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+//===- SjLjEHPrepare.cpp - Eliminate Invoke & Unwind instructions ---------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This transformation is designed for use by code generators which use SjLj
+// based exception handling.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "sjljehprepare"
+
+STATISTIC(NumInvokes, "Number of invokes replaced");
+STATISTIC(NumSpilled, "Number of registers live across unwind edges");
+
+namespace {
+class SjLjEHPrepare : public FunctionPass {
+ Type *doubleUnderDataTy;
+ Type *doubleUnderJBufTy;
+ Type *FunctionContextTy;
+ FunctionCallee RegisterFn;
+ FunctionCallee UnregisterFn;
+ Function *BuiltinSetupDispatchFn;
+ Function *FrameAddrFn;
+ Function *StackAddrFn;
+ Function *StackRestoreFn;
+ Function *LSDAAddrFn;
+ Function *CallSiteFn;
+ Function *FuncCtxFn;
+ AllocaInst *FuncCtx;
+
+public:
+ static char ID; // Pass identification, replacement for typeid
+ explicit SjLjEHPrepare() : FunctionPass(ID) {}
+ bool doInitialization(Module &M) override;
+ bool runOnFunction(Function &F) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {}
+ StringRef getPassName() const override {
+ return "SJLJ Exception Handling preparation";
+ }
+
+private:
+ bool setupEntryBlockAndCallSites(Function &F);
+ void substituteLPadValues(LandingPadInst *LPI, Value *ExnVal, Value *SelVal);
+ Value *setupFunctionContext(Function &F, ArrayRef<LandingPadInst *> LPads);
+ void lowerIncomingArguments(Function &F);
+ void lowerAcrossUnwindEdges(Function &F, ArrayRef<InvokeInst *> Invokes);
+ void insertCallSiteStore(Instruction *I, int Number);
+};
+} // end anonymous namespace
+
+char SjLjEHPrepare::ID = 0;
+INITIALIZE_PASS(SjLjEHPrepare, DEBUG_TYPE, "Prepare SjLj exceptions",
+ false, false)
+
+// Public Interface To the SjLjEHPrepare pass.
+FunctionPass *llvm::createSjLjEHPreparePass() { return new SjLjEHPrepare(); }
+// doInitialization - Set up decalarations and types needed to process
+// exceptions.
+bool SjLjEHPrepare::doInitialization(Module &M) {
+ // Build the function context structure.
+ // builtin_setjmp uses a five word jbuf
+ Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
+ Type *Int32Ty = Type::getInt32Ty(M.getContext());
+ doubleUnderDataTy = ArrayType::get(Int32Ty, 4);
+ doubleUnderJBufTy = ArrayType::get(VoidPtrTy, 5);
+ FunctionContextTy = StructType::get(VoidPtrTy, // __prev
+ Int32Ty, // call_site
+ doubleUnderDataTy, // __data
+ VoidPtrTy, // __personality
+ VoidPtrTy, // __lsda
+ doubleUnderJBufTy // __jbuf
+ );
+
+ return true;
+}
+
+/// insertCallSiteStore - Insert a store of the call-site value to the
+/// function context
+void SjLjEHPrepare::insertCallSiteStore(Instruction *I, int Number) {
+ IRBuilder<> Builder(I);
+
+ // Get a reference to the call_site field.
+ Type *Int32Ty = Type::getInt32Ty(I->getContext());
+ Value *Zero = ConstantInt::get(Int32Ty, 0);
+ Value *One = ConstantInt::get(Int32Ty, 1);
+ Value *Idxs[2] = { Zero, One };
+ Value *CallSite =
+ Builder.CreateGEP(FunctionContextTy, FuncCtx, Idxs, "call_site");
+
+ // Insert a store of the call-site number
+ ConstantInt *CallSiteNoC =
+ ConstantInt::get(Type::getInt32Ty(I->getContext()), Number);
+ Builder.CreateStore(CallSiteNoC, CallSite, true /*volatile*/);
+}
+
+/// MarkBlocksLiveIn - Insert BB and all of its predecessors into LiveBBs until
+/// we reach blocks we've already seen.
+static void MarkBlocksLiveIn(BasicBlock *BB,
+ SmallPtrSetImpl<BasicBlock *> &LiveBBs) {
+ if (!LiveBBs.insert(BB).second)
+ return; // already been here.
+
+ df_iterator_default_set<BasicBlock*> Visited;
+
+ for (BasicBlock *B : inverse_depth_first_ext(BB, Visited))
+ LiveBBs.insert(B);
+
+}
+
+/// substituteLPadValues - Substitute the values returned by the landingpad
+/// instruction with those returned by the personality function.
+void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
+ Value *SelVal) {
+ SmallVector<Value *, 8> UseWorkList(LPI->user_begin(), LPI->user_end());
+ while (!UseWorkList.empty()) {
+ Value *Val = UseWorkList.pop_back_val();
+ auto *EVI = dyn_cast<ExtractValueInst>(Val);
+ if (!EVI)
+ continue;
+ if (EVI->getNumIndices() != 1)
+ continue;
+ if (*EVI->idx_begin() == 0)
+ EVI->replaceAllUsesWith(ExnVal);
+ else if (*EVI->idx_begin() == 1)
+ EVI->replaceAllUsesWith(SelVal);
+ if (EVI->use_empty())
+ EVI->eraseFromParent();
+ }
+
+ if (LPI->use_empty())
+ return;
+
+ // There are still some uses of LPI. Construct an aggregate with the exception
+ // values and replace the LPI with that aggregate.
+ Type *LPadType = LPI->getType();
+ Value *LPadVal = UndefValue::get(LPadType);
+ auto *SelI = cast<Instruction>(SelVal);
+ IRBuilder<> Builder(SelI->getParent(), std::next(SelI->getIterator()));
+ LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val");
+ LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val");
+
+ LPI->replaceAllUsesWith(LPadVal);
+}
+
+/// setupFunctionContext - Allocate the function context on the stack and fill
+/// it with all of the data that we know at this point.
+Value *SjLjEHPrepare::setupFunctionContext(Function &F,
+ ArrayRef<LandingPadInst *> LPads) {
+ BasicBlock *EntryBB = &F.front();
+
+ // Create an alloca for the incoming jump buffer ptr and the new jump buffer
+ // that needs to be restored on all exits from the function. This is an alloca
+ // because the value needs to be added to the global context list.
+ auto &DL = F.getParent()->getDataLayout();
+ unsigned Align = DL.getPrefTypeAlignment(FunctionContextTy);
+ FuncCtx = new AllocaInst(FunctionContextTy, DL.getAllocaAddrSpace(),
+ nullptr, Align, "fn_context", &EntryBB->front());
+
+ // Fill in the function context structure.
+ for (LandingPadInst *LPI : LPads) {
+ IRBuilder<> Builder(LPI->getParent(),
+ LPI->getParent()->getFirstInsertionPt());
+
+ // Reference the __data field.
+ Value *FCData =
+ Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 2, "__data");
+
+ // The exception values come back in context->__data[0].
+ Type *Int32Ty = Type::getInt32Ty(F.getContext());
+ Value *ExceptionAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
+ 0, 0, "exception_gep");
+ Value *ExnVal = Builder.CreateLoad(Int32Ty, ExceptionAddr, true, "exn_val");
+ ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy());
+
+ Value *SelectorAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
+ 0, 1, "exn_selector_gep");
+ Value *SelVal =
+ Builder.CreateLoad(Int32Ty, SelectorAddr, true, "exn_selector_val");
+
+ substituteLPadValues(LPI, ExnVal, SelVal);
+ }
+
+ // Personality function
+ IRBuilder<> Builder(EntryBB->getTerminator());
+ Value *PersonalityFn = F.getPersonalityFn();
+ Value *PersonalityFieldPtr = Builder.CreateConstGEP2_32(
+ FunctionContextTy, FuncCtx, 0, 3, "pers_fn_gep");
+ Builder.CreateStore(
+ Builder.CreateBitCast(PersonalityFn, Builder.getInt8PtrTy()),
+ PersonalityFieldPtr, /*isVolatile=*/true);
+
+ // LSDA address
+ Value *LSDA = Builder.CreateCall(LSDAAddrFn, {}, "lsda_addr");
+ Value *LSDAFieldPtr =
+ Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 4, "lsda_gep");
+ Builder.CreateStore(LSDA, LSDAFieldPtr, /*isVolatile=*/true);
+
+ return FuncCtx;
+}
+
+/// lowerIncomingArguments - To avoid having to handle incoming arguments
+/// specially, we lower each arg to a copy instruction in the entry block. This
+/// ensures that the argument value itself cannot be live out of the entry
+/// block.
+void SjLjEHPrepare::lowerIncomingArguments(Function &F) {
+ BasicBlock::iterator AfterAllocaInsPt = F.begin()->begin();
+ while (isa<AllocaInst>(AfterAllocaInsPt) &&
+ cast<AllocaInst>(AfterAllocaInsPt)->isStaticAlloca())
+ ++AfterAllocaInsPt;
+ assert(AfterAllocaInsPt != F.front().end());
+
+ for (auto &AI : F.args()) {
+ // Swift error really is a register that we model as memory -- instruction
+ // selection will perform mem-to-reg for us and spill/reload appropriately
+ // around calls that clobber it. There is no need to spill this
+ // value to the stack and doing so would not be allowed.
+ if (AI.isSwiftError())
+ continue;
+
+ Type *Ty = AI.getType();
+
+ // Use 'select i8 true, %arg, undef' to simulate a 'no-op' instruction.
+ Value *TrueValue = ConstantInt::getTrue(F.getContext());
+ Value *UndefValue = UndefValue::get(Ty);
+ Instruction *SI = SelectInst::Create(
+ TrueValue, &AI, UndefValue, AI.getName() + ".tmp", &*AfterAllocaInsPt);
+ AI.replaceAllUsesWith(SI);
+
+ // Reset the operand, because it was clobbered by the RAUW above.
+ SI->setOperand(1, &AI);
+ }
+}
+
+/// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
+/// edge and spill them.
+void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
+ ArrayRef<InvokeInst *> Invokes) {
+ // Finally, scan the code looking for instructions with bad live ranges.
+ for (BasicBlock &BB : F) {
+ for (Instruction &Inst : BB) {
+ // Ignore obvious cases we don't have to handle. In particular, most
+ // instructions either have no uses or only have a single use inside the
+ // current block. Ignore them quickly.
+ if (Inst.use_empty())
+ continue;
+ if (Inst.hasOneUse() &&
+ cast<Instruction>(Inst.user_back())->getParent() == &BB &&
+ !isa<PHINode>(Inst.user_back()))
+ continue;
+
+ // If this is an alloca in the entry block, it's not a real register
+ // value.
+ if (auto *AI = dyn_cast<AllocaInst>(&Inst))
+ if (AI->isStaticAlloca())
+ continue;
+
+ // Avoid iterator invalidation by copying users to a temporary vector.
+ SmallVector<Instruction *, 16> Users;
+ for (User *U : Inst.users()) {
+ Instruction *UI = cast<Instruction>(U);
+ if (UI->getParent() != &BB || isa<PHINode>(UI))
+ Users.push_back(UI);
+ }
+
+ // Find all of the blocks that this value is live in.
+ SmallPtrSet<BasicBlock *, 32> LiveBBs;
+ LiveBBs.insert(&BB);
+ while (!Users.empty()) {
+ Instruction *U = Users.pop_back_val();
+
+ if (!isa<PHINode>(U)) {
+ MarkBlocksLiveIn(U->getParent(), LiveBBs);
+ } else {
+ // Uses for a PHI node occur in their predecessor block.
+ PHINode *PN = cast<PHINode>(U);
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (PN->getIncomingValue(i) == &Inst)
+ MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
+ }
+ }
+
+ // Now that we know all of the blocks that this thing is live in, see if
+ // it includes any of the unwind locations.
+ bool NeedsSpill = false;
+ for (InvokeInst *Invoke : Invokes) {
+ BasicBlock *UnwindBlock = Invoke->getUnwindDest();
+ if (UnwindBlock != &BB && LiveBBs.count(UnwindBlock)) {
+ LLVM_DEBUG(dbgs() << "SJLJ Spill: " << Inst << " around "
+ << UnwindBlock->getName() << "\n");
+ NeedsSpill = true;
+ break;
+ }
+ }
+
+ // If we decided we need a spill, do it.
+ // FIXME: Spilling this way is overkill, as it forces all uses of
+ // the value to be reloaded from the stack slot, even those that aren't
+ // in the unwind blocks. We should be more selective.
+ if (NeedsSpill) {
+ DemoteRegToStack(Inst, true);
+ ++NumSpilled;
+ }
+ }
+ }
+
+ // Go through the landing pads and remove any PHIs there.
+ for (InvokeInst *Invoke : Invokes) {
+ BasicBlock *UnwindBlock = Invoke->getUnwindDest();
+ LandingPadInst *LPI = UnwindBlock->getLandingPadInst();
+
+ // Place PHIs into a set to avoid invalidating the iterator.
+ SmallPtrSet<PHINode *, 8> PHIsToDemote;
+ for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
+ PHIsToDemote.insert(cast<PHINode>(PN));
+ if (PHIsToDemote.empty())
+ continue;
+
+ // Demote the PHIs to the stack.
+ for (PHINode *PN : PHIsToDemote)
+ DemotePHIToStack(PN);
+
+ // Move the landingpad instruction back to the top of the landing pad block.
+ LPI->moveBefore(&UnwindBlock->front());
+ }
+}
+
+/// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
+/// the function context and marking the call sites with the appropriate
+/// values. These values are used by the DWARF EH emitter.
+bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
+ SmallVector<ReturnInst *, 16> Returns;
+ SmallVector<InvokeInst *, 16> Invokes;
+ SmallSetVector<LandingPadInst *, 16> LPads;
+
+ // Look through the terminators of the basic blocks to find invokes.
+ for (BasicBlock &BB : F)
+ if (auto *II = dyn_cast<InvokeInst>(BB.getTerminator())) {
+ if (Function *Callee = II->getCalledFunction())
+ if (Callee->getIntrinsicID() == Intrinsic::donothing) {
+ // Remove the NOP invoke.
+ BranchInst::Create(II->getNormalDest(), II);
+ II->eraseFromParent();
+ continue;
+ }
+
+ Invokes.push_back(II);
+ LPads.insert(II->getUnwindDest()->getLandingPadInst());
+ } else if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator())) {
+ Returns.push_back(RI);
+ }
+
+ if (Invokes.empty())
+ return false;
+
+ NumInvokes += Invokes.size();
+
+ lowerIncomingArguments(F);
+ lowerAcrossUnwindEdges(F, Invokes);
+
+ Value *FuncCtx =
+ setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
+ BasicBlock *EntryBB = &F.front();
+ IRBuilder<> Builder(EntryBB->getTerminator());
+
+ // Get a reference to the jump buffer.
+ Value *JBufPtr =
+ Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 5, "jbuf_gep");
+
+ // Save the frame pointer.
+ Value *FramePtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 0,
+ "jbuf_fp_gep");
+
+ Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
+ Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);
+
+ // Save the stack pointer.
+ Value *StackPtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 2,
+ "jbuf_sp_gep");
+
+ Val = Builder.CreateCall(StackAddrFn, {}, "sp");
+ Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);
+
+ // Call the setup_dispatch instrinsic. It fills in the rest of the jmpbuf.
+ Builder.CreateCall(BuiltinSetupDispatchFn, {});
+
+ // Store a pointer to the function context so that the back-end will know
+ // where to look for it.
+ Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy());
+ Builder.CreateCall(FuncCtxFn, FuncCtxArg);
+
+ // At this point, we are all set up, update the invoke instructions to mark
+ // their call_site values.
+ for (unsigned I = 0, E = Invokes.size(); I != E; ++I) {
+ insertCallSiteStore(Invokes[I], I + 1);
+
+ ConstantInt *CallSiteNum =
+ ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);
+
+ // Record the call site value for the back end so it stays associated with
+ // the invoke.
+ CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
+ }
+
+ // Mark call instructions that aren't nounwind as no-action (call_site ==
+ // -1). Skip the entry block, as prior to then, no function context has been
+ // created for this function and any unexpected exceptions thrown will go
+ // directly to the caller's context, which is what we want anyway, so no need
+ // to do anything here.
+ for (BasicBlock &BB : F) {
+ if (&BB == &F.front())
+ continue;
+ for (Instruction &I : BB)
+ if (I.mayThrow())
+ insertCallSiteStore(&I, -1);
+ }
+
+ // Register the function context and make sure it's known to not throw
+ CallInst *Register =
+ CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator());
+ Register->setDoesNotThrow();
+
+ // Following any allocas not in the entry block, update the saved SP in the
+ // jmpbuf to the new value.
+ for (BasicBlock &BB : F) {
+ if (&BB == &F.front())
+ continue;
+ for (Instruction &I : BB) {
+ if (auto *CI = dyn_cast<CallInst>(&I)) {
+ if (CI->getCalledFunction() != StackRestoreFn)
+ continue;
+ } else if (!isa<AllocaInst>(&I)) {
+ continue;
+ }
+ Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
+ StackAddr->insertAfter(&I);
+ Instruction *StoreStackAddr = new StoreInst(StackAddr, StackPtr, true);
+ StoreStackAddr->insertAfter(StackAddr);
+ }
+ }
+
+ // Finally, for any returns from this function, if this function contains an
+ // invoke, add a call to unregister the function context.
+ for (ReturnInst *Return : Returns)
+ CallInst::Create(UnregisterFn, FuncCtx, "", Return);
+
+ return true;
+}
+
+bool SjLjEHPrepare::runOnFunction(Function &F) {
+ Module &M = *F.getParent();
+ RegisterFn = M.getOrInsertFunction(
+ "_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()),
+ PointerType::getUnqual(FunctionContextTy));
+ UnregisterFn = M.getOrInsertFunction(
+ "_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()),
+ PointerType::getUnqual(FunctionContextTy));
+ FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress);
+ StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
+ StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
+ BuiltinSetupDispatchFn =
+ Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setup_dispatch);
+ LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
+ CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
+ FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext);
+
+ bool Res = setupEntryBlockAndCallSites(F);
+ return Res;
+}
generated by cgit v1.2.3 (git 2.25.1) at 2025-10-31 20:08:59 +0000