1 //===- SjLjEHPrepare.cpp - Eliminate Invoke & Unwind instructions ---------===//
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 transformation is designed for use by code generators which use SjLj
11 // based exception handling.
13 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "sjljehprepare"
16 #include "llvm/Constants.h"
17 #include "llvm/DerivedTypes.h"
18 #include "llvm/IRBuilder.h"
19 #include "llvm/Instructions.h"
20 #include "llvm/Intrinsics.h"
21 #include "llvm/LLVMContext.h"
22 #include "llvm/Module.h"
23 #include "llvm/Pass.h"
24 #include "llvm/ADT/DenseMap.h"
25 #include "llvm/ADT/SetVector.h"
26 #include "llvm/ADT/SmallPtrSet.h"
27 #include "llvm/ADT/SmallVector.h"
28 #include "llvm/ADT/Statistic.h"
29 #include "llvm/CodeGen/Passes.h"
30 #include "llvm/Support/CommandLine.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Support/raw_ostream.h"
33 #include "llvm/DataLayout.h"
34 #include "llvm/Target/TargetLowering.h"
35 #include "llvm/Transforms/Scalar.h"
36 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
37 #include "llvm/Transforms/Utils/Local.h"
41 STATISTIC(NumInvokes, "Number of invokes replaced");
42 STATISTIC(NumSpilled, "Number of registers live across unwind edges");
45 class SjLjEHPrepare : public FunctionPass {
46 const TargetLowering *TLI;
47 Type *FunctionContextTy;
49 Constant *UnregisterFn;
50 Constant *BuiltinSetjmpFn;
51 Constant *FrameAddrFn;
52 Constant *StackAddrFn;
53 Constant *StackRestoreFn;
60 static char ID; // Pass identification, replacement for typeid
61 explicit SjLjEHPrepare(const TargetLowering *tli = NULL)
62 : FunctionPass(ID), TLI(tli) { }
63 bool doInitialization(Module &M);
64 bool runOnFunction(Function &F);
66 virtual void getAnalysisUsage(AnalysisUsage &AU) const {}
67 const char *getPassName() const {
68 return "SJLJ Exception Handling preparation";
72 bool setupEntryBlockAndCallSites(Function &F);
73 void substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
75 Value *setupFunctionContext(Function &F, ArrayRef<LandingPadInst*> LPads);
76 void lowerIncomingArguments(Function &F);
77 void lowerAcrossUnwindEdges(Function &F, ArrayRef<InvokeInst*> Invokes);
78 void insertCallSiteStore(Instruction *I, int Number);
80 } // end anonymous namespace
82 char SjLjEHPrepare::ID = 0;
84 // Public Interface To the SjLjEHPrepare pass.
85 FunctionPass *llvm::createSjLjEHPreparePass(const TargetLowering *TLI) {
86 return new SjLjEHPrepare(TLI);
88 // doInitialization - Set up decalarations and types needed to process
90 bool SjLjEHPrepare::doInitialization(Module &M) {
91 // Build the function context structure.
92 // builtin_setjmp uses a five word jbuf
93 Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
94 Type *Int32Ty = Type::getInt32Ty(M.getContext());
96 StructType::get(VoidPtrTy, // __prev
98 ArrayType::get(Int32Ty, 4), // __data
99 VoidPtrTy, // __personality
101 ArrayType::get(VoidPtrTy, 5), // __jbuf
103 RegisterFn = M.getOrInsertFunction("_Unwind_SjLj_Register",
104 Type::getVoidTy(M.getContext()),
105 PointerType::getUnqual(FunctionContextTy),
108 M.getOrInsertFunction("_Unwind_SjLj_Unregister",
109 Type::getVoidTy(M.getContext()),
110 PointerType::getUnqual(FunctionContextTy),
112 FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress);
113 StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
114 StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
115 BuiltinSetjmpFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setjmp);
116 LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
117 CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
118 FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext);
124 /// insertCallSiteStore - Insert a store of the call-site value to the
126 void SjLjEHPrepare::insertCallSiteStore(Instruction *I, int Number) {
127 IRBuilder<> Builder(I);
129 // Get a reference to the call_site field.
130 Type *Int32Ty = Type::getInt32Ty(I->getContext());
131 Value *Zero = ConstantInt::get(Int32Ty, 0);
132 Value *One = ConstantInt::get(Int32Ty, 1);
133 Value *Idxs[2] = { Zero, One };
134 Value *CallSite = Builder.CreateGEP(FuncCtx, Idxs, "call_site");
136 // Insert a store of the call-site number
137 ConstantInt *CallSiteNoC = ConstantInt::get(Type::getInt32Ty(I->getContext()),
139 Builder.CreateStore(CallSiteNoC, CallSite, true/*volatile*/);
142 /// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
143 /// we reach blocks we've already seen.
144 static void MarkBlocksLiveIn(BasicBlock *BB,
145 SmallPtrSet<BasicBlock*, 64> &LiveBBs) {
146 if (!LiveBBs.insert(BB)) return; // already been here.
148 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
149 MarkBlocksLiveIn(*PI, LiveBBs);
152 /// substituteLPadValues - Substitute the values returned by the landingpad
153 /// instruction with those returned by the personality function.
154 void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
156 SmallVector<Value*, 8> UseWorkList(LPI->use_begin(), LPI->use_end());
157 while (!UseWorkList.empty()) {
158 Value *Val = UseWorkList.pop_back_val();
159 ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Val);
161 if (EVI->getNumIndices() != 1) continue;
162 if (*EVI->idx_begin() == 0)
163 EVI->replaceAllUsesWith(ExnVal);
164 else if (*EVI->idx_begin() == 1)
165 EVI->replaceAllUsesWith(SelVal);
166 if (EVI->getNumUses() == 0)
167 EVI->eraseFromParent();
170 if (LPI->getNumUses() == 0) return;
172 // There are still some uses of LPI. Construct an aggregate with the exception
173 // values and replace the LPI with that aggregate.
174 Type *LPadType = LPI->getType();
175 Value *LPadVal = UndefValue::get(LPadType);
177 Builder(llvm::next(BasicBlock::iterator(cast<Instruction>(SelVal))));
178 LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val");
179 LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val");
181 LPI->replaceAllUsesWith(LPadVal);
184 /// setupFunctionContext - Allocate the function context on the stack and fill
185 /// it with all of the data that we know at this point.
186 Value *SjLjEHPrepare::
187 setupFunctionContext(Function &F, ArrayRef<LandingPadInst*> LPads) {
188 BasicBlock *EntryBB = F.begin();
190 // Create an alloca for the incoming jump buffer ptr and the new jump buffer
191 // that needs to be restored on all exits from the function. This is an alloca
192 // because the value needs to be added to the global context list.
194 TLI->getDataLayout()->getPrefTypeAlignment(FunctionContextTy);
196 new AllocaInst(FunctionContextTy, 0, Align, "fn_context", EntryBB->begin());
198 // Fill in the function context structure.
199 for (unsigned I = 0, E = LPads.size(); I != E; ++I) {
200 LandingPadInst *LPI = LPads[I];
201 IRBuilder<> Builder(LPI->getParent()->getFirstInsertionPt());
203 // Reference the __data field.
204 Value *FCData = Builder.CreateConstGEP2_32(FuncCtx, 0, 2, "__data");
206 // The exception values come back in context->__data[0].
207 Value *ExceptionAddr = Builder.CreateConstGEP2_32(FCData, 0, 0,
209 Value *ExnVal = Builder.CreateLoad(ExceptionAddr, true, "exn_val");
210 ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy());
212 Value *SelectorAddr = Builder.CreateConstGEP2_32(FCData, 0, 1,
214 Value *SelVal = Builder.CreateLoad(SelectorAddr, true, "exn_selector_val");
216 substituteLPadValues(LPI, ExnVal, SelVal);
219 // Personality function
220 IRBuilder<> Builder(EntryBB->getTerminator());
222 PersonalityFn = LPads[0]->getPersonalityFn();
223 Value *PersonalityFieldPtr = Builder.CreateConstGEP2_32(FuncCtx, 0, 3,
225 Builder.CreateStore(PersonalityFn, PersonalityFieldPtr, /*isVolatile=*/true);
228 Value *LSDA = Builder.CreateCall(LSDAAddrFn, "lsda_addr");
229 Value *LSDAFieldPtr = Builder.CreateConstGEP2_32(FuncCtx, 0, 4, "lsda_gep");
230 Builder.CreateStore(LSDA, LSDAFieldPtr, /*isVolatile=*/true);
235 /// lowerIncomingArguments - To avoid having to handle incoming arguments
236 /// specially, we lower each arg to a copy instruction in the entry block. This
237 /// ensures that the argument value itself cannot be live out of the entry
239 void SjLjEHPrepare::lowerIncomingArguments(Function &F) {
240 BasicBlock::iterator AfterAllocaInsPt = F.begin()->begin();
241 while (isa<AllocaInst>(AfterAllocaInsPt) &&
242 isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsPt)->getArraySize()))
245 for (Function::arg_iterator
246 AI = F.arg_begin(), AE = F.arg_end(); AI != AE; ++AI) {
247 Type *Ty = AI->getType();
249 // Aggregate types can't be cast, but are legal argument types, so we have
250 // to handle them differently. We use an extract/insert pair as a
251 // lightweight method to achieve the same goal.
252 if (isa<StructType>(Ty) || isa<ArrayType>(Ty) || isa<VectorType>(Ty)) {
253 Instruction *EI = ExtractValueInst::Create(AI, 0, "", AfterAllocaInsPt);
254 Instruction *NI = InsertValueInst::Create(AI, EI, 0);
256 AI->replaceAllUsesWith(NI);
258 // Set the operand of the instructions back to the AllocaInst.
259 EI->setOperand(0, AI);
260 NI->setOperand(0, AI);
262 // This is always a no-op cast because we're casting AI to AI->getType()
263 // so src and destination types are identical. BitCast is the only
266 new BitCastInst(AI, AI->getType(), AI->getName() + ".tmp",
268 AI->replaceAllUsesWith(NC);
270 // Set the operand of the cast instruction back to the AllocaInst.
271 // Normally it's forbidden to replace a CastInst's operand because it
272 // could cause the opcode to reflect an illegal conversion. However, we're
273 // replacing it here with the same value it was constructed with. We do
274 // this because the above replaceAllUsesWith() clobbered the operand, but
275 // we want this one to remain.
276 NC->setOperand(0, AI);
281 /// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
282 /// edge and spill them.
283 void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
284 ArrayRef<InvokeInst*> Invokes) {
285 // Finally, scan the code looking for instructions with bad live ranges.
286 for (Function::iterator
287 BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
288 for (BasicBlock::iterator
289 II = BB->begin(), IIE = BB->end(); II != IIE; ++II) {
290 // Ignore obvious cases we don't have to handle. In particular, most
291 // instructions either have no uses or only have a single use inside the
292 // current block. Ignore them quickly.
293 Instruction *Inst = II;
294 if (Inst->use_empty()) continue;
295 if (Inst->hasOneUse() &&
296 cast<Instruction>(Inst->use_back())->getParent() == BB &&
297 !isa<PHINode>(Inst->use_back())) continue;
299 // If this is an alloca in the entry block, it's not a real register
301 if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
302 if (isa<ConstantInt>(AI->getArraySize()) && BB == F.begin())
305 // Avoid iterator invalidation by copying users to a temporary vector.
306 SmallVector<Instruction*, 16> Users;
307 for (Value::use_iterator
308 UI = Inst->use_begin(), E = Inst->use_end(); UI != E; ++UI) {
309 Instruction *User = cast<Instruction>(*UI);
310 if (User->getParent() != BB || isa<PHINode>(User))
311 Users.push_back(User);
314 // Find all of the blocks that this value is live in.
315 SmallPtrSet<BasicBlock*, 64> LiveBBs;
316 LiveBBs.insert(Inst->getParent());
317 while (!Users.empty()) {
318 Instruction *U = Users.back();
321 if (!isa<PHINode>(U)) {
322 MarkBlocksLiveIn(U->getParent(), LiveBBs);
324 // Uses for a PHI node occur in their predecessor block.
325 PHINode *PN = cast<PHINode>(U);
326 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
327 if (PN->getIncomingValue(i) == Inst)
328 MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
332 // Now that we know all of the blocks that this thing is live in, see if
333 // it includes any of the unwind locations.
334 bool NeedsSpill = false;
335 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
336 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
337 if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
338 DEBUG(dbgs() << "SJLJ Spill: " << *Inst << " around "
339 << UnwindBlock->getName() << "\n");
345 // If we decided we need a spill, do it.
346 // FIXME: Spilling this way is overkill, as it forces all uses of
347 // the value to be reloaded from the stack slot, even those that aren't
348 // in the unwind blocks. We should be more selective.
350 DemoteRegToStack(*Inst, true);
356 // Go through the landing pads and remove any PHIs there.
357 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
358 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
359 LandingPadInst *LPI = UnwindBlock->getLandingPadInst();
361 // Place PHIs into a set to avoid invalidating the iterator.
362 SmallPtrSet<PHINode*, 8> PHIsToDemote;
363 for (BasicBlock::iterator
364 PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
365 PHIsToDemote.insert(cast<PHINode>(PN));
366 if (PHIsToDemote.empty()) continue;
368 // Demote the PHIs to the stack.
369 for (SmallPtrSet<PHINode*, 8>::iterator
370 I = PHIsToDemote.begin(), E = PHIsToDemote.end(); I != E; ++I)
371 DemotePHIToStack(*I);
373 // Move the landingpad instruction back to the top of the landing pad block.
374 LPI->moveBefore(UnwindBlock->begin());
378 /// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
379 /// the function context and marking the call sites with the appropriate
380 /// values. These values are used by the DWARF EH emitter.
381 bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
382 SmallVector<ReturnInst*, 16> Returns;
383 SmallVector<InvokeInst*, 16> Invokes;
384 SmallSetVector<LandingPadInst*, 16> LPads;
386 // Look through the terminators of the basic blocks to find invokes.
387 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
388 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
389 Invokes.push_back(II);
390 LPads.insert(II->getUnwindDest()->getLandingPadInst());
391 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
392 Returns.push_back(RI);
395 if (Invokes.empty()) return false;
397 NumInvokes += Invokes.size();
399 lowerIncomingArguments(F);
400 lowerAcrossUnwindEdges(F, Invokes);
403 setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
404 BasicBlock *EntryBB = F.begin();
405 IRBuilder<> Builder(EntryBB->getTerminator());
407 // Get a reference to the jump buffer.
408 Value *JBufPtr = Builder.CreateConstGEP2_32(FuncCtx, 0, 5, "jbuf_gep");
410 // Save the frame pointer.
411 Value *FramePtr = Builder.CreateConstGEP2_32(JBufPtr, 0, 0, "jbuf_fp_gep");
413 Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
414 Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);
416 // Save the stack pointer.
417 Value *StackPtr = Builder.CreateConstGEP2_32(JBufPtr, 0, 2, "jbuf_sp_gep");
419 Val = Builder.CreateCall(StackAddrFn, "sp");
420 Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);
422 // Call the setjmp instrinsic. It fills in the rest of the jmpbuf.
423 Value *SetjmpArg = Builder.CreateBitCast(JBufPtr, Builder.getInt8PtrTy());
424 Builder.CreateCall(BuiltinSetjmpFn, SetjmpArg);
426 // Store a pointer to the function context so that the back-end will know
427 // where to look for it.
428 Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy());
429 Builder.CreateCall(FuncCtxFn, FuncCtxArg);
431 // At this point, we are all set up, update the invoke instructions to mark
432 // their call_site values.
433 for (unsigned I = 0, E = Invokes.size(); I != E; ++I) {
434 insertCallSiteStore(Invokes[I], I + 1);
436 ConstantInt *CallSiteNum =
437 ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);
439 // Record the call site value for the back end so it stays associated with
441 CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
444 // Mark call instructions that aren't nounwind as no-action (call_site ==
445 // -1). Skip the entry block, as prior to then, no function context has been
446 // created for this function and any unexpected exceptions thrown will go
447 // directly to the caller's context, which is what we want anyway, so no need
448 // to do anything here.
449 for (Function::iterator BB = F.begin(), E = F.end(); ++BB != E;)
450 for (BasicBlock::iterator I = BB->begin(), end = BB->end(); I != end; ++I)
451 if (CallInst *CI = dyn_cast<CallInst>(I)) {
452 if (!CI->doesNotThrow())
453 insertCallSiteStore(CI, -1);
454 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(I)) {
455 insertCallSiteStore(RI, -1);
458 // Register the function context and make sure it's known to not throw
459 CallInst *Register = CallInst::Create(RegisterFn, FuncCtx, "",
460 EntryBB->getTerminator());
461 Register->setDoesNotThrow();
463 // Following any allocas not in the entry block, update the saved SP in the
464 // jmpbuf to the new value.
465 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
468 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
469 if (CallInst *CI = dyn_cast<CallInst>(I)) {
470 if (CI->getCalledFunction() != StackRestoreFn)
472 } else if (!isa<AllocaInst>(I)) {
475 Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
476 StackAddr->insertAfter(I);
477 Instruction *StoreStackAddr = new StoreInst(StackAddr, StackPtr, true);
478 StoreStackAddr->insertAfter(StackAddr);
482 // Finally, for any returns from this function, if this function contains an
483 // invoke, add a call to unregister the function context.
484 for (unsigned I = 0, E = Returns.size(); I != E; ++I)
485 CallInst::Create(UnregisterFn, FuncCtx, "", Returns[I]);
490 bool SjLjEHPrepare::runOnFunction(Function &F) {
491 bool Res = setupEntryBlockAndCallSites(F);