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Diffstat (limited to 'gnu/llvm/lib/CodeGen/WasmEHPrepare.cpp')
| -rw-r--r-- | gnu/llvm/lib/CodeGen/WasmEHPrepare.cpp | 430 |
1 files changed, 0 insertions, 430 deletions
diff --git a/gnu/llvm/lib/CodeGen/WasmEHPrepare.cpp b/gnu/llvm/lib/CodeGen/WasmEHPrepare.cpp deleted file mode 100644 index e5002eb9534..00000000000 --- a/gnu/llvm/lib/CodeGen/WasmEHPrepare.cpp +++ /dev/null @@ -1,430 +0,0 @@ -//===-- WasmEHPrepare - Prepare excepton handling for WebAssembly --------===// -// -// The LLVM Compiler Infrastructure -// -// This file is distributed under the University of Illinois Open Source -// License. See LICENSE.TXT for details. -// -//===----------------------------------------------------------------------===// -// -// This transformation is designed for use by code generators which use -// WebAssembly exception handling scheme. -// -// WebAssembly exception handling uses Windows exception IR for the middle level -// representation. This pass does the following transformation for every -// catchpad block: -// (In C-style pseudocode) -// -// - Before: -// catchpad ... -// exn = wasm.get.exception(); -// selector = wasm.get.selector(); -// ... -// -// - After: -// catchpad ... -// exn = wasm.catch(0); // 0 is a tag for C++ -// wasm.landingpad.index(index); -// // Only add below in case it's not a single catch (...) -// __wasm_lpad_context.lpad_index = index; -// __wasm_lpad_context.lsda = wasm.lsda(); -// _Unwind_CallPersonality(exn); -// int selector = __wasm.landingpad_context.selector; -// ... -// -// Also, does the following for a cleanuppad block with a call to -// __clang_call_terminate(): -// - Before: -// cleanuppad ... -// exn = wasm.get.exception(); -// __clang_call_terminate(exn); -// -// - After: -// cleanuppad ... -// exn = wasm.catch(0); // 0 is a tag for C++ -// __clang_call_terminate(exn); -// -// -// * Background: WebAssembly EH instructions -// WebAssembly's try and catch instructions are structured as follows: -// try -// instruction* -// catch (C++ tag) -// instruction* -// ... -// catch_all -// instruction* -// try_end -// -// A catch instruction in WebAssembly does not correspond to a C++ catch clause. -// In WebAssembly, there is a single catch instruction for all C++ exceptions. -// There can be more catch instructions for exceptions in other languages, but -// they are not generated for now. catch_all catches all exceptions including -// foreign exceptions (e.g. JavaScript). We turn catchpads into catch (C++ tag) -// and cleanuppads into catch_all, with one exception: cleanuppad with a call to -// __clang_call_terminate should be both in catch (C++ tag) and catch_all. -// -// -// * Background: Direct personality function call -// In WebAssembly EH, the VM is responsible for unwinding the stack once an -// exception is thrown. After the stack is unwound, the control flow is -// transfered to WebAssembly 'catch' instruction, which returns a caught -// exception object. -// -// Unwinding the stack is not done by libunwind but the VM, so the personality -// function in libcxxabi cannot be called from libunwind during the unwinding -// process. So after a catch instruction, we insert a call to a wrapper function -// in libunwind that in turn calls the real personality function. -// -// In Itanium EH, if the personality function decides there is no matching catch -// clause in a call frame and no cleanup action to perform, the unwinder doesn't -// stop there and continues unwinding. But in Wasm EH, the unwinder stops at -// every call frame with a catch intruction, after which the personality -// function is called from the compiler-generated user code here. -// -// In libunwind, we have this struct that serves as a communincation channel -// between the compiler-generated user code and the personality function in -// libcxxabi. -// -// struct _Unwind_LandingPadContext { -// uintptr_t lpad_index; -// uintptr_t lsda; -// uintptr_t selector; -// }; -// struct _Unwind_LandingPadContext __wasm_lpad_context = ...; -// -// And this wrapper in libunwind calls the personality function. -// -// _Unwind_Reason_Code _Unwind_CallPersonality(void *exception_ptr) { -// struct _Unwind_Exception *exception_obj = -// (struct _Unwind_Exception *)exception_ptr; -// _Unwind_Reason_Code ret = __gxx_personality_v0( -// 1, _UA_CLEANUP_PHASE, exception_obj->exception_class, exception_obj, -// (struct _Unwind_Context *)__wasm_lpad_context); -// return ret; -// } -// -// We pass a landing pad index, and the address of LSDA for the current function -// to the wrapper function _Unwind_CallPersonality in libunwind, and we retrieve -// the selector after it returns. -// -//===----------------------------------------------------------------------===// - -#include "llvm/ADT/SetVector.h" -#include "llvm/ADT/Statistic.h" -#include "llvm/ADT/Triple.h" -#include "llvm/CodeGen/Passes.h" -#include "llvm/CodeGen/TargetLowering.h" -#include "llvm/CodeGen/TargetSubtargetInfo.h" -#include "llvm/CodeGen/WasmEHFuncInfo.h" -#include "llvm/IR/Dominators.h" -#include "llvm/IR/IRBuilder.h" -#include "llvm/IR/Intrinsics.h" -#include "llvm/Pass.h" -#include "llvm/Transforms/Utils/BasicBlockUtils.h" - -using namespace llvm; - -#define DEBUG_TYPE "wasmehprepare" - -namespace { -class WasmEHPrepare : public FunctionPass { - Type *LPadContextTy = nullptr; // type of 'struct _Unwind_LandingPadContext' - GlobalVariable *LPadContextGV = nullptr; // __wasm_lpad_context - - // Field addresses of struct _Unwind_LandingPadContext - Value *LPadIndexField = nullptr; // lpad_index field - Value *LSDAField = nullptr; // lsda field - Value *SelectorField = nullptr; // selector - - Function *ThrowF = nullptr; // wasm.throw() intrinsic - Function *CatchF = nullptr; // wasm.catch.extract() intrinsic - Function *LPadIndexF = nullptr; // wasm.landingpad.index() intrinsic - Function *LSDAF = nullptr; // wasm.lsda() intrinsic - Function *GetExnF = nullptr; // wasm.get.exception() intrinsic - Function *GetSelectorF = nullptr; // wasm.get.ehselector() intrinsic - Function *CallPersonalityF = nullptr; // _Unwind_CallPersonality() wrapper - Function *ClangCallTermF = nullptr; // __clang_call_terminate() function - - bool prepareEHPads(Function &F); - bool prepareThrows(Function &F); - - void prepareEHPad(BasicBlock *BB, unsigned Index); - void prepareTerminateCleanupPad(BasicBlock *BB); - -public: - static char ID; // Pass identification, replacement for typeid - - WasmEHPrepare() : FunctionPass(ID) {} - - bool doInitialization(Module &M) override; - bool runOnFunction(Function &F) override; - - StringRef getPassName() const override { - return "WebAssembly Exception handling preparation"; - } -}; -} // end anonymous namespace - -char WasmEHPrepare::ID = 0; -INITIALIZE_PASS(WasmEHPrepare, DEBUG_TYPE, "Prepare WebAssembly exceptions", - false, false) - -FunctionPass *llvm::createWasmEHPass() { return new WasmEHPrepare(); } - -bool WasmEHPrepare::doInitialization(Module &M) { - IRBuilder<> IRB(M.getContext()); - LPadContextTy = StructType::get(IRB.getInt32Ty(), // lpad_index - IRB.getInt8PtrTy(), // lsda - IRB.getInt32Ty() // selector - ); - return false; -} - -// Erase the specified BBs if the BB does not have any remaining predecessors, -// and also all its dead children. -template <typename Container> -static void eraseDeadBBsAndChildren(const Container &BBs) { - SmallVector<BasicBlock *, 8> WL(BBs.begin(), BBs.end()); - while (!WL.empty()) { - auto *BB = WL.pop_back_val(); - if (pred_begin(BB) != pred_end(BB)) - continue; - WL.append(succ_begin(BB), succ_end(BB)); - DeleteDeadBlock(BB); - } -} - -bool WasmEHPrepare::runOnFunction(Function &F) { - bool Changed = false; - Changed |= prepareThrows(F); - Changed |= prepareEHPads(F); - return Changed; -} - -bool WasmEHPrepare::prepareThrows(Function &F) { - Module &M = *F.getParent(); - IRBuilder<> IRB(F.getContext()); - bool Changed = false; - - // wasm.throw() intinsic, which will be lowered to wasm 'throw' instruction. - ThrowF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_throw); - - // Insert an unreachable instruction after a call to @llvm.wasm.throw and - // delete all following instructions within the BB, and delete all the dead - // children of the BB as well. - for (User *U : ThrowF->users()) { - // A call to @llvm.wasm.throw() is only generated from - // __builtin_wasm_throw() builtin call within libcxxabi, and cannot be an - // InvokeInst. - auto *ThrowI = cast<CallInst>(U); - if (ThrowI->getFunction() != &F) - continue; - Changed = true; - auto *BB = ThrowI->getParent(); - SmallVector<BasicBlock *, 4> Succs(succ_begin(BB), succ_end(BB)); - auto &InstList = BB->getInstList(); - InstList.erase(std::next(BasicBlock::iterator(ThrowI)), InstList.end()); - IRB.SetInsertPoint(BB); - IRB.CreateUnreachable(); - eraseDeadBBsAndChildren(Succs); - } - - return Changed; -} - -bool WasmEHPrepare::prepareEHPads(Function &F) { - Module &M = *F.getParent(); - IRBuilder<> IRB(F.getContext()); - - SmallVector<BasicBlock *, 16> CatchPads; - SmallVector<BasicBlock *, 16> CleanupPads; - for (BasicBlock &BB : F) { - if (!BB.isEHPad()) - continue; - auto *Pad = BB.getFirstNonPHI(); - if (isa<CatchPadInst>(Pad)) - CatchPads.push_back(&BB); - else if (isa<CleanupPadInst>(Pad)) - CleanupPads.push_back(&BB); - } - - if (CatchPads.empty() && CleanupPads.empty()) - return false; - assert(F.hasPersonalityFn() && "Personality function not found"); - - // __wasm_lpad_context global variable - LPadContextGV = cast<GlobalVariable>( - M.getOrInsertGlobal("__wasm_lpad_context", LPadContextTy)); - LPadIndexField = IRB.CreateConstGEP2_32(LPadContextTy, LPadContextGV, 0, 0, - "lpad_index_gep"); - LSDAField = - IRB.CreateConstGEP2_32(LPadContextTy, LPadContextGV, 0, 1, "lsda_gep"); - SelectorField = IRB.CreateConstGEP2_32(LPadContextTy, LPadContextGV, 0, 2, - "selector_gep"); - - // wasm.catch() intinsic, which will be lowered to wasm 'catch' instruction. - CatchF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_catch); - // wasm.landingpad.index() intrinsic, which is to specify landingpad index - LPadIndexF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_landingpad_index); - // wasm.lsda() intrinsic. Returns the address of LSDA table for the current - // function. - LSDAF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_lsda); - // wasm.get.exception() and wasm.get.ehselector() intrinsics. Calls to these - // are generated in clang. - GetExnF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_get_exception); - GetSelectorF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_get_ehselector); - - // _Unwind_CallPersonality() wrapper function, which calls the personality - CallPersonalityF = cast<Function>(M.getOrInsertFunction( - "_Unwind_CallPersonality", IRB.getInt32Ty(), IRB.getInt8PtrTy())); - CallPersonalityF->setDoesNotThrow(); - - // __clang_call_terminate() function, which is inserted by clang in case a - // cleanup throws - ClangCallTermF = M.getFunction("__clang_call_terminate"); - - unsigned Index = 0; - for (auto *BB : CatchPads) { - auto *CPI = cast<CatchPadInst>(BB->getFirstNonPHI()); - // In case of a single catch (...), we don't need to emit LSDA - if (CPI->getNumArgOperands() == 1 && - cast<Constant>(CPI->getArgOperand(0))->isNullValue()) - prepareEHPad(BB, -1); - else - prepareEHPad(BB, Index++); - } - - if (!ClangCallTermF) - return !CatchPads.empty(); - - // Cleanuppads will turn into catch_all later, but cleanuppads with a call to - // __clang_call_terminate() is a special case. __clang_call_terminate() takes - // an exception object, so we have to duplicate call in both 'catch <C++ tag>' - // and 'catch_all' clauses. Here we only insert a call to catch; the - // duplication will be done later. In catch_all, the exception object will be - // set to null. - for (auto *BB : CleanupPads) - for (auto &I : *BB) - if (auto *CI = dyn_cast<CallInst>(&I)) - if (CI->getCalledValue() == ClangCallTermF) - prepareEHPad(BB, -1); - - return true; -} - -void WasmEHPrepare::prepareEHPad(BasicBlock *BB, unsigned Index) { - assert(BB->isEHPad() && "BB is not an EHPad!"); - IRBuilder<> IRB(BB->getContext()); - - IRB.SetInsertPoint(&*BB->getFirstInsertionPt()); - // The argument to wasm.catch() is the tag for C++ exceptions, which we set to - // 0 for this module. - // Pseudocode: void *exn = wasm.catch(0); - Instruction *Exn = IRB.CreateCall(CatchF, IRB.getInt32(0), "exn"); - // Replace the return value of wasm.get.exception() with the return value from - // wasm.catch(). - auto *FPI = cast<FuncletPadInst>(BB->getFirstNonPHI()); - Instruction *GetExnCI = nullptr, *GetSelectorCI = nullptr; - for (auto &U : FPI->uses()) { - if (auto *CI = dyn_cast<CallInst>(U.getUser())) { - if (CI->getCalledValue() == GetExnF) - GetExnCI = CI; - else if (CI->getCalledValue() == GetSelectorF) - GetSelectorCI = CI; - } - } - - assert(GetExnCI && "wasm.get.exception() call does not exist"); - GetExnCI->replaceAllUsesWith(Exn); - GetExnCI->eraseFromParent(); - - // In case it is a catchpad with single catch (...) or a cleanuppad, we don't - // need to call personality function because we don't need a selector. - if (FPI->getNumArgOperands() == 0 || - (FPI->getNumArgOperands() == 1 && - cast<Constant>(FPI->getArgOperand(0))->isNullValue())) { - if (GetSelectorCI) { - assert(GetSelectorCI->use_empty() && - "wasm.get.ehselector() still has uses!"); - GetSelectorCI->eraseFromParent(); - } - return; - } - IRB.SetInsertPoint(Exn->getNextNode()); - - // This is to create a map of <landingpad EH label, landingpad index> in - // SelectionDAGISel, which is to be used in EHStreamer to emit LSDA tables. - // Pseudocode: wasm.landingpad.index(Index); - IRB.CreateCall(LPadIndexF, {FPI, IRB.getInt32(Index)}); - - // Pseudocode: __wasm_lpad_context.lpad_index = index; - IRB.CreateStore(IRB.getInt32(Index), LPadIndexField); - - // Store LSDA address only if this catchpad belongs to a top-level - // catchswitch. If there is another catchpad that dominates this pad, we don't - // need to store LSDA address again, because they are the same throughout the - // function and have been already stored before. - // TODO Can we not store LSDA address in user function but make libcxxabi - // compute it? - auto *CPI = cast<CatchPadInst>(FPI); - if (isa<ConstantTokenNone>(CPI->getCatchSwitch()->getParentPad())) - // Pseudocode: __wasm_lpad_context.lsda = wasm.lsda(); - IRB.CreateStore(IRB.CreateCall(LSDAF), LSDAField); - - // Pseudocode: _Unwind_CallPersonality(exn); - CallInst *PersCI = - IRB.CreateCall(CallPersonalityF, Exn, OperandBundleDef("funclet", CPI)); - PersCI->setDoesNotThrow(); - - // Pseudocode: int selector = __wasm.landingpad_context.selector; - Instruction *Selector = IRB.CreateLoad(SelectorField, "selector"); - - // Replace the return value from wasm.get.ehselector() with the selector value - // loaded from __wasm_lpad_context.selector. - assert(GetSelectorCI && "wasm.get.ehselector() call does not exist"); - GetSelectorCI->replaceAllUsesWith(Selector); - GetSelectorCI->eraseFromParent(); -} - -void llvm::calculateWasmEHInfo(const Function *F, WasmEHFuncInfo &EHInfo) { - for (const auto &BB : *F) { - if (!BB.isEHPad()) - continue; - const Instruction *Pad = BB.getFirstNonPHI(); - - // If an exception is not caught by a catchpad (i.e., it is a foreign - // exception), it will unwind to its parent catchswitch's unwind - // destination. We don't record an unwind destination for cleanuppads - // because every exception should be caught by it. - if (const auto *CatchPad = dyn_cast<CatchPadInst>(Pad)) { - const auto *UnwindBB = CatchPad->getCatchSwitch()->getUnwindDest(); - if (!UnwindBB) - continue; - const Instruction *UnwindPad = UnwindBB->getFirstNonPHI(); - if (const auto *CatchSwitch = dyn_cast<CatchSwitchInst>(UnwindPad)) - // Currently there should be only one handler per a catchswitch. - EHInfo.setEHPadUnwindDest(&BB, *CatchSwitch->handlers().begin()); - else // cleanuppad - EHInfo.setEHPadUnwindDest(&BB, UnwindBB); - } - } - - // Record the unwind destination for invoke and cleanupret instructions. - for (const auto &BB : *F) { - const Instruction *TI = BB.getTerminator(); - BasicBlock *UnwindBB = nullptr; - if (const auto *Invoke = dyn_cast<InvokeInst>(TI)) - UnwindBB = Invoke->getUnwindDest(); - else if (const auto *CleanupRet = dyn_cast<CleanupReturnInst>(TI)) - UnwindBB = CleanupRet->getUnwindDest(); - if (!UnwindBB) - continue; - const Instruction *UnwindPad = UnwindBB->getFirstNonPHI(); - if (const auto *CatchSwitch = dyn_cast<CatchSwitchInst>(UnwindPad)) - // Currently there should be only one handler per a catchswitch. - EHInfo.setThrowUnwindDest(&BB, *CatchSwitch->handlers().begin()); - else // cleanuppad - EHInfo.setThrowUnwindDest(&BB, UnwindBB); - } -} |