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 const TargetMachine *TM;
49 Type *doubleUnderDataTy;
50 Type *doubleUnderJBufTy;
51 Type *FunctionContextTy;
52 Constant *RegisterFn;
53 Constant *UnregisterFn;
54 Constant *BuiltinSetjmpFn;
55 Constant *FrameAddrFn;
56 Constant *StackAddrFn;
57 Constant *StackRestoreFn;
58 Constant *LSDAAddrFn;
59 Value *PersonalityFn;
60 Constant *CallSiteFn;
61 Constant *FuncCtxFn;
62 AllocaInst *FuncCtx;
63
64 public:
65 static char ID; // Pass identification, replacement for typeid
SjLjEHPrepare(const TargetMachine * TM)66 explicit SjLjEHPrepare(const TargetMachine *TM) : FunctionPass(ID), TM(TM) {}
67 bool doInitialization(Module &M) override;
68 bool runOnFunction(Function &F) override;
69
getAnalysisUsage(AnalysisUsage & AU) const70 void getAnalysisUsage(AnalysisUsage &AU) const override {}
getPassName() const71 const char *getPassName() const override {
72 return "SJLJ Exception Handling preparation";
73 }
74
75 private:
76 bool setupEntryBlockAndCallSites(Function &F);
77 void substituteLPadValues(LandingPadInst *LPI, Value *ExnVal, Value *SelVal);
78 Value *setupFunctionContext(Function &F, ArrayRef<LandingPadInst *> LPads);
79 void lowerIncomingArguments(Function &F);
80 void lowerAcrossUnwindEdges(Function &F, ArrayRef<InvokeInst *> Invokes);
81 void insertCallSiteStore(Instruction *I, int Number);
82 };
83 } // end anonymous namespace
84
85 char SjLjEHPrepare::ID = 0;
86
87 // Public Interface To the SjLjEHPrepare pass.
createSjLjEHPreparePass(const TargetMachine * TM)88 FunctionPass *llvm::createSjLjEHPreparePass(const TargetMachine *TM) {
89 return new SjLjEHPrepare(TM);
90 }
91 // doInitialization - Set up decalarations and types needed to process
92 // exceptions.
doInitialization(Module & M)93 bool SjLjEHPrepare::doInitialization(Module &M) {
94 // Build the function context structure.
95 // builtin_setjmp uses a five word jbuf
96 Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
97 Type *Int32Ty = Type::getInt32Ty(M.getContext());
98 doubleUnderDataTy = ArrayType::get(Int32Ty, 4);
99 doubleUnderJBufTy = ArrayType::get(VoidPtrTy, 5);
100 FunctionContextTy = StructType::get(VoidPtrTy, // __prev
101 Int32Ty, // call_site
102 doubleUnderDataTy, // __data
103 VoidPtrTy, // __personality
104 VoidPtrTy, // __lsda
105 doubleUnderJBufTy, // __jbuf
106 nullptr);
107 RegisterFn = M.getOrInsertFunction(
108 "_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()),
109 PointerType::getUnqual(FunctionContextTy), (Type *)nullptr);
110 UnregisterFn = M.getOrInsertFunction(
111 "_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()),
112 PointerType::getUnqual(FunctionContextTy), (Type *)nullptr);
113 FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress);
114 StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
115 StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
116 BuiltinSetjmpFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setjmp);
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 IRBuilder<> Builder(
183 std::next(BasicBlock::iterator(cast<Instruction>(SelVal))));
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.begin();
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 const TargetLowering *TLI = TM->getSubtargetImpl(F)->getTargetLowering();
200 unsigned Align =
201 TLI->getDataLayout()->getPrefTypeAlignment(FunctionContextTy);
202 FuncCtx = new AllocaInst(FunctionContextTy, nullptr, Align, "fn_context",
203 EntryBB->begin());
204
205 // Fill in the function context structure.
206 for (unsigned I = 0, E = LPads.size(); I != E; ++I) {
207 LandingPadInst *LPI = LPads[I];
208 IRBuilder<> Builder(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 = LPads[0]->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
256 for (Function::arg_iterator AI = F.arg_begin(), AE = F.arg_end(); AI != AE;
257 ++AI) {
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(TrueValue, AI, UndefValue,
264 AI->getName() + ".tmp",
265 AfterAllocaInsPt);
266 AI->replaceAllUsesWith(SI);
267
268 // Reset the operand, because it was clobbered by the RAUW above.
269 SI->setOperand(1, AI);
270 }
271 }
272
273 /// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
274 /// edge and spill them.
lowerAcrossUnwindEdges(Function & F,ArrayRef<InvokeInst * > Invokes)275 void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
276 ArrayRef<InvokeInst *> Invokes) {
277 // Finally, scan the code looking for instructions with bad live ranges.
278 for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
279 for (BasicBlock::iterator II = BB->begin(), IIE = BB->end(); II != IIE;
280 ++II) {
281 // Ignore obvious cases we don't have to handle. In particular, most
282 // instructions either have no uses or only have a single use inside the
283 // current block. Ignore them quickly.
284 Instruction *Inst = II;
285 if (Inst->use_empty())
286 continue;
287 if (Inst->hasOneUse() &&
288 cast<Instruction>(Inst->user_back())->getParent() == BB &&
289 !isa<PHINode>(Inst->user_back()))
290 continue;
291
292 // If this is an alloca in the entry block, it's not a real register
293 // value.
294 if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
295 if (isa<ConstantInt>(AI->getArraySize()) && BB == F.begin())
296 continue;
297
298 // Avoid iterator invalidation by copying users to a temporary vector.
299 SmallVector<Instruction *, 16> Users;
300 for (User *U : Inst->users()) {
301 Instruction *UI = cast<Instruction>(U);
302 if (UI->getParent() != BB || isa<PHINode>(UI))
303 Users.push_back(UI);
304 }
305
306 // Find all of the blocks that this value is live in.
307 SmallPtrSet<BasicBlock *, 64> LiveBBs;
308 LiveBBs.insert(Inst->getParent());
309 while (!Users.empty()) {
310 Instruction *U = Users.back();
311 Users.pop_back();
312
313 if (!isa<PHINode>(U)) {
314 MarkBlocksLiveIn(U->getParent(), LiveBBs);
315 } else {
316 // Uses for a PHI node occur in their predecessor block.
317 PHINode *PN = cast<PHINode>(U);
318 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
319 if (PN->getIncomingValue(i) == Inst)
320 MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
321 }
322 }
323
324 // Now that we know all of the blocks that this thing is live in, see if
325 // it includes any of the unwind locations.
326 bool NeedsSpill = false;
327 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
328 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
329 if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
330 DEBUG(dbgs() << "SJLJ Spill: " << *Inst << " around "
331 << UnwindBlock->getName() << "\n");
332 NeedsSpill = true;
333 break;
334 }
335 }
336
337 // If we decided we need a spill, do it.
338 // FIXME: Spilling this way is overkill, as it forces all uses of
339 // the value to be reloaded from the stack slot, even those that aren't
340 // in the unwind blocks. We should be more selective.
341 if (NeedsSpill) {
342 DemoteRegToStack(*Inst, true);
343 ++NumSpilled;
344 }
345 }
346 }
347
348 // Go through the landing pads and remove any PHIs there.
349 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
350 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
351 LandingPadInst *LPI = UnwindBlock->getLandingPadInst();
352
353 // Place PHIs into a set to avoid invalidating the iterator.
354 SmallPtrSet<PHINode *, 8> PHIsToDemote;
355 for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
356 PHIsToDemote.insert(cast<PHINode>(PN));
357 if (PHIsToDemote.empty())
358 continue;
359
360 // Demote the PHIs to the stack.
361 for (PHINode *PN : PHIsToDemote)
362 DemotePHIToStack(PN);
363
364 // Move the landingpad instruction back to the top of the landing pad block.
365 LPI->moveBefore(UnwindBlock->begin());
366 }
367 }
368
369 /// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
370 /// the function context and marking the call sites with the appropriate
371 /// values. These values are used by the DWARF EH emitter.
setupEntryBlockAndCallSites(Function & F)372 bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
373 SmallVector<ReturnInst *, 16> Returns;
374 SmallVector<InvokeInst *, 16> Invokes;
375 SmallSetVector<LandingPadInst *, 16> LPads;
376
377 // Look through the terminators of the basic blocks to find invokes.
378 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
379 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
380 if (Function *Callee = II->getCalledFunction())
381 if (Callee->isIntrinsic() &&
382 Callee->getIntrinsicID() == Intrinsic::donothing) {
383 // Remove the NOP invoke.
384 BranchInst::Create(II->getNormalDest(), II);
385 II->eraseFromParent();
386 continue;
387 }
388
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);
393 }
394
395 if (Invokes.empty())
396 return false;
397
398 NumInvokes += Invokes.size();
399
400 lowerIncomingArguments(F);
401 lowerAcrossUnwindEdges(F, Invokes);
402
403 Value *FuncCtx =
404 setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
405 BasicBlock *EntryBB = F.begin();
406 IRBuilder<> Builder(EntryBB->getTerminator());
407
408 // Get a reference to the jump buffer.
409 Value *JBufPtr =
410 Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 5, "jbuf_gep");
411
412 // Save the frame pointer.
413 Value *FramePtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 0,
414 "jbuf_fp_gep");
415
416 Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
417 Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);
418
419 // Save the stack pointer.
420 Value *StackPtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 2,
421 "jbuf_sp_gep");
422
423 Val = Builder.CreateCall(StackAddrFn, "sp");
424 Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);
425
426 // Call the setjmp instrinsic. It fills in the rest of the jmpbuf.
427 Value *SetjmpArg = Builder.CreateBitCast(JBufPtr, Builder.getInt8PtrTy());
428 Builder.CreateCall(BuiltinSetjmpFn, SetjmpArg);
429
430 // Store a pointer to the function context so that the back-end will know
431 // where to look for it.
432 Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy());
433 Builder.CreateCall(FuncCtxFn, FuncCtxArg);
434
435 // At this point, we are all set up, update the invoke instructions to mark
436 // their call_site values.
437 for (unsigned I = 0, E = Invokes.size(); I != E; ++I) {
438 insertCallSiteStore(Invokes[I], I + 1);
439
440 ConstantInt *CallSiteNum =
441 ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);
442
443 // Record the call site value for the back end so it stays associated with
444 // the invoke.
445 CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
446 }
447
448 // Mark call instructions that aren't nounwind as no-action (call_site ==
449 // -1). Skip the entry block, as prior to then, no function context has been
450 // created for this function and any unexpected exceptions thrown will go
451 // directly to the caller's context, which is what we want anyway, so no need
452 // to do anything here.
453 for (Function::iterator BB = F.begin(), E = F.end(); ++BB != E;)
454 for (BasicBlock::iterator I = BB->begin(), end = BB->end(); I != end; ++I)
455 if (CallInst *CI = dyn_cast<CallInst>(I)) {
456 if (!CI->doesNotThrow())
457 insertCallSiteStore(CI, -1);
458 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(I)) {
459 insertCallSiteStore(RI, -1);
460 }
461
462 // Register the function context and make sure it's known to not throw
463 CallInst *Register =
464 CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator());
465 Register->setDoesNotThrow();
466
467 // Following any allocas not in the entry block, update the saved SP in the
468 // jmpbuf to the new value.
469 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
470 if (BB == F.begin())
471 continue;
472 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
473 if (CallInst *CI = dyn_cast<CallInst>(I)) {
474 if (CI->getCalledFunction() != StackRestoreFn)
475 continue;
476 } else if (!isa<AllocaInst>(I)) {
477 continue;
478 }
479 Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
480 StackAddr->insertAfter(I);
481 Instruction *StoreStackAddr = new StoreInst(StackAddr, StackPtr, true);
482 StoreStackAddr->insertAfter(StackAddr);
483 }
484 }
485
486 // Finally, for any returns from this function, if this function contains an
487 // invoke, add a call to unregister the function context.
488 for (unsigned I = 0, E = Returns.size(); I != E; ++I)
489 CallInst::Create(UnregisterFn, FuncCtx, "", Returns[I]);
490
491 return true;
492 }
493
runOnFunction(Function & F)494 bool SjLjEHPrepare::runOnFunction(Function &F) {
495 bool Res = setupEntryBlockAndCallSites(F);
496 return Res;
497 }
498