1 //===- LowerSetJmp.cpp - Code pertaining to lowering set/long jumps -------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source 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/Module.h"
43 #include "llvm/Pass.h"
44 #include "llvm/Support/CFG.h"
45 #include "llvm/Support/Compiler.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"
50 #include "llvm/ADT/StringExtras.h"
51 #include "llvm/ADT/VectorExtras.h"
52 #include "llvm/ADT/SmallVector.h"
55 STATISTIC(LongJmpsTransformed, "Number of longjmps transformed");
56 STATISTIC(SetJmpsTransformed , "Number of setjmps transformed");
57 STATISTIC(CallsTransformed , "Number of calls invokified");
58 STATISTIC(InvokesTransformed , "Number of invokes modified");
61 //===--------------------------------------------------------------------===//
62 // LowerSetJmp pass implementation.
63 class VISIBILITY_HIDDEN LowerSetJmp : public ModulePass,
64 public InstVisitor<LowerSetJmp> {
65 // LLVM library functions...
66 Constant *InitSJMap; // __llvm_sjljeh_init_setjmpmap
67 Constant *DestroySJMap; // __llvm_sjljeh_destroy_setjmpmap
68 Constant *AddSJToMap; // __llvm_sjljeh_add_setjmp_to_map
69 Constant *ThrowLongJmp; // __llvm_sjljeh_throw_longjmp
70 Constant *TryCatchLJ; // __llvm_sjljeh_try_catching_longjmp_exception
71 Constant *IsLJException; // __llvm_sjljeh_is_longjmp_exception
72 Constant *GetLJValue; // __llvm_sjljeh_get_longjmp_value
74 typedef std::pair<SwitchInst*, CallInst*> SwitchValuePair;
76 // Keep track of those basic blocks reachable via a depth-first search of
77 // the CFG from a setjmp call. We only need to transform those "call" and
78 // "invoke" instructions that are reachable from the setjmp call site.
79 std::set<BasicBlock*> DFSBlocks;
81 // The setjmp map is going to hold information about which setjmps
82 // were called (each setjmp gets its own number) and with which
83 // buffer it was called.
84 std::map<Function*, AllocaInst*> SJMap;
86 // The rethrow basic block map holds the basic block to branch to if
87 // the exception isn't handled in the current function and needs to
89 std::map<const Function*, BasicBlock*> RethrowBBMap;
91 // The preliminary basic block map holds a basic block that grabs the
92 // exception and determines if it's handled by the current function.
93 std::map<const Function*, BasicBlock*> PrelimBBMap;
95 // The switch/value map holds a switch inst/call inst pair. The
96 // switch inst controls which handler (if any) gets called and the
97 // value is the value returned to that handler by the call to
98 // __llvm_sjljeh_get_longjmp_value.
99 std::map<const Function*, SwitchValuePair> SwitchValMap;
101 // A map of which setjmps we've seen so far in a function.
102 std::map<const Function*, unsigned> SetJmpIDMap;
104 AllocaInst* GetSetJmpMap(Function* Func);
105 BasicBlock* GetRethrowBB(Function* Func);
106 SwitchValuePair GetSJSwitch(Function* Func, BasicBlock* Rethrow);
108 void TransformLongJmpCall(CallInst* Inst);
109 void TransformSetJmpCall(CallInst* Inst);
111 bool IsTransformableFunction(const std::string& Name);
113 static char ID; // Pass identification, replacement for typeid
114 LowerSetJmp() : ModulePass((intptr_t)&ID) {}
116 void visitCallInst(CallInst& CI);
117 void visitInvokeInst(InvokeInst& II);
118 void visitReturnInst(ReturnInst& RI);
119 void visitUnwindInst(UnwindInst& UI);
121 bool runOnModule(Module& M);
122 bool doInitialization(Module& M);
125 char LowerSetJmp::ID = 0;
126 RegisterPass<LowerSetJmp> X("lowersetjmp", "Lower Set Jump");
127 } // end anonymous namespace
129 // run - Run the transformation on the program. We grab the function
130 // prototypes for longjmp and setjmp. If they are used in the program,
131 // then we can go directly to the places they're at and transform them.
132 bool LowerSetJmp::runOnModule(Module& M) {
133 bool Changed = false;
135 // These are what the functions are called.
136 Function* SetJmp = M.getFunction("llvm.setjmp");
137 Function* LongJmp = M.getFunction("llvm.longjmp");
139 // This program doesn't have longjmp and setjmp calls.
140 if ((!LongJmp || LongJmp->use_empty()) &&
141 (!SetJmp || SetJmp->use_empty())) return false;
143 // Initialize some values and functions we'll need to transform the
144 // setjmp/longjmp functions.
148 for (Value::use_iterator B = SetJmp->use_begin(), E = SetJmp->use_end();
150 BasicBlock* BB = cast<Instruction>(*B)->getParent();
151 for (df_ext_iterator<BasicBlock*> I = df_ext_begin(BB, DFSBlocks),
152 E = df_ext_end(BB, DFSBlocks); I != E; ++I)
156 while (!SetJmp->use_empty()) {
157 assert(isa<CallInst>(SetJmp->use_back()) &&
158 "User of setjmp intrinsic not a call?");
159 TransformSetJmpCall(cast<CallInst>(SetJmp->use_back()));
165 while (!LongJmp->use_empty()) {
166 assert(isa<CallInst>(LongJmp->use_back()) &&
167 "User of longjmp intrinsic not a call?");
168 TransformLongJmpCall(cast<CallInst>(LongJmp->use_back()));
172 // Now go through the affected functions and convert calls and invokes
174 for (std::map<Function*, AllocaInst*>::iterator
175 B = SJMap.begin(), E = SJMap.end(); B != E; ++B) {
176 Function* F = B->first;
177 for (Function::iterator BB = F->begin(), BE = F->end(); BB != BE; ++BB)
178 for (BasicBlock::iterator IB = BB->begin(), IE = BB->end(); IB != IE; ) {
180 if (IB != BB->end() && IB->getParent() != BB)
181 break; // The next instruction got moved to a different block!
187 RethrowBBMap.clear();
189 SwitchValMap.clear();
195 // doInitialization - For the lower long/setjmp pass, this ensures that a
196 // module contains a declaration for the intrisic functions we are going
197 // to call to convert longjmp and setjmp calls.
199 // This function is always successful, unless it isn't.
200 bool LowerSetJmp::doInitialization(Module& M)
202 const Type *SBPTy = PointerType::get(Type::Int8Ty);
203 const Type *SBPPTy = PointerType::get(SBPTy);
205 // N.B. See llvm/runtime/GCCLibraries/libexception/SJLJ-Exception.h for
206 // a description of the following library functions.
208 // void __llvm_sjljeh_init_setjmpmap(void**)
209 InitSJMap = M.getOrInsertFunction("__llvm_sjljeh_init_setjmpmap",
210 Type::VoidTy, SBPPTy, (Type *)0);
211 // void __llvm_sjljeh_destroy_setjmpmap(void**)
212 DestroySJMap = M.getOrInsertFunction("__llvm_sjljeh_destroy_setjmpmap",
213 Type::VoidTy, SBPPTy, (Type *)0);
215 // void __llvm_sjljeh_add_setjmp_to_map(void**, void*, unsigned)
216 AddSJToMap = M.getOrInsertFunction("__llvm_sjljeh_add_setjmp_to_map",
217 Type::VoidTy, SBPPTy, SBPTy,
218 Type::Int32Ty, (Type *)0);
220 // void __llvm_sjljeh_throw_longjmp(int*, int)
221 ThrowLongJmp = M.getOrInsertFunction("__llvm_sjljeh_throw_longjmp",
222 Type::VoidTy, SBPTy, Type::Int32Ty,
225 // unsigned __llvm_sjljeh_try_catching_longjmp_exception(void **)
227 M.getOrInsertFunction("__llvm_sjljeh_try_catching_longjmp_exception",
228 Type::Int32Ty, SBPPTy, (Type *)0);
230 // bool __llvm_sjljeh_is_longjmp_exception()
231 IsLJException = M.getOrInsertFunction("__llvm_sjljeh_is_longjmp_exception",
232 Type::Int1Ty, (Type *)0);
234 // int __llvm_sjljeh_get_longjmp_value()
235 GetLJValue = M.getOrInsertFunction("__llvm_sjljeh_get_longjmp_value",
236 Type::Int32Ty, (Type *)0);
240 // IsTransformableFunction - Return true if the function name isn't one
241 // of the ones we don't want transformed. Currently, don't transform any
242 // "llvm.{setjmp,longjmp}" functions and none of the setjmp/longjmp error
243 // handling functions (beginning with __llvm_sjljeh_...they don't throw
245 bool LowerSetJmp::IsTransformableFunction(const std::string& Name) {
246 std::string SJLJEh("__llvm_sjljeh");
248 if (Name.size() > SJLJEh.size())
249 return std::string(Name.begin(), Name.begin() + SJLJEh.size()) != SJLJEh;
254 // TransformLongJmpCall - Transform a longjmp call into a call to the
255 // internal __llvm_sjljeh_throw_longjmp function. It then takes care of
256 // throwing the exception for us.
257 void LowerSetJmp::TransformLongJmpCall(CallInst* Inst)
259 const Type* SBPTy = PointerType::get(Type::Int8Ty);
261 // Create the call to "__llvm_sjljeh_throw_longjmp". This takes the
262 // same parameters as "longjmp", except that the buffer is cast to a
263 // char*. It returns "void", so it doesn't need to replace any of
264 // Inst's uses and doesn't get a name.
266 new BitCastInst(Inst->getOperand(1), SBPTy, "LJBuf", Inst);
267 SmallVector<Value *, 2> Args;
269 Args.push_back(Inst->getOperand(2));
270 new CallInst(ThrowLongJmp, Args.begin(), Args.end(), "", Inst);
272 SwitchValuePair& SVP = SwitchValMap[Inst->getParent()->getParent()];
274 // If the function has a setjmp call in it (they are transformed first)
275 // we should branch to the basic block that determines if this longjmp
276 // is applicable here. Otherwise, issue an unwind.
278 new BranchInst(SVP.first->getParent(), Inst);
280 new UnwindInst(Inst);
282 // Remove all insts after the branch/unwind inst. Go from back to front to
283 // avoid replaceAllUsesWith if possible.
284 BasicBlock *BB = Inst->getParent();
285 Instruction *Removed;
287 Removed = &BB->back();
288 // If the removed instructions have any users, replace them now.
289 if (!Removed->use_empty())
290 Removed->replaceAllUsesWith(UndefValue::get(Removed->getType()));
291 Removed->eraseFromParent();
292 } while (Removed != Inst);
294 ++LongJmpsTransformed;
297 // GetSetJmpMap - Retrieve (create and initialize, if necessary) the
298 // setjmp map. This map is going to hold information about which setjmps
299 // were called (each setjmp gets its own number) and with which buffer it
300 // was called. There can be only one!
301 AllocaInst* LowerSetJmp::GetSetJmpMap(Function* Func)
303 if (SJMap[Func]) return SJMap[Func];
305 // Insert the setjmp map initialization before the first instruction in
307 Instruction* Inst = Func->getEntryBlock().begin();
308 assert(Inst && "Couldn't find even ONE instruction in entry block!");
310 // Fill in the alloca and call to initialize the SJ map.
311 const Type *SBPTy = PointerType::get(Type::Int8Ty);
312 AllocaInst* Map = new AllocaInst(SBPTy, 0, "SJMap", Inst);
313 new CallInst(InitSJMap, Map, "", Inst);
314 return SJMap[Func] = Map;
317 // GetRethrowBB - Only one rethrow basic block is needed per function.
318 // If this is a longjmp exception but not handled in this block, this BB
319 // performs the rethrow.
320 BasicBlock* LowerSetJmp::GetRethrowBB(Function* Func)
322 if (RethrowBBMap[Func]) return RethrowBBMap[Func];
324 // The basic block we're going to jump to if we need to rethrow the
326 BasicBlock* Rethrow = new BasicBlock("RethrowExcept", Func);
328 // Fill in the "Rethrow" BB with a call to rethrow the exception. This
329 // is the last instruction in the BB since at this point the runtime
330 // should exit this function and go to the next function.
331 new UnwindInst(Rethrow);
332 return RethrowBBMap[Func] = Rethrow;
335 // GetSJSwitch - Return the switch statement that controls which handler
336 // (if any) gets called and the value returned to that handler.
337 LowerSetJmp::SwitchValuePair LowerSetJmp::GetSJSwitch(Function* Func,
340 if (SwitchValMap[Func].first) return SwitchValMap[Func];
342 BasicBlock* LongJmpPre = new BasicBlock("LongJmpBlkPre", Func);
343 BasicBlock::InstListType& LongJmpPreIL = LongJmpPre->getInstList();
345 // Keep track of the preliminary basic block for some of the other
347 PrelimBBMap[Func] = LongJmpPre;
349 // Grab the exception.
350 CallInst* Cond = new CallInst(IsLJException, "IsLJExcept");
351 LongJmpPreIL.push_back(Cond);
353 // The "decision basic block" gets the number associated with the
354 // setjmp call returning to switch on and the value returned by
356 BasicBlock* DecisionBB = new BasicBlock("LJDecisionBB", Func);
357 BasicBlock::InstListType& DecisionBBIL = DecisionBB->getInstList();
359 new BranchInst(DecisionBB, Rethrow, Cond, LongJmpPre);
361 // Fill in the "decision" basic block.
362 CallInst* LJVal = new CallInst(GetLJValue, "LJVal");
363 DecisionBBIL.push_back(LJVal);
364 CallInst* SJNum = new CallInst(TryCatchLJ, GetSetJmpMap(Func), "SJNum");
365 DecisionBBIL.push_back(SJNum);
367 SwitchInst* SI = new SwitchInst(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 = PointerType::get(Type::Int8Ty);
383 new BitCastInst(Inst->getOperand(1), SBPTy, "SBJmpBuf", Inst);
384 std::vector<Value*> Args =
385 make_vector<Value*>(GetSetJmpMap(Func), BufPtr,
386 ConstantInt::get(Type::Int32Ty,
387 SetJmpIDMap[Func]++), 0);
388 new CallInst(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 = new PHINode(Type::Int32Ty, "SetJmpReturn", Inst);
432 // Coming from a call to setjmp, the return is 0.
433 PHI->addIncoming(ConstantInt::getNullValue(Type::Int32Ty), ABlock);
435 // Add the case for this setjmp's number...
436 SwitchValuePair SVP = GetSJSwitch(Func, GetRethrowBB(Func));
437 SVP.first->addCase(ConstantInt::get(Type::Int32Ty, SetJmpIDMap[Func] - 1),
440 // Value coming from the handling of the exception.
441 PHI->addIncoming(SVP.second, SVP.second->getParent());
443 // Replace all uses of this instruction with the PHI node created by
444 // the eradication of setjmp.
445 Inst->replaceAllUsesWith(PHI);
446 Inst->getParent()->getInstList().erase(Inst);
448 ++SetJmpsTransformed;
451 // visitCallInst - This converts all LLVM call instructions into invoke
452 // instructions. The except part of the invoke goes to the "LongJmpBlkPre"
453 // that grabs the exception and proceeds to determine if it's a longjmp
455 void LowerSetJmp::visitCallInst(CallInst& CI)
457 if (CI.getCalledFunction())
458 if (!IsTransformableFunction(CI.getCalledFunction()->getName()) ||
459 CI.getCalledFunction()->isIntrinsic()) return;
461 BasicBlock* OldBB = CI.getParent();
463 // If not reachable from a setjmp call, don't transform.
464 if (!DFSBlocks.count(OldBB)) return;
466 BasicBlock* NewBB = OldBB->splitBasicBlock(CI);
467 assert(NewBB && "Couldn't split BB of \"call\" instruction!!");
468 DFSBlocks.insert(NewBB);
469 NewBB->setName("Call2Invoke");
471 Function* Func = OldBB->getParent();
473 // Construct the new "invoke" instruction.
474 TerminatorInst* Term = OldBB->getTerminator();
475 std::vector<Value*> Params(CI.op_begin() + 1, CI.op_end());
477 InvokeInst(CI.getCalledValue(), NewBB, PrelimBBMap[Func],
478 Params.begin(), Params.end(), CI.getName(), Term);
480 // Replace the old call inst with the invoke inst and remove the call.
481 CI.replaceAllUsesWith(II);
482 CI.getParent()->getInstList().erase(&CI);
484 // The old terminator is useless now that we have the invoke inst.
485 Term->getParent()->getInstList().erase(Term);
489 // visitInvokeInst - Converting the "invoke" instruction is fairly
490 // straight-forward. The old exception part is replaced by a query asking
491 // if this is a longjmp exception. If it is, then it goes to the longjmp
492 // exception blocks. Otherwise, control is passed the old exception.
493 void LowerSetJmp::visitInvokeInst(InvokeInst& II)
495 if (II.getCalledFunction())
496 if (!IsTransformableFunction(II.getCalledFunction()->getName()) ||
497 II.getCalledFunction()->isIntrinsic()) return;
499 BasicBlock* BB = II.getParent();
501 // If not reachable from a setjmp call, don't transform.
502 if (!DFSBlocks.count(BB)) return;
504 BasicBlock* ExceptBB = II.getUnwindDest();
506 Function* Func = BB->getParent();
507 BasicBlock* NewExceptBB = new BasicBlock("InvokeExcept", Func);
508 BasicBlock::InstListType& InstList = NewExceptBB->getInstList();
510 // If this is a longjmp exception, then branch to the preliminary BB of
511 // the longjmp exception handling. Otherwise, go to the old exception.
512 CallInst* IsLJExcept = new CallInst(IsLJException, "IsLJExcept");
513 InstList.push_back(IsLJExcept);
515 new BranchInst(PrelimBBMap[Func], ExceptBB, IsLJExcept, NewExceptBB);
517 II.setUnwindDest(NewExceptBB);
518 ++InvokesTransformed;
521 // visitReturnInst - We want to destroy the setjmp map upon exit from the
523 void LowerSetJmp::visitReturnInst(ReturnInst &RI) {
524 Function* Func = RI.getParent()->getParent();
525 new CallInst(DestroySJMap, GetSetJmpMap(Func), "", &RI);
528 // visitUnwindInst - We want to destroy the setjmp map upon exit from the
530 void LowerSetJmp::visitUnwindInst(UnwindInst &UI) {
531 Function* Func = UI.getParent()->getParent();
532 new CallInst(DestroySJMap, GetSetJmpMap(Func), "", &UI);
535 ModulePass *llvm::createLowerSetJmpPass() {
536 return new LowerSetJmp();