1//===- SjLjEHPrepare.cpp - Eliminate Invoke & Unwind instructions ---------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This transformation is designed for use by code generators which use SjLj
11// based exception handling.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/CodeGen/Passes.h"
16#include "llvm/ADT/DenseMap.h"
17#include "llvm/ADT/SetVector.h"
18#include "llvm/ADT/SmallPtrSet.h"
19#include "llvm/ADT/SmallVector.h"
20#include "llvm/ADT/Statistic.h"
21#include "llvm/IR/Constants.h"
22#include "llvm/IR/DataLayout.h"
23#include "llvm/IR/DerivedTypes.h"
24#include "llvm/IR/IRBuilder.h"
25#include "llvm/IR/Instructions.h"
26#include "llvm/IR/Intrinsics.h"
27#include "llvm/IR/LLVMContext.h"
28#include "llvm/IR/Module.h"
29#include "llvm/Pass.h"
30#include "llvm/Support/CommandLine.h"
31#include "llvm/Support/Debug.h"
32#include "llvm/Support/raw_ostream.h"
33#include "llvm/Target/TargetLowering.h"
34#include "llvm/Target/TargetSubtargetInfo.h"
35#include "llvm/Transforms/Scalar.h"
36#include "llvm/Transforms/Utils/BasicBlockUtils.h"
37#include "llvm/Transforms/Utils/Local.h"
38#include <set>
39using namespace llvm;
40
41#define DEBUG_TYPE "sjljehprepare"
42
43STATISTIC(NumInvokes, "Number of invokes replaced");
44STATISTIC(NumSpilled, "Number of registers live across unwind edges");
45
46namespace {
47class SjLjEHPrepare : public FunctionPass {
48  Type *doubleUnderDataTy;
49  Type *doubleUnderJBufTy;
50  Type *FunctionContextTy;
51  Constant *RegisterFn;
52  Constant *UnregisterFn;
53  Constant *BuiltinSetupDispatchFn;
54  Constant *FrameAddrFn;
55  Constant *StackAddrFn;
56  Constant *StackRestoreFn;
57  Constant *LSDAAddrFn;
58  Value *PersonalityFn;
59  Constant *CallSiteFn;
60  Constant *FuncCtxFn;
61  AllocaInst *FuncCtx;
62
63public:
64  static char ID; // Pass identification, replacement for typeid
65  explicit SjLjEHPrepare() : FunctionPass(ID) {}
66  bool doInitialization(Module &M) override;
67  bool runOnFunction(Function &F) override;
68
69  void getAnalysisUsage(AnalysisUsage &AU) const override {}
70  const char *getPassName() const override {
71    return "SJLJ Exception Handling preparation";
72  }
73
74private:
75  bool setupEntryBlockAndCallSites(Function &F);
76  void substituteLPadValues(LandingPadInst *LPI, Value *ExnVal, Value *SelVal);
77  Value *setupFunctionContext(Function &F, ArrayRef<LandingPadInst *> LPads);
78  void lowerIncomingArguments(Function &F);
79  void lowerAcrossUnwindEdges(Function &F, ArrayRef<InvokeInst *> Invokes);
80  void insertCallSiteStore(Instruction *I, int Number);
81};
82} // end anonymous namespace
83
84char SjLjEHPrepare::ID = 0;
85INITIALIZE_PASS(SjLjEHPrepare, "sjljehprepare", "Prepare SjLj exceptions",
86                false, false)
87
88// Public Interface To the SjLjEHPrepare pass.
89FunctionPass *llvm::createSjLjEHPreparePass() { return new SjLjEHPrepare(); }
90// doInitialization - Set up decalarations and types needed to process
91// exceptions.
92bool SjLjEHPrepare::doInitialization(Module &M) {
93  // Build the function context structure.
94  // builtin_setjmp uses a five word jbuf
95  Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
96  Type *Int32Ty = Type::getInt32Ty(M.getContext());
97  doubleUnderDataTy = ArrayType::get(Int32Ty, 4);
98  doubleUnderJBufTy = ArrayType::get(VoidPtrTy, 5);
99  FunctionContextTy = StructType::get(VoidPtrTy,         // __prev
100                                      Int32Ty,           // call_site
101                                      doubleUnderDataTy, // __data
102                                      VoidPtrTy,         // __personality
103                                      VoidPtrTy,         // __lsda
104                                      doubleUnderJBufTy, // __jbuf
105                                      nullptr);
106  RegisterFn = M.getOrInsertFunction(
107      "_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()),
108      PointerType::getUnqual(FunctionContextTy), (Type *)nullptr);
109  UnregisterFn = M.getOrInsertFunction(
110      "_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()),
111      PointerType::getUnqual(FunctionContextTy), (Type *)nullptr);
112  FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress);
113  StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
114  StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
115  BuiltinSetupDispatchFn =
116    Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setup_dispatch);
117  LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
118  CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
119  FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext);
120  PersonalityFn = nullptr;
121
122  return true;
123}
124
125/// insertCallSiteStore - Insert a store of the call-site value to the
126/// function context
127void SjLjEHPrepare::insertCallSiteStore(Instruction *I, int Number) {
128  IRBuilder<> Builder(I);
129
130  // Get a reference to the call_site field.
131  Type *Int32Ty = Type::getInt32Ty(I->getContext());
132  Value *Zero = ConstantInt::get(Int32Ty, 0);
133  Value *One = ConstantInt::get(Int32Ty, 1);
134  Value *Idxs[2] = { Zero, One };
135  Value *CallSite =
136      Builder.CreateGEP(FunctionContextTy, FuncCtx, Idxs, "call_site");
137
138  // Insert a store of the call-site number
139  ConstantInt *CallSiteNoC =
140      ConstantInt::get(Type::getInt32Ty(I->getContext()), Number);
141  Builder.CreateStore(CallSiteNoC, CallSite, true /*volatile*/);
142}
143
144/// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
145/// we reach blocks we've already seen.
146static void MarkBlocksLiveIn(BasicBlock *BB,
147                             SmallPtrSetImpl<BasicBlock *> &LiveBBs) {
148  if (!LiveBBs.insert(BB).second)
149    return; // already been here.
150
151  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
152    MarkBlocksLiveIn(*PI, LiveBBs);
153}
154
155/// substituteLPadValues - Substitute the values returned by the landingpad
156/// instruction with those returned by the personality function.
157void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
158                                         Value *SelVal) {
159  SmallVector<Value *, 8> UseWorkList(LPI->user_begin(), LPI->user_end());
160  while (!UseWorkList.empty()) {
161    Value *Val = UseWorkList.pop_back_val();
162    ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Val);
163    if (!EVI)
164      continue;
165    if (EVI->getNumIndices() != 1)
166      continue;
167    if (*EVI->idx_begin() == 0)
168      EVI->replaceAllUsesWith(ExnVal);
169    else if (*EVI->idx_begin() == 1)
170      EVI->replaceAllUsesWith(SelVal);
171    if (EVI->getNumUses() == 0)
172      EVI->eraseFromParent();
173  }
174
175  if (LPI->getNumUses() == 0)
176    return;
177
178  // There are still some uses of LPI. Construct an aggregate with the exception
179  // values and replace the LPI with that aggregate.
180  Type *LPadType = LPI->getType();
181  Value *LPadVal = UndefValue::get(LPadType);
182  auto *SelI = cast<Instruction>(SelVal);
183  IRBuilder<> Builder(SelI->getParent(), std::next(SelI->getIterator()));
184  LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val");
185  LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val");
186
187  LPI->replaceAllUsesWith(LPadVal);
188}
189
190/// setupFunctionContext - Allocate the function context on the stack and fill
191/// it with all of the data that we know at this point.
192Value *SjLjEHPrepare::setupFunctionContext(Function &F,
193                                           ArrayRef<LandingPadInst *> LPads) {
194  BasicBlock *EntryBB = &F.front();
195
196  // Create an alloca for the incoming jump buffer ptr and the new jump buffer
197  // that needs to be restored on all exits from the function. This is an alloca
198  // because the value needs to be added to the global context list.
199  auto &DL = F.getParent()->getDataLayout();
200  unsigned Align = DL.getPrefTypeAlignment(FunctionContextTy);
201  FuncCtx = new AllocaInst(FunctionContextTy, nullptr, Align, "fn_context",
202                           &EntryBB->front());
203
204  // Fill in the function context structure.
205  for (unsigned I = 0, E = LPads.size(); I != E; ++I) {
206    LandingPadInst *LPI = LPads[I];
207    IRBuilder<> Builder(LPI->getParent(),
208                        LPI->getParent()->getFirstInsertionPt());
209
210    // Reference the __data field.
211    Value *FCData =
212        Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 2, "__data");
213
214    // The exception values come back in context->__data[0].
215    Value *ExceptionAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
216                                                      0, 0, "exception_gep");
217    Value *ExnVal = Builder.CreateLoad(ExceptionAddr, true, "exn_val");
218    ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy());
219
220    Value *SelectorAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
221                                                     0, 1, "exn_selector_gep");
222    Value *SelVal = Builder.CreateLoad(SelectorAddr, true, "exn_selector_val");
223
224    substituteLPadValues(LPI, ExnVal, SelVal);
225  }
226
227  // Personality function
228  IRBuilder<> Builder(EntryBB->getTerminator());
229  if (!PersonalityFn)
230    PersonalityFn = F.getPersonalityFn();
231  Value *PersonalityFieldPtr = Builder.CreateConstGEP2_32(
232      FunctionContextTy, FuncCtx, 0, 3, "pers_fn_gep");
233  Builder.CreateStore(
234      Builder.CreateBitCast(PersonalityFn, Builder.getInt8PtrTy()),
235      PersonalityFieldPtr, /*isVolatile=*/true);
236
237  // LSDA address
238  Value *LSDA = Builder.CreateCall(LSDAAddrFn, {}, "lsda_addr");
239  Value *LSDAFieldPtr =
240      Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 4, "lsda_gep");
241  Builder.CreateStore(LSDA, LSDAFieldPtr, /*isVolatile=*/true);
242
243  return FuncCtx;
244}
245
246/// lowerIncomingArguments - To avoid having to handle incoming arguments
247/// specially, we lower each arg to a copy instruction in the entry block. This
248/// ensures that the argument value itself cannot be live out of the entry
249/// block.
250void SjLjEHPrepare::lowerIncomingArguments(Function &F) {
251  BasicBlock::iterator AfterAllocaInsPt = F.begin()->begin();
252  while (isa<AllocaInst>(AfterAllocaInsPt) &&
253         isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsPt)->getArraySize()))
254    ++AfterAllocaInsPt;
255  assert(AfterAllocaInsPt != F.front().end());
256
257  for (auto &AI : F.args()) {
258    Type *Ty = AI.getType();
259
260    // Use 'select i8 true, %arg, undef' to simulate a 'no-op' instruction.
261    Value *TrueValue = ConstantInt::getTrue(F.getContext());
262    Value *UndefValue = UndefValue::get(Ty);
263    Instruction *SI = SelectInst::Create(
264        TrueValue, &AI, UndefValue, AI.getName() + ".tmp", &*AfterAllocaInsPt);
265    AI.replaceAllUsesWith(SI);
266
267    // Reset the operand, because it  was clobbered by the RAUW above.
268    SI->setOperand(1, &AI);
269  }
270}
271
272/// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
273/// edge and spill them.
274void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
275                                           ArrayRef<InvokeInst *> Invokes) {
276  // Finally, scan the code looking for instructions with bad live ranges.
277  for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
278    for (BasicBlock::iterator II = BB->begin(), IIE = BB->end(); II != IIE;
279         ++II) {
280      // Ignore obvious cases we don't have to handle. In particular, most
281      // instructions either have no uses or only have a single use inside the
282      // current block. Ignore them quickly.
283      Instruction *Inst = &*II;
284      if (Inst->use_empty())
285        continue;
286      if (Inst->hasOneUse() &&
287          cast<Instruction>(Inst->user_back())->getParent() == BB &&
288          !isa<PHINode>(Inst->user_back()))
289        continue;
290
291      // If this is an alloca in the entry block, it's not a real register
292      // value.
293      if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
294        if (isa<ConstantInt>(AI->getArraySize()) && BB == F.begin())
295          continue;
296
297      // Avoid iterator invalidation by copying users to a temporary vector.
298      SmallVector<Instruction *, 16> Users;
299      for (User *U : Inst->users()) {
300        Instruction *UI = cast<Instruction>(U);
301        if (UI->getParent() != BB || isa<PHINode>(UI))
302          Users.push_back(UI);
303      }
304
305      // Find all of the blocks that this value is live in.
306      SmallPtrSet<BasicBlock *, 64> LiveBBs;
307      LiveBBs.insert(Inst->getParent());
308      while (!Users.empty()) {
309        Instruction *U = Users.back();
310        Users.pop_back();
311
312        if (!isa<PHINode>(U)) {
313          MarkBlocksLiveIn(U->getParent(), LiveBBs);
314        } else {
315          // Uses for a PHI node occur in their predecessor block.
316          PHINode *PN = cast<PHINode>(U);
317          for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
318            if (PN->getIncomingValue(i) == Inst)
319              MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
320        }
321      }
322
323      // Now that we know all of the blocks that this thing is live in, see if
324      // it includes any of the unwind locations.
325      bool NeedsSpill = false;
326      for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
327        BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
328        if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
329          DEBUG(dbgs() << "SJLJ Spill: " << *Inst << " around "
330                       << UnwindBlock->getName() << "\n");
331          NeedsSpill = true;
332          break;
333        }
334      }
335
336      // If we decided we need a spill, do it.
337      // FIXME: Spilling this way is overkill, as it forces all uses of
338      // the value to be reloaded from the stack slot, even those that aren't
339      // in the unwind blocks. We should be more selective.
340      if (NeedsSpill) {
341        DemoteRegToStack(*Inst, true);
342        ++NumSpilled;
343      }
344    }
345  }
346
347  // Go through the landing pads and remove any PHIs there.
348  for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
349    BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
350    LandingPadInst *LPI = UnwindBlock->getLandingPadInst();
351
352    // Place PHIs into a set to avoid invalidating the iterator.
353    SmallPtrSet<PHINode *, 8> PHIsToDemote;
354    for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
355      PHIsToDemote.insert(cast<PHINode>(PN));
356    if (PHIsToDemote.empty())
357      continue;
358
359    // Demote the PHIs to the stack.
360    for (PHINode *PN : PHIsToDemote)
361      DemotePHIToStack(PN);
362
363    // Move the landingpad instruction back to the top of the landing pad block.
364    LPI->moveBefore(&UnwindBlock->front());
365  }
366}
367
368/// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
369/// the function context and marking the call sites with the appropriate
370/// values. These values are used by the DWARF EH emitter.
371bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
372  SmallVector<ReturnInst *, 16> Returns;
373  SmallVector<InvokeInst *, 16> Invokes;
374  SmallSetVector<LandingPadInst *, 16> LPads;
375
376  // Look through the terminators of the basic blocks to find invokes.
377  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
378    if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
379      if (Function *Callee = II->getCalledFunction())
380        if (Callee->isIntrinsic() &&
381            Callee->getIntrinsicID() == Intrinsic::donothing) {
382          // Remove the NOP invoke.
383          BranchInst::Create(II->getNormalDest(), II);
384          II->eraseFromParent();
385          continue;
386        }
387
388      Invokes.push_back(II);
389      LPads.insert(II->getUnwindDest()->getLandingPadInst());
390    } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
391      Returns.push_back(RI);
392    }
393
394  if (Invokes.empty())
395    return false;
396
397  NumInvokes += Invokes.size();
398
399  lowerIncomingArguments(F);
400  lowerAcrossUnwindEdges(F, Invokes);
401
402  Value *FuncCtx =
403      setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
404  BasicBlock *EntryBB = &F.front();
405  IRBuilder<> Builder(EntryBB->getTerminator());
406
407  // Get a reference to the jump buffer.
408  Value *JBufPtr =
409      Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 5, "jbuf_gep");
410
411  // Save the frame pointer.
412  Value *FramePtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 0,
413                                               "jbuf_fp_gep");
414
415  Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
416  Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);
417
418  // Save the stack pointer.
419  Value *StackPtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 2,
420                                               "jbuf_sp_gep");
421
422  Val = Builder.CreateCall(StackAddrFn, {}, "sp");
423  Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);
424
425  // Call the setup_dispatch instrinsic. It fills in the rest of the jmpbuf.
426  Builder.CreateCall(BuiltinSetupDispatchFn, {});
427
428  // Store a pointer to the function context so that the back-end will know
429  // where to look for it.
430  Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy());
431  Builder.CreateCall(FuncCtxFn, FuncCtxArg);
432
433  // At this point, we are all set up, update the invoke instructions to mark
434  // their call_site values.
435  for (unsigned I = 0, E = Invokes.size(); I != E; ++I) {
436    insertCallSiteStore(Invokes[I], I + 1);
437
438    ConstantInt *CallSiteNum =
439        ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);
440
441    // Record the call site value for the back end so it stays associated with
442    // the invoke.
443    CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
444  }
445
446  // Mark call instructions that aren't nounwind as no-action (call_site ==
447  // -1). Skip the entry block, as prior to then, no function context has been
448  // created for this function and any unexpected exceptions thrown will go
449  // directly to the caller's context, which is what we want anyway, so no need
450  // to do anything here.
451  for (Function::iterator BB = F.begin(), E = F.end(); ++BB != E;)
452    for (BasicBlock::iterator I = BB->begin(), end = BB->end(); I != end; ++I)
453      if (CallInst *CI = dyn_cast<CallInst>(I)) {
454        if (!CI->doesNotThrow())
455          insertCallSiteStore(CI, -1);
456      } else if (ResumeInst *RI = dyn_cast<ResumeInst>(I)) {
457        insertCallSiteStore(RI, -1);
458      }
459
460  // Register the function context and make sure it's known to not throw
461  CallInst *Register =
462      CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator());
463  Register->setDoesNotThrow();
464
465  // Following any allocas not in the entry block, update the saved SP in the
466  // jmpbuf to the new value.
467  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
468    if (BB == F.begin())
469      continue;
470    for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
471      if (CallInst *CI = dyn_cast<CallInst>(I)) {
472        if (CI->getCalledFunction() != StackRestoreFn)
473          continue;
474      } else if (!isa<AllocaInst>(I)) {
475        continue;
476      }
477      Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
478      StackAddr->insertAfter(&*I);
479      Instruction *StoreStackAddr = new StoreInst(StackAddr, StackPtr, true);
480      StoreStackAddr->insertAfter(StackAddr);
481    }
482  }
483
484  // Finally, for any returns from this function, if this function contains an
485  // invoke, add a call to unregister the function context.
486  for (unsigned I = 0, E = Returns.size(); I != E; ++I)
487    CallInst::Create(UnregisterFn, FuncCtx, "", Returns[I]);
488
489  return true;
490}
491
492bool SjLjEHPrepare::runOnFunction(Function &F) {
493  bool Res = setupEntryBlockAndCallSites(F);
494  return Res;
495}
496