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 // These are what the functions are called.
138 Function* SetJmp = M.getFunction("llvm.setjmp");
139 Function* LongJmp = M.getFunction("llvm.longjmp");
141 // This program doesn't have longjmp and setjmp calls.
142 if ((!LongJmp || LongJmp->use_empty()) &&
143 (!SetJmp || SetJmp->use_empty())) return false;
145 // Initialize some values and functions we'll need to transform the
146 // setjmp/longjmp functions.
150 for (Value::use_iterator B = SetJmp->use_begin(), E = SetJmp->use_end();
152 BasicBlock* BB = cast<Instruction>(*B)->getParent();
153 for (df_ext_iterator<BasicBlock*> I = df_ext_begin(BB, DFSBlocks),
154 E = df_ext_end(BB, DFSBlocks); I != E; ++I)
158 while (!SetJmp->use_empty()) {
159 assert(isa<CallInst>(SetJmp->use_back()) &&
160 "User of setjmp intrinsic not a call?");
161 TransformSetJmpCall(cast<CallInst>(SetJmp->use_back()));
167 while (!LongJmp->use_empty()) {
168 assert(isa<CallInst>(LongJmp->use_back()) &&
169 "User of longjmp intrinsic not a call?");
170 TransformLongJmpCall(cast<CallInst>(LongJmp->use_back()));
174 // Now go through the affected functions and convert calls and invokes
176 for (std::map<Function*, AllocaInst*>::iterator
177 B = SJMap.begin(), E = SJMap.end(); B != E; ++B) {
178 Function* F = B->first;
179 for (Function::iterator BB = F->begin(), BE = F->end(); BB != BE; ++BB)
180 for (BasicBlock::iterator IB = BB->begin(), IE = BB->end(); IB != IE; ) {
182 if (IB != BB->end() && IB->getParent() != BB)
183 break; // The next instruction got moved to a different block!
189 RethrowBBMap.clear();
191 SwitchValMap.clear();
197 // doInitialization - For the lower long/setjmp pass, this ensures that a
198 // module contains a declaration for the intrisic functions we are going
199 // to call to convert longjmp and setjmp calls.
201 // This function is always successful, unless it isn't.
202 bool LowerSetJmp::doInitialization(Module& M)
204 const Type *SBPTy = Context->getPointerTypeUnqual(Type::Int8Ty);
205 const Type *SBPPTy = Context->getPointerTypeUnqual(SBPTy);
207 // N.B. See llvm/runtime/GCCLibraries/libexception/SJLJ-Exception.h for
208 // a description of the following library functions.
210 // void __llvm_sjljeh_init_setjmpmap(void**)
211 InitSJMap = M.getOrInsertFunction("__llvm_sjljeh_init_setjmpmap",
212 Type::VoidTy, SBPPTy, (Type *)0);
213 // void __llvm_sjljeh_destroy_setjmpmap(void**)
214 DestroySJMap = M.getOrInsertFunction("__llvm_sjljeh_destroy_setjmpmap",
215 Type::VoidTy, SBPPTy, (Type *)0);
217 // void __llvm_sjljeh_add_setjmp_to_map(void**, void*, unsigned)
218 AddSJToMap = M.getOrInsertFunction("__llvm_sjljeh_add_setjmp_to_map",
219 Type::VoidTy, SBPPTy, SBPTy,
220 Type::Int32Ty, (Type *)0);
222 // void __llvm_sjljeh_throw_longjmp(int*, int)
223 ThrowLongJmp = M.getOrInsertFunction("__llvm_sjljeh_throw_longjmp",
224 Type::VoidTy, SBPTy, Type::Int32Ty,
227 // unsigned __llvm_sjljeh_try_catching_longjmp_exception(void **)
229 M.getOrInsertFunction("__llvm_sjljeh_try_catching_longjmp_exception",
230 Type::Int32Ty, SBPPTy, (Type *)0);
232 // bool __llvm_sjljeh_is_longjmp_exception()
233 IsLJException = M.getOrInsertFunction("__llvm_sjljeh_is_longjmp_exception",
234 Type::Int1Ty, (Type *)0);
236 // int __llvm_sjljeh_get_longjmp_value()
237 GetLJValue = M.getOrInsertFunction("__llvm_sjljeh_get_longjmp_value",
238 Type::Int32Ty, (Type *)0);
242 // IsTransformableFunction - Return true if the function name isn't one
243 // of the ones we don't want transformed. Currently, don't transform any
244 // "llvm.{setjmp,longjmp}" functions and none of the setjmp/longjmp error
245 // handling functions (beginning with __llvm_sjljeh_...they don't throw
247 bool LowerSetJmp::IsTransformableFunction(const std::string& Name) {
248 std::string SJLJEh("__llvm_sjljeh");
250 if (Name.size() > SJLJEh.size())
251 return std::string(Name.begin(), Name.begin() + SJLJEh.size()) != SJLJEh;
256 // TransformLongJmpCall - Transform a longjmp call into a call to the
257 // internal __llvm_sjljeh_throw_longjmp function. It then takes care of
258 // throwing the exception for us.
259 void LowerSetJmp::TransformLongJmpCall(CallInst* Inst)
261 const Type* SBPTy = Context->getPointerTypeUnqual(Type::Int8Ty);
263 // Create the call to "__llvm_sjljeh_throw_longjmp". This takes the
264 // same parameters as "longjmp", except that the buffer is cast to a
265 // char*. It returns "void", so it doesn't need to replace any of
266 // Inst's uses and doesn't get a name.
268 new BitCastInst(Inst->getOperand(1), SBPTy, "LJBuf", Inst);
269 SmallVector<Value *, 2> Args;
271 Args.push_back(Inst->getOperand(2));
272 CallInst::Create(ThrowLongJmp, Args.begin(), Args.end(), "", Inst);
274 SwitchValuePair& SVP = SwitchValMap[Inst->getParent()->getParent()];
276 // If the function has a setjmp call in it (they are transformed first)
277 // we should branch to the basic block that determines if this longjmp
278 // is applicable here. Otherwise, issue an unwind.
280 BranchInst::Create(SVP.first->getParent(), Inst);
282 new UnwindInst(Inst);
284 // Remove all insts after the branch/unwind inst. Go from back to front to
285 // avoid replaceAllUsesWith if possible.
286 BasicBlock *BB = Inst->getParent();
287 Instruction *Removed;
289 Removed = &BB->back();
290 // If the removed instructions have any users, replace them now.
291 if (!Removed->use_empty())
292 Removed->replaceAllUsesWith(Context->getUndef(Removed->getType()));
293 Removed->eraseFromParent();
294 } while (Removed != Inst);
296 ++LongJmpsTransformed;
299 // GetSetJmpMap - Retrieve (create and initialize, if necessary) the
300 // setjmp map. This map is going to hold information about which setjmps
301 // were called (each setjmp gets its own number) and with which buffer it
302 // was called. There can be only one!
303 AllocaInst* LowerSetJmp::GetSetJmpMap(Function* Func)
305 if (SJMap[Func]) return SJMap[Func];
307 // Insert the setjmp map initialization before the first instruction in
309 Instruction* Inst = Func->getEntryBlock().begin();
310 assert(Inst && "Couldn't find even ONE instruction in entry block!");
312 // Fill in the alloca and call to initialize the SJ map.
313 const Type *SBPTy = Context->getPointerTypeUnqual(Type::Int8Ty);
314 AllocaInst* Map = new AllocaInst(SBPTy, 0, "SJMap", Inst);
315 CallInst::Create(InitSJMap, Map, "", Inst);
316 return SJMap[Func] = Map;
319 // GetRethrowBB - Only one rethrow basic block is needed per function.
320 // If this is a longjmp exception but not handled in this block, this BB
321 // performs the rethrow.
322 BasicBlock* LowerSetJmp::GetRethrowBB(Function* Func)
324 if (RethrowBBMap[Func]) return RethrowBBMap[Func];
326 // The basic block we're going to jump to if we need to rethrow the
328 BasicBlock* Rethrow = BasicBlock::Create("RethrowExcept", Func);
330 // Fill in the "Rethrow" BB with a call to rethrow the exception. This
331 // is the last instruction in the BB since at this point the runtime
332 // should exit this function and go to the next function.
333 new UnwindInst(Rethrow);
334 return RethrowBBMap[Func] = Rethrow;
337 // GetSJSwitch - Return the switch statement that controls which handler
338 // (if any) gets called and the value returned to that handler.
339 LowerSetJmp::SwitchValuePair LowerSetJmp::GetSJSwitch(Function* Func,
342 if (SwitchValMap[Func].first) return SwitchValMap[Func];
344 BasicBlock* LongJmpPre = BasicBlock::Create("LongJmpBlkPre", Func);
346 // Keep track of the preliminary basic block for some of the other
348 PrelimBBMap[Func] = LongJmpPre;
350 // Grab the exception.
351 CallInst* Cond = CallInst::Create(IsLJException, "IsLJExcept", LongJmpPre);
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 = BasicBlock::Create("LJDecisionBB", Func);
358 BranchInst::Create(DecisionBB, Rethrow, Cond, LongJmpPre);
360 // Fill in the "decision" basic block.
361 CallInst* LJVal = CallInst::Create(GetLJValue, "LJVal", DecisionBB);
362 CallInst* SJNum = CallInst::Create(TryCatchLJ, GetSetJmpMap(Func), "SJNum",
365 SwitchInst* SI = SwitchInst::Create(SJNum, Rethrow, 0, DecisionBB);
366 return SwitchValMap[Func] = SwitchValuePair(SI, LJVal);
369 // TransformSetJmpCall - The setjmp call is a bit trickier to transform.
370 // We're going to convert all setjmp calls to nops. Then all "call" and
371 // "invoke" instructions in the function are converted to "invoke" where
372 // the "except" branch is used when returning from a longjmp call.
373 void LowerSetJmp::TransformSetJmpCall(CallInst* Inst)
375 BasicBlock* ABlock = Inst->getParent();
376 Function* Func = ABlock->getParent();
378 // Add this setjmp to the setjmp map.
379 const Type* SBPTy = Context->getPointerTypeUnqual(Type::Int8Ty);
381 new BitCastInst(Inst->getOperand(1), SBPTy, "SBJmpBuf", Inst);
382 std::vector<Value*> Args =
383 make_vector<Value*>(GetSetJmpMap(Func), BufPtr,
384 Context->getConstantInt(Type::Int32Ty,
385 SetJmpIDMap[Func]++), 0);
386 CallInst::Create(AddSJToMap, Args.begin(), Args.end(), "", 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::Int32Ty, "SetJmpReturn", Inst);
430 // Coming from a call to setjmp, the return is 0.
431 PHI->addIncoming(Context->getNullValue(Type::Int32Ty), ABlock);
433 // Add the case for this setjmp's number...
434 SwitchValuePair SVP = GetSJSwitch(Func, GetRethrowBB(Func));
435 SVP.first->addCase(Context->getConstantInt(Type::Int32Ty,
436 SetJmpIDMap[Func] - 1),
439 // Value coming from the handling of the exception.
440 PHI->addIncoming(SVP.second, SVP.second->getParent());
442 // Replace all uses of this instruction with the PHI node created by
443 // the eradication of setjmp.
444 Inst->replaceAllUsesWith(PHI);
445 Inst->eraseFromParent();
447 ++SetJmpsTransformed;
450 // visitCallInst - This converts all LLVM call instructions into invoke
451 // instructions. The except part of the invoke goes to the "LongJmpBlkPre"
452 // that grabs the exception and proceeds to determine if it's a longjmp
454 void LowerSetJmp::visitCallInst(CallInst& CI)
456 if (CI.getCalledFunction())
457 if (!IsTransformableFunction(CI.getCalledFunction()->getName()) ||
458 CI.getCalledFunction()->isIntrinsic()) return;
460 BasicBlock* OldBB = CI.getParent();
462 // If not reachable from a setjmp call, don't transform.
463 if (!DFSBlocks.count(OldBB)) return;
465 BasicBlock* NewBB = OldBB->splitBasicBlock(CI);
466 assert(NewBB && "Couldn't split BB of \"call\" instruction!!");
467 DFSBlocks.insert(NewBB);
468 NewBB->setName("Call2Invoke");
470 Function* Func = OldBB->getParent();
472 // Construct the new "invoke" instruction.
473 TerminatorInst* Term = OldBB->getTerminator();
474 std::vector<Value*> Params(CI.op_begin() + 1, CI.op_end());
476 InvokeInst::Create(CI.getCalledValue(), NewBB, PrelimBBMap[Func],
477 Params.begin(), Params.end(), CI.getName(), Term);
478 II->setCallingConv(CI.getCallingConv());
479 II->setAttributes(CI.getAttributes());
481 // Replace the old call inst with the invoke inst and remove the call.
482 CI.replaceAllUsesWith(II);
483 CI.eraseFromParent();
485 // The old terminator is useless now that we have the invoke inst.
486 Term->eraseFromParent();
490 // visitInvokeInst - Converting the "invoke" instruction is fairly
491 // straight-forward. The old exception part is replaced by a query asking
492 // if this is a longjmp exception. If it is, then it goes to the longjmp
493 // exception blocks. Otherwise, control is passed the old exception.
494 void LowerSetJmp::visitInvokeInst(InvokeInst& II)
496 if (II.getCalledFunction())
497 if (!IsTransformableFunction(II.getCalledFunction()->getName()) ||
498 II.getCalledFunction()->isIntrinsic()) return;
500 BasicBlock* BB = II.getParent();
502 // If not reachable from a setjmp call, don't transform.
503 if (!DFSBlocks.count(BB)) return;
505 BasicBlock* ExceptBB = II.getUnwindDest();
507 Function* Func = BB->getParent();
508 BasicBlock* NewExceptBB = BasicBlock::Create("InvokeExcept", Func);
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 = CallInst::Create(IsLJException, "IsLJExcept",
515 BranchInst::Create(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 CallInst::Create(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 CallInst::Create(DestroySJMap, GetSetJmpMap(Func), "", &UI);
535 ModulePass *llvm::createLowerSetJmpPass() {
536 return new LowerSetJmp();