1 //===- EscapeEnumerator.cpp -----------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // Defines a helper class that enumerates all possible exits from a function,
10 // including exception handling.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Transforms/Utils/EscapeEnumerator.h"
15 #include "llvm/Analysis/EHPersonalities.h"
16 #include "llvm/Transforms/Utils/Local.h"
17 #include "llvm/IR/CallSite.h"
18 #include "llvm/IR/Module.h"
19 using namespace llvm;
20 
21 static FunctionCallee getDefaultPersonalityFn(Module *M) {
22   LLVMContext &C = M->getContext();
23   Triple T(M->getTargetTriple());
24   EHPersonality Pers = getDefaultEHPersonality(T);
25   return M->getOrInsertFunction(getEHPersonalityName(Pers),
26                                 FunctionType::get(Type::getInt32Ty(C), true));
27 }
28 
29 IRBuilder<> *EscapeEnumerator::Next() {
30   if (Done)
31     return nullptr;
32 
33   // Find all 'return', 'resume', and 'unwind' instructions.
34   while (StateBB != StateE) {
35     BasicBlock *CurBB = &*StateBB++;
36 
37     // Branches and invokes do not escape, only unwind, resume, and return
38     // do.
39     Instruction *TI = CurBB->getTerminator();
40     if (!isa<ReturnInst>(TI) && !isa<ResumeInst>(TI))
41       continue;
42 
43     Builder.SetInsertPoint(TI);
44     return &Builder;
45   }
46 
47   Done = true;
48 
49   if (!HandleExceptions)
50     return nullptr;
51 
52   if (F.doesNotThrow())
53     return nullptr;
54 
55   // Find all 'call' instructions that may throw.
56   SmallVector<Instruction *, 16> Calls;
57   for (BasicBlock &BB : F)
58     for (Instruction &II : BB)
59       if (CallInst *CI = dyn_cast<CallInst>(&II))
60         if (!CI->doesNotThrow())
61           Calls.push_back(CI);
62 
63   if (Calls.empty())
64     return nullptr;
65 
66   // Create a cleanup block.
67   LLVMContext &C = F.getContext();
68   BasicBlock *CleanupBB = BasicBlock::Create(C, CleanupBBName, &F);
69   Type *ExnTy = StructType::get(Type::getInt8PtrTy(C), Type::getInt32Ty(C));
70   if (!F.hasPersonalityFn()) {
71     FunctionCallee PersFn = getDefaultPersonalityFn(F.getParent());
72     F.setPersonalityFn(cast<Constant>(PersFn.getCallee()));
73   }
74 
75   if (isScopedEHPersonality(classifyEHPersonality(F.getPersonalityFn()))) {
76     report_fatal_error("Scoped EH not supported");
77   }
78 
79   LandingPadInst *LPad =
80       LandingPadInst::Create(ExnTy, 1, "cleanup.lpad", CleanupBB);
81   LPad->setCleanup(true);
82   ResumeInst *RI = ResumeInst::Create(LPad, CleanupBB);
83 
84   // Transform the 'call' instructions into 'invoke's branching to the
85   // cleanup block. Go in reverse order to make prettier BB names.
86   SmallVector<Value *, 16> Args;
87   for (unsigned I = Calls.size(); I != 0;) {
88     CallInst *CI = cast<CallInst>(Calls[--I]);
89     changeToInvokeAndSplitBasicBlock(CI, CleanupBB);
90   }
91 
92   Builder.SetInsertPoint(RI);
93   return &Builder;
94 }
95