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/Compiler.h"
47 #include "llvm/Support/InstVisitor.h"
48 #include "llvm/Transforms/Utils/Local.h"
49 #include "llvm/ADT/DepthFirstIterator.h"
50 #include "llvm/ADT/Statistic.h"
51 #include "llvm/ADT/StringExtras.h"
52 #include "llvm/ADT/VectorExtras.h"
53 #include "llvm/ADT/SmallVector.h"
57 STATISTIC(LongJmpsTransformed, "Number of longjmps transformed");
58 STATISTIC(SetJmpsTransformed , "Number of setjmps transformed");
59 STATISTIC(CallsTransformed , "Number of calls invokified");
60 STATISTIC(InvokesTransformed , "Number of invokes modified");
63 //===--------------------------------------------------------------------===//
64 // LowerSetJmp pass implementation.
65 class LowerSetJmp : public ModulePass, public InstVisitor<LowerSetJmp> {
66 // LLVM library functions...
67 Constant *InitSJMap; // __llvm_sjljeh_init_setjmpmap
68 Constant *DestroySJMap; // __llvm_sjljeh_destroy_setjmpmap
69 Constant *AddSJToMap; // __llvm_sjljeh_add_setjmp_to_map
70 Constant *ThrowLongJmp; // __llvm_sjljeh_throw_longjmp
71 Constant *TryCatchLJ; // __llvm_sjljeh_try_catching_longjmp_exception
72 Constant *IsLJException; // __llvm_sjljeh_is_longjmp_exception
73 Constant *GetLJValue; // __llvm_sjljeh_get_longjmp_value
75 typedef std::pair<SwitchInst*, CallInst*> SwitchValuePair;
77 // Keep track of those basic blocks reachable via a depth-first search of
78 // the CFG from a setjmp call. We only need to transform those "call" and
79 // "invoke" instructions that are reachable from the setjmp call site.
80 std::set<BasicBlock*> DFSBlocks;
82 // The setjmp map is going to hold information about which setjmps
83 // were called (each setjmp gets its own number) and with which
84 // buffer it was called.
85 std::map<Function*, AllocaInst*> SJMap;
87 // The rethrow basic block map holds the basic block to branch to if
88 // the exception isn't handled in the current function and needs to
90 std::map<const Function*, BasicBlock*> RethrowBBMap;
92 // The preliminary basic block map holds a basic block that grabs the
93 // exception and determines if it's handled by the current function.
94 std::map<const Function*, BasicBlock*> PrelimBBMap;
96 // The switch/value map holds a switch inst/call inst pair. The
97 // switch inst controls which handler (if any) gets called and the
98 // value is the value returned to that handler by the call to
99 // __llvm_sjljeh_get_longjmp_value.
100 std::map<const Function*, SwitchValuePair> SwitchValMap;
102 // A map of which setjmps we've seen so far in a function.
103 std::map<const Function*, unsigned> SetJmpIDMap;
105 AllocaInst* GetSetJmpMap(Function* Func);
106 BasicBlock* GetRethrowBB(Function* Func);
107 SwitchValuePair GetSJSwitch(Function* Func, BasicBlock* Rethrow);
109 void TransformLongJmpCall(CallInst* Inst);
110 void TransformSetJmpCall(CallInst* Inst);
112 bool IsTransformableFunction(const std::string& Name);
114 static char ID; // Pass identification, replacement for typeid
115 LowerSetJmp() : ModulePass(&ID) {}
117 void visitCallInst(CallInst& CI);
118 void visitInvokeInst(InvokeInst& II);
119 void visitReturnInst(ReturnInst& RI);
120 void visitUnwindInst(UnwindInst& UI);
122 bool runOnModule(Module& M);
123 bool doInitialization(Module& M);
125 } // end anonymous namespace
127 char LowerSetJmp::ID = 0;
128 static RegisterPass<LowerSetJmp> X("lowersetjmp", "Lower Set Jump");
130 // run - Run the transformation on the program. We grab the function
131 // prototypes for longjmp and setjmp. If they are used in the program,
132 // then we can go directly to the places they're at and transform them.
133 bool LowerSetJmp::runOnModule(Module& M) {
134 bool Changed = false;
136 // These are what the functions are called.
137 Function* SetJmp = M.getFunction("llvm.setjmp");
138 Function* LongJmp = M.getFunction("llvm.longjmp");
140 // This program doesn't have longjmp and setjmp calls.
141 if ((!LongJmp || LongJmp->use_empty()) &&
142 (!SetJmp || SetJmp->use_empty())) return false;
144 // Initialize some values and functions we'll need to transform the
145 // setjmp/longjmp functions.
149 for (Value::use_iterator B = SetJmp->use_begin(), E = SetJmp->use_end();
151 BasicBlock* BB = cast<Instruction>(*B)->getParent();
152 for (df_ext_iterator<BasicBlock*> I = df_ext_begin(BB, DFSBlocks),
153 E = df_ext_end(BB, DFSBlocks); I != E; ++I)
157 while (!SetJmp->use_empty()) {
158 assert(isa<CallInst>(SetJmp->use_back()) &&
159 "User of setjmp intrinsic not a call?");
160 TransformSetJmpCall(cast<CallInst>(SetJmp->use_back()));
166 while (!LongJmp->use_empty()) {
167 assert(isa<CallInst>(LongJmp->use_back()) &&
168 "User of longjmp intrinsic not a call?");
169 TransformLongJmpCall(cast<CallInst>(LongJmp->use_back()));
173 // Now go through the affected functions and convert calls and invokes
175 for (std::map<Function*, AllocaInst*>::iterator
176 B = SJMap.begin(), E = SJMap.end(); B != E; ++B) {
177 Function* F = B->first;
178 for (Function::iterator BB = F->begin(), BE = F->end(); BB != BE; ++BB)
179 for (BasicBlock::iterator IB = BB->begin(), IE = BB->end(); IB != IE; ) {
181 if (IB != BB->end() && IB->getParent() != BB)
182 break; // The next instruction got moved to a different block!
188 RethrowBBMap.clear();
190 SwitchValMap.clear();
196 // doInitialization - For the lower long/setjmp pass, this ensures that a
197 // module contains a declaration for the intrisic functions we are going
198 // to call to convert longjmp and setjmp calls.
200 // This function is always successful, unless it isn't.
201 bool LowerSetJmp::doInitialization(Module& M)
203 const Type *SBPTy = Type::getInt8PtrTy(M.getContext());
204 const Type *SBPPTy = PointerType::getUnqual(SBPTy);
206 // N.B. See llvm/runtime/GCCLibraries/libexception/SJLJ-Exception.h for
207 // a description of the following library functions.
209 // void __llvm_sjljeh_init_setjmpmap(void**)
210 InitSJMap = M.getOrInsertFunction("__llvm_sjljeh_init_setjmpmap",
211 Type::getVoidTy(M.getContext()),
213 // void __llvm_sjljeh_destroy_setjmpmap(void**)
214 DestroySJMap = M.getOrInsertFunction("__llvm_sjljeh_destroy_setjmpmap",
215 Type::getVoidTy(M.getContext()),
218 // void __llvm_sjljeh_add_setjmp_to_map(void**, void*, unsigned)
219 AddSJToMap = M.getOrInsertFunction("__llvm_sjljeh_add_setjmp_to_map",
220 Type::getVoidTy(M.getContext()),
222 Type::getInt32Ty(M.getContext()),
225 // void __llvm_sjljeh_throw_longjmp(int*, int)
226 ThrowLongJmp = M.getOrInsertFunction("__llvm_sjljeh_throw_longjmp",
227 Type::getVoidTy(M.getContext()), SBPTy,
228 Type::getInt32Ty(M.getContext()),
231 // unsigned __llvm_sjljeh_try_catching_longjmp_exception(void **)
233 M.getOrInsertFunction("__llvm_sjljeh_try_catching_longjmp_exception",
234 Type::getInt32Ty(M.getContext()), SBPPTy, (Type *)0);
236 // bool __llvm_sjljeh_is_longjmp_exception()
237 IsLJException = M.getOrInsertFunction("__llvm_sjljeh_is_longjmp_exception",
238 Type::getInt1Ty(M.getContext()),
241 // int __llvm_sjljeh_get_longjmp_value()
242 GetLJValue = M.getOrInsertFunction("__llvm_sjljeh_get_longjmp_value",
243 Type::getInt32Ty(M.getContext()),
248 // IsTransformableFunction - Return true if the function name isn't one
249 // of the ones we don't want transformed. Currently, don't transform any
250 // "llvm.{setjmp,longjmp}" functions and none of the setjmp/longjmp error
251 // handling functions (beginning with __llvm_sjljeh_...they don't throw
253 bool LowerSetJmp::IsTransformableFunction(const std::string& Name) {
254 std::string SJLJEh("__llvm_sjljeh");
256 if (Name.size() > SJLJEh.size())
257 return std::string(Name.begin(), Name.begin() + SJLJEh.size()) != SJLJEh;
262 // TransformLongJmpCall - Transform a longjmp call into a call to the
263 // internal __llvm_sjljeh_throw_longjmp function. It then takes care of
264 // throwing the exception for us.
265 void LowerSetJmp::TransformLongJmpCall(CallInst* Inst)
268 Type::getInt8PtrTy(Inst->getContext());
270 // Create the call to "__llvm_sjljeh_throw_longjmp". This takes the
271 // same parameters as "longjmp", except that the buffer is cast to a
272 // char*. It returns "void", so it doesn't need to replace any of
273 // Inst's uses and doesn't get a name.
275 new BitCastInst(Inst->getOperand(1), SBPTy, "LJBuf", Inst);
276 SmallVector<Value *, 2> Args;
278 Args.push_back(Inst->getOperand(2));
279 CallInst::Create(ThrowLongJmp, Args.begin(), Args.end(), "", Inst);
281 SwitchValuePair& SVP = SwitchValMap[Inst->getParent()->getParent()];
283 // If the function has a setjmp call in it (they are transformed first)
284 // we should branch to the basic block that determines if this longjmp
285 // is applicable here. Otherwise, issue an unwind.
287 BranchInst::Create(SVP.first->getParent(), Inst);
289 new UnwindInst(Inst->getContext(), Inst);
291 // Remove all insts after the branch/unwind inst. Go from back to front to
292 // avoid replaceAllUsesWith if possible.
293 BasicBlock *BB = Inst->getParent();
294 Instruction *Removed;
296 Removed = &BB->back();
297 // If the removed instructions have any users, replace them now.
298 if (!Removed->use_empty())
299 Removed->replaceAllUsesWith(UndefValue::get(Removed->getType()));
300 Removed->eraseFromParent();
301 } while (Removed != Inst);
303 ++LongJmpsTransformed;
306 // GetSetJmpMap - Retrieve (create and initialize, if necessary) the
307 // setjmp map. This map is going to hold information about which setjmps
308 // were called (each setjmp gets its own number) and with which buffer it
309 // was called. There can be only one!
310 AllocaInst* LowerSetJmp::GetSetJmpMap(Function* Func)
312 if (SJMap[Func]) return SJMap[Func];
314 // Insert the setjmp map initialization before the first instruction in
316 Instruction* Inst = Func->getEntryBlock().begin();
317 assert(Inst && "Couldn't find even ONE instruction in entry block!");
319 // Fill in the alloca and call to initialize the SJ map.
321 Type::getInt8PtrTy(Func->getContext());
322 AllocaInst* Map = new AllocaInst(SBPTy, 0, "SJMap", Inst);
323 CallInst::Create(InitSJMap, Map, "", Inst);
324 return SJMap[Func] = Map;
327 // GetRethrowBB - Only one rethrow basic block is needed per function.
328 // If this is a longjmp exception but not handled in this block, this BB
329 // performs the rethrow.
330 BasicBlock* LowerSetJmp::GetRethrowBB(Function* Func)
332 if (RethrowBBMap[Func]) return RethrowBBMap[Func];
334 // The basic block we're going to jump to if we need to rethrow the
336 BasicBlock* Rethrow =
337 BasicBlock::Create(Func->getContext(), "RethrowExcept", Func);
339 // Fill in the "Rethrow" BB with a call to rethrow the exception. This
340 // is the last instruction in the BB since at this point the runtime
341 // should exit this function and go to the next function.
342 new UnwindInst(Func->getContext(), Rethrow);
343 return RethrowBBMap[Func] = Rethrow;
346 // GetSJSwitch - Return the switch statement that controls which handler
347 // (if any) gets called and the value returned to that handler.
348 LowerSetJmp::SwitchValuePair LowerSetJmp::GetSJSwitch(Function* Func,
351 if (SwitchValMap[Func].first) return SwitchValMap[Func];
353 BasicBlock* LongJmpPre =
354 BasicBlock::Create(Func->getContext(), "LongJmpBlkPre", Func);
356 // Keep track of the preliminary basic block for some of the other
358 PrelimBBMap[Func] = LongJmpPre;
360 // Grab the exception.
361 CallInst* Cond = CallInst::Create(IsLJException, "IsLJExcept", LongJmpPre);
363 // The "decision basic block" gets the number associated with the
364 // setjmp call returning to switch on and the value returned by
366 BasicBlock* DecisionBB =
367 BasicBlock::Create(Func->getContext(), "LJDecisionBB", Func);
369 BranchInst::Create(DecisionBB, Rethrow, Cond, LongJmpPre);
371 // Fill in the "decision" basic block.
372 CallInst* LJVal = CallInst::Create(GetLJValue, "LJVal", DecisionBB);
373 CallInst* SJNum = CallInst::Create(TryCatchLJ, GetSetJmpMap(Func), "SJNum",
376 SwitchInst* SI = SwitchInst::Create(SJNum, Rethrow, 0, DecisionBB);
377 return SwitchValMap[Func] = SwitchValuePair(SI, LJVal);
380 // TransformSetJmpCall - The setjmp call is a bit trickier to transform.
381 // We're going to convert all setjmp calls to nops. Then all "call" and
382 // "invoke" instructions in the function are converted to "invoke" where
383 // the "except" branch is used when returning from a longjmp call.
384 void LowerSetJmp::TransformSetJmpCall(CallInst* Inst)
386 BasicBlock* ABlock = Inst->getParent();
387 Function* Func = ABlock->getParent();
389 // Add this setjmp to the setjmp map.
391 Type::getInt8PtrTy(Inst->getContext());
393 new BitCastInst(Inst->getOperand(1), SBPTy, "SBJmpBuf", Inst);
394 std::vector<Value*> Args =
395 make_vector<Value*>(GetSetJmpMap(Func), BufPtr,
396 ConstantInt::get(Type::getInt32Ty(Inst->getContext()),
397 SetJmpIDMap[Func]++), 0);
398 CallInst::Create(AddSJToMap, Args.begin(), Args.end(), "", Inst);
400 // We are guaranteed that there are no values live across basic blocks
401 // (because we are "not in SSA form" yet), but there can still be values live
402 // in basic blocks. Because of this, splitting the setjmp block can cause
403 // values above the setjmp to not dominate uses which are after the setjmp
404 // call. For all of these occasions, we must spill the value to the stack.
406 std::set<Instruction*> InstrsAfterCall;
408 // The call is probably very close to the end of the basic block, for the
409 // common usage pattern of: 'if (setjmp(...))', so keep track of the
410 // instructions after the call.
411 for (BasicBlock::iterator I = ++BasicBlock::iterator(Inst), E = ABlock->end();
413 InstrsAfterCall.insert(I);
415 for (BasicBlock::iterator II = ABlock->begin();
416 II != BasicBlock::iterator(Inst); ++II)
417 // Loop over all of the uses of instruction. If any of them are after the
418 // call, "spill" the value to the stack.
419 for (Value::use_iterator UI = II->use_begin(), E = II->use_end();
421 if (cast<Instruction>(*UI)->getParent() != ABlock ||
422 InstrsAfterCall.count(cast<Instruction>(*UI))) {
423 DemoteRegToStack(*II);
426 InstrsAfterCall.clear();
428 // Change the setjmp call into a branch statement. We'll remove the
429 // setjmp call in a little bit. No worries.
430 BasicBlock* SetJmpContBlock = ABlock->splitBasicBlock(Inst);
431 assert(SetJmpContBlock && "Couldn't split setjmp BB!!");
433 SetJmpContBlock->setName(ABlock->getName()+"SetJmpCont");
435 // Add the SetJmpContBlock to the set of blocks reachable from a setjmp.
436 DFSBlocks.insert(SetJmpContBlock);
438 // This PHI node will be in the new block created from the
439 // splitBasicBlock call.
440 PHINode* PHI = PHINode::Create(Type::getInt32Ty(Inst->getContext()),
441 "SetJmpReturn", Inst);
443 // Coming from a call to setjmp, the return is 0.
444 PHI->addIncoming(Constant::getNullValue(Type::getInt32Ty(Inst->getContext())),
447 // Add the case for this setjmp's number...
448 SwitchValuePair SVP = GetSJSwitch(Func, GetRethrowBB(Func));
449 SVP.first->addCase(ConstantInt::get(Type::getInt32Ty(Inst->getContext()),
450 SetJmpIDMap[Func] - 1),
453 // Value coming from the handling of the exception.
454 PHI->addIncoming(SVP.second, SVP.second->getParent());
456 // Replace all uses of this instruction with the PHI node created by
457 // the eradication of setjmp.
458 Inst->replaceAllUsesWith(PHI);
459 Inst->eraseFromParent();
461 ++SetJmpsTransformed;
464 // visitCallInst - This converts all LLVM call instructions into invoke
465 // instructions. The except part of the invoke goes to the "LongJmpBlkPre"
466 // that grabs the exception and proceeds to determine if it's a longjmp
468 void LowerSetJmp::visitCallInst(CallInst& CI)
470 if (CI.getCalledFunction())
471 if (!IsTransformableFunction(CI.getCalledFunction()->getName()) ||
472 CI.getCalledFunction()->isIntrinsic()) return;
474 BasicBlock* OldBB = CI.getParent();
476 // If not reachable from a setjmp call, don't transform.
477 if (!DFSBlocks.count(OldBB)) return;
479 BasicBlock* NewBB = OldBB->splitBasicBlock(CI);
480 assert(NewBB && "Couldn't split BB of \"call\" instruction!!");
481 DFSBlocks.insert(NewBB);
482 NewBB->setName("Call2Invoke");
484 Function* Func = OldBB->getParent();
486 // Construct the new "invoke" instruction.
487 TerminatorInst* Term = OldBB->getTerminator();
488 std::vector<Value*> Params(CI.op_begin() + 1, CI.op_end());
490 InvokeInst::Create(CI.getCalledValue(), NewBB, PrelimBBMap[Func],
491 Params.begin(), Params.end(), CI.getName(), Term);
492 II->setCallingConv(CI.getCallingConv());
493 II->setAttributes(CI.getAttributes());
495 // Replace the old call inst with the invoke inst and remove the call.
496 CI.replaceAllUsesWith(II);
497 CI.eraseFromParent();
499 // The old terminator is useless now that we have the invoke inst.
500 Term->eraseFromParent();
504 // visitInvokeInst - Converting the "invoke" instruction is fairly
505 // straight-forward. The old exception part is replaced by a query asking
506 // if this is a longjmp exception. If it is, then it goes to the longjmp
507 // exception blocks. Otherwise, control is passed the old exception.
508 void LowerSetJmp::visitInvokeInst(InvokeInst& II)
510 if (II.getCalledFunction())
511 if (!IsTransformableFunction(II.getCalledFunction()->getName()) ||
512 II.getCalledFunction()->isIntrinsic()) return;
514 BasicBlock* BB = II.getParent();
516 // If not reachable from a setjmp call, don't transform.
517 if (!DFSBlocks.count(BB)) return;
519 BasicBlock* ExceptBB = II.getUnwindDest();
521 Function* Func = BB->getParent();
522 BasicBlock* NewExceptBB = BasicBlock::Create(II.getContext(),
523 "InvokeExcept", Func);
525 // If this is a longjmp exception, then branch to the preliminary BB of
526 // the longjmp exception handling. Otherwise, go to the old exception.
527 CallInst* IsLJExcept = CallInst::Create(IsLJException, "IsLJExcept",
530 BranchInst::Create(PrelimBBMap[Func], ExceptBB, IsLJExcept, NewExceptBB);
532 II.setUnwindDest(NewExceptBB);
533 ++InvokesTransformed;
536 // visitReturnInst - We want to destroy the setjmp map upon exit from the
538 void LowerSetJmp::visitReturnInst(ReturnInst &RI) {
539 Function* Func = RI.getParent()->getParent();
540 CallInst::Create(DestroySJMap, GetSetJmpMap(Func), "", &RI);
543 // visitUnwindInst - We want to destroy the setjmp map upon exit from the
545 void LowerSetJmp::visitUnwindInst(UnwindInst &UI) {
546 Function* Func = UI.getParent()->getParent();
547 CallInst::Create(DestroySJMap, GetSetJmpMap(Func), "", &UI);
550 ModulePass *llvm::createLowerSetJmpPass() {
551 return new LowerSetJmp();