llvm/lib/CodeGen/SjLjEHPrepare.cpp

   1 //===- SjLjEHPrepare.cpp - Eliminate Invoke & Unwind instructions ---------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This transformation is designed for use by code generators which use SjLj
  10 // based exception handling.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/ADT/SetVector.h"
  15 #include "llvm/ADT/SmallPtrSet.h"
  16 #include "llvm/ADT/SmallVector.h"
  17 #include "llvm/ADT/Statistic.h"
  18 #include "llvm/CodeGen/Passes.h"
  19 #include "llvm/IR/Constants.h"
  20 #include "llvm/IR/DataLayout.h"
  21 #include "llvm/IR/DerivedTypes.h"
  22 #include "llvm/IR/IRBuilder.h"
  23 #include "llvm/IR/Instructions.h"
  24 #include "llvm/IR/Intrinsics.h"
  25 #include "llvm/IR/Module.h"
  26 #include "llvm/InitializePasses.h"
  27 #include "llvm/Pass.h"
  28 #include "llvm/Support/Debug.h"
  29 #include "llvm/Support/raw_ostream.h"
  30 #include "llvm/Target/TargetMachine.h"
  31 #include "llvm/Transforms/Utils/Local.h"
  32 using namespace llvm;
  33
  34 #define DEBUG_TYPE "sjljehprepare"
  35
  36 STATISTIC(NumInvokes, "Number of invokes replaced");
  37 STATISTIC(NumSpilled, "Number of registers live across unwind edges");
  38
  39 namespace {
  40 class SjLjEHPrepare : public FunctionPass {
  41   IntegerType *DataTy;
  42   Type *doubleUnderDataTy;
  43   Type *doubleUnderJBufTy;
  44   Type *FunctionContextTy;
  45   FunctionCallee RegisterFn;
  46   FunctionCallee UnregisterFn;
  47   Function *BuiltinSetupDispatchFn;
  48   Function *FrameAddrFn;
  49   Function *StackAddrFn;
  50   Function *StackRestoreFn;
  51   Function *LSDAAddrFn;
  52   Function *CallSiteFn;
  53   Function *FuncCtxFn;
  54   AllocaInst *FuncCtx;
  55   const TargetMachine *TM;
  56
  57 public:
  58   static char ID; // Pass identification, replacement for typeid
  59   explicit SjLjEHPrepare(const TargetMachine *TM = nullptr)
  60       : FunctionPass(ID), TM(TM) {}
  61   bool doInitialization(Module &M) override;
  62   bool runOnFunction(Function &F) override;
  63
  64   void getAnalysisUsage(AnalysisUsage &AU) const override {}
  65   StringRef getPassName() const override {
  66     return "SJLJ Exception Handling preparation";
  67   }
  68
  69 private:
  70   bool setupEntryBlockAndCallSites(Function &F);
  71   void substituteLPadValues(LandingPadInst *LPI, Value *ExnVal, Value *SelVal);
  72   Value *setupFunctionContext(Function &F, ArrayRef<LandingPadInst *> LPads);
  73   void lowerIncomingArguments(Function &F);
  74   void lowerAcrossUnwindEdges(Function &F, ArrayRef<InvokeInst *> Invokes);
  75   void insertCallSiteStore(Instruction *I, int Number);
  76 };
  77 } // end anonymous namespace
  78
  79 char SjLjEHPrepare::ID = 0;
  80 INITIALIZE_PASS(SjLjEHPrepare, DEBUG_TYPE, "Prepare SjLj exceptions",
  81                 false, false)
  82
  83 // Public Interface To the SjLjEHPrepare pass.
  84 FunctionPass *llvm::createSjLjEHPreparePass(const TargetMachine *TM) {
  85   return new SjLjEHPrepare(TM);
  86 }
  87
  88 // doInitialization - Set up decalarations and types needed to process
  89 // exceptions.
  90 bool SjLjEHPrepare::doInitialization(Module &M) {
  91   // Build the function context structure.
  92   // builtin_setjmp uses a five word jbuf
  93   Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
  94   unsigned DataBits =
  95       TM ? TM->getSjLjDataSize() : TargetMachine::DefaultSjLjDataSize;
  96   DataTy = Type::getIntNTy(M.getContext(), DataBits);
  97   doubleUnderDataTy = ArrayType::get(DataTy, 4);
  98   doubleUnderJBufTy = ArrayType::get(VoidPtrTy, 5);
  99   FunctionContextTy = StructType::get(VoidPtrTy,         // __prev
 100                                       DataTy,            // call_site
 101                                       doubleUnderDataTy, // __data
 102                                       VoidPtrTy,         // __personality
 103                                       VoidPtrTy,         // __lsda
 104                                       doubleUnderJBufTy  // __jbuf
 105   );
 106
 107   return true;
 108 }
 109
 110 /// insertCallSiteStore - Insert a store of the call-site value to the
 111 /// function context
 112 void SjLjEHPrepare::insertCallSiteStore(Instruction *I, int Number) {
 113   IRBuilder<> Builder(I);
 114
 115   // Get a reference to the call_site field.
 116   Type *Int32Ty = Type::getInt32Ty(I->getContext());
 117   Value *Zero = ConstantInt::get(Int32Ty, 0);
 118   Value *One = ConstantInt::get(Int32Ty, 1);
 119   Value *Idxs[2] = { Zero, One };
 120   Value *CallSite =
 121       Builder.CreateGEP(FunctionContextTy, FuncCtx, Idxs, "call_site");
 122
 123   // Insert a store of the call-site number
 124   ConstantInt *CallSiteNoC = ConstantInt::get(DataTy, Number);
 125   Builder.CreateStore(CallSiteNoC, CallSite, true /*volatile*/);
 126 }
 127
 128 /// MarkBlocksLiveIn - Insert BB and all of its predecessors into LiveBBs until
 129 /// we reach blocks we've already seen.
 130 static void MarkBlocksLiveIn(BasicBlock *BB,
 131                              SmallPtrSetImpl<BasicBlock *> &LiveBBs) {
 132   if (!LiveBBs.insert(BB).second)
 133     return; // already been here.
 134
 135   df_iterator_default_set<BasicBlock*> Visited;
 136
 137   for (BasicBlock *B : inverse_depth_first_ext(BB, Visited))
 138     LiveBBs.insert(B);
 139 }
 140
 141 /// substituteLPadValues - Substitute the values returned by the landingpad
 142 /// instruction with those returned by the personality function.
 143 void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
 144                                          Value *SelVal) {
 145   SmallVector<Value *, 8> UseWorkList(LPI->users());
 146   while (!UseWorkList.empty()) {
 147     Value *Val = UseWorkList.pop_back_val();
 148     auto *EVI = dyn_cast<ExtractValueInst>(Val);
 149     if (!EVI)
 150       continue;
 151     if (EVI->getNumIndices() != 1)
 152       continue;
 153     if (*EVI->idx_begin() == 0)
 154       EVI->replaceAllUsesWith(ExnVal);
 155     else if (*EVI->idx_begin() == 1)
 156       EVI->replaceAllUsesWith(SelVal);
 157     if (EVI->use_empty())
 158       EVI->eraseFromParent();
 159   }
 160
 161   if (LPI->use_empty())
 162     return;
 163
 164   // There are still some uses of LPI. Construct an aggregate with the exception
 165   // values and replace the LPI with that aggregate.
 166   Type *LPadType = LPI->getType();
 167   Value *LPadVal = UndefValue::get(LPadType);
 168   auto *SelI = cast<Instruction>(SelVal);
 169   IRBuilder<> Builder(SelI->getParent(), std::next(SelI->getIterator()));
 170   LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val");
 171   LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val");
 172
 173   LPI->replaceAllUsesWith(LPadVal);
 174 }
 175
 176 /// setupFunctionContext - Allocate the function context on the stack and fill
 177 /// it with all of the data that we know at this point.
 178 Value *SjLjEHPrepare::setupFunctionContext(Function &F,
 179                                            ArrayRef<LandingPadInst *> LPads) {
 180   BasicBlock *EntryBB = &F.front();
 181
 182   // Create an alloca for the incoming jump buffer ptr and the new jump buffer
 183   // that needs to be restored on all exits from the function. This is an alloca
 184   // because the value needs to be added to the global context list.
 185   auto &DL = F.getParent()->getDataLayout();
 186   const Align Alignment(DL.getPrefTypeAlignment(FunctionContextTy));
 187   FuncCtx = new AllocaInst(FunctionContextTy, DL.getAllocaAddrSpace(), nullptr,
 188                            Alignment, "fn_context", &EntryBB->front());
 189
 190   // Fill in the function context structure.
 191   for (LandingPadInst *LPI : LPads) {
 192     IRBuilder<> Builder(LPI->getParent(),
 193                         LPI->getParent()->getFirstInsertionPt());
 194
 195     // Reference the __data field.
 196     Value *FCData =
 197         Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 2, "__data");
 198
 199     // The exception values come back in context->__data[0].
 200     Value *ExceptionAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
 201                                                       0, 0, "exception_gep");
 202     Value *ExnVal = Builder.CreateLoad(DataTy, ExceptionAddr, true, "exn_val");
 203     ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy());
 204
 205     Value *SelectorAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
 206                                                      0, 1, "exn_selector_gep");
 207     Value *SelVal =
 208         Builder.CreateLoad(DataTy, SelectorAddr, true, "exn_selector_val");
 209
 210     // SelVal must be Int32Ty, so trunc it
 211     SelVal = Builder.CreateTrunc(SelVal, Type::getInt32Ty(F.getContext()));
 212
 213     substituteLPadValues(LPI, ExnVal, SelVal);
 214   }
 215
 216   // Personality function
 217   IRBuilder<> Builder(EntryBB->getTerminator());
 218   Value *PersonalityFn = F.getPersonalityFn();
 219   Value *PersonalityFieldPtr = Builder.CreateConstGEP2_32(
 220       FunctionContextTy, FuncCtx, 0, 3, "pers_fn_gep");
 221   Builder.CreateStore(
 222       Builder.CreateBitCast(PersonalityFn, Builder.getInt8PtrTy()),
 223       PersonalityFieldPtr, /*isVolatile=*/true);
 224
 225   // LSDA address
 226   Value *LSDA = Builder.CreateCall(LSDAAddrFn, {}, "lsda_addr");
 227   Value *LSDAFieldPtr =
 228       Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 4, "lsda_gep");
 229   Builder.CreateStore(LSDA, LSDAFieldPtr, /*isVolatile=*/true);
 230
 231   return FuncCtx;
 232 }
 233
 234 /// lowerIncomingArguments - To avoid having to handle incoming arguments
 235 /// specially, we lower each arg to a copy instruction in the entry block. This
 236 /// ensures that the argument value itself cannot be live out of the entry
 237 /// block.
 238 void SjLjEHPrepare::lowerIncomingArguments(Function &F) {
 239   BasicBlock::iterator AfterAllocaInsPt = F.begin()->begin();
 240   while (isa<AllocaInst>(AfterAllocaInsPt) &&
 241          cast<AllocaInst>(AfterAllocaInsPt)->isStaticAlloca())
 242     ++AfterAllocaInsPt;
 243   assert(AfterAllocaInsPt != F.front().end());
 244
 245   for (auto &AI : F.args()) {
 246     // Swift error really is a register that we model as memory -- instruction
 247     // selection will perform mem-to-reg for us and spill/reload appropriately
 248     // around calls that clobber it. There is no need to spill this
 249     // value to the stack and doing so would not be allowed.
 250     if (AI.isSwiftError())
 251       continue;
 252
 253     Type *Ty = AI.getType();
 254
 255     // Use 'select i8 true, %arg, undef' to simulate a 'no-op' instruction.
 256     Value *TrueValue = ConstantInt::getTrue(F.getContext());
 257     Value *UndefValue = UndefValue::get(Ty);
 258     Instruction *SI = SelectInst::Create(
 259         TrueValue, &AI, UndefValue, AI.getName() + ".tmp", &*AfterAllocaInsPt);
 260     AI.replaceAllUsesWith(SI);
 261
 262     // Reset the operand, because it  was clobbered by the RAUW above.
 263     SI->setOperand(1, &AI);
 264   }
 265 }
 266
 267 /// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
 268 /// edge and spill them.
 269 void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
 270                                            ArrayRef<InvokeInst *> Invokes) {
 271   // Finally, scan the code looking for instructions with bad live ranges.
 272   for (BasicBlock &BB : F) {
 273     for (Instruction &Inst : BB) {
 274       // Ignore obvious cases we don't have to handle. In particular, most
 275       // instructions either have no uses or only have a single use inside the
 276       // current block. Ignore them quickly.
 277       if (Inst.use_empty())
 278         continue;
 279       if (Inst.hasOneUse() &&
 280           cast<Instruction>(Inst.user_back())->getParent() == &BB &&
 281           !isa<PHINode>(Inst.user_back()))
 282         continue;
 283
 284       // If this is an alloca in the entry block, it's not a real register
 285       // value.
 286       if (auto *AI = dyn_cast<AllocaInst>(&Inst))
 287         if (AI->isStaticAlloca())
 288           continue;
 289
 290       // Avoid iterator invalidation by copying users to a temporary vector.
 291       SmallVector<Instruction *, 16> Users;
 292       for (User *U : Inst.users()) {
 293         Instruction *UI = cast<Instruction>(U);
 294         if (UI->getParent() != &BB || isa<PHINode>(UI))
 295           Users.push_back(UI);
 296       }
 297
 298       // Find all of the blocks that this value is live in.
 299       SmallPtrSet<BasicBlock *, 32> LiveBBs;
 300       LiveBBs.insert(&BB);
 301       while (!Users.empty()) {
 302         Instruction *U = Users.pop_back_val();
 303
 304         if (!isa<PHINode>(U)) {
 305           MarkBlocksLiveIn(U->getParent(), LiveBBs);
 306         } else {
 307           // Uses for a PHI node occur in their predecessor block.
 308           PHINode *PN = cast<PHINode>(U);
 309           for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
 310             if (PN->getIncomingValue(i) == &Inst)
 311               MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
 312         }
 313       }
 314
 315       // Now that we know all of the blocks that this thing is live in, see if
 316       // it includes any of the unwind locations.
 317       bool NeedsSpill = false;
 318       for (InvokeInst *Invoke : Invokes) {
 319         BasicBlock *UnwindBlock = Invoke->getUnwindDest();
 320         if (UnwindBlock != &BB && LiveBBs.count(UnwindBlock)) {
 321           LLVM_DEBUG(dbgs() << "SJLJ Spill: " << Inst << " around "
 322                             << UnwindBlock->getName() << "\n");
 323           NeedsSpill = true;
 324           break;
 325         }
 326       }
 327
 328       // If we decided we need a spill, do it.
 329       // FIXME: Spilling this way is overkill, as it forces all uses of
 330       // the value to be reloaded from the stack slot, even those that aren't
 331       // in the unwind blocks. We should be more selective.
 332       if (NeedsSpill) {
 333         DemoteRegToStack(Inst, true);
 334         ++NumSpilled;
 335       }
 336     }
 337   }
 338
 339   // Go through the landing pads and remove any PHIs there.
 340   for (InvokeInst *Invoke : Invokes) {
 341     BasicBlock *UnwindBlock = Invoke->getUnwindDest();
 342     LandingPadInst *LPI = UnwindBlock->getLandingPadInst();
 343
 344     // Place PHIs into a set to avoid invalidating the iterator.
 345     SmallPtrSet<PHINode *, 8> PHIsToDemote;
 346     for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
 347       PHIsToDemote.insert(cast<PHINode>(PN));
 348     if (PHIsToDemote.empty())
 349       continue;
 350
 351     // Demote the PHIs to the stack.
 352     for (PHINode *PN : PHIsToDemote)
 353       DemotePHIToStack(PN);
 354
 355     // Move the landingpad instruction back to the top of the landing pad block.
 356     LPI->moveBefore(&UnwindBlock->front());
 357   }
 358 }
 359
 360 /// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
 361 /// the function context and marking the call sites with the appropriate
 362 /// values. These values are used by the DWARF EH emitter.
 363 bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
 364   SmallVector<ReturnInst *, 16> Returns;
 365   SmallVector<InvokeInst *, 16> Invokes;
 366   SmallSetVector<LandingPadInst *, 16> LPads;
 367
 368   // Look through the terminators of the basic blocks to find invokes.
 369   for (BasicBlock &BB : F)
 370     if (auto *II = dyn_cast<InvokeInst>(BB.getTerminator())) {
 371       if (Function *Callee = II->getCalledFunction())
 372         if (Callee->getIntrinsicID() == Intrinsic::donothing) {
 373           // Remove the NOP invoke.
 374           BranchInst::Create(II->getNormalDest(), II);
 375           II->eraseFromParent();
 376           continue;
 377         }
 378
 379       Invokes.push_back(II);
 380       LPads.insert(II->getUnwindDest()->getLandingPadInst());
 381     } else if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator())) {
 382       Returns.push_back(RI);
 383     }
 384
 385   if (Invokes.empty())
 386     return false;
 387
 388   NumInvokes += Invokes.size();
 389
 390   lowerIncomingArguments(F);
 391   lowerAcrossUnwindEdges(F, Invokes);
 392
 393   Value *FuncCtx =
 394       setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
 395   BasicBlock *EntryBB = &F.front();
 396   IRBuilder<> Builder(EntryBB->getTerminator());
 397
 398   // Get a reference to the jump buffer.
 399   Value *JBufPtr =
 400       Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 5, "jbuf_gep");
 401
 402   // Save the frame pointer.
 403   Value *FramePtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 0,
 404                                                "jbuf_fp_gep");
 405
 406   Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
 407   Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);
 408
 409   // Save the stack pointer.
 410   Value *StackPtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 2,
 411                                                "jbuf_sp_gep");
 412
 413   Val = Builder.CreateCall(StackAddrFn, {}, "sp");
 414   Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);
 415
 416   // Call the setup_dispatch instrinsic. It fills in the rest of the jmpbuf.
 417   Builder.CreateCall(BuiltinSetupDispatchFn, {});
 418
 419   // Store a pointer to the function context so that the back-end will know
 420   // where to look for it.
 421   Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy());
 422   Builder.CreateCall(FuncCtxFn, FuncCtxArg);
 423
 424   // At this point, we are all set up, update the invoke instructions to mark
 425   // their call_site values.
 426   for (unsigned I = 0, E = Invokes.size(); I != E; ++I) {
 427     insertCallSiteStore(Invokes[I], I + 1);
 428
 429     ConstantInt *CallSiteNum =
 430         ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);
 431
 432     // Record the call site value for the back end so it stays associated with
 433     // the invoke.
 434     CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
 435   }
 436
 437   // Mark call instructions that aren't nounwind as no-action (call_site ==
 438   // -1). Skip the entry block, as prior to then, no function context has been
 439   // created for this function and any unexpected exceptions thrown will go
 440   // directly to the caller's context, which is what we want anyway, so no need
 441   // to do anything here.
 442   for (BasicBlock &BB : F) {
 443     if (&BB == &F.front())
 444       continue;
 445     for (Instruction &I : BB)
 446       if (I.mayThrow())
 447         insertCallSiteStore(&I, -1);
 448   }
 449
 450   // Register the function context and make sure it's known to not throw
 451   CallInst *Register =
 452       CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator());
 453   Register->setDoesNotThrow();
 454
 455   // Following any allocas not in the entry block, update the saved SP in the
 456   // jmpbuf to the new value.
 457   for (BasicBlock &BB : F) {
 458     if (&BB == &F.front())
 459       continue;
 460     for (Instruction &I : BB) {
 461       if (auto *CI = dyn_cast<CallInst>(&I)) {
 462         if (CI->getCalledFunction() != StackRestoreFn)
 463           continue;
 464       } else if (!isa<AllocaInst>(&I)) {
 465         continue;
 466       }
 467       Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
 468       StackAddr->insertAfter(&I);
 469       new StoreInst(StackAddr, StackPtr, true, StackAddr->getNextNode());
 470     }
 471   }
 472
 473   // Finally, for any returns from this function, if this function contains an
 474   // invoke, add a call to unregister the function context.
 475   for (ReturnInst *Return : Returns) {
 476     Instruction *InsertPoint = Return;
 477     if (CallInst *CI = Return->getParent()->getTerminatingMustTailCall())
 478       InsertPoint = CI;
 479     CallInst::Create(UnregisterFn, FuncCtx, "", InsertPoint);
 480   }
 481
 482   return true;
 483 }
 484
 485 bool SjLjEHPrepare::runOnFunction(Function &F) {
 486   Module &M = *F.getParent();
 487   RegisterFn = M.getOrInsertFunction(
 488       "_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()),
 489       PointerType::getUnqual(FunctionContextTy));
 490   UnregisterFn = M.getOrInsertFunction(
 491       "_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()),
 492       PointerType::getUnqual(FunctionContextTy));
 493   FrameAddrFn = Intrinsic::getDeclaration(
 494       &M, Intrinsic::frameaddress,
 495       {Type::getInt8PtrTy(M.getContext(),
 496                           M.getDataLayout().getAllocaAddrSpace())});
 497   StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
 498   StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
 499   BuiltinSetupDispatchFn =
 500     Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setup_dispatch);
 501   LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
 502   CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
 503   FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext);
 504
 505   bool Res = setupEntryBlockAndCallSites(F);
 506   return Res;
 507 }