1 //===- SjLjEHPrepare.cpp - Eliminate Invoke & Unwind instructions ---------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This transformation is designed for use by code generators which use SjLj
11 // based exception handling.
12 //
13 //===----------------------------------------------------------------------===//
14
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"
38 #include <set>
39 using namespace llvm;
40
41 #define DEBUG_TYPE "sjljehprepare"
42
43 STATISTIC(NumInvokes, "Number of invokes replaced");
44 STATISTIC(NumSpilled, "Number of registers live across unwind edges");
45
46 namespace {
47 class SjLjEHPrepare : public FunctionPass {
48 Type *doubleUnderDataTy;
49 Type *doubleUnderJBufTy;
50 Type *FunctionContextTy;
51 Constant *RegisterFn;
52 Constant *UnregisterFn;
53 Constant *BuiltinSetupDispatchFn;
54 Constant *FrameAddrFn;
55 Constant *StackAddrFn;
56 Constant *StackRestoreFn;
57 Constant *LSDAAddrFn;
58 Value *PersonalityFn;
59 Constant *CallSiteFn;
60 Constant *FuncCtxFn;
61 AllocaInst *FuncCtx;
62
63 public:
64 static char ID; // Pass identification, replacement for typeid
SjLjEHPrepare()65 explicit SjLjEHPrepare() : FunctionPass(ID) {}
66 bool doInitialization(Module &M) override;
67 bool runOnFunction(Function &F) override;
68
getAnalysisUsage(AnalysisUsage & AU) const69 void getAnalysisUsage(AnalysisUsage &AU) const override {}
getPassName() const70 const char *getPassName() const override {
71 return "SJLJ Exception Handling preparation";
72 }
73
74 private:
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);
81 };
82 } // end anonymous namespace
83
84 char SjLjEHPrepare::ID = 0;
85 INITIALIZE_PASS(SjLjEHPrepare, "sjljehprepare", "Prepare SjLj exceptions",
86 false, false)
87
88 // Public Interface To the SjLjEHPrepare pass.
createSjLjEHPreparePass()89 FunctionPass *llvm::createSjLjEHPreparePass() { return new SjLjEHPrepare(); }
90 // doInitialization - Set up decalarations and types needed to process
91 // exceptions.
doInitialization(Module & M)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
103 VoidPtrTy, // __lsda
104 doubleUnderJBufTy, // __jbuf
105 nullptr);
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 BuiltinSetupDispatchFn =
116 Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setup_dispatch);
117 LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
118 CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
119 FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext);
120 PersonalityFn = nullptr;
121
122 return true;
123 }
124
125 /// insertCallSiteStore - Insert a store of the call-site value to the
126 /// function context
insertCallSiteStore(Instruction * I,int Number)127 void SjLjEHPrepare::insertCallSiteStore(Instruction *I, int Number) {
128 IRBuilder<> Builder(I);
129
130 // Get a reference to the call_site field.
131 Type *Int32Ty = Type::getInt32Ty(I->getContext());
132 Value *Zero = ConstantInt::get(Int32Ty, 0);
133 Value *One = ConstantInt::get(Int32Ty, 1);
134 Value *Idxs[2] = { Zero, One };
135 Value *CallSite =
136 Builder.CreateGEP(FunctionContextTy, FuncCtx, Idxs, "call_site");
137
138 // Insert a store of the call-site number
139 ConstantInt *CallSiteNoC =
140 ConstantInt::get(Type::getInt32Ty(I->getContext()), Number);
141 Builder.CreateStore(CallSiteNoC, CallSite, true /*volatile*/);
142 }
143
144 /// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
145 /// we reach blocks we've already seen.
MarkBlocksLiveIn(BasicBlock * BB,SmallPtrSetImpl<BasicBlock * > & LiveBBs)146 static void MarkBlocksLiveIn(BasicBlock *BB,
147 SmallPtrSetImpl<BasicBlock *> &LiveBBs) {
148 if (!LiveBBs.insert(BB).second)
149 return; // already been here.
150
151 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
152 MarkBlocksLiveIn(*PI, LiveBBs);
153 }
154
155 /// substituteLPadValues - Substitute the values returned by the landingpad
156 /// instruction with those returned by the personality function.
substituteLPadValues(LandingPadInst * LPI,Value * ExnVal,Value * SelVal)157 void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
158 Value *SelVal) {
159 SmallVector<Value *, 8> UseWorkList(LPI->user_begin(), LPI->user_end());
160 while (!UseWorkList.empty()) {
161 Value *Val = UseWorkList.pop_back_val();
162 ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Val);
163 if (!EVI)
164 continue;
165 if (EVI->getNumIndices() != 1)
166 continue;
167 if (*EVI->idx_begin() == 0)
168 EVI->replaceAllUsesWith(ExnVal);
169 else if (*EVI->idx_begin() == 1)
170 EVI->replaceAllUsesWith(SelVal);
171 if (EVI->getNumUses() == 0)
172 EVI->eraseFromParent();
173 }
174
175 if (LPI->getNumUses() == 0)
176 return;
177
178 // There are still some uses of LPI. Construct an aggregate with the exception
179 // values and replace the LPI with that aggregate.
180 Type *LPadType = LPI->getType();
181 Value *LPadVal = UndefValue::get(LPadType);
182 auto *SelI = cast<Instruction>(SelVal);
183 IRBuilder<> Builder(SelI->getParent(), std::next(SelI->getIterator()));
184 LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val");
185 LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val");
186
187 LPI->replaceAllUsesWith(LPadVal);
188 }
189
190 /// setupFunctionContext - Allocate the function context on the stack and fill
191 /// it with all of the data that we know at this point.
setupFunctionContext(Function & F,ArrayRef<LandingPadInst * > LPads)192 Value *SjLjEHPrepare::setupFunctionContext(Function &F,
193 ArrayRef<LandingPadInst *> LPads) {
194 BasicBlock *EntryBB = &F.front();
195
196 // Create an alloca for the incoming jump buffer ptr and the new jump buffer
197 // that needs to be restored on all exits from the function. This is an alloca
198 // because the value needs to be added to the global context list.
199 auto &DL = F.getParent()->getDataLayout();
200 unsigned Align = DL.getPrefTypeAlignment(FunctionContextTy);
201 FuncCtx = new AllocaInst(FunctionContextTy, nullptr, Align, "fn_context",
202 &EntryBB->front());
203
204 // Fill in the function context structure.
205 for (unsigned I = 0, E = LPads.size(); I != E; ++I) {
206 LandingPadInst *LPI = LPads[I];
207 IRBuilder<> Builder(LPI->getParent(),
208 LPI->getParent()->getFirstInsertionPt());
209
210 // Reference the __data field.
211 Value *FCData =
212 Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 2, "__data");
213
214 // The exception values come back in context->__data[0].
215 Value *ExceptionAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
216 0, 0, "exception_gep");
217 Value *ExnVal = Builder.CreateLoad(ExceptionAddr, true, "exn_val");
218 ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy());
219
220 Value *SelectorAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
221 0, 1, "exn_selector_gep");
222 Value *SelVal = Builder.CreateLoad(SelectorAddr, true, "exn_selector_val");
223
224 substituteLPadValues(LPI, ExnVal, SelVal);
225 }
226
227 // Personality function
228 IRBuilder<> Builder(EntryBB->getTerminator());
229 if (!PersonalityFn)
230 PersonalityFn = F.getPersonalityFn();
231 Value *PersonalityFieldPtr = Builder.CreateConstGEP2_32(
232 FunctionContextTy, FuncCtx, 0, 3, "pers_fn_gep");
233 Builder.CreateStore(
234 Builder.CreateBitCast(PersonalityFn, Builder.getInt8PtrTy()),
235 PersonalityFieldPtr, /*isVolatile=*/true);
236
237 // LSDA address
238 Value *LSDA = Builder.CreateCall(LSDAAddrFn, {}, "lsda_addr");
239 Value *LSDAFieldPtr =
240 Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 4, "lsda_gep");
241 Builder.CreateStore(LSDA, LSDAFieldPtr, /*isVolatile=*/true);
242
243 return FuncCtx;
244 }
245
246 /// lowerIncomingArguments - To avoid having to handle incoming arguments
247 /// specially, we lower each arg to a copy instruction in the entry block. This
248 /// ensures that the argument value itself cannot be live out of the entry
249 /// block.
lowerIncomingArguments(Function & F)250 void SjLjEHPrepare::lowerIncomingArguments(Function &F) {
251 BasicBlock::iterator AfterAllocaInsPt = F.begin()->begin();
252 while (isa<AllocaInst>(AfterAllocaInsPt) &&
253 isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsPt)->getArraySize()))
254 ++AfterAllocaInsPt;
255 assert(AfterAllocaInsPt != F.front().end());
256
257 for (auto &AI : F.args()) {
258 Type *Ty = AI.getType();
259
260 // Use 'select i8 true, %arg, undef' to simulate a 'no-op' instruction.
261 Value *TrueValue = ConstantInt::getTrue(F.getContext());
262 Value *UndefValue = UndefValue::get(Ty);
263 Instruction *SI = SelectInst::Create(
264 TrueValue, &AI, UndefValue, AI.getName() + ".tmp", &*AfterAllocaInsPt);
265 AI.replaceAllUsesWith(SI);
266
267 // Reset the operand, because it was clobbered by the RAUW above.
268 SI->setOperand(1, &AI);
269 }
270 }
271
272 /// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
273 /// edge and spill them.
lowerAcrossUnwindEdges(Function & F,ArrayRef<InvokeInst * > Invokes)274 void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
275 ArrayRef<InvokeInst *> Invokes) {
276 // Finally, scan the code looking for instructions with bad live ranges.
277 for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
278 for (BasicBlock::iterator II = BB->begin(), IIE = BB->end(); II != IIE;
279 ++II) {
280 // Ignore obvious cases we don't have to handle. In particular, most
281 // instructions either have no uses or only have a single use inside the
282 // current block. Ignore them quickly.
283 Instruction *Inst = &*II;
284 if (Inst->use_empty())
285 continue;
286 if (Inst->hasOneUse() &&
287 cast<Instruction>(Inst->user_back())->getParent() == BB &&
288 !isa<PHINode>(Inst->user_back()))
289 continue;
290
291 // If this is an alloca in the entry block, it's not a real register
292 // value.
293 if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
294 if (isa<ConstantInt>(AI->getArraySize()) && BB == F.begin())
295 continue;
296
297 // Avoid iterator invalidation by copying users to a temporary vector.
298 SmallVector<Instruction *, 16> Users;
299 for (User *U : Inst->users()) {
300 Instruction *UI = cast<Instruction>(U);
301 if (UI->getParent() != BB || isa<PHINode>(UI))
302 Users.push_back(UI);
303 }
304
305 // Find all of the blocks that this value is live in.
306 SmallPtrSet<BasicBlock *, 64> LiveBBs;
307 LiveBBs.insert(Inst->getParent());
308 while (!Users.empty()) {
309 Instruction *U = Users.back();
310 Users.pop_back();
311
312 if (!isa<PHINode>(U)) {
313 MarkBlocksLiveIn(U->getParent(), LiveBBs);
314 } else {
315 // Uses for a PHI node occur in their predecessor block.
316 PHINode *PN = cast<PHINode>(U);
317 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
318 if (PN->getIncomingValue(i) == Inst)
319 MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
320 }
321 }
322
323 // Now that we know all of the blocks that this thing is live in, see if
324 // it includes any of the unwind locations.
325 bool NeedsSpill = false;
326 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
327 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
328 if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
329 DEBUG(dbgs() << "SJLJ Spill: " << *Inst << " around "
330 << UnwindBlock->getName() << "\n");
331 NeedsSpill = true;
332 break;
333 }
334 }
335
336 // If we decided we need a spill, do it.
337 // FIXME: Spilling this way is overkill, as it forces all uses of
338 // the value to be reloaded from the stack slot, even those that aren't
339 // in the unwind blocks. We should be more selective.
340 if (NeedsSpill) {
341 DemoteRegToStack(*Inst, true);
342 ++NumSpilled;
343 }
344 }
345 }
346
347 // Go through the landing pads and remove any PHIs there.
348 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
349 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
350 LandingPadInst *LPI = UnwindBlock->getLandingPadInst();
351
352 // Place PHIs into a set to avoid invalidating the iterator.
353 SmallPtrSet<PHINode *, 8> PHIsToDemote;
354 for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
355 PHIsToDemote.insert(cast<PHINode>(PN));
356 if (PHIsToDemote.empty())
357 continue;
358
359 // Demote the PHIs to the stack.
360 for (PHINode *PN : PHIsToDemote)
361 DemotePHIToStack(PN);
362
363 // Move the landingpad instruction back to the top of the landing pad block.
364 LPI->moveBefore(&UnwindBlock->front());
365 }
366 }
367
368 /// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
369 /// the function context and marking the call sites with the appropriate
370 /// values. These values are used by the DWARF EH emitter.
setupEntryBlockAndCallSites(Function & F)371 bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
372 SmallVector<ReturnInst *, 16> Returns;
373 SmallVector<InvokeInst *, 16> Invokes;
374 SmallSetVector<LandingPadInst *, 16> LPads;
375
376 // Look through the terminators of the basic blocks to find invokes.
377 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
378 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
379 if (Function *Callee = II->getCalledFunction())
380 if (Callee->isIntrinsic() &&
381 Callee->getIntrinsicID() == Intrinsic::donothing) {
382 // Remove the NOP invoke.
383 BranchInst::Create(II->getNormalDest(), II);
384 II->eraseFromParent();
385 continue;
386 }
387
388 Invokes.push_back(II);
389 LPads.insert(II->getUnwindDest()->getLandingPadInst());
390 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
391 Returns.push_back(RI);
392 }
393
394 if (Invokes.empty())
395 return false;
396
397 NumInvokes += Invokes.size();
398
399 lowerIncomingArguments(F);
400 lowerAcrossUnwindEdges(F, Invokes);
401
402 Value *FuncCtx =
403 setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
404 BasicBlock *EntryBB = &F.front();
405 IRBuilder<> Builder(EntryBB->getTerminator());
406
407 // Get a reference to the jump buffer.
408 Value *JBufPtr =
409 Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 5, "jbuf_gep");
410
411 // Save the frame pointer.
412 Value *FramePtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 0,
413 "jbuf_fp_gep");
414
415 Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
416 Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);
417
418 // Save the stack pointer.
419 Value *StackPtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 2,
420 "jbuf_sp_gep");
421
422 Val = Builder.CreateCall(StackAddrFn, {}, "sp");
423 Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);
424
425 // Call the setup_dispatch instrinsic. It fills in the rest of the jmpbuf.
426 Builder.CreateCall(BuiltinSetupDispatchFn, {});
427
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);
432
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);
437
438 ConstantInt *CallSiteNum =
439 ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);
440
441 // Record the call site value for the back end so it stays associated with
442 // the invoke.
443 CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
444 }
445
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);
458 }
459
460 // Register the function context and make sure it's known to not throw
461 CallInst *Register =
462 CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator());
463 Register->setDoesNotThrow();
464
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) {
468 if (BB == F.begin())
469 continue;
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)
473 continue;
474 } else if (!isa<AllocaInst>(I)) {
475 continue;
476 }
477 Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
478 StackAddr->insertAfter(&*I);
479 Instruction *StoreStackAddr = new StoreInst(StackAddr, StackPtr, true);
480 StoreStackAddr->insertAfter(StackAddr);
481 }
482 }
483
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]);
488
489 return true;
490 }
491
runOnFunction(Function & F)492 bool SjLjEHPrepare::runOnFunction(Function &F) {
493 bool Res = setupEntryBlockAndCallSites(F);
494 return Res;
495 }
496