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 #include "llvm/CodeGen/Passes.h"
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/ADT/SetVector.h"
18 #include "llvm/ADT/SmallPtrSet.h"
19 #include "llvm/ADT/SmallVector.h"
20 #include "llvm/ADT/Statistic.h"
21 #include "llvm/IR/Constants.h"
22 #include "llvm/IR/DataLayout.h"
23 #include "llvm/IR/DerivedTypes.h"
24 #include "llvm/IR/IRBuilder.h"
25 #include "llvm/IR/Instructions.h"
26 #include "llvm/IR/Intrinsics.h"
27 #include "llvm/IR/LLVMContext.h"
28 #include "llvm/IR/Module.h"
29 #include "llvm/Pass.h"
30 #include "llvm/Support/CommandLine.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Support/raw_ostream.h"
33 #include "llvm/Target/TargetLowering.h"
34 #include "llvm/Transforms/Scalar.h"
35 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
36 #include "llvm/Transforms/Utils/Local.h"
40 #define DEBUG_TYPE "sjljehprepare"
42 STATISTIC(NumInvokes, "Number of invokes replaced");
43 STATISTIC(NumSpilled, "Number of registers live across unwind edges");
46 class SjLjEHPrepare : public FunctionPass {
47 const TargetMachine *TM;
48 Type *FunctionContextTy;
50 Constant *UnregisterFn;
51 Constant *BuiltinSetjmpFn;
52 Constant *FrameAddrFn;
53 Constant *StackAddrFn;
54 Constant *StackRestoreFn;
62 static char ID; // Pass identification, replacement for typeid
63 explicit SjLjEHPrepare(const TargetMachine *TM) : FunctionPass(ID), TM(TM) {}
64 bool doInitialization(Module &M) override;
65 bool runOnFunction(Function &F) override;
67 void getAnalysisUsage(AnalysisUsage &AU) const override {}
68 const char *getPassName() const override {
69 return "SJLJ Exception Handling preparation";
73 bool setupEntryBlockAndCallSites(Function &F);
74 void substituteLPadValues(LandingPadInst *LPI, Value *ExnVal, Value *SelVal);
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 TargetMachine *TM) {
86 return new SjLjEHPrepare(TM);
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());
95 FunctionContextTy = StructType::get(VoidPtrTy, // __prev
97 ArrayType::get(Int32Ty, 4), // __data
98 VoidPtrTy, // __personality
100 ArrayType::get(VoidPtrTy, 5), // __jbuf
102 RegisterFn = M.getOrInsertFunction(
103 "_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()),
104 PointerType::getUnqual(FunctionContextTy), (Type *)nullptr);
105 UnregisterFn = M.getOrInsertFunction(
106 "_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()),
107 PointerType::getUnqual(FunctionContextTy), (Type *)nullptr);
108 FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress);
109 StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
110 StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
111 BuiltinSetjmpFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setjmp);
112 LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
113 CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
114 FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext);
115 PersonalityFn = nullptr;
120 /// insertCallSiteStore - Insert a store of the call-site value to the
122 void SjLjEHPrepare::insertCallSiteStore(Instruction *I, int Number) {
123 IRBuilder<> Builder(I);
125 // Get a reference to the call_site field.
126 Type *Int32Ty = Type::getInt32Ty(I->getContext());
127 Value *Zero = ConstantInt::get(Int32Ty, 0);
128 Value *One = ConstantInt::get(Int32Ty, 1);
129 Value *Idxs[2] = { Zero, One };
130 Value *CallSite = Builder.CreateGEP(FuncCtx, Idxs, "call_site");
132 // Insert a store of the call-site number
133 ConstantInt *CallSiteNoC =
134 ConstantInt::get(Type::getInt32Ty(I->getContext()), Number);
135 Builder.CreateStore(CallSiteNoC, CallSite, true /*volatile*/);
138 /// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
139 /// we reach blocks we've already seen.
140 static void MarkBlocksLiveIn(BasicBlock *BB,
141 SmallPtrSet<BasicBlock *, 64> &LiveBBs) {
142 if (!LiveBBs.insert(BB))
143 return; // already been here.
145 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
146 MarkBlocksLiveIn(*PI, LiveBBs);
149 /// substituteLPadValues - Substitute the values returned by the landingpad
150 /// instruction with those returned by the personality function.
151 void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
153 SmallVector<Value *, 8> UseWorkList(LPI->user_begin(), LPI->user_end());
154 while (!UseWorkList.empty()) {
155 Value *Val = UseWorkList.pop_back_val();
156 ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Val);
159 if (EVI->getNumIndices() != 1)
161 if (*EVI->idx_begin() == 0)
162 EVI->replaceAllUsesWith(ExnVal);
163 else if (*EVI->idx_begin() == 1)
164 EVI->replaceAllUsesWith(SelVal);
165 if (EVI->getNumUses() == 0)
166 EVI->eraseFromParent();
169 if (LPI->getNumUses() == 0)
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 std::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::setupFunctionContext(Function &F,
187 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.
193 const TargetLowering *TLI = TM->getTargetLowering();
195 TLI->getDataLayout()->getPrefTypeAlignment(FunctionContextTy);
196 FuncCtx = new AllocaInst(FunctionContextTy, nullptr, Align, "fn_context",
199 // Fill in the function context structure.
200 for (unsigned I = 0, E = LPads.size(); I != E; ++I) {
201 LandingPadInst *LPI = LPads[I];
202 IRBuilder<> Builder(LPI->getParent()->getFirstInsertionPt());
204 // Reference the __data field.
205 Value *FCData = Builder.CreateConstGEP2_32(FuncCtx, 0, 2, "__data");
207 // The exception values come back in context->__data[0].
208 Value *ExceptionAddr =
209 Builder.CreateConstGEP2_32(FCData, 0, 0, "exception_gep");
210 Value *ExnVal = Builder.CreateLoad(ExceptionAddr, true, "exn_val");
211 ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy());
213 Value *SelectorAddr =
214 Builder.CreateConstGEP2_32(FCData, 0, 1, "exn_selector_gep");
215 Value *SelVal = Builder.CreateLoad(SelectorAddr, true, "exn_selector_val");
217 substituteLPadValues(LPI, ExnVal, SelVal);
220 // Personality function
221 IRBuilder<> Builder(EntryBB->getTerminator());
223 PersonalityFn = LPads[0]->getPersonalityFn();
224 Value *PersonalityFieldPtr =
225 Builder.CreateConstGEP2_32(FuncCtx, 0, 3, "pers_fn_gep");
227 Builder.CreateBitCast(PersonalityFn, Builder.getInt8PtrTy()),
228 PersonalityFieldPtr, /*isVolatile=*/true);
231 Value *LSDA = Builder.CreateCall(LSDAAddrFn, "lsda_addr");
232 Value *LSDAFieldPtr = Builder.CreateConstGEP2_32(FuncCtx, 0, 4, "lsda_gep");
233 Builder.CreateStore(LSDA, LSDAFieldPtr, /*isVolatile=*/true);
238 /// lowerIncomingArguments - To avoid having to handle incoming arguments
239 /// specially, we lower each arg to a copy instruction in the entry block. This
240 /// ensures that the argument value itself cannot be live out of the entry
242 void SjLjEHPrepare::lowerIncomingArguments(Function &F) {
243 BasicBlock::iterator AfterAllocaInsPt = F.begin()->begin();
244 while (isa<AllocaInst>(AfterAllocaInsPt) &&
245 isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsPt)->getArraySize()))
248 for (Function::arg_iterator AI = F.arg_begin(), AE = F.arg_end(); AI != AE;
250 Type *Ty = AI->getType();
252 if (isa<StructType>(Ty) || isa<ArrayType>(Ty)) {
253 // Aggregate types can't be cast, but are legal argument types,
254 // so we have to handle them differently. We use
255 // select i8 true, %arg, undef to achieve the same goal
256 Value *TrueValue = ConstantInt::getTrue(F.getContext());
257 Value *UndefValue = UndefValue::get(Ty);
258 Instruction *SI = SelectInst::Create(TrueValue, AI, UndefValue,
259 AI->getName() + ".tmp",
261 AI->replaceAllUsesWith(SI);
263 SI->setOperand(1, AI);
265 // This is always a no-op cast because we're casting AI to AI->getType()
266 // so src and destination types are identical. BitCast is the only
268 CastInst *NC = new BitCastInst(AI, AI->getType(), AI->getName() + ".tmp",
270 AI->replaceAllUsesWith(NC);
272 // Set the operand of the cast instruction back to the AllocaInst.
273 // Normally it's forbidden to replace a CastInst's operand because it
274 // could cause the opcode to reflect an illegal conversion. However, we're
275 // replacing it here with the same value it was constructed with. We do
276 // this because the above replaceAllUsesWith() clobbered the operand, but
277 // we want this one to remain.
278 NC->setOperand(0, AI);
283 /// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
284 /// edge and spill them.
285 void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
286 ArrayRef<InvokeInst *> Invokes) {
287 // Finally, scan the code looking for instructions with bad live ranges.
288 for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
289 for (BasicBlock::iterator II = BB->begin(), IIE = BB->end(); II != IIE;
291 // Ignore obvious cases we don't have to handle. In particular, most
292 // instructions either have no uses or only have a single use inside the
293 // current block. Ignore them quickly.
294 Instruction *Inst = II;
295 if (Inst->use_empty())
297 if (Inst->hasOneUse() &&
298 cast<Instruction>(Inst->user_back())->getParent() == BB &&
299 !isa<PHINode>(Inst->user_back()))
302 // If this is an alloca in the entry block, it's not a real register
304 if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
305 if (isa<ConstantInt>(AI->getArraySize()) && BB == F.begin())
308 // Avoid iterator invalidation by copying users to a temporary vector.
309 SmallVector<Instruction *, 16> Users;
310 for (User *U : Inst->users()) {
311 Instruction *UI = cast<Instruction>(U);
312 if (UI->getParent() != BB || isa<PHINode>(UI))
316 // Find all of the blocks that this value is live in.
317 SmallPtrSet<BasicBlock *, 64> LiveBBs;
318 LiveBBs.insert(Inst->getParent());
319 while (!Users.empty()) {
320 Instruction *U = Users.back();
323 if (!isa<PHINode>(U)) {
324 MarkBlocksLiveIn(U->getParent(), LiveBBs);
326 // Uses for a PHI node occur in their predecessor block.
327 PHINode *PN = cast<PHINode>(U);
328 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
329 if (PN->getIncomingValue(i) == Inst)
330 MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
334 // Now that we know all of the blocks that this thing is live in, see if
335 // it includes any of the unwind locations.
336 bool NeedsSpill = false;
337 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
338 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
339 if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
340 DEBUG(dbgs() << "SJLJ Spill: " << *Inst << " around "
341 << UnwindBlock->getName() << "\n");
347 // If we decided we need a spill, do it.
348 // FIXME: Spilling this way is overkill, as it forces all uses of
349 // the value to be reloaded from the stack slot, even those that aren't
350 // in the unwind blocks. We should be more selective.
352 DemoteRegToStack(*Inst, true);
358 // Go through the landing pads and remove any PHIs there.
359 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
360 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
361 LandingPadInst *LPI = UnwindBlock->getLandingPadInst();
363 // Place PHIs into a set to avoid invalidating the iterator.
364 SmallPtrSet<PHINode *, 8> PHIsToDemote;
365 for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
366 PHIsToDemote.insert(cast<PHINode>(PN));
367 if (PHIsToDemote.empty())
370 // Demote the PHIs to the stack.
371 for (SmallPtrSet<PHINode *, 8>::iterator I = PHIsToDemote.begin(),
372 E = PHIsToDemote.end();
374 DemotePHIToStack(*I);
376 // Move the landingpad instruction back to the top of the landing pad block.
377 LPI->moveBefore(UnwindBlock->begin());
381 /// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
382 /// the function context and marking the call sites with the appropriate
383 /// values. These values are used by the DWARF EH emitter.
384 bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
385 SmallVector<ReturnInst *, 16> Returns;
386 SmallVector<InvokeInst *, 16> Invokes;
387 SmallSetVector<LandingPadInst *, 16> LPads;
389 // Look through the terminators of the basic blocks to find invokes.
390 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
391 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
392 if (Function *Callee = II->getCalledFunction())
393 if (Callee->isIntrinsic() &&
394 Callee->getIntrinsicID() == Intrinsic::donothing) {
395 // Remove the NOP invoke.
396 BranchInst::Create(II->getNormalDest(), II);
397 II->eraseFromParent();
401 Invokes.push_back(II);
402 LPads.insert(II->getUnwindDest()->getLandingPadInst());
403 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
404 Returns.push_back(RI);
410 NumInvokes += Invokes.size();
412 lowerIncomingArguments(F);
413 lowerAcrossUnwindEdges(F, Invokes);
416 setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
417 BasicBlock *EntryBB = F.begin();
418 IRBuilder<> Builder(EntryBB->getTerminator());
420 // Get a reference to the jump buffer.
421 Value *JBufPtr = Builder.CreateConstGEP2_32(FuncCtx, 0, 5, "jbuf_gep");
423 // Save the frame pointer.
424 Value *FramePtr = Builder.CreateConstGEP2_32(JBufPtr, 0, 0, "jbuf_fp_gep");
426 Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
427 Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);
429 // Save the stack pointer.
430 Value *StackPtr = Builder.CreateConstGEP2_32(JBufPtr, 0, 2, "jbuf_sp_gep");
432 Val = Builder.CreateCall(StackAddrFn, "sp");
433 Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);
435 // Call the setjmp instrinsic. It fills in the rest of the jmpbuf.
436 Value *SetjmpArg = Builder.CreateBitCast(JBufPtr, Builder.getInt8PtrTy());
437 Builder.CreateCall(BuiltinSetjmpFn, SetjmpArg);
439 // Store a pointer to the function context so that the back-end will know
440 // where to look for it.
441 Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy());
442 Builder.CreateCall(FuncCtxFn, FuncCtxArg);
444 // At this point, we are all set up, update the invoke instructions to mark
445 // their call_site values.
446 for (unsigned I = 0, E = Invokes.size(); I != E; ++I) {
447 insertCallSiteStore(Invokes[I], I + 1);
449 ConstantInt *CallSiteNum =
450 ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);
452 // Record the call site value for the back end so it stays associated with
454 CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
457 // Mark call instructions that aren't nounwind as no-action (call_site ==
458 // -1). Skip the entry block, as prior to then, no function context has been
459 // created for this function and any unexpected exceptions thrown will go
460 // directly to the caller's context, which is what we want anyway, so no need
461 // to do anything here.
462 for (Function::iterator BB = F.begin(), E = F.end(); ++BB != E;)
463 for (BasicBlock::iterator I = BB->begin(), end = BB->end(); I != end; ++I)
464 if (CallInst *CI = dyn_cast<CallInst>(I)) {
465 if (!CI->doesNotThrow())
466 insertCallSiteStore(CI, -1);
467 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(I)) {
468 insertCallSiteStore(RI, -1);
471 // Register the function context and make sure it's known to not throw
473 CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator());
474 Register->setDoesNotThrow();
476 // Following any allocas not in the entry block, update the saved SP in the
477 // jmpbuf to the new value.
478 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
481 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
482 if (CallInst *CI = dyn_cast<CallInst>(I)) {
483 if (CI->getCalledFunction() != StackRestoreFn)
485 } else if (!isa<AllocaInst>(I)) {
488 Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
489 StackAddr->insertAfter(I);
490 Instruction *StoreStackAddr = new StoreInst(StackAddr, StackPtr, true);
491 StoreStackAddr->insertAfter(StackAddr);
495 // Finally, for any returns from this function, if this function contains an
496 // invoke, add a call to unregister the function context.
497 for (unsigned I = 0, E = Returns.size(); I != E; ++I)
498 CallInst::Create(UnregisterFn, FuncCtx, "", Returns[I]);
503 bool SjLjEHPrepare::runOnFunction(Function &F) {
504 bool Res = setupEntryBlockAndCallSites(F);