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 VISIBILITY_HIDDEN LowerSetJmp : public ModulePass,
66 public InstVisitor<LowerSetJmp> {
67 // LLVM library functions...
68 Constant *InitSJMap; // __llvm_sjljeh_init_setjmpmap
69 Constant *DestroySJMap; // __llvm_sjljeh_destroy_setjmpmap
70 Constant *AddSJToMap; // __llvm_sjljeh_add_setjmp_to_map
71 Constant *ThrowLongJmp; // __llvm_sjljeh_throw_longjmp
72 Constant *TryCatchLJ; // __llvm_sjljeh_try_catching_longjmp_exception
73 Constant *IsLJException; // __llvm_sjljeh_is_longjmp_exception
74 Constant *GetLJValue; // __llvm_sjljeh_get_longjmp_value
76 typedef std::pair<SwitchInst*, CallInst*> SwitchValuePair;
78 // Keep track of those basic blocks reachable via a depth-first search of
79 // the CFG from a setjmp call. We only need to transform those "call" and
80 // "invoke" instructions that are reachable from the setjmp call site.
81 std::set<BasicBlock*> DFSBlocks;
83 // The setjmp map is going to hold information about which setjmps
84 // were called (each setjmp gets its own number) and with which
85 // buffer it was called.
86 std::map<Function*, AllocaInst*> SJMap;
88 // The rethrow basic block map holds the basic block to branch to if
89 // the exception isn't handled in the current function and needs to
91 std::map<const Function*, BasicBlock*> RethrowBBMap;
93 // The preliminary basic block map holds a basic block that grabs the
94 // exception and determines if it's handled by the current function.
95 std::map<const Function*, BasicBlock*> PrelimBBMap;
97 // The switch/value map holds a switch inst/call inst pair. The
98 // switch inst controls which handler (if any) gets called and the
99 // value is the value returned to that handler by the call to
100 // __llvm_sjljeh_get_longjmp_value.
101 std::map<const Function*, SwitchValuePair> SwitchValMap;
103 // A map of which setjmps we've seen so far in a function.
104 std::map<const Function*, unsigned> SetJmpIDMap;
106 AllocaInst* GetSetJmpMap(Function* Func);
107 BasicBlock* GetRethrowBB(Function* Func);
108 SwitchValuePair GetSJSwitch(Function* Func, BasicBlock* Rethrow);
110 void TransformLongJmpCall(CallInst* Inst);
111 void TransformSetJmpCall(CallInst* Inst);
113 bool IsTransformableFunction(const std::string& Name);
115 static char ID; // Pass identification, replacement for typeid
116 LowerSetJmp() : ModulePass(&ID) {}
118 void visitCallInst(CallInst& CI);
119 void visitInvokeInst(InvokeInst& II);
120 void visitReturnInst(ReturnInst& RI);
121 void visitUnwindInst(UnwindInst& UI);
123 bool runOnModule(Module& M);
124 bool doInitialization(Module& M);
126 } // end anonymous namespace
128 char LowerSetJmp::ID = 0;
129 static RegisterPass<LowerSetJmp> X("lowersetjmp", "Lower Set Jump");
131 // run - Run the transformation on the program. We grab the function
132 // prototypes for longjmp and setjmp. If they are used in the program,
133 // then we can go directly to the places they're at and transform them.
134 bool LowerSetJmp::runOnModule(Module& M) {
135 bool Changed = false;
137 Context = &M.getContext();
139 // These are what the functions are called.
140 Function* SetJmp = M.getFunction("llvm.setjmp");
141 Function* LongJmp = M.getFunction("llvm.longjmp");
143 // This program doesn't have longjmp and setjmp calls.
144 if ((!LongJmp || LongJmp->use_empty()) &&
145 (!SetJmp || SetJmp->use_empty())) return false;
147 // Initialize some values and functions we'll need to transform the
148 // setjmp/longjmp functions.
152 for (Value::use_iterator B = SetJmp->use_begin(), E = SetJmp->use_end();
154 BasicBlock* BB = cast<Instruction>(*B)->getParent();
155 for (df_ext_iterator<BasicBlock*> I = df_ext_begin(BB, DFSBlocks),
156 E = df_ext_end(BB, DFSBlocks); I != E; ++I)
160 while (!SetJmp->use_empty()) {
161 assert(isa<CallInst>(SetJmp->use_back()) &&
162 "User of setjmp intrinsic not a call?");
163 TransformSetJmpCall(cast<CallInst>(SetJmp->use_back()));
169 while (!LongJmp->use_empty()) {
170 assert(isa<CallInst>(LongJmp->use_back()) &&
171 "User of longjmp intrinsic not a call?");
172 TransformLongJmpCall(cast<CallInst>(LongJmp->use_back()));
176 // Now go through the affected functions and convert calls and invokes
178 for (std::map<Function*, AllocaInst*>::iterator
179 B = SJMap.begin(), E = SJMap.end(); B != E; ++B) {
180 Function* F = B->first;
181 for (Function::iterator BB = F->begin(), BE = F->end(); BB != BE; ++BB)
182 for (BasicBlock::iterator IB = BB->begin(), IE = BB->end(); IB != IE; ) {
184 if (IB != BB->end() && IB->getParent() != BB)
185 break; // The next instruction got moved to a different block!
191 RethrowBBMap.clear();
193 SwitchValMap.clear();
199 // doInitialization - For the lower long/setjmp pass, this ensures that a
200 // module contains a declaration for the intrisic functions we are going
201 // to call to convert longjmp and setjmp calls.
203 // This function is always successful, unless it isn't.
204 bool LowerSetJmp::doInitialization(Module& M)
206 const Type *SBPTy = Context->getPointerTypeUnqual(Type::Int8Ty);
207 const Type *SBPPTy = Context->getPointerTypeUnqual(SBPTy);
209 // N.B. See llvm/runtime/GCCLibraries/libexception/SJLJ-Exception.h for
210 // a description of the following library functions.
212 // void __llvm_sjljeh_init_setjmpmap(void**)
213 InitSJMap = M.getOrInsertFunction("__llvm_sjljeh_init_setjmpmap",
214 Type::VoidTy, SBPPTy, (Type *)0);
215 // void __llvm_sjljeh_destroy_setjmpmap(void**)
216 DestroySJMap = M.getOrInsertFunction("__llvm_sjljeh_destroy_setjmpmap",
217 Type::VoidTy, SBPPTy, (Type *)0);
219 // void __llvm_sjljeh_add_setjmp_to_map(void**, void*, unsigned)
220 AddSJToMap = M.getOrInsertFunction("__llvm_sjljeh_add_setjmp_to_map",
221 Type::VoidTy, SBPPTy, SBPTy,
222 Type::Int32Ty, (Type *)0);
224 // void __llvm_sjljeh_throw_longjmp(int*, int)
225 ThrowLongJmp = M.getOrInsertFunction("__llvm_sjljeh_throw_longjmp",
226 Type::VoidTy, SBPTy, Type::Int32Ty,
229 // unsigned __llvm_sjljeh_try_catching_longjmp_exception(void **)
231 M.getOrInsertFunction("__llvm_sjljeh_try_catching_longjmp_exception",
232 Type::Int32Ty, SBPPTy, (Type *)0);
234 // bool __llvm_sjljeh_is_longjmp_exception()
235 IsLJException = M.getOrInsertFunction("__llvm_sjljeh_is_longjmp_exception",
236 Type::Int1Ty, (Type *)0);
238 // int __llvm_sjljeh_get_longjmp_value()
239 GetLJValue = M.getOrInsertFunction("__llvm_sjljeh_get_longjmp_value",
240 Type::Int32Ty, (Type *)0);
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(const std::string& Name) {
250 std::string SJLJEh("__llvm_sjljeh");
252 if (Name.size() > SJLJEh.size())
253 return std::string(Name.begin(), Name.begin() + SJLJEh.size()) != SJLJEh;
258 // TransformLongJmpCall - Transform a longjmp call into a call to the
259 // internal __llvm_sjljeh_throw_longjmp function. It then takes care of
260 // throwing the exception for us.
261 void LowerSetJmp::TransformLongJmpCall(CallInst* Inst)
263 const Type* SBPTy = Context->getPointerTypeUnqual(Type::Int8Ty);
265 // Create the call to "__llvm_sjljeh_throw_longjmp". This takes the
266 // same parameters as "longjmp", except that the buffer is cast to a
267 // char*. It returns "void", so it doesn't need to replace any of
268 // Inst's uses and doesn't get a name.
270 new BitCastInst(Inst->getOperand(1), SBPTy, "LJBuf", Inst);
271 SmallVector<Value *, 2> Args;
273 Args.push_back(Inst->getOperand(2));
274 CallInst::Create(ThrowLongJmp, Args.begin(), Args.end(), "", Inst);
276 SwitchValuePair& SVP = SwitchValMap[Inst->getParent()->getParent()];
278 // If the function has a setjmp call in it (they are transformed first)
279 // we should branch to the basic block that determines if this longjmp
280 // is applicable here. Otherwise, issue an unwind.
282 BranchInst::Create(SVP.first->getParent(), Inst);
284 new UnwindInst(Inst);
286 // Remove all insts after the branch/unwind inst. Go from back to front to
287 // avoid replaceAllUsesWith if possible.
288 BasicBlock *BB = Inst->getParent();
289 Instruction *Removed;
291 Removed = &BB->back();
292 // If the removed instructions have any users, replace them now.
293 if (!Removed->use_empty())
294 Removed->replaceAllUsesWith(Context->getUndef(Removed->getType()));
295 Removed->eraseFromParent();
296 } while (Removed != Inst);
298 ++LongJmpsTransformed;
301 // GetSetJmpMap - Retrieve (create and initialize, if necessary) the
302 // setjmp map. This map is going to hold information about which setjmps
303 // were called (each setjmp gets its own number) and with which buffer it
304 // was called. There can be only one!
305 AllocaInst* LowerSetJmp::GetSetJmpMap(Function* Func)
307 if (SJMap[Func]) return SJMap[Func];
309 // Insert the setjmp map initialization before the first instruction in
311 Instruction* Inst = Func->getEntryBlock().begin();
312 assert(Inst && "Couldn't find even ONE instruction in entry block!");
314 // Fill in the alloca and call to initialize the SJ map.
315 const Type *SBPTy = Context->getPointerTypeUnqual(Type::Int8Ty);
316 AllocaInst* Map = new AllocaInst(SBPTy, 0, "SJMap", Inst);
317 CallInst::Create(InitSJMap, Map, "", Inst);
318 return SJMap[Func] = Map;
321 // GetRethrowBB - Only one rethrow basic block is needed per function.
322 // If this is a longjmp exception but not handled in this block, this BB
323 // performs the rethrow.
324 BasicBlock* LowerSetJmp::GetRethrowBB(Function* Func)
326 if (RethrowBBMap[Func]) return RethrowBBMap[Func];
328 // The basic block we're going to jump to if we need to rethrow the
330 BasicBlock* Rethrow = BasicBlock::Create("RethrowExcept", Func);
332 // Fill in the "Rethrow" BB with a call to rethrow the exception. This
333 // is the last instruction in the BB since at this point the runtime
334 // should exit this function and go to the next function.
335 new UnwindInst(Rethrow);
336 return RethrowBBMap[Func] = Rethrow;
339 // GetSJSwitch - Return the switch statement that controls which handler
340 // (if any) gets called and the value returned to that handler.
341 LowerSetJmp::SwitchValuePair LowerSetJmp::GetSJSwitch(Function* Func,
344 if (SwitchValMap[Func].first) return SwitchValMap[Func];
346 BasicBlock* LongJmpPre = BasicBlock::Create("LongJmpBlkPre", Func);
348 // Keep track of the preliminary basic block for some of the other
350 PrelimBBMap[Func] = LongJmpPre;
352 // Grab the exception.
353 CallInst* Cond = CallInst::Create(IsLJException, "IsLJExcept", LongJmpPre);
355 // The "decision basic block" gets the number associated with the
356 // setjmp call returning to switch on and the value returned by
358 BasicBlock* DecisionBB = BasicBlock::Create("LJDecisionBB", Func);
360 BranchInst::Create(DecisionBB, Rethrow, Cond, LongJmpPre);
362 // Fill in the "decision" basic block.
363 CallInst* LJVal = CallInst::Create(GetLJValue, "LJVal", DecisionBB);
364 CallInst* SJNum = CallInst::Create(TryCatchLJ, GetSetJmpMap(Func), "SJNum",
367 SwitchInst* SI = SwitchInst::Create(SJNum, Rethrow, 0, DecisionBB);
368 return SwitchValMap[Func] = SwitchValuePair(SI, LJVal);
371 // TransformSetJmpCall - The setjmp call is a bit trickier to transform.
372 // We're going to convert all setjmp calls to nops. Then all "call" and
373 // "invoke" instructions in the function are converted to "invoke" where
374 // the "except" branch is used when returning from a longjmp call.
375 void LowerSetJmp::TransformSetJmpCall(CallInst* Inst)
377 BasicBlock* ABlock = Inst->getParent();
378 Function* Func = ABlock->getParent();
380 // Add this setjmp to the setjmp map.
381 const Type* SBPTy = Context->getPointerTypeUnqual(Type::Int8Ty);
383 new BitCastInst(Inst->getOperand(1), SBPTy, "SBJmpBuf", Inst);
384 std::vector<Value*> Args =
385 make_vector<Value*>(GetSetJmpMap(Func), BufPtr,
386 Context->getConstantInt(Type::Int32Ty,
387 SetJmpIDMap[Func]++), 0);
388 CallInst::Create(AddSJToMap, Args.begin(), Args.end(), "", Inst);
390 // We are guaranteed that there are no values live across basic blocks
391 // (because we are "not in SSA form" yet), but there can still be values live
392 // in basic blocks. Because of this, splitting the setjmp block can cause
393 // values above the setjmp to not dominate uses which are after the setjmp
394 // call. For all of these occasions, we must spill the value to the stack.
396 std::set<Instruction*> InstrsAfterCall;
398 // The call is probably very close to the end of the basic block, for the
399 // common usage pattern of: 'if (setjmp(...))', so keep track of the
400 // instructions after the call.
401 for (BasicBlock::iterator I = ++BasicBlock::iterator(Inst), E = ABlock->end();
403 InstrsAfterCall.insert(I);
405 for (BasicBlock::iterator II = ABlock->begin();
406 II != BasicBlock::iterator(Inst); ++II)
407 // Loop over all of the uses of instruction. If any of them are after the
408 // call, "spill" the value to the stack.
409 for (Value::use_iterator UI = II->use_begin(), E = II->use_end();
411 if (cast<Instruction>(*UI)->getParent() != ABlock ||
412 InstrsAfterCall.count(cast<Instruction>(*UI))) {
413 DemoteRegToStack(*II);
416 InstrsAfterCall.clear();
418 // Change the setjmp call into a branch statement. We'll remove the
419 // setjmp call in a little bit. No worries.
420 BasicBlock* SetJmpContBlock = ABlock->splitBasicBlock(Inst);
421 assert(SetJmpContBlock && "Couldn't split setjmp BB!!");
423 SetJmpContBlock->setName(ABlock->getName()+"SetJmpCont");
425 // Add the SetJmpContBlock to the set of blocks reachable from a setjmp.
426 DFSBlocks.insert(SetJmpContBlock);
428 // This PHI node will be in the new block created from the
429 // splitBasicBlock call.
430 PHINode* PHI = PHINode::Create(Type::Int32Ty, "SetJmpReturn", Inst);
432 // Coming from a call to setjmp, the return is 0.
433 PHI->addIncoming(Context->getNullValue(Type::Int32Ty), ABlock);
435 // Add the case for this setjmp's number...
436 SwitchValuePair SVP = GetSJSwitch(Func, GetRethrowBB(Func));
437 SVP.first->addCase(Context->getConstantInt(Type::Int32Ty,
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("InvokeExcept", Func);
512 // If this is a longjmp exception, then branch to the preliminary BB of
513 // the longjmp exception handling. Otherwise, go to the old exception.
514 CallInst* IsLJExcept = CallInst::Create(IsLJException, "IsLJExcept",
517 BranchInst::Create(PrelimBBMap[Func], ExceptBB, IsLJExcept, NewExceptBB);
519 II.setUnwindDest(NewExceptBB);
520 ++InvokesTransformed;
523 // visitReturnInst - We want to destroy the setjmp map upon exit from the
525 void LowerSetJmp::visitReturnInst(ReturnInst &RI) {
526 Function* Func = RI.getParent()->getParent();
527 CallInst::Create(DestroySJMap, GetSetJmpMap(Func), "", &RI);
530 // visitUnwindInst - We want to destroy the setjmp map upon exit from the
532 void LowerSetJmp::visitUnwindInst(UnwindInst &UI) {
533 Function* Func = UI.getParent()->getParent();
534 CallInst::Create(DestroySJMap, GetSetJmpMap(Func), "", &UI);
537 ModulePass *llvm::createLowerSetJmpPass() {
538 return new LowerSetJmp();