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/Target/TargetSubtargetInfo.h"
35 #include "llvm/Transforms/Scalar.h"
36 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
37 #include "llvm/Transforms/Utils/Local.h"
41 #define DEBUG_TYPE "sjljehprepare"
43 STATISTIC(NumInvokes, "Number of invokes replaced");
44 STATISTIC(NumSpilled, "Number of registers live across unwind edges");
47 class SjLjEHPrepare : public FunctionPass {
48 Type *doubleUnderDataTy;
49 Type *doubleUnderJBufTy;
50 Type *FunctionContextTy;
52 Constant *UnregisterFn;
53 Constant *BuiltinSetjmpFn;
54 Constant *FrameAddrFn;
55 Constant *StackAddrFn;
56 Constant *StackRestoreFn;
64 static char ID; // Pass identification, replacement for typeid
65 explicit SjLjEHPrepare() : FunctionPass(ID) {}
66 bool doInitialization(Module &M) override;
67 bool runOnFunction(Function &F) override;
69 void getAnalysisUsage(AnalysisUsage &AU) const override {}
70 const char *getPassName() const override {
71 return "SJLJ Exception Handling preparation";
75 bool setupEntryBlockAndCallSites(Function &F);
76 void substituteLPadValues(LandingPadInst *LPI, Value *ExnVal, Value *SelVal);
77 Value *setupFunctionContext(Function &F, ArrayRef<LandingPadInst *> LPads);
78 void lowerIncomingArguments(Function &F);
79 void lowerAcrossUnwindEdges(Function &F, ArrayRef<InvokeInst *> Invokes);
80 void insertCallSiteStore(Instruction *I, int Number);
82 } // end anonymous namespace
84 char SjLjEHPrepare::ID = 0;
85 INITIALIZE_PASS(SjLjEHPrepare, "sjljehprepare", "Prepare SjLj exceptions",
88 // Public Interface To the SjLjEHPrepare pass.
89 FunctionPass *llvm::createSjLjEHPreparePass() { return new SjLjEHPrepare(); }
90 // doInitialization - Set up decalarations and types needed to process
92 bool SjLjEHPrepare::doInitialization(Module &M) {
93 // Build the function context structure.
94 // builtin_setjmp uses a five word jbuf
95 Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
96 Type *Int32Ty = Type::getInt32Ty(M.getContext());
97 doubleUnderDataTy = ArrayType::get(Int32Ty, 4);
98 doubleUnderJBufTy = ArrayType::get(VoidPtrTy, 5);
99 FunctionContextTy = StructType::get(VoidPtrTy, // __prev
100 Int32Ty, // call_site
101 doubleUnderDataTy, // __data
102 VoidPtrTy, // __personality
104 doubleUnderJBufTy, // __jbuf
106 RegisterFn = M.getOrInsertFunction(
107 "_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()),
108 PointerType::getUnqual(FunctionContextTy), (Type *)nullptr);
109 UnregisterFn = M.getOrInsertFunction(
110 "_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()),
111 PointerType::getUnqual(FunctionContextTy), (Type *)nullptr);
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);
119 PersonalityFn = nullptr;
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 };
135 Builder.CreateGEP(FunctionContextTy, FuncCtx, Idxs, "call_site");
137 // Insert a store of the call-site number
138 ConstantInt *CallSiteNoC =
139 ConstantInt::get(Type::getInt32Ty(I->getContext()), Number);
140 Builder.CreateStore(CallSiteNoC, CallSite, true /*volatile*/);
143 /// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
144 /// we reach blocks we've already seen.
145 static void MarkBlocksLiveIn(BasicBlock *BB,
146 SmallPtrSetImpl<BasicBlock *> &LiveBBs) {
147 if (!LiveBBs.insert(BB).second)
148 return; // already been here.
150 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
151 MarkBlocksLiveIn(*PI, LiveBBs);
154 /// substituteLPadValues - Substitute the values returned by the landingpad
155 /// instruction with those returned by the personality function.
156 void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
158 SmallVector<Value *, 8> UseWorkList(LPI->user_begin(), LPI->user_end());
159 while (!UseWorkList.empty()) {
160 Value *Val = UseWorkList.pop_back_val();
161 ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Val);
164 if (EVI->getNumIndices() != 1)
166 if (*EVI->idx_begin() == 0)
167 EVI->replaceAllUsesWith(ExnVal);
168 else if (*EVI->idx_begin() == 1)
169 EVI->replaceAllUsesWith(SelVal);
170 if (EVI->getNumUses() == 0)
171 EVI->eraseFromParent();
174 if (LPI->getNumUses() == 0)
177 // There are still some uses of LPI. Construct an aggregate with the exception
178 // values and replace the LPI with that aggregate.
179 Type *LPadType = LPI->getType();
180 Value *LPadVal = UndefValue::get(LPadType);
182 std::next(BasicBlock::iterator(cast<Instruction>(SelVal))));
183 LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val");
184 LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val");
186 LPI->replaceAllUsesWith(LPadVal);
189 /// setupFunctionContext - Allocate the function context on the stack and fill
190 /// it with all of the data that we know at this point.
191 Value *SjLjEHPrepare::setupFunctionContext(Function &F,
192 ArrayRef<LandingPadInst *> LPads) {
193 BasicBlock *EntryBB = F.begin();
195 // Create an alloca for the incoming jump buffer ptr and the new jump buffer
196 // that needs to be restored on all exits from the function. This is an alloca
197 // because the value needs to be added to the global context list.
198 auto &DL = F.getParent()->getDataLayout();
199 unsigned Align = DL.getPrefTypeAlignment(FunctionContextTy);
200 FuncCtx = new AllocaInst(FunctionContextTy, nullptr, Align, "fn_context",
203 // Fill in the function context structure.
204 for (unsigned I = 0, E = LPads.size(); I != E; ++I) {
205 LandingPadInst *LPI = LPads[I];
206 IRBuilder<> Builder(LPI->getParent()->getFirstInsertionPt());
208 // Reference the __data field.
210 Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 2, "__data");
212 // The exception values come back in context->__data[0].
213 Value *ExceptionAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
214 0, 0, "exception_gep");
215 Value *ExnVal = Builder.CreateLoad(ExceptionAddr, true, "exn_val");
216 ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy());
218 Value *SelectorAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
219 0, 1, "exn_selector_gep");
220 Value *SelVal = Builder.CreateLoad(SelectorAddr, true, "exn_selector_val");
222 substituteLPadValues(LPI, ExnVal, SelVal);
225 // Personality function
226 IRBuilder<> Builder(EntryBB->getTerminator());
228 PersonalityFn = F.getPersonalityFn();
229 Value *PersonalityFieldPtr = Builder.CreateConstGEP2_32(
230 FunctionContextTy, FuncCtx, 0, 3, "pers_fn_gep");
232 Builder.CreateBitCast(PersonalityFn, Builder.getInt8PtrTy()),
233 PersonalityFieldPtr, /*isVolatile=*/true);
236 Value *LSDA = Builder.CreateCall(LSDAAddrFn, {}, "lsda_addr");
237 Value *LSDAFieldPtr =
238 Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 4, "lsda_gep");
239 Builder.CreateStore(LSDA, LSDAFieldPtr, /*isVolatile=*/true);
244 /// lowerIncomingArguments - To avoid having to handle incoming arguments
245 /// specially, we lower each arg to a copy instruction in the entry block. This
246 /// ensures that the argument value itself cannot be live out of the entry
248 void SjLjEHPrepare::lowerIncomingArguments(Function &F) {
249 BasicBlock::iterator AfterAllocaInsPt = F.begin()->begin();
250 while (isa<AllocaInst>(AfterAllocaInsPt) &&
251 isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsPt)->getArraySize()))
254 for (Function::arg_iterator AI = F.arg_begin(), AE = F.arg_end(); AI != AE;
256 Type *Ty = AI->getType();
258 // Use 'select i8 true, %arg, undef' to simulate a 'no-op' instruction.
259 Value *TrueValue = ConstantInt::getTrue(F.getContext());
260 Value *UndefValue = UndefValue::get(Ty);
261 Instruction *SI = SelectInst::Create(TrueValue, AI, UndefValue,
262 AI->getName() + ".tmp",
264 AI->replaceAllUsesWith(SI);
266 // Reset the operand, because it was clobbered by the RAUW above.
267 SI->setOperand(1, AI);
271 /// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
272 /// edge and spill them.
273 void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
274 ArrayRef<InvokeInst *> Invokes) {
275 // Finally, scan the code looking for instructions with bad live ranges.
276 for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
277 for (BasicBlock::iterator II = BB->begin(), IIE = BB->end(); II != IIE;
279 // Ignore obvious cases we don't have to handle. In particular, most
280 // instructions either have no uses or only have a single use inside the
281 // current block. Ignore them quickly.
282 Instruction *Inst = II;
283 if (Inst->use_empty())
285 if (Inst->hasOneUse() &&
286 cast<Instruction>(Inst->user_back())->getParent() == BB &&
287 !isa<PHINode>(Inst->user_back()))
290 // If this is an alloca in the entry block, it's not a real register
292 if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
293 if (isa<ConstantInt>(AI->getArraySize()) && BB == F.begin())
296 // Avoid iterator invalidation by copying users to a temporary vector.
297 SmallVector<Instruction *, 16> Users;
298 for (User *U : Inst->users()) {
299 Instruction *UI = cast<Instruction>(U);
300 if (UI->getParent() != BB || isa<PHINode>(UI))
304 // Find all of the blocks that this value is live in.
305 SmallPtrSet<BasicBlock *, 64> LiveBBs;
306 LiveBBs.insert(Inst->getParent());
307 while (!Users.empty()) {
308 Instruction *U = Users.back();
311 if (!isa<PHINode>(U)) {
312 MarkBlocksLiveIn(U->getParent(), LiveBBs);
314 // Uses for a PHI node occur in their predecessor block.
315 PHINode *PN = cast<PHINode>(U);
316 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
317 if (PN->getIncomingValue(i) == Inst)
318 MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
322 // Now that we know all of the blocks that this thing is live in, see if
323 // it includes any of the unwind locations.
324 bool NeedsSpill = false;
325 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
326 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
327 if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
328 DEBUG(dbgs() << "SJLJ Spill: " << *Inst << " around "
329 << UnwindBlock->getName() << "\n");
335 // If we decided we need a spill, do it.
336 // FIXME: Spilling this way is overkill, as it forces all uses of
337 // the value to be reloaded from the stack slot, even those that aren't
338 // in the unwind blocks. We should be more selective.
340 DemoteRegToStack(*Inst, true);
346 // Go through the landing pads and remove any PHIs there.
347 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
348 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
349 LandingPadInst *LPI = UnwindBlock->getLandingPadInst();
351 // Place PHIs into a set to avoid invalidating the iterator.
352 SmallPtrSet<PHINode *, 8> PHIsToDemote;
353 for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
354 PHIsToDemote.insert(cast<PHINode>(PN));
355 if (PHIsToDemote.empty())
358 // Demote the PHIs to the stack.
359 for (PHINode *PN : PHIsToDemote)
360 DemotePHIToStack(PN);
362 // Move the landingpad instruction back to the top of the landing pad block.
363 LPI->moveBefore(UnwindBlock->begin());
367 /// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
368 /// the function context and marking the call sites with the appropriate
369 /// values. These values are used by the DWARF EH emitter.
370 bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
371 SmallVector<ReturnInst *, 16> Returns;
372 SmallVector<InvokeInst *, 16> Invokes;
373 SmallSetVector<LandingPadInst *, 16> LPads;
375 // Look through the terminators of the basic blocks to find invokes.
376 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
377 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
378 if (Function *Callee = II->getCalledFunction())
379 if (Callee->isIntrinsic() &&
380 Callee->getIntrinsicID() == Intrinsic::donothing) {
381 // Remove the NOP invoke.
382 BranchInst::Create(II->getNormalDest(), II);
383 II->eraseFromParent();
387 Invokes.push_back(II);
388 LPads.insert(II->getUnwindDest()->getLandingPadInst());
389 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
390 Returns.push_back(RI);
396 NumInvokes += Invokes.size();
398 lowerIncomingArguments(F);
399 lowerAcrossUnwindEdges(F, Invokes);
402 setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
403 BasicBlock *EntryBB = F.begin();
404 IRBuilder<> Builder(EntryBB->getTerminator());
406 // Get a reference to the jump buffer.
408 Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 5, "jbuf_gep");
410 // Save the frame pointer.
411 Value *FramePtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 0,
414 Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
415 Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);
417 // Save the stack pointer.
418 Value *StackPtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 2,
421 Val = Builder.CreateCall(StackAddrFn, {}, "sp");
422 Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);
424 // Call the setjmp instrinsic. It fills in the rest of the jmpbuf.
425 Value *SetjmpArg = Builder.CreateBitCast(JBufPtr, Builder.getInt8PtrTy());
426 Builder.CreateCall(BuiltinSetjmpFn, SetjmpArg);
428 // Store a pointer to the function context so that the back-end will know
429 // where to look for it.
430 Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy());
431 Builder.CreateCall(FuncCtxFn, FuncCtxArg);
433 // At this point, we are all set up, update the invoke instructions to mark
434 // their call_site values.
435 for (unsigned I = 0, E = Invokes.size(); I != E; ++I) {
436 insertCallSiteStore(Invokes[I], I + 1);
438 ConstantInt *CallSiteNum =
439 ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);
441 // Record the call site value for the back end so it stays associated with
443 CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
446 // Mark call instructions that aren't nounwind as no-action (call_site ==
447 // -1). Skip the entry block, as prior to then, no function context has been
448 // created for this function and any unexpected exceptions thrown will go
449 // directly to the caller's context, which is what we want anyway, so no need
450 // to do anything here.
451 for (Function::iterator BB = F.begin(), E = F.end(); ++BB != E;)
452 for (BasicBlock::iterator I = BB->begin(), end = BB->end(); I != end; ++I)
453 if (CallInst *CI = dyn_cast<CallInst>(I)) {
454 if (!CI->doesNotThrow())
455 insertCallSiteStore(CI, -1);
456 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(I)) {
457 insertCallSiteStore(RI, -1);
460 // Register the function context and make sure it's known to not throw
462 CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator());
463 Register->setDoesNotThrow();
465 // Following any allocas not in the entry block, update the saved SP in the
466 // jmpbuf to the new value.
467 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
470 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
471 if (CallInst *CI = dyn_cast<CallInst>(I)) {
472 if (CI->getCalledFunction() != StackRestoreFn)
474 } else if (!isa<AllocaInst>(I)) {
477 Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
478 StackAddr->insertAfter(I);
479 Instruction *StoreStackAddr = new StoreInst(StackAddr, StackPtr, true);
480 StoreStackAddr->insertAfter(StackAddr);
484 // Finally, for any returns from this function, if this function contains an
485 // invoke, add a call to unregister the function context.
486 for (unsigned I = 0, E = Returns.size(); I != E; ++I)
487 CallInst::Create(UnregisterFn, FuncCtx, "", Returns[I]);
492 bool SjLjEHPrepare::runOnFunction(Function &F) {
493 bool Res = setupEntryBlockAndCallSites(F);