1 //===- LowerSetJmp.cpp - Code pertaining to lowering set/long jumps -------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the lowering of setjmp and longjmp to use the
11 // LLVM invoke and unwind instructions as necessary.
13 // Lowering of longjmp is fairly trivial. We replace the call with a
14 // call to the LLVM library function "__llvm_sjljeh_throw_longjmp()".
15 // This unwinds the stack for us calling all of the destructors for
16 // objects allocated on the stack.
18 // At a setjmp call, the basic block is split and the setjmp removed.
19 // The calls in a function that have a setjmp are converted to invoke
20 // where the except part checks to see if it's a longjmp exception and,
21 // if so, if it's handled in the function. If it is, then it gets the
22 // value returned by the longjmp and goes to where the basic block was
23 // split. Invoke instructions are handled in a similar fashion with the
24 // original except block being executed if it isn't a longjmp except
25 // that is handled by that function.
27 //===----------------------------------------------------------------------===//
29 //===----------------------------------------------------------------------===//
30 // FIXME: This pass doesn't deal with PHI statements just yet. That is,
31 // we expect this to occur before SSAification is done. This would seem
32 // to make sense, but in general, it might be a good idea to make this
33 // pass invokable via the "opt" command at will.
34 //===----------------------------------------------------------------------===//
36 #define DEBUG_TYPE "lowersetjmp"
37 #include "llvm/Transforms/IPO.h"
38 #include "llvm/Constants.h"
39 #include "llvm/DerivedTypes.h"
40 #include "llvm/Instructions.h"
41 #include "llvm/Intrinsics.h"
42 #include "llvm/LLVMContext.h"
43 #include "llvm/Module.h"
44 #include "llvm/Pass.h"
45 #include "llvm/Support/CFG.h"
46 #include "llvm/Support/InstVisitor.h"
47 #include "llvm/Transforms/Utils/Local.h"
48 #include "llvm/ADT/DepthFirstIterator.h"
49 #include "llvm/ADT/Statistic.h"
53 STATISTIC(LongJmpsTransformed, "Number of longjmps transformed");
54 STATISTIC(SetJmpsTransformed , "Number of setjmps transformed");
55 STATISTIC(CallsTransformed , "Number of calls invokified");
56 STATISTIC(InvokesTransformed , "Number of invokes modified");
59 //===--------------------------------------------------------------------===//
60 // LowerSetJmp pass implementation.
61 class LowerSetJmp : public ModulePass, public InstVisitor<LowerSetJmp> {
62 // LLVM library functions...
63 Constant *InitSJMap; // __llvm_sjljeh_init_setjmpmap
64 Constant *DestroySJMap; // __llvm_sjljeh_destroy_setjmpmap
65 Constant *AddSJToMap; // __llvm_sjljeh_add_setjmp_to_map
66 Constant *ThrowLongJmp; // __llvm_sjljeh_throw_longjmp
67 Constant *TryCatchLJ; // __llvm_sjljeh_try_catching_longjmp_exception
68 Constant *IsLJException; // __llvm_sjljeh_is_longjmp_exception
69 Constant *GetLJValue; // __llvm_sjljeh_get_longjmp_value
71 typedef std::pair<SwitchInst*, CallInst*> SwitchValuePair;
73 // Keep track of those basic blocks reachable via a depth-first search of
74 // the CFG from a setjmp call. We only need to transform those "call" and
75 // "invoke" instructions that are reachable from the setjmp call site.
76 std::set<BasicBlock*> DFSBlocks;
78 // The setjmp map is going to hold information about which setjmps
79 // were called (each setjmp gets its own number) and with which
80 // buffer it was called.
81 std::map<Function*, AllocaInst*> SJMap;
83 // The rethrow basic block map holds the basic block to branch to if
84 // the exception isn't handled in the current function and needs to
86 std::map<const Function*, BasicBlock*> RethrowBBMap;
88 // The preliminary basic block map holds a basic block that grabs the
89 // exception and determines if it's handled by the current function.
90 std::map<const Function*, BasicBlock*> PrelimBBMap;
92 // The switch/value map holds a switch inst/call inst pair. The
93 // switch inst controls which handler (if any) gets called and the
94 // value is the value returned to that handler by the call to
95 // __llvm_sjljeh_get_longjmp_value.
96 std::map<const Function*, SwitchValuePair> SwitchValMap;
98 // A map of which setjmps we've seen so far in a function.
99 std::map<const Function*, unsigned> SetJmpIDMap;
101 AllocaInst* GetSetJmpMap(Function* Func);
102 BasicBlock* GetRethrowBB(Function* Func);
103 SwitchValuePair GetSJSwitch(Function* Func, BasicBlock* Rethrow);
105 void TransformLongJmpCall(CallInst* Inst);
106 void TransformSetJmpCall(CallInst* Inst);
108 bool IsTransformableFunction(StringRef Name);
110 static char ID; // Pass identification, replacement for typeid
111 LowerSetJmp() : ModulePass(&ID) {}
113 void visitCallInst(CallInst& CI);
114 void visitInvokeInst(InvokeInst& II);
115 void visitReturnInst(ReturnInst& RI);
116 void visitUnwindInst(UnwindInst& UI);
118 bool runOnModule(Module& M);
119 bool doInitialization(Module& M);
121 } // end anonymous namespace
123 char LowerSetJmp::ID = 0;
124 static RegisterPass<LowerSetJmp> X("lowersetjmp", "Lower Set Jump");
126 // run - Run the transformation on the program. We grab the function
127 // prototypes for longjmp and setjmp. If they are used in the program,
128 // then we can go directly to the places they're at and transform them.
129 bool LowerSetJmp::runOnModule(Module& M) {
130 bool Changed = false;
132 // These are what the functions are called.
133 Function* SetJmp = M.getFunction("llvm.setjmp");
134 Function* LongJmp = M.getFunction("llvm.longjmp");
136 // This program doesn't have longjmp and setjmp calls.
137 if ((!LongJmp || LongJmp->use_empty()) &&
138 (!SetJmp || SetJmp->use_empty())) return false;
140 // Initialize some values and functions we'll need to transform the
141 // setjmp/longjmp functions.
145 for (Value::use_iterator B = SetJmp->use_begin(), E = SetJmp->use_end();
147 BasicBlock* BB = cast<Instruction>(*B)->getParent();
148 for (df_ext_iterator<BasicBlock*> I = df_ext_begin(BB, DFSBlocks),
149 E = df_ext_end(BB, DFSBlocks); I != E; ++I)
153 while (!SetJmp->use_empty()) {
154 assert(isa<CallInst>(SetJmp->use_back()) &&
155 "User of setjmp intrinsic not a call?");
156 TransformSetJmpCall(cast<CallInst>(SetJmp->use_back()));
162 while (!LongJmp->use_empty()) {
163 assert(isa<CallInst>(LongJmp->use_back()) &&
164 "User of longjmp intrinsic not a call?");
165 TransformLongJmpCall(cast<CallInst>(LongJmp->use_back()));
169 // Now go through the affected functions and convert calls and invokes
171 for (std::map<Function*, AllocaInst*>::iterator
172 B = SJMap.begin(), E = SJMap.end(); B != E; ++B) {
173 Function* F = B->first;
174 for (Function::iterator BB = F->begin(), BE = F->end(); BB != BE; ++BB)
175 for (BasicBlock::iterator IB = BB->begin(), IE = BB->end(); IB != IE; ) {
177 if (IB != BB->end() && IB->getParent() != BB)
178 break; // The next instruction got moved to a different block!
184 RethrowBBMap.clear();
186 SwitchValMap.clear();
192 // doInitialization - For the lower long/setjmp pass, this ensures that a
193 // module contains a declaration for the intrisic functions we are going
194 // to call to convert longjmp and setjmp calls.
196 // This function is always successful, unless it isn't.
197 bool LowerSetJmp::doInitialization(Module& M)
199 const Type *SBPTy = Type::getInt8PtrTy(M.getContext());
200 const Type *SBPPTy = PointerType::getUnqual(SBPTy);
202 // N.B. See llvm/runtime/GCCLibraries/libexception/SJLJ-Exception.h for
203 // a description of the following library functions.
205 // void __llvm_sjljeh_init_setjmpmap(void**)
206 InitSJMap = M.getOrInsertFunction("__llvm_sjljeh_init_setjmpmap",
207 Type::getVoidTy(M.getContext()),
209 // void __llvm_sjljeh_destroy_setjmpmap(void**)
210 DestroySJMap = M.getOrInsertFunction("__llvm_sjljeh_destroy_setjmpmap",
211 Type::getVoidTy(M.getContext()),
214 // void __llvm_sjljeh_add_setjmp_to_map(void**, void*, unsigned)
215 AddSJToMap = M.getOrInsertFunction("__llvm_sjljeh_add_setjmp_to_map",
216 Type::getVoidTy(M.getContext()),
218 Type::getInt32Ty(M.getContext()),
221 // void __llvm_sjljeh_throw_longjmp(int*, int)
222 ThrowLongJmp = M.getOrInsertFunction("__llvm_sjljeh_throw_longjmp",
223 Type::getVoidTy(M.getContext()), SBPTy,
224 Type::getInt32Ty(M.getContext()),
227 // unsigned __llvm_sjljeh_try_catching_longjmp_exception(void **)
229 M.getOrInsertFunction("__llvm_sjljeh_try_catching_longjmp_exception",
230 Type::getInt32Ty(M.getContext()), SBPPTy, (Type *)0);
232 // bool __llvm_sjljeh_is_longjmp_exception()
233 IsLJException = M.getOrInsertFunction("__llvm_sjljeh_is_longjmp_exception",
234 Type::getInt1Ty(M.getContext()),
237 // int __llvm_sjljeh_get_longjmp_value()
238 GetLJValue = M.getOrInsertFunction("__llvm_sjljeh_get_longjmp_value",
239 Type::getInt32Ty(M.getContext()),
244 // IsTransformableFunction - Return true if the function name isn't one
245 // of the ones we don't want transformed. Currently, don't transform any
246 // "llvm.{setjmp,longjmp}" functions and none of the setjmp/longjmp error
247 // handling functions (beginning with __llvm_sjljeh_...they don't throw
249 bool LowerSetJmp::IsTransformableFunction(StringRef Name) {
250 return !Name.startswith("__llvm_sjljeh_");
253 // TransformLongJmpCall - Transform a longjmp call into a call to the
254 // internal __llvm_sjljeh_throw_longjmp function. It then takes care of
255 // throwing the exception for us.
256 void LowerSetJmp::TransformLongJmpCall(CallInst* Inst)
258 const Type* SBPTy = Type::getInt8PtrTy(Inst->getContext());
260 // Create the call to "__llvm_sjljeh_throw_longjmp". This takes the
261 // same parameters as "longjmp", except that the buffer is cast to a
262 // char*. It returns "void", so it doesn't need to replace any of
263 // Inst's uses and doesn't get a name.
265 new BitCastInst(Inst->getOperand(1), SBPTy, "LJBuf", Inst);
266 Value *Args[] = { CI, Inst->getOperand(2) };
267 CallInst::Create(ThrowLongJmp, Args, Args + 2, "", Inst);
269 SwitchValuePair& SVP = SwitchValMap[Inst->getParent()->getParent()];
271 // If the function has a setjmp call in it (they are transformed first)
272 // we should branch to the basic block that determines if this longjmp
273 // is applicable here. Otherwise, issue an unwind.
275 BranchInst::Create(SVP.first->getParent(), Inst);
277 new UnwindInst(Inst->getContext(), Inst);
279 // Remove all insts after the branch/unwind inst. Go from back to front to
280 // avoid replaceAllUsesWith if possible.
281 BasicBlock *BB = Inst->getParent();
282 Instruction *Removed;
284 Removed = &BB->back();
285 // If the removed instructions have any users, replace them now.
286 if (!Removed->use_empty())
287 Removed->replaceAllUsesWith(UndefValue::get(Removed->getType()));
288 Removed->eraseFromParent();
289 } while (Removed != Inst);
291 ++LongJmpsTransformed;
294 // GetSetJmpMap - Retrieve (create and initialize, if necessary) the
295 // setjmp map. This map is going to hold information about which setjmps
296 // were called (each setjmp gets its own number) and with which buffer it
297 // was called. There can be only one!
298 AllocaInst* LowerSetJmp::GetSetJmpMap(Function* Func)
300 if (SJMap[Func]) return SJMap[Func];
302 // Insert the setjmp map initialization before the first instruction in
304 Instruction* Inst = Func->getEntryBlock().begin();
305 assert(Inst && "Couldn't find even ONE instruction in entry block!");
307 // Fill in the alloca and call to initialize the SJ map.
309 Type::getInt8PtrTy(Func->getContext());
310 AllocaInst* Map = new AllocaInst(SBPTy, 0, "SJMap", Inst);
311 CallInst::Create(InitSJMap, Map, "", Inst);
312 return SJMap[Func] = Map;
315 // GetRethrowBB - Only one rethrow basic block is needed per function.
316 // If this is a longjmp exception but not handled in this block, this BB
317 // performs the rethrow.
318 BasicBlock* LowerSetJmp::GetRethrowBB(Function* Func)
320 if (RethrowBBMap[Func]) return RethrowBBMap[Func];
322 // The basic block we're going to jump to if we need to rethrow the
324 BasicBlock* Rethrow =
325 BasicBlock::Create(Func->getContext(), "RethrowExcept", Func);
327 // Fill in the "Rethrow" BB with a call to rethrow the exception. This
328 // is the last instruction in the BB since at this point the runtime
329 // should exit this function and go to the next function.
330 new UnwindInst(Func->getContext(), Rethrow);
331 return RethrowBBMap[Func] = Rethrow;
334 // GetSJSwitch - Return the switch statement that controls which handler
335 // (if any) gets called and the value returned to that handler.
336 LowerSetJmp::SwitchValuePair LowerSetJmp::GetSJSwitch(Function* Func,
339 if (SwitchValMap[Func].first) return SwitchValMap[Func];
341 BasicBlock* LongJmpPre =
342 BasicBlock::Create(Func->getContext(), "LongJmpBlkPre", Func);
344 // Keep track of the preliminary basic block for some of the other
346 PrelimBBMap[Func] = LongJmpPre;
348 // Grab the exception.
349 CallInst* Cond = CallInst::Create(IsLJException, "IsLJExcept", LongJmpPre);
351 // The "decision basic block" gets the number associated with the
352 // setjmp call returning to switch on and the value returned by
354 BasicBlock* DecisionBB =
355 BasicBlock::Create(Func->getContext(), "LJDecisionBB", Func);
357 BranchInst::Create(DecisionBB, Rethrow, Cond, LongJmpPre);
359 // Fill in the "decision" basic block.
360 CallInst* LJVal = CallInst::Create(GetLJValue, "LJVal", DecisionBB);
361 CallInst* SJNum = CallInst::Create(TryCatchLJ, GetSetJmpMap(Func), "SJNum",
364 SwitchInst* SI = SwitchInst::Create(SJNum, Rethrow, 0, DecisionBB);
365 return SwitchValMap[Func] = SwitchValuePair(SI, LJVal);
368 // TransformSetJmpCall - The setjmp call is a bit trickier to transform.
369 // We're going to convert all setjmp calls to nops. Then all "call" and
370 // "invoke" instructions in the function are converted to "invoke" where
371 // the "except" branch is used when returning from a longjmp call.
372 void LowerSetJmp::TransformSetJmpCall(CallInst* Inst)
374 BasicBlock* ABlock = Inst->getParent();
375 Function* Func = ABlock->getParent();
377 // Add this setjmp to the setjmp map.
379 Type::getInt8PtrTy(Inst->getContext());
381 new BitCastInst(Inst->getOperand(1), SBPTy, "SBJmpBuf", Inst);
383 GetSetJmpMap(Func), BufPtr,
384 ConstantInt::get(Type::getInt32Ty(Inst->getContext()), SetJmpIDMap[Func]++)
386 CallInst::Create(AddSJToMap, Args, Args + 3, "", Inst);
388 // We are guaranteed that there are no values live across basic blocks
389 // (because we are "not in SSA form" yet), but there can still be values live
390 // in basic blocks. Because of this, splitting the setjmp block can cause
391 // values above the setjmp to not dominate uses which are after the setjmp
392 // call. For all of these occasions, we must spill the value to the stack.
394 std::set<Instruction*> InstrsAfterCall;
396 // The call is probably very close to the end of the basic block, for the
397 // common usage pattern of: 'if (setjmp(...))', so keep track of the
398 // instructions after the call.
399 for (BasicBlock::iterator I = ++BasicBlock::iterator(Inst), E = ABlock->end();
401 InstrsAfterCall.insert(I);
403 for (BasicBlock::iterator II = ABlock->begin();
404 II != BasicBlock::iterator(Inst); ++II)
405 // Loop over all of the uses of instruction. If any of them are after the
406 // call, "spill" the value to the stack.
407 for (Value::use_iterator UI = II->use_begin(), E = II->use_end();
409 if (cast<Instruction>(*UI)->getParent() != ABlock ||
410 InstrsAfterCall.count(cast<Instruction>(*UI))) {
411 DemoteRegToStack(*II);
414 InstrsAfterCall.clear();
416 // Change the setjmp call into a branch statement. We'll remove the
417 // setjmp call in a little bit. No worries.
418 BasicBlock* SetJmpContBlock = ABlock->splitBasicBlock(Inst);
419 assert(SetJmpContBlock && "Couldn't split setjmp BB!!");
421 SetJmpContBlock->setName(ABlock->getName()+"SetJmpCont");
423 // Add the SetJmpContBlock to the set of blocks reachable from a setjmp.
424 DFSBlocks.insert(SetJmpContBlock);
426 // This PHI node will be in the new block created from the
427 // splitBasicBlock call.
428 PHINode* PHI = PHINode::Create(Type::getInt32Ty(Inst->getContext()),
429 "SetJmpReturn", Inst);
431 // Coming from a call to setjmp, the return is 0.
432 PHI->addIncoming(Constant::getNullValue(Type::getInt32Ty(Inst->getContext())),
435 // Add the case for this setjmp's number...
436 SwitchValuePair SVP = GetSJSwitch(Func, GetRethrowBB(Func));
437 SVP.first->addCase(ConstantInt::get(Type::getInt32Ty(Inst->getContext()),
438 SetJmpIDMap[Func] - 1),
441 // Value coming from the handling of the exception.
442 PHI->addIncoming(SVP.second, SVP.second->getParent());
444 // Replace all uses of this instruction with the PHI node created by
445 // the eradication of setjmp.
446 Inst->replaceAllUsesWith(PHI);
447 Inst->eraseFromParent();
449 ++SetJmpsTransformed;
452 // visitCallInst - This converts all LLVM call instructions into invoke
453 // instructions. The except part of the invoke goes to the "LongJmpBlkPre"
454 // that grabs the exception and proceeds to determine if it's a longjmp
456 void LowerSetJmp::visitCallInst(CallInst& CI)
458 if (CI.getCalledFunction())
459 if (!IsTransformableFunction(CI.getCalledFunction()->getName()) ||
460 CI.getCalledFunction()->isIntrinsic()) return;
462 BasicBlock* OldBB = CI.getParent();
464 // If not reachable from a setjmp call, don't transform.
465 if (!DFSBlocks.count(OldBB)) return;
467 BasicBlock* NewBB = OldBB->splitBasicBlock(CI);
468 assert(NewBB && "Couldn't split BB of \"call\" instruction!!");
469 DFSBlocks.insert(NewBB);
470 NewBB->setName("Call2Invoke");
472 Function* Func = OldBB->getParent();
474 // Construct the new "invoke" instruction.
475 TerminatorInst* Term = OldBB->getTerminator();
476 std::vector<Value*> Params(CI.op_begin() + 1, CI.op_end());
478 InvokeInst::Create(CI.getCalledValue(), NewBB, PrelimBBMap[Func],
479 Params.begin(), Params.end(), CI.getName(), Term);
480 II->setCallingConv(CI.getCallingConv());
481 II->setAttributes(CI.getAttributes());
483 // Replace the old call inst with the invoke inst and remove the call.
484 CI.replaceAllUsesWith(II);
485 CI.eraseFromParent();
487 // The old terminator is useless now that we have the invoke inst.
488 Term->eraseFromParent();
492 // visitInvokeInst - Converting the "invoke" instruction is fairly
493 // straight-forward. The old exception part is replaced by a query asking
494 // if this is a longjmp exception. If it is, then it goes to the longjmp
495 // exception blocks. Otherwise, control is passed the old exception.
496 void LowerSetJmp::visitInvokeInst(InvokeInst& II)
498 if (II.getCalledFunction())
499 if (!IsTransformableFunction(II.getCalledFunction()->getName()) ||
500 II.getCalledFunction()->isIntrinsic()) return;
502 BasicBlock* BB = II.getParent();
504 // If not reachable from a setjmp call, don't transform.
505 if (!DFSBlocks.count(BB)) return;
507 BasicBlock* ExceptBB = II.getUnwindDest();
509 Function* Func = BB->getParent();
510 BasicBlock* NewExceptBB = BasicBlock::Create(II.getContext(),
511 "InvokeExcept", Func);
513 // If this is a longjmp exception, then branch to the preliminary BB of
514 // the longjmp exception handling. Otherwise, go to the old exception.
515 CallInst* IsLJExcept = CallInst::Create(IsLJException, "IsLJExcept",
518 BranchInst::Create(PrelimBBMap[Func], ExceptBB, IsLJExcept, NewExceptBB);
520 II.setUnwindDest(NewExceptBB);
521 ++InvokesTransformed;
524 // visitReturnInst - We want to destroy the setjmp map upon exit from the
526 void LowerSetJmp::visitReturnInst(ReturnInst &RI) {
527 Function* Func = RI.getParent()->getParent();
528 CallInst::Create(DestroySJMap, GetSetJmpMap(Func), "", &RI);
531 // visitUnwindInst - We want to destroy the setjmp map upon exit from the
533 void LowerSetJmp::visitUnwindInst(UnwindInst &UI) {
534 Function* Func = UI.getParent()->getParent();
535 CallInst::Create(DestroySJMap, GetSetJmpMap(Func), "", &UI);
538 ModulePass *llvm::createLowerSetJmpPass() {
539 return new LowerSetJmp();