SjLjEHPrepare.cpp revision 202375
1//===- SjLjEHPass.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#define DEBUG_TYPE "sjljehprepare" 16#include "llvm/Transforms/Scalar.h" 17#include "llvm/Constants.h" 18#include "llvm/DerivedTypes.h" 19#include "llvm/Instructions.h" 20#include "llvm/Intrinsics.h" 21#include "llvm/LLVMContext.h" 22#include "llvm/Module.h" 23#include "llvm/Pass.h" 24#include "llvm/CodeGen/Passes.h" 25#include "llvm/Transforms/Utils/BasicBlockUtils.h" 26#include "llvm/Transforms/Utils/Local.h" 27#include "llvm/ADT/Statistic.h" 28#include "llvm/ADT/SmallVector.h" 29#include "llvm/Support/CommandLine.h" 30#include "llvm/Support/Debug.h" 31#include "llvm/Support/raw_ostream.h" 32#include "llvm/Target/TargetLowering.h" 33using namespace llvm; 34 35STATISTIC(NumInvokes, "Number of invokes replaced"); 36STATISTIC(NumUnwinds, "Number of unwinds replaced"); 37STATISTIC(NumSpilled, "Number of registers live across unwind edges"); 38 39namespace { 40 class SjLjEHPass : public FunctionPass { 41 42 const TargetLowering *TLI; 43 44 const Type *FunctionContextTy; 45 Constant *RegisterFn; 46 Constant *UnregisterFn; 47 Constant *ResumeFn; 48 Constant *BuiltinSetjmpFn; 49 Constant *FrameAddrFn; 50 Constant *LSDAAddrFn; 51 Value *PersonalityFn; 52 Constant *SelectorFn; 53 Constant *ExceptionFn; 54 55 Value *CallSite; 56 public: 57 static char ID; // Pass identification, replacement for typeid 58 explicit SjLjEHPass(const TargetLowering *tli = NULL) 59 : FunctionPass(&ID), TLI(tli) { } 60 bool doInitialization(Module &M); 61 bool runOnFunction(Function &F); 62 63 virtual void getAnalysisUsage(AnalysisUsage &AU) const { } 64 const char *getPassName() const { 65 return "SJLJ Exception Handling preparation"; 66 } 67 68 private: 69 void markInvokeCallSite(InvokeInst *II, unsigned InvokeNo, 70 Value *CallSite, 71 SwitchInst *CatchSwitch); 72 void splitLiveRangesLiveAcrossInvokes(SmallVector<InvokeInst*,16> &Invokes); 73 bool insertSjLjEHSupport(Function &F); 74 }; 75} // end anonymous namespace 76 77char SjLjEHPass::ID = 0; 78 79// Public Interface To the SjLjEHPass pass. 80FunctionPass *llvm::createSjLjEHPass(const TargetLowering *TLI) { 81 return new SjLjEHPass(TLI); 82} 83// doInitialization - Set up decalarations and types needed to process 84// exceptions. 85bool SjLjEHPass::doInitialization(Module &M) { 86 // Build the function context structure. 87 // builtin_setjmp uses a five word jbuf 88 const Type *VoidPtrTy = 89 Type::getInt8PtrTy(M.getContext()); 90 const Type *Int32Ty = Type::getInt32Ty(M.getContext()); 91 FunctionContextTy = 92 StructType::get(M.getContext(), 93 VoidPtrTy, // __prev 94 Int32Ty, // call_site 95 ArrayType::get(Int32Ty, 4), // __data 96 VoidPtrTy, // __personality 97 VoidPtrTy, // __lsda 98 ArrayType::get(VoidPtrTy, 5), // __jbuf 99 NULL); 100 RegisterFn = M.getOrInsertFunction("_Unwind_SjLj_Register", 101 Type::getVoidTy(M.getContext()), 102 PointerType::getUnqual(FunctionContextTy), 103 (Type *)0); 104 UnregisterFn = 105 M.getOrInsertFunction("_Unwind_SjLj_Unregister", 106 Type::getVoidTy(M.getContext()), 107 PointerType::getUnqual(FunctionContextTy), 108 (Type *)0); 109 ResumeFn = 110 M.getOrInsertFunction("_Unwind_SjLj_Resume", 111 Type::getVoidTy(M.getContext()), 112 VoidPtrTy, 113 (Type *)0); 114 FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress); 115 BuiltinSetjmpFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setjmp); 116 LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda); 117 SelectorFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_selector); 118 ExceptionFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_exception); 119 PersonalityFn = 0; 120 121 return true; 122} 123 124/// markInvokeCallSite - Insert code to mark the call_site for this invoke 125void SjLjEHPass::markInvokeCallSite(InvokeInst *II, unsigned InvokeNo, 126 Value *CallSite, 127 SwitchInst *CatchSwitch) { 128 ConstantInt *CallSiteNoC= ConstantInt::get(Type::getInt32Ty(II->getContext()), 129 InvokeNo); 130 // The runtime comes back to the dispatcher with the call_site - 1 in 131 // the context. Odd, but there it is. 132 ConstantInt *SwitchValC = ConstantInt::get(Type::getInt32Ty(II->getContext()), 133 InvokeNo - 1); 134 135 // If the unwind edge has phi nodes, split the edge. 136 if (isa<PHINode>(II->getUnwindDest()->begin())) { 137 SplitCriticalEdge(II, 1, this); 138 139 // If there are any phi nodes left, they must have a single predecessor. 140 while (PHINode *PN = dyn_cast<PHINode>(II->getUnwindDest()->begin())) { 141 PN->replaceAllUsesWith(PN->getIncomingValue(0)); 142 PN->eraseFromParent(); 143 } 144 } 145 146 // Insert a store of the invoke num before the invoke and store zero into the 147 // location afterward. 148 new StoreInst(CallSiteNoC, CallSite, true, II); // volatile 149 150 // Add a switch case to our unwind block. 151 CatchSwitch->addCase(SwitchValC, II->getUnwindDest()); 152 // We still want this to look like an invoke so we emit the LSDA properly 153 // FIXME: ??? Or will this cause strangeness with mis-matched IDs like 154 // when it was in the front end? 155} 156 157/// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until 158/// we reach blocks we've already seen. 159static void MarkBlocksLiveIn(BasicBlock *BB, std::set<BasicBlock*> &LiveBBs) { 160 if (!LiveBBs.insert(BB).second) return; // already been here. 161 162 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 163 MarkBlocksLiveIn(*PI, LiveBBs); 164} 165 166/// splitLiveRangesAcrossInvokes - Each value that is live across an unwind edge 167/// we spill into a stack location, guaranteeing that there is nothing live 168/// across the unwind edge. This process also splits all critical edges 169/// coming out of invoke's. 170void SjLjEHPass:: 171splitLiveRangesLiveAcrossInvokes(SmallVector<InvokeInst*,16> &Invokes) { 172 // First step, split all critical edges from invoke instructions. 173 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) { 174 InvokeInst *II = Invokes[i]; 175 SplitCriticalEdge(II, 0, this); 176 SplitCriticalEdge(II, 1, this); 177 assert(!isa<PHINode>(II->getNormalDest()) && 178 !isa<PHINode>(II->getUnwindDest()) && 179 "critical edge splitting left single entry phi nodes?"); 180 } 181 182 Function *F = Invokes.back()->getParent()->getParent(); 183 184 // To avoid having to handle incoming arguments specially, we lower each arg 185 // to a copy instruction in the entry block. This ensures that the argument 186 // value itself cannot be live across the entry block. 187 BasicBlock::iterator AfterAllocaInsertPt = F->begin()->begin(); 188 while (isa<AllocaInst>(AfterAllocaInsertPt) && 189 isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsertPt)->getArraySize())) 190 ++AfterAllocaInsertPt; 191 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); 192 AI != E; ++AI) { 193 // This is always a no-op cast because we're casting AI to AI->getType() so 194 // src and destination types are identical. BitCast is the only possibility. 195 CastInst *NC = new BitCastInst( 196 AI, AI->getType(), AI->getName()+".tmp", AfterAllocaInsertPt); 197 AI->replaceAllUsesWith(NC); 198 // Normally its is forbidden to replace a CastInst's operand because it 199 // could cause the opcode to reflect an illegal conversion. However, we're 200 // replacing it here with the same value it was constructed with to simply 201 // make NC its user. 202 NC->setOperand(0, AI); 203 } 204 205 // Finally, scan the code looking for instructions with bad live ranges. 206 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) 207 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) { 208 // Ignore obvious cases we don't have to handle. In particular, most 209 // instructions either have no uses or only have a single use inside the 210 // current block. Ignore them quickly. 211 Instruction *Inst = II; 212 if (Inst->use_empty()) continue; 213 if (Inst->hasOneUse() && 214 cast<Instruction>(Inst->use_back())->getParent() == BB && 215 !isa<PHINode>(Inst->use_back())) continue; 216 217 // If this is an alloca in the entry block, it's not a real register 218 // value. 219 if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst)) 220 if (isa<ConstantInt>(AI->getArraySize()) && BB == F->begin()) 221 continue; 222 223 // Avoid iterator invalidation by copying users to a temporary vector. 224 SmallVector<Instruction*,16> Users; 225 for (Value::use_iterator UI = Inst->use_begin(), E = Inst->use_end(); 226 UI != E; ++UI) { 227 Instruction *User = cast<Instruction>(*UI); 228 if (User->getParent() != BB || isa<PHINode>(User)) 229 Users.push_back(User); 230 } 231 232 // Find all of the blocks that this value is live in. 233 std::set<BasicBlock*> LiveBBs; 234 LiveBBs.insert(Inst->getParent()); 235 while (!Users.empty()) { 236 Instruction *U = Users.back(); 237 Users.pop_back(); 238 239 if (!isa<PHINode>(U)) { 240 MarkBlocksLiveIn(U->getParent(), LiveBBs); 241 } else { 242 // Uses for a PHI node occur in their predecessor block. 243 PHINode *PN = cast<PHINode>(U); 244 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 245 if (PN->getIncomingValue(i) == Inst) 246 MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs); 247 } 248 } 249 250 // Now that we know all of the blocks that this thing is live in, see if 251 // it includes any of the unwind locations. 252 bool NeedsSpill = false; 253 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) { 254 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest(); 255 if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) { 256 NeedsSpill = true; 257 } 258 } 259 260 // If we decided we need a spill, do it. 261 if (NeedsSpill) { 262 ++NumSpilled; 263 DemoteRegToStack(*Inst, true); 264 } 265 } 266} 267 268bool SjLjEHPass::insertSjLjEHSupport(Function &F) { 269 SmallVector<ReturnInst*,16> Returns; 270 SmallVector<UnwindInst*,16> Unwinds; 271 SmallVector<InvokeInst*,16> Invokes; 272 273 // Look through the terminators of the basic blocks to find invokes, returns 274 // and unwinds 275 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 276 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 277 // Remember all return instructions in case we insert an invoke into this 278 // function. 279 Returns.push_back(RI); 280 } else if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) { 281 Invokes.push_back(II); 282 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) { 283 Unwinds.push_back(UI); 284 } 285 // If we don't have any invokes or unwinds, there's nothing to do. 286 if (Unwinds.empty() && Invokes.empty()) return false; 287 288 // Find the eh.selector.* and eh.exception calls. We'll use the first 289 // eh.selector to determine the right personality function to use. For 290 // SJLJ, we always use the same personality for the whole function, 291 // not on a per-selector basis. 292 // FIXME: That's a bit ugly. Better way? 293 SmallVector<CallInst*,16> EH_Selectors; 294 SmallVector<CallInst*,16> EH_Exceptions; 295 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 296 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 297 if (CallInst *CI = dyn_cast<CallInst>(I)) { 298 if (CI->getCalledFunction() == SelectorFn) { 299 if (!PersonalityFn) PersonalityFn = CI->getOperand(2); 300 EH_Selectors.push_back(CI); 301 } else if (CI->getCalledFunction() == ExceptionFn) { 302 EH_Exceptions.push_back(CI); 303 } 304 } 305 } 306 } 307 // If we don't have any eh.selector calls, we can't determine the personality 308 // function. Without a personality function, we can't process exceptions. 309 if (!PersonalityFn) return false; 310 311 NumInvokes += Invokes.size(); 312 NumUnwinds += Unwinds.size(); 313 314 if (!Invokes.empty()) { 315 // We have invokes, so we need to add register/unregister calls to get 316 // this function onto the global unwind stack. 317 // 318 // First thing we need to do is scan the whole function for values that are 319 // live across unwind edges. Each value that is live across an unwind edge 320 // we spill into a stack location, guaranteeing that there is nothing live 321 // across the unwind edge. This process also splits all critical edges 322 // coming out of invoke's. 323 splitLiveRangesLiveAcrossInvokes(Invokes); 324 325 BasicBlock *EntryBB = F.begin(); 326 // Create an alloca for the incoming jump buffer ptr and the new jump buffer 327 // that needs to be restored on all exits from the function. This is an 328 // alloca because the value needs to be added to the global context list. 329 unsigned Align = 4; // FIXME: Should be a TLI check? 330 AllocaInst *FunctionContext = 331 new AllocaInst(FunctionContextTy, 0, Align, 332 "fcn_context", F.begin()->begin()); 333 334 Value *Idxs[2]; 335 const Type *Int32Ty = Type::getInt32Ty(F.getContext()); 336 Value *Zero = ConstantInt::get(Int32Ty, 0); 337 // We need to also keep around a reference to the call_site field 338 Idxs[0] = Zero; 339 Idxs[1] = ConstantInt::get(Int32Ty, 1); 340 CallSite = GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2, 341 "call_site", 342 EntryBB->getTerminator()); 343 344 // The exception selector comes back in context->data[1] 345 Idxs[1] = ConstantInt::get(Int32Ty, 2); 346 Value *FCData = GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2, 347 "fc_data", 348 EntryBB->getTerminator()); 349 Idxs[1] = ConstantInt::get(Int32Ty, 1); 350 Value *SelectorAddr = GetElementPtrInst::Create(FCData, Idxs, Idxs+2, 351 "exc_selector_gep", 352 EntryBB->getTerminator()); 353 // The exception value comes back in context->data[0] 354 Idxs[1] = Zero; 355 Value *ExceptionAddr = GetElementPtrInst::Create(FCData, Idxs, Idxs+2, 356 "exception_gep", 357 EntryBB->getTerminator()); 358 359 // The result of the eh.selector call will be replaced with a 360 // a reference to the selector value returned in the function 361 // context. We leave the selector itself so the EH analysis later 362 // can use it. 363 for (int i = 0, e = EH_Selectors.size(); i < e; ++i) { 364 CallInst *I = EH_Selectors[i]; 365 Value *SelectorVal = new LoadInst(SelectorAddr, "select_val", true, I); 366 I->replaceAllUsesWith(SelectorVal); 367 } 368 // eh.exception calls are replaced with references to the proper 369 // location in the context. Unlike eh.selector, the eh.exception 370 // calls are removed entirely. 371 for (int i = 0, e = EH_Exceptions.size(); i < e; ++i) { 372 CallInst *I = EH_Exceptions[i]; 373 // Possible for there to be duplicates, so check to make sure 374 // the instruction hasn't already been removed. 375 if (!I->getParent()) continue; 376 Value *Val = new LoadInst(ExceptionAddr, "exception", true, I); 377 const Type *Ty = Type::getInt8PtrTy(F.getContext()); 378 Val = CastInst::Create(Instruction::IntToPtr, Val, Ty, "", I); 379 380 I->replaceAllUsesWith(Val); 381 I->eraseFromParent(); 382 } 383 384 // The entry block changes to have the eh.sjlj.setjmp, with a conditional 385 // branch to a dispatch block for non-zero returns. If we return normally, 386 // we're not handling an exception and just register the function context 387 // and continue. 388 389 // Create the dispatch block. The dispatch block is basically a big switch 390 // statement that goes to all of the invoke landing pads. 391 BasicBlock *DispatchBlock = 392 BasicBlock::Create(F.getContext(), "eh.sjlj.setjmp.catch", &F); 393 394 // Insert a load in the Catch block, and a switch on its value. By default, 395 // we go to a block that just does an unwind (which is the correct action 396 // for a standard call). 397 BasicBlock *UnwindBlock = 398 BasicBlock::Create(F.getContext(), "unwindbb", &F); 399 Unwinds.push_back(new UnwindInst(F.getContext(), UnwindBlock)); 400 401 Value *DispatchLoad = new LoadInst(CallSite, "invoke.num", true, 402 DispatchBlock); 403 SwitchInst *DispatchSwitch = 404 SwitchInst::Create(DispatchLoad, UnwindBlock, Invokes.size(), 405 DispatchBlock); 406 // Split the entry block to insert the conditional branch for the setjmp. 407 BasicBlock *ContBlock = EntryBB->splitBasicBlock(EntryBB->getTerminator(), 408 "eh.sjlj.setjmp.cont"); 409 410 // Populate the Function Context 411 // 1. LSDA address 412 // 2. Personality function address 413 // 3. jmpbuf (save FP and call eh.sjlj.setjmp) 414 415 // LSDA address 416 Idxs[0] = Zero; 417 Idxs[1] = ConstantInt::get(Int32Ty, 4); 418 Value *LSDAFieldPtr = 419 GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2, 420 "lsda_gep", 421 EntryBB->getTerminator()); 422 Value *LSDA = CallInst::Create(LSDAAddrFn, "lsda_addr", 423 EntryBB->getTerminator()); 424 new StoreInst(LSDA, LSDAFieldPtr, true, EntryBB->getTerminator()); 425 426 Idxs[1] = ConstantInt::get(Int32Ty, 3); 427 Value *PersonalityFieldPtr = 428 GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2, 429 "lsda_gep", 430 EntryBB->getTerminator()); 431 new StoreInst(PersonalityFn, PersonalityFieldPtr, true, 432 EntryBB->getTerminator()); 433 434 // Save the frame pointer. 435 Idxs[1] = ConstantInt::get(Int32Ty, 5); 436 Value *FieldPtr 437 = GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2, 438 "jbuf_gep", 439 EntryBB->getTerminator()); 440 Idxs[1] = ConstantInt::get(Int32Ty, 0); 441 Value *ElemPtr = 442 GetElementPtrInst::Create(FieldPtr, Idxs, Idxs+2, "jbuf_fp_gep", 443 EntryBB->getTerminator()); 444 445 Value *Val = CallInst::Create(FrameAddrFn, 446 ConstantInt::get(Int32Ty, 0), 447 "fp", 448 EntryBB->getTerminator()); 449 new StoreInst(Val, ElemPtr, true, EntryBB->getTerminator()); 450 // Call the setjmp instrinsic. It fills in the rest of the jmpbuf 451 Value *SetjmpArg = 452 CastInst::Create(Instruction::BitCast, FieldPtr, 453 Type::getInt8PtrTy(F.getContext()), "", 454 EntryBB->getTerminator()); 455 Value *DispatchVal = CallInst::Create(BuiltinSetjmpFn, SetjmpArg, 456 "dispatch", 457 EntryBB->getTerminator()); 458 // check the return value of the setjmp. non-zero goes to dispatcher 459 Value *IsNormal = new ICmpInst(EntryBB->getTerminator(), 460 ICmpInst::ICMP_EQ, DispatchVal, Zero, 461 "notunwind"); 462 // Nuke the uncond branch. 463 EntryBB->getTerminator()->eraseFromParent(); 464 465 // Put in a new condbranch in its place. 466 BranchInst::Create(ContBlock, DispatchBlock, IsNormal, EntryBB); 467 468 // Register the function context and make sure it's known to not throw 469 CallInst *Register = 470 CallInst::Create(RegisterFn, FunctionContext, "", 471 ContBlock->getTerminator()); 472 Register->setDoesNotThrow(); 473 474 // At this point, we are all set up, update the invoke instructions 475 // to mark their call_site values, and fill in the dispatch switch 476 // accordingly. 477 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) 478 markInvokeCallSite(Invokes[i], i+1, CallSite, DispatchSwitch); 479 480 // The front end has likely added calls to _Unwind_Resume. We need 481 // to find those calls and mark the call_site as -1 immediately prior. 482 // resume is a noreturn function, so any block that has a call to it 483 // should end in an 'unreachable' instruction with the call immediately 484 // prior. That's how we'll search. 485 // ??? There's got to be a better way. this is fugly. 486 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 487 if ((dyn_cast<UnreachableInst>(BB->getTerminator()))) { 488 BasicBlock::iterator I = BB->getTerminator(); 489 // Check the previous instruction and see if it's a resume call 490 if (I == BB->begin()) continue; 491 if (CallInst *CI = dyn_cast<CallInst>(--I)) { 492 if (CI->getCalledFunction() == ResumeFn) { 493 Value *NegativeOne = Constant::getAllOnesValue(Int32Ty); 494 new StoreInst(NegativeOne, CallSite, true, I); // volatile 495 } 496 } 497 } 498 499 // Replace all unwinds with a branch to the unwind handler. 500 // ??? Should this ever happen with sjlj exceptions? 501 for (unsigned i = 0, e = Unwinds.size(); i != e; ++i) { 502 BranchInst::Create(UnwindBlock, Unwinds[i]); 503 Unwinds[i]->eraseFromParent(); 504 } 505 506 // Finally, for any returns from this function, if this function contains an 507 // invoke, add a call to unregister the function context. 508 for (unsigned i = 0, e = Returns.size(); i != e; ++i) 509 CallInst::Create(UnregisterFn, FunctionContext, "", Returns[i]); 510 } 511 512 return true; 513} 514 515bool SjLjEHPass::runOnFunction(Function &F) { 516 bool Res = insertSjLjEHSupport(F); 517 return Res; 518} 519