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  const TargetMachine *TM;
49  Type *doubleUnderDataTy;
50  Type *doubleUnderJBufTy;
51  Type *FunctionContextTy;
52  Constant *RegisterFn;
53  Constant *UnregisterFn;
54  Constant *BuiltinSetjmpFn;
55  Constant *FrameAddrFn;
56  Constant *StackAddrFn;
57  Constant *StackRestoreFn;
58  Constant *LSDAAddrFn;
59  Value *PersonalityFn;
60  Constant *CallSiteFn;
61  Constant *FuncCtxFn;
62  AllocaInst *FuncCtx;
63
64public:
65  static char ID; // Pass identification, replacement for typeid
66  explicit SjLjEHPrepare(const TargetMachine *TM) : FunctionPass(ID), TM(TM) {}
67  bool doInitialization(Module &M) override;
68  bool runOnFunction(Function &F) override;
69
70  void getAnalysisUsage(AnalysisUsage &AU) const override {}
71  const char *getPassName() const override {
72    return "SJLJ Exception Handling preparation";
73  }
74
75private:
76  bool setupEntryBlockAndCallSites(Function &F);
77  void substituteLPadValues(LandingPadInst *LPI, Value *ExnVal, Value *SelVal);
78  Value *setupFunctionContext(Function &F, ArrayRef<LandingPadInst *> LPads);
79  void lowerIncomingArguments(Function &F);
80  void lowerAcrossUnwindEdges(Function &F, ArrayRef<InvokeInst *> Invokes);
81  void insertCallSiteStore(Instruction *I, int Number);
82};
83} // end anonymous namespace
84
85char SjLjEHPrepare::ID = 0;
86
87// Public Interface To the SjLjEHPrepare pass.
88FunctionPass *llvm::createSjLjEHPreparePass(const TargetMachine *TM) {
89  return new SjLjEHPrepare(TM);
90}
91// doInitialization - Set up decalarations and types needed to process
92// exceptions.
93bool SjLjEHPrepare::doInitialization(Module &M) {
94  // Build the function context structure.
95  // builtin_setjmp uses a five word jbuf
96  Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
97  Type *Int32Ty = Type::getInt32Ty(M.getContext());
98  doubleUnderDataTy = ArrayType::get(Int32Ty, 4);
99  doubleUnderJBufTy = ArrayType::get(VoidPtrTy, 5);
100  FunctionContextTy = StructType::get(VoidPtrTy,         // __prev
101                                      Int32Ty,           // call_site
102                                      doubleUnderDataTy, // __data
103                                      VoidPtrTy,         // __personality
104                                      VoidPtrTy,         // __lsda
105                                      doubleUnderJBufTy, // __jbuf
106                                      nullptr);
107  RegisterFn = M.getOrInsertFunction(
108      "_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()),
109      PointerType::getUnqual(FunctionContextTy), (Type *)nullptr);
110  UnregisterFn = M.getOrInsertFunction(
111      "_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()),
112      PointerType::getUnqual(FunctionContextTy), (Type *)nullptr);
113  FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress);
114  StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
115  StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
116  BuiltinSetjmpFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setjmp);
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  IRBuilder<> Builder(
183      std::next(BasicBlock::iterator(cast<Instruction>(SelVal))));
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.begin();
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  const TargetLowering *TLI = TM->getSubtargetImpl(F)->getTargetLowering();
200  unsigned Align =
201      TLI->getDataLayout()->getPrefTypeAlignment(FunctionContextTy);
202  FuncCtx = new AllocaInst(FunctionContextTy, nullptr, Align, "fn_context",
203                           EntryBB->begin());
204
205  // Fill in the function context structure.
206  for (unsigned I = 0, E = LPads.size(); I != E; ++I) {
207    LandingPadInst *LPI = LPads[I];
208    IRBuilder<> Builder(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 = LPads[0]->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
256  for (Function::arg_iterator AI = F.arg_begin(), AE = F.arg_end(); AI != AE;
257       ++AI) {
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(TrueValue, AI, UndefValue,
264                                         AI->getName() + ".tmp",
265                                         AfterAllocaInsPt);
266    AI->replaceAllUsesWith(SI);
267
268    // Reset the operand, because it  was clobbered by the RAUW above.
269    SI->setOperand(1, AI);
270  }
271}
272
273/// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
274/// edge and spill them.
275void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
276                                           ArrayRef<InvokeInst *> Invokes) {
277  // Finally, scan the code looking for instructions with bad live ranges.
278  for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
279    for (BasicBlock::iterator II = BB->begin(), IIE = BB->end(); II != IIE;
280         ++II) {
281      // Ignore obvious cases we don't have to handle. In particular, most
282      // instructions either have no uses or only have a single use inside the
283      // current block. Ignore them quickly.
284      Instruction *Inst = II;
285      if (Inst->use_empty())
286        continue;
287      if (Inst->hasOneUse() &&
288          cast<Instruction>(Inst->user_back())->getParent() == BB &&
289          !isa<PHINode>(Inst->user_back()))
290        continue;
291
292      // If this is an alloca in the entry block, it's not a real register
293      // value.
294      if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
295        if (isa<ConstantInt>(AI->getArraySize()) && BB == F.begin())
296          continue;
297
298      // Avoid iterator invalidation by copying users to a temporary vector.
299      SmallVector<Instruction *, 16> Users;
300      for (User *U : Inst->users()) {
301        Instruction *UI = cast<Instruction>(U);
302        if (UI->getParent() != BB || isa<PHINode>(UI))
303          Users.push_back(UI);
304      }
305
306      // Find all of the blocks that this value is live in.
307      SmallPtrSet<BasicBlock *, 64> LiveBBs;
308      LiveBBs.insert(Inst->getParent());
309      while (!Users.empty()) {
310        Instruction *U = Users.back();
311        Users.pop_back();
312
313        if (!isa<PHINode>(U)) {
314          MarkBlocksLiveIn(U->getParent(), LiveBBs);
315        } else {
316          // Uses for a PHI node occur in their predecessor block.
317          PHINode *PN = cast<PHINode>(U);
318          for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
319            if (PN->getIncomingValue(i) == Inst)
320              MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
321        }
322      }
323
324      // Now that we know all of the blocks that this thing is live in, see if
325      // it includes any of the unwind locations.
326      bool NeedsSpill = false;
327      for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
328        BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
329        if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
330          DEBUG(dbgs() << "SJLJ Spill: " << *Inst << " around "
331                       << UnwindBlock->getName() << "\n");
332          NeedsSpill = true;
333          break;
334        }
335      }
336
337      // If we decided we need a spill, do it.
338      // FIXME: Spilling this way is overkill, as it forces all uses of
339      // the value to be reloaded from the stack slot, even those that aren't
340      // in the unwind blocks. We should be more selective.
341      if (NeedsSpill) {
342        DemoteRegToStack(*Inst, true);
343        ++NumSpilled;
344      }
345    }
346  }
347
348  // Go through the landing pads and remove any PHIs there.
349  for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
350    BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
351    LandingPadInst *LPI = UnwindBlock->getLandingPadInst();
352
353    // Place PHIs into a set to avoid invalidating the iterator.
354    SmallPtrSet<PHINode *, 8> PHIsToDemote;
355    for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
356      PHIsToDemote.insert(cast<PHINode>(PN));
357    if (PHIsToDemote.empty())
358      continue;
359
360    // Demote the PHIs to the stack.
361    for (PHINode *PN : PHIsToDemote)
362      DemotePHIToStack(PN);
363
364    // Move the landingpad instruction back to the top of the landing pad block.
365    LPI->moveBefore(UnwindBlock->begin());
366  }
367}
368
369/// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
370/// the function context and marking the call sites with the appropriate
371/// values. These values are used by the DWARF EH emitter.
372bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
373  SmallVector<ReturnInst *, 16> Returns;
374  SmallVector<InvokeInst *, 16> Invokes;
375  SmallSetVector<LandingPadInst *, 16> LPads;
376
377  // Look through the terminators of the basic blocks to find invokes.
378  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
379    if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
380      if (Function *Callee = II->getCalledFunction())
381        if (Callee->isIntrinsic() &&
382            Callee->getIntrinsicID() == Intrinsic::donothing) {
383          // Remove the NOP invoke.
384          BranchInst::Create(II->getNormalDest(), II);
385          II->eraseFromParent();
386          continue;
387        }
388
389      Invokes.push_back(II);
390      LPads.insert(II->getUnwindDest()->getLandingPadInst());
391    } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
392      Returns.push_back(RI);
393    }
394
395  if (Invokes.empty())
396    return false;
397
398  NumInvokes += Invokes.size();
399
400  lowerIncomingArguments(F);
401  lowerAcrossUnwindEdges(F, Invokes);
402
403  Value *FuncCtx =
404      setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
405  BasicBlock *EntryBB = F.begin();
406  IRBuilder<> Builder(EntryBB->getTerminator());
407
408  // Get a reference to the jump buffer.
409  Value *JBufPtr =
410      Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 5, "jbuf_gep");
411
412  // Save the frame pointer.
413  Value *FramePtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 0,
414                                               "jbuf_fp_gep");
415
416  Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
417  Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);
418
419  // Save the stack pointer.
420  Value *StackPtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 2,
421                                               "jbuf_sp_gep");
422
423  Val = Builder.CreateCall(StackAddrFn, "sp");
424  Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);
425
426  // Call the setjmp instrinsic. It fills in the rest of the jmpbuf.
427  Value *SetjmpArg = Builder.CreateBitCast(JBufPtr, Builder.getInt8PtrTy());
428  Builder.CreateCall(BuiltinSetjmpFn, SetjmpArg);
429
430  // Store a pointer to the function context so that the back-end will know
431  // where to look for it.
432  Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy());
433  Builder.CreateCall(FuncCtxFn, FuncCtxArg);
434
435  // At this point, we are all set up, update the invoke instructions to mark
436  // their call_site values.
437  for (unsigned I = 0, E = Invokes.size(); I != E; ++I) {
438    insertCallSiteStore(Invokes[I], I + 1);
439
440    ConstantInt *CallSiteNum =
441        ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);
442
443    // Record the call site value for the back end so it stays associated with
444    // the invoke.
445    CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
446  }
447
448  // Mark call instructions that aren't nounwind as no-action (call_site ==
449  // -1). Skip the entry block, as prior to then, no function context has been
450  // created for this function and any unexpected exceptions thrown will go
451  // directly to the caller's context, which is what we want anyway, so no need
452  // to do anything here.
453  for (Function::iterator BB = F.begin(), E = F.end(); ++BB != E;)
454    for (BasicBlock::iterator I = BB->begin(), end = BB->end(); I != end; ++I)
455      if (CallInst *CI = dyn_cast<CallInst>(I)) {
456        if (!CI->doesNotThrow())
457          insertCallSiteStore(CI, -1);
458      } else if (ResumeInst *RI = dyn_cast<ResumeInst>(I)) {
459        insertCallSiteStore(RI, -1);
460      }
461
462  // Register the function context and make sure it's known to not throw
463  CallInst *Register =
464      CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator());
465  Register->setDoesNotThrow();
466
467  // Following any allocas not in the entry block, update the saved SP in the
468  // jmpbuf to the new value.
469  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
470    if (BB == F.begin())
471      continue;
472    for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
473      if (CallInst *CI = dyn_cast<CallInst>(I)) {
474        if (CI->getCalledFunction() != StackRestoreFn)
475          continue;
476      } else if (!isa<AllocaInst>(I)) {
477        continue;
478      }
479      Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
480      StackAddr->insertAfter(I);
481      Instruction *StoreStackAddr = new StoreInst(StackAddr, StackPtr, true);
482      StoreStackAddr->insertAfter(StackAddr);
483    }
484  }
485
486  // Finally, for any returns from this function, if this function contains an
487  // invoke, add a call to unregister the function context.
488  for (unsigned I = 0, E = Returns.size(); I != E; ++I)
489    CallInst::Create(UnregisterFn, FuncCtx, "", Returns[I]);
490
491  return true;
492}
493
494bool SjLjEHPrepare::runOnFunction(Function &F) {
495  bool Res = setupEntryBlockAndCallSites(F);
496  return Res;
497}
498