SjLjEHPrepare.cpp revision b58a59b3c1563ab5bd7225748e32933bf6d76c03
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 *BuiltinSetjmpFn; 48 Constant *FrameAddrFn; 49 Constant *LSDAAddrFn; 50 Value *PersonalityFn; 51 Constant *SelectorFn; 52 Constant *ExceptionFn; 53 Constant *CallSiteFn; 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 insertCallSiteStore(Instruction *I, int Number, Value *CallSite); 70 void markInvokeCallSite(InvokeInst *II, int InvokeNo, 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 FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress); 110 BuiltinSetjmpFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setjmp); 111 LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda); 112 SelectorFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_selector); 113 ExceptionFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_exception); 114 CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite); 115 PersonalityFn = 0; 116 117 return true; 118} 119 120/// insertCallSiteStore - Insert a store of the call-site value to the 121/// function context 122void SjLjEHPass::insertCallSiteStore(Instruction *I, int Number, 123 Value *CallSite) { 124 ConstantInt *CallSiteNoC = ConstantInt::get(Type::getInt32Ty(I->getContext()), 125 Number); 126 // Insert a store of the call-site number 127 new StoreInst(CallSiteNoC, CallSite, true, I); // volatile 128} 129 130/// markInvokeCallSite - Insert code to mark the call_site for this invoke 131void SjLjEHPass::markInvokeCallSite(InvokeInst *II, int InvokeNo, 132 Value *CallSite, 133 SwitchInst *CatchSwitch) { 134 ConstantInt *CallSiteNoC= ConstantInt::get(Type::getInt32Ty(II->getContext()), 135 InvokeNo); 136 // The runtime comes back to the dispatcher with the call_site - 1 in 137 // the context. Odd, but there it is. 138 ConstantInt *SwitchValC = ConstantInt::get(Type::getInt32Ty(II->getContext()), 139 InvokeNo - 1); 140 141 // If the unwind edge has phi nodes, split the edge. 142 if (isa<PHINode>(II->getUnwindDest()->begin())) { 143 SplitCriticalEdge(II, 1, this); 144 145 // If there are any phi nodes left, they must have a single predecessor. 146 while (PHINode *PN = dyn_cast<PHINode>(II->getUnwindDest()->begin())) { 147 PN->replaceAllUsesWith(PN->getIncomingValue(0)); 148 PN->eraseFromParent(); 149 } 150 } 151 152 // Insert the store of the call site value 153 insertCallSiteStore(II, InvokeNo, CallSite); 154 155 // Record the call site value for the back end so it stays associated with 156 // the invoke. 157 CallInst::Create(CallSiteFn, CallSiteNoC, "", II); 158 159 // Add a switch case to our unwind block. 160 CatchSwitch->addCase(SwitchValC, II->getUnwindDest()); 161 // We still want this to look like an invoke so we emit the LSDA properly, 162 // so we don't transform the invoke into a call here. 163} 164 165/// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until 166/// we reach blocks we've already seen. 167static void MarkBlocksLiveIn(BasicBlock *BB, std::set<BasicBlock*> &LiveBBs) { 168 if (!LiveBBs.insert(BB).second) return; // already been here. 169 170 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 171 MarkBlocksLiveIn(*PI, LiveBBs); 172} 173 174/// splitLiveRangesAcrossInvokes - Each value that is live across an unwind edge 175/// we spill into a stack location, guaranteeing that there is nothing live 176/// across the unwind edge. This process also splits all critical edges 177/// coming out of invoke's. 178void SjLjEHPass:: 179splitLiveRangesLiveAcrossInvokes(SmallVector<InvokeInst*,16> &Invokes) { 180 // First step, split all critical edges from invoke instructions. 181 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) { 182 InvokeInst *II = Invokes[i]; 183 SplitCriticalEdge(II, 0, this); 184 SplitCriticalEdge(II, 1, this); 185 assert(!isa<PHINode>(II->getNormalDest()) && 186 !isa<PHINode>(II->getUnwindDest()) && 187 "critical edge splitting left single entry phi nodes?"); 188 } 189 190 Function *F = Invokes.back()->getParent()->getParent(); 191 192 // To avoid having to handle incoming arguments specially, we lower each arg 193 // to a copy instruction in the entry block. This ensures that the argument 194 // value itself cannot be live across the entry block. 195 BasicBlock::iterator AfterAllocaInsertPt = F->begin()->begin(); 196 while (isa<AllocaInst>(AfterAllocaInsertPt) && 197 isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsertPt)->getArraySize())) 198 ++AfterAllocaInsertPt; 199 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); 200 AI != E; ++AI) { 201 // This is always a no-op cast because we're casting AI to AI->getType() so 202 // src and destination types are identical. BitCast is the only possibility. 203 CastInst *NC = new BitCastInst( 204 AI, AI->getType(), AI->getName()+".tmp", AfterAllocaInsertPt); 205 AI->replaceAllUsesWith(NC); 206 // Normally its is forbidden to replace a CastInst's operand because it 207 // could cause the opcode to reflect an illegal conversion. However, we're 208 // replacing it here with the same value it was constructed with to simply 209 // make NC its user. 210 NC->setOperand(0, AI); 211 } 212 213 // Finally, scan the code looking for instructions with bad live ranges. 214 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) 215 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) { 216 // Ignore obvious cases we don't have to handle. In particular, most 217 // instructions either have no uses or only have a single use inside the 218 // current block. Ignore them quickly. 219 Instruction *Inst = II; 220 if (Inst->use_empty()) continue; 221 if (Inst->hasOneUse() && 222 cast<Instruction>(Inst->use_back())->getParent() == BB && 223 !isa<PHINode>(Inst->use_back())) continue; 224 225 // If this is an alloca in the entry block, it's not a real register 226 // value. 227 if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst)) 228 if (isa<ConstantInt>(AI->getArraySize()) && BB == F->begin()) 229 continue; 230 231 // Avoid iterator invalidation by copying users to a temporary vector. 232 SmallVector<Instruction*,16> Users; 233 for (Value::use_iterator UI = Inst->use_begin(), E = Inst->use_end(); 234 UI != E; ++UI) { 235 Instruction *User = cast<Instruction>(*UI); 236 if (User->getParent() != BB || isa<PHINode>(User)) 237 Users.push_back(User); 238 } 239 240 // Find all of the blocks that this value is live in. 241 std::set<BasicBlock*> LiveBBs; 242 LiveBBs.insert(Inst->getParent()); 243 while (!Users.empty()) { 244 Instruction *U = Users.back(); 245 Users.pop_back(); 246 247 if (!isa<PHINode>(U)) { 248 MarkBlocksLiveIn(U->getParent(), LiveBBs); 249 } else { 250 // Uses for a PHI node occur in their predecessor block. 251 PHINode *PN = cast<PHINode>(U); 252 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 253 if (PN->getIncomingValue(i) == Inst) 254 MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs); 255 } 256 } 257 258 // Now that we know all of the blocks that this thing is live in, see if 259 // it includes any of the unwind locations. 260 bool NeedsSpill = false; 261 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) { 262 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest(); 263 if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) { 264 NeedsSpill = true; 265 } 266 } 267 268 // If we decided we need a spill, do it. 269 if (NeedsSpill) { 270 ++NumSpilled; 271 DemoteRegToStack(*Inst, true); 272 } 273 } 274} 275 276bool SjLjEHPass::insertSjLjEHSupport(Function &F) { 277 SmallVector<ReturnInst*,16> Returns; 278 SmallVector<UnwindInst*,16> Unwinds; 279 SmallVector<InvokeInst*,16> Invokes; 280 281 // Look through the terminators of the basic blocks to find invokes, returns 282 // and unwinds. 283 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 284 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 285 // Remember all return instructions in case we insert an invoke into this 286 // function. 287 Returns.push_back(RI); 288 } else if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) { 289 Invokes.push_back(II); 290 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) { 291 Unwinds.push_back(UI); 292 } 293 } 294 // If we don't have any invokes or unwinds, there's nothing to do. 295 if (Unwinds.empty() && Invokes.empty()) return false; 296 297 // Find the eh.selector.* and eh.exception calls. We'll use the first 298 // eh.selector to determine the right personality function to use. For 299 // SJLJ, we always use the same personality for the whole function, 300 // not on a per-selector basis. 301 // FIXME: That's a bit ugly. Better way? 302 SmallVector<CallInst*,16> EH_Selectors; 303 SmallVector<CallInst*,16> EH_Exceptions; 304 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 305 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 306 if (CallInst *CI = dyn_cast<CallInst>(I)) { 307 if (CI->getCalledFunction() == SelectorFn) { 308 if (!PersonalityFn) PersonalityFn = CI->getOperand(2); 309 EH_Selectors.push_back(CI); 310 } else if (CI->getCalledFunction() == ExceptionFn) { 311 EH_Exceptions.push_back(CI); 312 } 313 } 314 } 315 } 316 // If we don't have any eh.selector calls, we can't determine the personality 317 // function. Without a personality function, we can't process exceptions. 318 if (!PersonalityFn) return false; 319 320 NumInvokes += Invokes.size(); 321 NumUnwinds += Unwinds.size(); 322 323 if (!Invokes.empty()) { 324 // We have invokes, so we need to add register/unregister calls to get 325 // this function onto the global unwind stack. 326 // 327 // First thing we need to do is scan the whole function for values that are 328 // live across unwind edges. Each value that is live across an unwind edge 329 // we spill into a stack location, guaranteeing that there is nothing live 330 // across the unwind edge. This process also splits all critical edges 331 // coming out of invoke's. 332 splitLiveRangesLiveAcrossInvokes(Invokes); 333 334 BasicBlock *EntryBB = F.begin(); 335 // Create an alloca for the incoming jump buffer ptr and the new jump buffer 336 // that needs to be restored on all exits from the function. This is an 337 // alloca because the value needs to be added to the global context list. 338 unsigned Align = 4; // FIXME: Should be a TLI check? 339 AllocaInst *FunctionContext = 340 new AllocaInst(FunctionContextTy, 0, Align, 341 "fcn_context", F.begin()->begin()); 342 343 Value *Idxs[2]; 344 const Type *Int32Ty = Type::getInt32Ty(F.getContext()); 345 Value *Zero = ConstantInt::get(Int32Ty, 0); 346 // We need to also keep around a reference to the call_site field 347 Idxs[0] = Zero; 348 Idxs[1] = ConstantInt::get(Int32Ty, 1); 349 CallSite = GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2, 350 "call_site", 351 EntryBB->getTerminator()); 352 353 // The exception selector comes back in context->data[1] 354 Idxs[1] = ConstantInt::get(Int32Ty, 2); 355 Value *FCData = GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2, 356 "fc_data", 357 EntryBB->getTerminator()); 358 Idxs[1] = ConstantInt::get(Int32Ty, 1); 359 Value *SelectorAddr = GetElementPtrInst::Create(FCData, Idxs, Idxs+2, 360 "exc_selector_gep", 361 EntryBB->getTerminator()); 362 // The exception value comes back in context->data[0] 363 Idxs[1] = Zero; 364 Value *ExceptionAddr = GetElementPtrInst::Create(FCData, Idxs, Idxs+2, 365 "exception_gep", 366 EntryBB->getTerminator()); 367 368 // The result of the eh.selector call will be replaced with a 369 // a reference to the selector value returned in the function 370 // context. We leave the selector itself so the EH analysis later 371 // can use it. 372 for (int i = 0, e = EH_Selectors.size(); i < e; ++i) { 373 CallInst *I = EH_Selectors[i]; 374 Value *SelectorVal = new LoadInst(SelectorAddr, "select_val", true, I); 375 I->replaceAllUsesWith(SelectorVal); 376 } 377 // eh.exception calls are replaced with references to the proper 378 // location in the context. Unlike eh.selector, the eh.exception 379 // calls are removed entirely. 380 for (int i = 0, e = EH_Exceptions.size(); i < e; ++i) { 381 CallInst *I = EH_Exceptions[i]; 382 // Possible for there to be duplicates, so check to make sure 383 // the instruction hasn't already been removed. 384 if (!I->getParent()) continue; 385 Value *Val = new LoadInst(ExceptionAddr, "exception", true, I); 386 const Type *Ty = Type::getInt8PtrTy(F.getContext()); 387 Val = CastInst::Create(Instruction::IntToPtr, Val, Ty, "", I); 388 389 I->replaceAllUsesWith(Val); 390 I->eraseFromParent(); 391 } 392 393 // The entry block changes to have the eh.sjlj.setjmp, with a conditional 394 // branch to a dispatch block for non-zero returns. If we return normally, 395 // we're not handling an exception and just register the function context 396 // and continue. 397 398 // Create the dispatch block. The dispatch block is basically a big switch 399 // statement that goes to all of the invoke landing pads. 400 BasicBlock *DispatchBlock = 401 BasicBlock::Create(F.getContext(), "eh.sjlj.setjmp.catch", &F); 402 403 // Insert a load in the Catch block, and a switch on its value. By default, 404 // we go to a block that just does an unwind (which is the correct action 405 // for a standard call). 406 BasicBlock *UnwindBlock = 407 BasicBlock::Create(F.getContext(), "unwindbb", &F); 408 Unwinds.push_back(new UnwindInst(F.getContext(), UnwindBlock)); 409 410 Value *DispatchLoad = new LoadInst(CallSite, "invoke.num", true, 411 DispatchBlock); 412 SwitchInst *DispatchSwitch = 413 SwitchInst::Create(DispatchLoad, UnwindBlock, Invokes.size(), 414 DispatchBlock); 415 // Split the entry block to insert the conditional branch for the setjmp. 416 BasicBlock *ContBlock = EntryBB->splitBasicBlock(EntryBB->getTerminator(), 417 "eh.sjlj.setjmp.cont"); 418 419 // Populate the Function Context 420 // 1. LSDA address 421 // 2. Personality function address 422 // 3. jmpbuf (save FP and call eh.sjlj.setjmp) 423 424 // LSDA address 425 Idxs[0] = Zero; 426 Idxs[1] = ConstantInt::get(Int32Ty, 4); 427 Value *LSDAFieldPtr = 428 GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2, 429 "lsda_gep", 430 EntryBB->getTerminator()); 431 Value *LSDA = CallInst::Create(LSDAAddrFn, "lsda_addr", 432 EntryBB->getTerminator()); 433 new StoreInst(LSDA, LSDAFieldPtr, true, EntryBB->getTerminator()); 434 435 Idxs[1] = ConstantInt::get(Int32Ty, 3); 436 Value *PersonalityFieldPtr = 437 GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2, 438 "lsda_gep", 439 EntryBB->getTerminator()); 440 new StoreInst(PersonalityFn, PersonalityFieldPtr, true, 441 EntryBB->getTerminator()); 442 443 // Save the frame pointer. 444 Idxs[1] = ConstantInt::get(Int32Ty, 5); 445 Value *FieldPtr 446 = GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2, 447 "jbuf_gep", 448 EntryBB->getTerminator()); 449 Idxs[1] = ConstantInt::get(Int32Ty, 0); 450 Value *ElemPtr = 451 GetElementPtrInst::Create(FieldPtr, Idxs, Idxs+2, "jbuf_fp_gep", 452 EntryBB->getTerminator()); 453 454 Value *Val = CallInst::Create(FrameAddrFn, 455 ConstantInt::get(Int32Ty, 0), 456 "fp", 457 EntryBB->getTerminator()); 458 new StoreInst(Val, ElemPtr, true, EntryBB->getTerminator()); 459 // Call the setjmp instrinsic. It fills in the rest of the jmpbuf 460 Value *SetjmpArg = 461 CastInst::Create(Instruction::BitCast, FieldPtr, 462 Type::getInt8PtrTy(F.getContext()), "", 463 EntryBB->getTerminator()); 464 Value *DispatchVal = CallInst::Create(BuiltinSetjmpFn, SetjmpArg, 465 "dispatch", 466 EntryBB->getTerminator()); 467 // check the return value of the setjmp. non-zero goes to dispatcher 468 Value *IsNormal = new ICmpInst(EntryBB->getTerminator(), 469 ICmpInst::ICMP_EQ, DispatchVal, Zero, 470 "notunwind"); 471 // Nuke the uncond branch. 472 EntryBB->getTerminator()->eraseFromParent(); 473 474 // Put in a new condbranch in its place. 475 BranchInst::Create(ContBlock, DispatchBlock, IsNormal, EntryBB); 476 477 // Register the function context and make sure it's known to not throw 478 CallInst *Register = 479 CallInst::Create(RegisterFn, FunctionContext, "", 480 ContBlock->getTerminator()); 481 Register->setDoesNotThrow(); 482 483 // At this point, we are all set up, update the invoke instructions 484 // to mark their call_site values, and fill in the dispatch switch 485 // accordingly. 486 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) 487 markInvokeCallSite(Invokes[i], i+1, CallSite, DispatchSwitch); 488 489 // Mark call instructions that aren't nounwind as no-action 490 // (call_site == -1). Skip the entry block, as prior to then, no function 491 // context has been created for this function and any unexpected exceptions 492 // thrown will go directly to the caller's context, which is what we want 493 // anyway, so no need to do anything here. 494 for (Function::iterator BB = F.begin(), E = F.end(); ++BB != E;) { 495 for (BasicBlock::iterator I = BB->begin(), end = BB->end(); I != end; ++I) 496 if (CallInst *CI = dyn_cast<CallInst>(I)) { 497 // Ignore calls to the EH builtins (eh.selector, eh.exception) 498 Constant *Callee = CI->getCalledFunction(); 499 if (Callee != SelectorFn && Callee != ExceptionFn 500 && !CI->doesNotThrow()) 501 insertCallSiteStore(CI, -1, CallSite); 502 } 503 } 504 505 // Replace all unwinds with a branch to the unwind handler. 506 // ??? Should this ever happen with sjlj exceptions? 507 for (unsigned i = 0, e = Unwinds.size(); i != e; ++i) { 508 BranchInst::Create(UnwindBlock, Unwinds[i]); 509 Unwinds[i]->eraseFromParent(); 510 } 511 512 // Finally, for any returns from this function, if this function contains an 513 // invoke, add a call to unregister the function context. 514 for (unsigned i = 0, e = Returns.size(); i != e; ++i) 515 CallInst::Create(UnregisterFn, FunctionContext, "", Returns[i]); 516 } 517 518 return true; 519} 520 521bool SjLjEHPass::runOnFunction(Function &F) { 522 bool Res = insertSjLjEHSupport(F); 523 return Res; 524} 525