lib/CodeGen/SjLjEHPrepare.cpp

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