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