds to, and jump to the right post-setjmp block.
/// We assume setjmp-longjmp handling always run after EH handling, which means
/// we don't expect any exception-related instructions when SjLj runs.
/// FIXME Currently this scheme does not support indirect call of setjmp,
/// because of the limitation of the scheme itself. fastcomp does not support it
/// either.
///
/// In detail, this pass does following things:
///
/// 1) Assumes the existence of global variables: __THREW__, __threwValue
/// __THREW__ and __threwValue are defined in compiler-rt in Emscripten.
/// These variables are used for both exceptions and setjmp/longjmps.
/// __THREW__ indicates whether an exception or a longjmp occurred or not. 0
/// means nothing occurred, 1 means an exception occurred, and other numbers
/// mean a longjmp occurred. In the case of longjmp, __THREW__ variable
/// indicates the corresponding setjmp buffer the longjmp corresponds to.
/// __threwValue is 0 for exceptions, and the argument to longjmp in case of
/// longjmp.
///
/// * Exception handling
///
/// 2) We assume the existence of setThrew and setTempRet0/getTempRet0 functions
/// at link time. setThrew exists in Emscripten's compiler-rt:
///
/// void setThrew(uintptr_t threw, int value) {
/// if (__THREW__ == 0) {
/// __THREW__ = threw;
/// __threwValue = value;
/// }
/// }
//
/// setTempRet0 is called from __cxa_find_matching_catch() in JS glue code.
/// In exception handling, getTempRet0 indicates the type of an exception
/// caught, and in setjmp/longjmp, it means the second argument to longjmp
/// function.
///
/// 3) Lower
/// invoke @func(arg1, arg2) to label %invoke.cont unwind label %lpad
/// into
/// __THREW__ = 0;
/// call @__invoke_SIG(func, arg1, arg2)
/// %__THREW__.val = __THREW__;
/// __THREW__ = 0;
/// if (%__THREW__.val == 1)
/// goto %lpad
/// else
/// goto %invoke.cont
/// SIG is a mangled string generated based on the LLVM IR-level function
/// signature. After LLVM IR types are lowered to the target wasm types,
/// the names for these wrappers will change based on wasm types as well,
/// as in invoke_vi (function takes an int and returns void). The bodies of
/// these wrappers will be generated in JS glue code, and inside those
/// wrappers we use JS try-catch to generate actual exception effects. It
/// also calls the original callee function. An example wrapper in JS code
/// would look like this:
/// function invoke_vi(index,a1) {
/// try {
/// Module["dynCall_vi"](index,a1); // This calls original callee
/// } catch(e) {
/// if (typeof e !== 'number' && e !== 'longjmp') throw e;
/// _setThrew(1, 0); // setThrew is called here
/// }
/// }
/// If an exception is thrown, __THREW__ will be set to true in a wrapper,
/// so we can jump to the right BB based on this value.
///
/// 4) Lower
/// %val = landingpad catch c1 catch c2 catch c3 ...
/// ... use %val ...
/// into
/// %fmc = call @__cxa_find_matching_catch_N(c1, c2, c3, ...)
/// %val = {%fmc, getTempRet0()}
/// ... use %val ...
/// Here N is a number calculated based on the number of clauses.
/// setTempRet0 is called from __cxa_find_matching_catch() in JS glue code.
///
/// 5) Lower
/// resume {%a, %b}
/// into
/// call @__resumeException(%a)
/// where __resumeException() is a function in JS glue code.
///
/// 6) Lower
/// call @llvm.eh.typeid.for(type) (intrinsic)
/// into
/// call @llvm_eh_typeid_for(type)
/// llvm_eh_typeid_for function will be generated in JS glue code.
///
/// * Setjmp / Longjmp handling
///
/// In case calls to longjmp() exists
///
/// 1) Lower
/// longjmp(buf, value)
/// into
/// emscripten_longjmp(buf, value)
///
/// In case calls to setjmp() exists
///
/// 2) In the function entry that calls setjmp, initialize setjmpTable and
/// sejmpTableSize as follows:
/// setjmpTableSize = 4;
/// setjmpTable = (int *) malloc(40);
/// setjmpTable[0] = 0;
/// setjmpTable and setjmpTableSize are used to call saveSetjmp() function in
/// Emscripten compiler-rt.
///
/// 3) Lower
/// setjmp(buf)
/// into
/// setjmpTable = saveSetjmp(buf, label, setjmpTable, setjmpTableSize);
/// setjmpTableSize = getTempRet0();
/// For each dynamic setjmp call, setjmpTable stores its ID (a number which
/// is incrementally assigned from 0) and its label (a unique number that
/// represents each callsite of setjmp). When we need more entries in
/// setjmpTable, it is reallocated in saveSetjmp() in Emscripten's
/// compiler-rt and it will return the new table address, and assign the new
/// table size in setTempRet0(). saveSetjmp also stores the setjmp's ID into
/// the buffer buf. A BB with setjmp is split into two after setjmp call in
/// order to make the post-setjmp BB the possible destination of longjmp BB.
///
///
/// 4) Lower every call that might longjmp into
/// __THREW__ = 0;
/// call @__invoke_SIG(func, arg1, arg2)
/// %__THREW__.val = __THREW__;
/// __THREW__ = 0;
/// %__threwValue.val = __threwValue;
/// if (%__THREW__.val != 0 & %__threwValue.val != 0) {
/// %label = testSetjmp(mem[%__THREW__.val], setjmpTable,
/// setjmpTableSize);
/// if (%label == 0)
/// emscripten_longjmp(%__THREW__.val, %__threwValue.val);
/// setTempRet0(%__threwValue.val);
/// } else {
/// %label = -1;
/// }
/// longjmp_result = getTempRet0();
/// switch label {
/// label 1: goto post-setjmp BB 1
/// label 2: goto post-setjmp BB 2
/// ...
/// default: goto splitted next BB
/// }
/// testSetjmp examines setjmpTable to see if there is a matching setjmp
/// call. After calling an invoke wrapper, if a longjmp occurred, __THREW__
/// will be the address of matching jmp_buf buffer and __threwValue be the
/// second argument to longjmp. mem[%__THREW__.val] is a setjmp ID that is
/// stored in saveSetjmp. testSetjmp returns a setjmp label, a unique ID to
/// each setjmp callsite. Label 0 means this longjmp buffer does not
/// correspond to one of the setjmp callsites in this function, so in this
/// case we just chain the longjmp to the caller. Label -1 means no longjmp
/// occurred. Otherwise we jump to the right post-setjmp BB based on the
/// label.
///
///===----------------------------------------------------------------------===//
#include "WebAssembly.h"
#include "WebAssemblyTargetMachine.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
using namespace llvm;
#define DEBUG_TYPE "wasm-lower-em-ehsjlj"
static cl::list<std::string>
EHAllowlist("emscripten-cxx-exceptions-allowed",
cl::desc("The list of function names in which Emscripten-style "
"exception handling is enabled (see emscripten "
"EMSCRIPTEN_CATCHING_ALLOWED options)"),
cl::CommaSeparated);
namespace {
class WebAssemblyLowerEmscriptenEHSjLj final : public ModulePass {
bool EnableEmEH; // Enable Emscripten exception handling
bool EnableEmSjLj; // Enable Emscripten setjmp/longjmp handling
bool DoSjLj; // Whether we actually perform setjmp/longjmp handling
GlobalVariable *ThrewGV = nullptr; // __THREW__ (Emscripten)
GlobalVariable *ThrewValueGV = nullptr; // __threwValue (Emscripten)
Function *GetTempRet0F = nullptr; // getTempRet0() (Emscripten)
Function *SetTempRet0F = nullptr; // setTempRet0() (Emscripten)
Function *ResumeF = nullptr; // __resumeException() (Emscripten)
Function *EHTypeIDF = nullptr; // llvm.eh.typeid.for() (intrinsic)
Function *EmLongjmpF = nullptr; // emscripten_longjmp() (Emscripten)
Function *SaveSetjmpF = nullptr; // saveSetjmp() (Emscripten)
Function *TestSetjmpF = nullptr; // testSetjmp() (Emscripten)
// __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 supportsException(const Function *F) const {
return EnableEmEH && (areAllExceptionsAllowed() ||
EHAllowlistSet.count(std::string(F->getName())));
}
void rebuildSSA(Function &F);
public:
static char ID;
WebAssemblyLowerEmscriptenEHSjLj(bool EnableEmEH = true,
bool EnableEmSjLj = true)
: ModulePass(ID), EnableEmEH(EnableEmEH), EnableEmSjLj(EnableEmSjLj) {
EHAllowlistSet.insert(EHAllowlist.begin(), EHAllowlist.end());
}
bool runOnModule(Module &M) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<DominatorTreeWrapperPass>();
}
};
} // End anonymous namespace
char WebAssemblyLowerEmscriptenEHSjLj::ID = 0;
INITIALIZE_PASS(WebAssemblyLowerEmscriptenEHSjLj, DEBUG_TYPE,
"WebAssembly Lower Emscripten Exceptions / Setjmp / Longjmp",
false, false)
ModulePass *llvm::createWebAssemblyLowerEmscriptenEHSjLj(bool EnableEmEH,
bool EnableEmSjLj) {
return new WebAssemblyLowerEmscriptenEHSjLj(EnableEmEH, EnableEmSjLj);
}
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" || 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,
// which will generate an import and assume that it will exist at link time.
static GlobalVariable *getGlobalVariable(Module &M, Type *Ty,
WebAssemblyTargetMachine &TM,
const char *Name) {
auto *GV = dyn_cast<GlobalVariable>(M.getOrInsertGlobal(Name, Ty));
if (!GV)
report_fatal_error(Twine("unable to create global: ") + Name);
// If the target supports TLS, make this variable thread-local. We can't just
// unconditionally make it thread-local and depend on
// CoalesceFeaturesAndStripAtomics to downgrade it, because stripping TLS has
// the side effect of disallowing the object from being linked into a
// shared-memory module, which we don't want to be responsible for.
auto *Subtarget = TM.getSubtargetImpl();
auto TLS = Subtarget->hasAtomics() && Subtarget->hasBulkMemory()
? GlobalValue::LocalExecTLSModel
: GlobalValue::NotThreadLocal;
GV->setThreadLocalMode(TLS);
return GV;
}
// Simple function name mangler.
// This function simply takes LLVM's string representation of parameter types
// and concatenate them with '_'. There are non-alphanumeric characters but llc
// is ok with it, and we need to postprocess these names after the lowering
// phase anyway.
static std::string getSignature(FunctionType *FTy) {
std::string Sig;
raw_string_ostream OS(Sig);
OS << *FTy->getReturnType();
for (Type *ParamTy : FTy->params())
OS << "_" << *ParamTy;
if (FTy->isVarArg())
OS << "_...";
Sig = OS.str();
erase_if(Sig, isSpace);
// When s2wasm parses .s file, a comma means the end of an argument. So a
// mangled function name can contain any character but a comma.
std::replace(Sig.begin(), Sig.end(), ',', '.');
return Sig;
}
static Function *getEmscriptenFunction(FunctionType *Ty, const Twine &Name,
Module *M) {
Function* F = Function::Create(Ty, GlobalValue::ExternalLinkage, Name, M);
// Tell the linker that this function is expected to be imported from the
// 'env' module.
if (!F->hasFnAttribute("wasm-import-module")) {
llvm::AttrBuilder B;
B.addAttribute("wasm-import-module", "env");
F->addFnAttrs(B);
}
if (!F->hasFnAttribute("wasm-import-name")) {
llvm::AttrBuilder B;
B.addAttribute("wasm-import-name", F->getName());
F->addFnAttrs(B);
}
return F;
}
// Returns an integer type for the target architecture's address space.
// i32 for wasm32 and i64 for wasm64.
static Type *getAddrIntType(Module *M) {
IRBuilder<> IRB(M->getContext());
return IRB.getIntNTy(M->getDataLayout().getPointerSizeInBits());
}
// Returns an integer pointer type for the target architecture's address space.
// i32* for wasm32 and i64* for wasm64.
static Type *getAddrPtrType(Module *M) {
return Type::getIntNPtrTy(M->getContext(),
M->getDataLayout().getPointerSizeInBits());
}
// Returns an integer whose type is the integer type for the target's address
// space. Returns (i32 C) for wasm32 and (i64 C) for wasm64, when C is the
// integer.
static Value *getAddrSizeInt(Module *M, uint64_t C) {
IRBuilder<> IRB(M->getContext());
return IRB.getIntN(M->getDataLayout().getPointerSizeInBits(), C);
}
// Returns __cxa_find_matching_catch_N function, where N = NumClauses + 2.
// This is because a landingpad instruction contains two more arguments, a
// personality function and a cleanup bit, and __cxa_find_matching_catch_N
// functions are named after the number of arguments in the original landingpad
// instruction.
Function *
WebAssemblyLowerEmscriptenEHSjLj::getFindMatchingCatch(Module &M,
unsigned NumClauses) {
if (FindMatchingCatches.count(NumClauses))
return FindMatchingCatches[NumClauses];
PointerType *Int8PtrTy = Type::getInt8PtrTy(M.getContext());
SmallVector<Type *, 16> Args(NumClauses, Int8PtrTy);
FunctionType *FTy = FunctionType::get(Int8PtrTy, Args, false);
Function *F = getEmscriptenFunction(
FTy, "__cxa_find_matching_catch_" + Twine(NumClauses + 2), &M);
FindMatchingCatches[NumClauses] = F;
return F;
}
// Generate invoke wrapper seqence with preamble and postamble
// Preamble:
// __THREW__ = 0;
// Postamble:
// %__THREW__.val = __THREW__; __THREW__ = 0;
// Returns %__THREW__.val, which indicates whether an exception is thrown (or
// whether longjmp occurred), for future use.
Value *WebAssemblyLowerEmscriptenEHSjLj::wrapInvoke(CallBase *CI) {
Module *M = CI->getModule();
LLVMContext &C = M->getContext();
// If we are calling a function that is noreturn, we must remove that
// attribute. The code we insert here does expect it to return, after we
// catch the exception.
if (CI->doesNotReturn()) {
if (auto *F = CI->getCalledFunction())
F->removeFnAttr(Attribute::NoReturn);
CI->removeFnAttr(Attribute::NoReturn);
}
IRBuilder<> IRB(C);
IRB.SetInsertPoint(CI);
// Pre-invoke
// __THREW__ = 0;
IRB.CreateStore(getAddrSizeInt(M, 0), ThrewGV);
// Invoke function wrapper in JavaScript
SmallVector<Value *, 16> Args;
// Put the pointer to the callee as first argument, so it can be called
// within the invoke wrapper later
Args.push_back(CI->getCalledOperand());
Args.append(CI->arg_begin(), CI->arg_end());
CallInst *NewCall = IRB.CreateCall(getInvokeWrapper(CI), Args);
NewCall->takeName(CI);
NewCall->setCallingConv(CallingConv::WASM_EmscriptenInvoke);
NewCall->setDebugLoc(CI->getDebugLoc());
// Because we added the pointer to the callee as first argument, all
// argument attribute indices have to be incremented by one.
SmallVector<AttributeSet, 8> ArgAttributes;
const AttributeList &InvokeAL = CI->getAttributes();
// No attributes for the callee pointer.
ArgAttributes.push_back(AttributeSet());
// Copy the argument attributes from the original
for (unsigned I = 0, E = CI->getNumArgOperands(); I < E; ++I)
ArgAttributes.push_back(InvokeAL.getParamAttrs(I));
AttrBuilder FnAttrs(InvokeAL.getFnAttrs());
if (FnAttrs.contains(Attribute::AllocSize)) {
// The allocsize attribute (if any) referes to parameters by index and needs
// to be adjusted.
unsigned SizeArg;
Optional<unsigned> NEltArg;
std::tie(SizeArg, NEltArg) = FnAttrs.getAllocSizeArgs();
SizeArg += 1;
if (NEltArg.hasValue())
NEltArg = NEltArg.getValue() + 1;
FnAttrs.addAllocSizeAttr(SizeArg, NEltArg);
}
// Reconstruct the AttributesList based on the vector we constructed.
AttributeList NewCallAL = AttributeList::get(
C, AttributeSet::get(C, FnAttrs), InvokeAL.getRetAttrs(), ArgAttributes);
NewCall->setAttributes(NewCallAL);
CI->replaceAllUsesWith(NewCall);
// Post-invoke
// %__THREW__.val = __THREW__; __THREW__ = 0;
Value *Threw =
IRB.CreateLoad(getAddrIntType(M), ThrewGV, ThrewGV->getName() + ".val");
IRB.CreateStore(getAddrSizeInt(M, 0), ThrewGV);
return Threw;
}
// Get matching invoke wrapper based on callee signature
Function *WebAssemblyLowerEmscriptenEHSjLj::getInvokeWrapper(CallBase *CI) {
Module *M = CI->getModule();
SmallVector<Type *, 16> ArgTys;
FunctionType *CalleeFTy = CI->getFunctionType();
std::string Sig = getSignature(CalleeFTy);
if (InvokeWrappers.find(Sig) != InvokeWrappers.end())
return InvokeWrappers[Sig];
// Put the pointer to the callee as first argument
ArgTys.push_back(PointerType::getUnqual(CalleeFTy));
// Add argument types
ArgTys.append(CalleeFTy->param_begin(), CalleeFTy->param_end());
FunctionType *FTy = FunctionType::get(CalleeFTy->getReturnType(), ArgTys,
CalleeFTy->isVarArg());
Function *F = getEmscriptenFunction(FTy, "__invoke_" + Sig, M);
InvokeWrappers[Sig] = F;
return F;
}
static bool canLongjmp(const Value *Callee) {
if (auto *CalleeF = dyn_cast<Function>(Callee))
if (CalleeF->isIntrinsic())
return false;
// Attempting to transform inline assembly will result in something like:
// call void @__invoke_void(void ()* asm ...)
// which is invalid because inline assembly blocks do not have addresses
// and can't be passed by pointer. The result is a crash with illegal IR.
if (isa<InlineAsm>(Callee))
return false;
StringRef CalleeName = Callee->getName();
// The reason we include malloc/free here is to exclude the malloc/free
// calls generated in setjmp prep / cleanup routines.
if (CalleeName == "setjmp" || CalleeName == "malloc" || CalleeName == "free")
return false;
// There are functions in Emscripten's JS glue code or compiler-rt
if (CalleeName == "__resumeException" || CalleeName == "llvm_eh_typeid_for" ||
CalleeName == "saveSetjmp" || CalleeName == "testSetjmp" ||
CalleeName == "getTempRet0" || CalleeName == "setTempRet0")
return false;
// __cxa_find_matching_catch_N functions cannot longjmp
if (Callee->getName().startswith("__cxa_find_matching_catch_"))
return false;
// Exception-catching related functions
if (CalleeName == "__cxa_begin_catch" || CalleeName == "__cxa_end_catch" ||
CalleeName == "__cxa_allocate_exception" || CalleeName == "__cxa_throw" ||
CalleeName == "__clang_call_terminate")
return false;
// Otherwise we don't know
return true;
}
static bool isEmAsmCall(const Value *Callee) {
StringRef CalleeName = Callee->getName();
// This is an exhaustive list from Emscripten's <emscripten/em_asm.h>.
return CalleeName == "emscripten_asm_const_int" ||
CalleeName == "emscripten_asm_const_double" ||
CalleeName == "emscripten_asm_const_int_sync_on_main_thread" ||
CalleeName == "emscripten_asm_const_double_sync_on_main_thread" ||
CalleeName == "emscripten_asm_const_async_on_main_thread";
}
// Generate testSetjmp function call seqence with preamble and postamble.
// The code this generates is equivalent to the following JavaScript code:
// %__threwValue.val = __threwValue;
// if (%__THREW__.val != 0 & %__threwValue.val != 0) {
// %label = testSetjmp(mem[%__THREW__.val], setjmpTable, setjmpTableSize);
// if (%label == 0)
// emscripten_longjmp(%__THREW__.val, %__threwValue.val);
// setTempRet0(%__threwValue.val);
// } else {
// %label = -1;
// }
// %longjmp_result = getTempRet0();
//
// As output parameters. returns %label, %longjmp_result, and the BB the last
// instruction (%longjmp_result = ...) is in.
void WebAssemblyLowerEmscriptenEHSjLj::wrapTestSetjmp(
BasicBlock *BB, DebugLoc DL, Value *Threw, Value *SetjmpTable,
Value *SetjmpTableSize, Value *&Label, Value *&LongjmpResult,
BasicBlock *&EndBB) {
Function *F = BB->getParent();
Module *M = F->getParent();
LLVMContext &C = M->getContext();
IRBuilder<> IRB(C);
IRB.SetCurrentDebugLocation(DL);
// if (%__THREW__.val != 0 & %__threwValue.val != 0)
IRB.SetInsertPoint(BB);
BasicBlock *ThenBB1 = BasicBlock::Create(C, "if.then1", F);
BasicBlock *ElseBB1 = BasicBlock::Create(C, "if.else1", F);
BasicBlock *EndBB1 = BasicBlock::Create(C, "if.end", F);
Value *ThrewCmp = IRB.CreateICmpNE(Threw, getAddrSizeInt(M, 0));
Value *ThrewValue = IRB.CreateLoad(IRB.getInt32Ty(), ThrewValueGV,
ThrewValueGV->getName() + ".val");
Value *ThrewValueCmp = IRB.CreateICmpNE(ThrewValue, IRB.getInt32(0));
Value *Cmp1 = IRB.CreateAnd(ThrewCmp, ThrewValueCmp, "cmp1");
IRB.CreateCondBr(Cmp1, ThenBB1, ElseBB1);
// %label = testSetjmp(mem[%__THREW__.val], setjmpTable, setjmpTableSize);
// if (%label == 0)
IRB.SetInsertPoint(ThenBB1);
BasicBlock *ThenBB2 = BasicBlock::Create(C, "if.then2", F);
BasicBlock *EndBB2 = BasicBlock::Create(C, "if.end2", F);
Value *ThrewPtr =
IRB.CreateIntToPtr(Threw, getAddrPtrType(M), Threw->getName() + ".p");
Value *LoadedThrew = IRB.CreateLoad(getAddrIntType(M), ThrewPtr,
ThrewPtr->getName() + ".loaded");
Value *ThenLabel = IRB.CreateCall(
TestSetjmpF, {LoadedThrew, SetjmpTable, SetjmpTableSize}, "label");
Value *Cmp2 = IRB.CreateICmpEQ(ThenLabel, IRB.getInt32(0));
IRB.CreateCondBr(Cmp2, ThenBB2, EndBB2);
// emscripten_longjmp(%__THREW__.val, %__threwValue.val);
IRB.SetInsertPoint(ThenBB2);
IRB.CreateCall(EmLongjmpF, {Threw, ThrewValue});
IRB.CreateUnreachable();
// setTempRet0(%__threwValue.val);
IRB.SetInsertPoint(EndBB2);
IRB.CreateCall(SetTempRet0F, ThrewValue);
IRB.CreateBr(EndBB1);
IRB.SetInsertPoint(ElseBB1);
IRB.CreateBr(EndBB1);
// longjmp_result = getTempRet0();
IRB.SetInsertPoint(EndBB1);
PHINode *LabelPHI = IRB.CreatePHI(IRB.getInt32Ty(), 2, "label");
LabelPHI->addIncoming(ThenLabel, EndBB2);
LabelPHI->addIncoming(IRB.getInt32(-1), ElseBB1);
// Output parameter assignment
Label = LabelPHI;
EndBB = EndBB1;
LongjmpResult = IRB.CreateCall(GetTempRet0F, None, "longjmp_result");
}
void WebAssemblyLowerEmscriptenEHSjLj::rebuildSSA(Function &F) {
DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(F).getDomTree();
DT.recalculate(F); // CFG has been changed
SSAUpdater SSA;
for (BasicBlock &BB : F) {
for (Instruction &I : BB) {
SSA.Initialize(I.getType(), I.getName());
SSA.AddAvailableValue(&BB, &I);
for (auto UI = I.use_begin(), UE = I.use_end(); UI != UE;) {
Use &U = *UI;
++UI;
auto *User = cast<Instruction>(U.getUser());
if (auto *UserPN = dyn_cast<PHINode>(User))
if (UserPN->getIncomingBlock(U) == &BB)
continue;
if (DT.dominates(&I, User))
continue;
SSA.RewriteUseAfterInsertions(U);
}
}
}
}
// Replace uses of longjmp with emscripten_longjmp. emscripten_longjmp takes
// arguments of type {i32, i32} (wasm32) / {i64, i32} (wasm64) and longjmp takes
// {jmp_buf*, i32}, so we need a ptrtoint instruction here to make the type
// match. jmp_buf* will eventually be lowered to i32/i64 in the wasm backend.
static void replaceLongjmpWithEmscriptenLongjmp(Function *LongjmpF,
Function *EmLongjmpF) {
Module *M = LongjmpF->getParent();
SmallVector<CallInst *, 8> ToErase;
LLVMContext &C = LongjmpF->getParent()->getContext();
IRBuilder<> IRB(C);
// For calls to longjmp, replace it with emscripten_longjmp and cast its first
// argument (jmp_buf*) to int
for (User *U : LongjmpF->users()) {
auto *CI = dyn_cast<CallInst>(U);
if (CI && CI->getCalledFunction() == LongjmpF) {
IRB.SetInsertPoint(CI);
Value *JmpBuf =
IRB.CreatePtrToInt(CI->getArgOperand(0), getAddrIntType(M), "jmpbuf");
IRB.CreateCall(EmLongjmpF, {JmpBuf, CI->getArgOperand(1)});
ToErase.push_back(CI);
}
}
for (auto *I : ToErase)
I->eraseFromParent();
// If we have any remaining uses of longjmp's function pointer, replace it
// with (int(*)(jmp_buf*, int))emscripten_longjmp.
if (!LongjmpF->uses().empty()) {
Value *EmLongjmp =
IRB.CreateBitCast(EmLongjmpF, LongjmpF->getType(), "em_longjmp");
LongjmpF->replaceAllUsesWith(EmLongjmp);
}
}
static bool containsLongjmpableCalls(const Function *F) {
for (const auto &BB : *F)
for (const auto &I : BB)
if (const auto *CB = dyn_cast<CallBase>(&I))
if (canLongjmp(CB->getCalledOperand()))
return true;
return false;
}
bool WebAssemblyLowerEmscriptenEHSjLj::runOnModule(Module &M) {
LLVM_DEBUG(dbgs() << "********** Lower Emscripten EH & SjLj **********\n");
LLVMContext &C = M.getContext();
IRBuilder<> IRB(C);
Function *SetjmpF = M.getFunction("setjmp");
Function *LongjmpF = M.getFunction("longjmp");
auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
assert(TPC && "Expected a TargetPassConfig");
auto &TM = TPC->getTM<WebAssemblyTargetMachine>();
if (EnableEmEH && 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");
GetTempRet0F = getEmscriptenFunction(
FunctionType::get(IRB.getInt32Ty(), false), "getTempRet0", &M);
SetTempRet0F = getEmscriptenFunction(
FunctionType::get(IRB.getVoidTy(), IRB.getInt32Ty(), false),
"setTempRet0", &M);
GetTempRet0F->setDoesNotThrow();
SetTempRet0F->setDoesNotThrow();
bool Changed = false;
// Function registration for exception handling
if (EnableEmEH) {
// 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);
}
if (EnableEmSjLj && SetjmpF) {
// Precompute setjmp users
for (User *U : SetjmpF->users()) {
Function *UserF = cast<Instruction>(U)->getFunction();
// If a function that calls setjmp does not contain any other calls that
// can longjmp, we don't need to do any transformation on that function,
// so can ignore it
if (containsLongjmpableCalls(UserF))
SetjmpUsers.insert(UserF);
}
}
bool SetjmpUsed = SetjmpF && !SetjmpUsers.empty();
bool LongjmpUsed = LongjmpF && !LongjmpF->use_empty();
DoSjLj = EnableEmSjLj && (SetjmpUsed || LongjmpUsed);
// Function registration and data pre-gathering for setjmp/longjmp handling
if (DoSjLj) {
// Register emscripten_longjmp function
FunctionType *FTy = FunctionType::get(
IRB.getVoidTy(), {getAddrIntType(&M), IRB.getInt32Ty()}, false);
EmLongjmpF = getEmscriptenFunction(FTy, "emscripten_longjmp", &M);
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);
}
}
// Exception handling transformation
if (EnableEmEH) {
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)
EmLongjmpF->eraseFromParent();
if (SaveSetjmpF)
SaveSetjmpF->eraseFromParent();
if (TestSetjmpF)
TestSetjmpF->eraseFromParent();
return false;
}
return true;
}
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;
for (BasicBlock &BB : F) {
auto *II = dyn_cast<InvokeInst>(BB.getTerminator());
if (!II)
continue;
Changed = true;
LandingPads.insert(II->getLandingPadInst());
IRB.SetInsertPoint(II);
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, and
// 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(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());
CallInst *NewCall =
IRB.CreateCall(II->getFunctionType(), II->getCalledOperand(), Args);
NewCall->takeName(II);
NewCall->setCallingConv(II->getCallingConv());
NewCall->setDebugLoc(II->getDebugLoc());
NewCall->setAttributes(II->getAttributes());
II->replaceAllUsesWith(NewCall);
ToErase.push_back(II);
IRB.CreateBr(II->getNormalDest());
// Remove any PHI node entries from the exception destination
II->getUnwindDest()->removePredecessor(&BB);
}
}
// Process resume instructions
for (BasicBlock &BB : F) {
// Scan the body of the basic block for resumes
for (Instruction &I : BB) {
auto *RI = dyn_cast<ResumeInst>(&I);
if (!RI)
continue;
Changed = true;
// Split the input into legal values
Value *Input = RI->getValue();
IRB.SetInsertPoint(RI);
Value *Low = IRB.CreateExtractValue(Input, 0, "low");
// Create a call to __resumeException function
IRB.CreateCall(ResumeF, {Low});
// Add a terminator to the block
IRB.CreateUnreachable();
ToErase.push_back(RI);
}
}
// Process llvm.eh.typeid.for intrinsics
for (BasicBlock &BB : F) {
for (Instruction &I : BB) {
auto *CI = dyn_cast<CallInst>(&I);
if (!CI)
continue;
const Function *Callee = CI->getCalledFunction();
if (!Callee)
continue;
if (Callee->getIntrinsicID() != Intrinsic::eh_typeid_for)
continue;
Changed = true;
IRB.SetInsertPoint(CI);
CallInst *NewCI =
IRB.CreateCall(EHTypeIDF, CI->getArgOperand(0), "typeid");
CI->replaceAllUsesWith(NewCI);
ToErase.push_back(CI);
}
}
// Look for orphan landingpads, can occur in blocks with no predecessors
for (BasicBlock &BB : F) {
Instruction *I = BB.getFirstNonPHI();
if (auto *LPI = dyn_cast<LandingPadInst>(I))
LandingPads.insert(LPI);
}
Changed |= !LandingPads.empty();
// Handle all the landingpad for this function together, as multiple invokes
// may share a single lp
for (LandingPadInst *LPI : LandingPads) {
IRB.SetInsertPoint(LPI);
SmallVector<Value *, 16> FMCArgs;
for (unsigned I = 0, E = LPI->getNumClauses(); I < E; ++I) {
Constant *Clause = LPI->getClause(I);
// TODO Handle filters (= exception specifications).
// https://bugs.llvm.org/show_bug.cgi?id=50396
if (LPI->isCatch(I))
FMCArgs.push_back(Clause);
}
// Create a call to __cxa_find_matching_catch_N function
Function *FMCF = getFindMatchingCatch(M, FMCArgs.size());
CallInst *FMCI = IRB.CreateCall(FMCF, FMCArgs, "fmc");
Value *Undef = UndefValue::get(LPI->getType());
Value *Pair0 = IRB.CreateInsertValue(Undef, FMCI, 0, "pair0");
Value *TempRet0 = IRB.CreateCall(GetTempRet0F, None, "tempret0");
Value *Pair1 = IRB.CreateInsertValue(Pair0, TempRet0, 1, "pair1");
LPI->replaceAllUsesWith(Pair1);
ToErase.push_back(LPI);
}
// Erase everything we no longer need in this function
for (Instruction *I : ToErase)
I->eraseFromParent();
return Changed;
}
// This tries to get debug info from the instruction before which a new
// instruction will be inserted, and if there's no debug info in that
// instruction, tries to get the info instead from the previous instruction (if
// any). If none of these has debug info and a DISubprogram is provided, it
// creates a dummy debug info with the first line of the function, because IR
// verifier requires all inlinable callsites should have debug info when both a
// caller and callee have DISubprogram. If none of these conditions are met,
// returns empty info.
static DebugLoc getOrCreateDebugLoc(const Instruction *InsertBefore,
DISubprogram *SP) {
assert(InsertBefore);
if (InsertBefore->getDebugLoc())
return InsertBefore->getDebugLoc();
const Instruction *Prev = InsertBefore->getPrevNode();
if (Prev && Prev->getDebugLoc())
return Prev->getDebugLoc();
if (SP)
return DILocation::get(SP->getContext(), SP->getLine(), 1, SP);
return DebugLoc();
}
bool WebAssemblyLowerEmscriptenEHSjLj::runSjLjOnFunction(Function &F) {
Module &M = *F.getParent();
LLVMContext &C = F.getContext();
IRBuilder<> IRB(C);
SmallVector<Instruction *, 64> ToErase;
// Vector of %setjmpTable values
SmallVector<Instruction *, 4> SetjmpTableInsts;
// Vector of %setjmpTableSize values
SmallVector<Instruction *, 4> SetjmpTableSizeInsts;
// Setjmp preparation
// This instruction effectively means %setjmpTableSize = 4.
// We create this as an instruction intentionally, and we don't want to fold
// this instruction to a constant 4, because this value will be used in
// SSAUpdater.AddAvailableValue(...) later.
BasicBlock *Entry = &F.getEntryBlock();
DebugLoc FirstDL = getOrCreateDebugLoc(&*Entry->begin(), F.getSubprogram());
BinaryOperator *SetjmpTableSize =
BinaryOperator::Create(Instruction::Add, IRB.getInt32(4), IRB.getInt32(0),
"setjmpTableSize", &*Entry->getFirstInsertionPt());
SetjmpTableSize->setDebugLoc(FirstDL);
// setjmpTable = (int *) malloc(40);
Instruction *SetjmpTable = CallInst::CreateMalloc(
SetjmpTableSize, IRB.getInt32Ty(), IRB.getInt32Ty(), IRB.getInt32(40),
nullptr, nullptr, "setjmpTable");
SetjmpTable->setDebugLoc(FirstDL);
// CallInst::CreateMalloc may return a bitcast instruction if the result types
// mismatch. We need to set the debug loc for the original call too.
auto *MallocCall = SetjmpTable->stripPointerCasts();
if (auto *MallocCallI = dyn_cast<Instruction>(MallocCall)) {
MallocCallI->setDebugLoc(FirstDL);
}
// setjmpTable[0] = 0;
IRB.SetInsertPoint(SetjmpTableSize);
IRB.CreateStore(IRB.getInt32(0), SetjmpTable);
SetjmpTableInsts.push_back(SetjmpTable);
SetjmpTableSizeInsts.push_back(SetjmpTableSize);
// Setjmp transformation
SmallVector<PHINode *, 4> SetjmpRetPHIs;
Function *SetjmpF = M.getFunction("setjmp");
for (User *U : SetjmpF->users()) {
auto *CI = dyn_cast<CallInst>(U);
if (!CI)
report_fatal_error("Does not support indirect calls to setjmp");
BasicBlock *BB = CI->getParent();
if (BB->getParent() != &F) // in other function
continue;
// The tail is everything right after the call, and will be reached once
// when setjmp is called, and later when longjmp returns to the setjmp
BasicBlock *Tail = SplitBlock(BB, CI->getNextNode());
// Add a phi to the tail, which will be the output of setjmp, which
// indicates if this is the first call or a longjmp back. The phi directly
// uses the right value based on where we arrive from
IRB.SetInsertPoint(Tail->getFirstNonPHI());
PHINode *SetjmpRet = IRB.CreatePHI(IRB.getInt32Ty(), 2, "setjmp.ret");
// setjmp initial call returns 0
SetjmpRet->addIncoming(IRB.getInt32(0), BB);
// The proper output is now this, not the setjmp call itself
CI->replaceAllUsesWith(SetjmpRet);
// longjmp returns to the setjmp will add themselves to this phi
SetjmpRetPHIs.push_back(SetjmpRet);
// Fix call target
// Our index in the function is our place in the array + 1 to avoid index
// 0, because index 0 means the longjmp is not ours to handle.
IRB.SetInsertPoint(CI);
Value *Args[] = {CI->getArgOperand(0), IRB.getInt32(SetjmpRetPHIs.size()),
SetjmpTable, SetjmpTableSize};
Instruction *NewSetjmpTable =
IRB.CreateCall(SaveSetjmpF, Args, "setjmpTable");
Instruction *NewSetjmpTableSize =
IRB.CreateCall(GetTempRet0F, None, "setjmpTableSize");
SetjmpTableInsts.push_back(NewSetjmpTable);
SetjmpTableSizeInsts.push_back(NewSetjmpTableSize);
ToErase.push_back(CI);
}
// Update each call that can longjmp so it can return to a setjmp where
// relevant.
// Because we are creating new BBs while processing and don't want to make
// all these newly created BBs candidates again for longjmp processing, we
// first make the vector of candidate BBs.
std::vector<BasicBlock *> BBs;
for (BasicBlock &BB : F)
BBs.push_back(&BB);
// BBs.size() will change within the loop, so we query it every time
for (unsigned I = 0; I < BBs.size(); I++) {
BasicBlock *BB = BBs[I];
for (Instruction &I : *BB) {
if (isa<InvokeInst>(&I))
report_fatal_error("When using Wasm EH with Emscripten SjLj, there is "
"a restriction that `setjmp` function call and "
"exception cannot be used within the same function");
auto *CI = dyn_cast<CallInst>(&I);
if (!CI)
continue;
const Value *Callee = CI->getCalledOperand();
if (!canLongjmp(Callee))
continue;
if (isEmAsmCall(Callee))
report_fatal_error("Cannot use EM_ASM* alongside setjmp/longjmp in " +
F.getName() +
". Please consider using EM_JS, or move the "
"EM_ASM into another function.",
false);
Value *Threw = nullptr;
BasicBlock *Tail;
if (Callee->getName().startswith("__invoke_")) {
// If invoke wrapper has already been generated for this call in
// previous EH phase, search for the load instruction
// %__THREW__.val = __THREW__;
// in postamble after the invoke wrapper call
LoadInst *ThrewLI = nullptr;
StoreInst *ThrewResetSI = nullptr;
for (auto I = std::next(BasicBlock::iterator(CI)), IE = BB->end();
I != IE; ++I) {
if (auto *LI = dyn_cast<LoadInst>(I))
if (auto *GV = dyn_cast<GlobalVariable>(LI->getPointerOperand()))
if (GV == ThrewGV) {
Threw = ThrewLI = LI;
break;
}
}
// Search for the store instruction after the load above
// __THREW__ = 0;
for (auto I = std::next(BasicBlock::iterator(ThrewLI)), IE = BB->end();
I != IE; ++I) {
if (auto *SI = dyn_cast<StoreInst>(I)) {
if (auto *GV = dyn_cast<GlobalVariable>(SI->getPointerOperand())) {
if (GV == ThrewGV &&
SI->getValueOperand() == getAddrSizeInt(&M, 0)) {
ThrewResetSI = SI;
break;
}
}
}
}
assert(Threw && ThrewLI && "Cannot find __THREW__ load after invoke");
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
// code to figure out (1) whether longjmp occurred (2) if longjmp
// occurred, which setjmp it corresponds to
Value *Label = nullptr;
Value *LongjmpResult = nullptr;
BasicBlock *EndBB = nullptr;
wrapTestSetjmp(BB, CI->getDebugLoc(), Threw, SetjmpTable, SetjmpTableSize,
Label, LongjmpResult, EndBB);
assert(Label && LongjmpResult && EndBB);
// Create switch instruction
IRB.SetInsertPoint(EndBB);
IRB.SetCurrentDebugLocation(EndBB->getInstList().back().getDebugLoc());
SwitchInst *SI = IRB.CreateSwitch(Label, Tail, SetjmpRetPHIs.size());
// -1 means no longjmp happened, continue normally (will hit the default
// switch case). 0 means a longjmp that is not ours to handle, needs a
// rethrow. Otherwise the index is the same as the index in P+1 (to avoid
// 0).
for (unsigned I = 0; I < SetjmpRetPHIs.size(); I++) {
SI->addCase(IRB.getInt32(I + 1), SetjmpRetPHIs[I]->getParent());
SetjmpRetPHIs[I]->addIncoming(LongjmpResult, EndBB);
}
// We are splitting the block here, and must continue to find other calls
// in the block - which is now split. so continue to traverse in the Tail
BBs.push_back(Tail);
}
}
// Erase everything we no longer need in this function
for (Instruction *I : ToErase)
I->eraseFromParent();
// Free setjmpTable buffer before each return instruction + function-exiting
// call
SmallVector<Instruction *, 16> ExitingInsts;
for (BasicBlock &BB : F) {
Instruction *TI = BB.getTerminator();
if (isa<ReturnInst>(TI))
ExitingInsts.push_back(TI);
for (auto &I : BB) {
if (auto *CB = dyn_cast<CallBase>(&I)) {
StringRef CalleeName = CB->getCalledOperand()->getName();
if (CalleeName == "__resumeException" ||
CalleeName == "emscripten_longjmp" || CalleeName == "__cxa_throw")
ExitingInsts.push_back(&I);
}
}
}
for (auto *I : ExitingInsts) {
DebugLoc DL = getOrCreateDebugLoc(I, F.getSubprogram());
auto *Free = CallInst::CreateFree(SetjmpTable, I);
Free->setDebugLoc(DL);
// CallInst::CreateFree may create a bitcast instruction if its argument
// types mismatch. We need to set the debug loc for the bitcast too.
if (auto *FreeCallI = dyn_cast<CallInst>(Free)) {
if (auto *BitCastI = dyn_cast<BitCastInst>(FreeCallI->getArgOperand(0)))
BitCastI->setDebugLoc(DL);
}
}
// Every call to saveSetjmp can change setjmpTable and setjmpTableSize
// (when buffer reallocation occurs)
// entry:
// setjmpTableSize = 4;
// setjmpTable = (int *) malloc(40);
// setjmpTable[0] = 0;
// ...
// somebb:
// setjmpTable = saveSetjmp(buf, label, setjmpTable, setjmpTableSize);
// setjmpTableSize = getTempRet0();
// So we need to make sure the SSA for these variables is valid so that every
// saveSetjmp and testSetjmp calls have the correct arguments.
SSAUpdater SetjmpTableSSA;
SSAUpdater SetjmpTableSizeSSA;
SetjmpTableSSA.Initialize(Type::getInt32PtrTy(C), "setjmpTable");
SetjmpTableSizeSSA.Initialize(Type::getInt32Ty(C), "setjmpTableSize");
for (Instruction *I : SetjmpTableInsts)
SetjmpTableSSA.AddAvailableValue(I->getParent(), I);
for (Instruction *I : SetjmpTableSizeInsts)
SetjmpTableSizeSSA.AddAvailableValue(I->getParent(), I);
for (auto UI = SetjmpTable->use_begin(), UE = SetjmpTable->use_end();
UI != UE;) {
// Grab the use before incrementing the iterator.
Use &U = *UI;
// Increment the iterator before removing the use from the list.
++UI;
if (auto *I = dyn_cast<Instruction>(U.getUser()))
if (I->getParent() != Entry)
SetjmpTableSSA.RewriteUse(U);
}
for (auto UI = SetjmpTableSize->use_begin(), UE = SetjmpTableSize->use_end();
UI != UE;) {
Use &U = *UI;
++UI;
if (auto *I = dyn_cast<Instruction>(U.getUser()))
if (I->getParent() != Entry)
SetjmpTableSizeSSA.RewriteUse(U);
}
// Finally, our modifications to the cfg can break dominance of SSA variables.
// For example, in this code,
// if (x()) { .. setjmp() .. }
// if (y()) { .. longjmp() .. }
// We must split the longjmp block, and it can jump into the block splitted
// from setjmp one. But that means that when we split the setjmp block, it's
// first part no longer dominates its second part - there is a theoretically
// possible control flow path where x() is false, then y() is true and we
// reach the second part of the setjmp block, without ever reaching the first
// part. So, we rebuild SSA form here.
rebuildSSA(F);
return true;
}
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