1 //===- ConstructionContext.cpp - CFG constructor information --------------===//
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 file defines the ConstructionContext class and its sub-classes,
11 // which represent various different ways of constructing C++ objects
12 // with the additional information the users may want to know about
13 // the constructor.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #include "clang/Analysis/ConstructionContext.h"
18 
19 using namespace clang;
20 
21 const ConstructionContextLayer *
22 ConstructionContextLayer::create(BumpVectorContext &C, TriggerTy Trigger,
23                                  const ConstructionContextLayer *Parent) {
24   ConstructionContextLayer *CC =
25       C.getAllocator().Allocate<ConstructionContextLayer>();
26   return new (CC) ConstructionContextLayer(Trigger, Parent);
27 }
28 
29 bool ConstructionContextLayer::isStrictlyMoreSpecificThan(
30     const ConstructionContextLayer *Other) const {
31   const ConstructionContextLayer *Self = this;
32   while (true) {
33     if (!Other)
34       return Self;
35     if (!Self || !Self->isSameLayer(Other))
36       return false;
37     Self = Self->getParent();
38     Other = Other->getParent();
39   }
40   llvm_unreachable("The above loop can only be terminated via return!");
41 }
42 
43 const ConstructionContext *ConstructionContext::createFromLayers(
44     BumpVectorContext &C, const ConstructionContextLayer *TopLayer) {
45   // Before this point all we've had was a stockpile of arbitrary layers.
46   // Now validate that it is shaped as one of the finite amount of expected
47   // patterns.
48   if (const Stmt *S = TopLayer->getTriggerStmt()) {
49     if (const auto *DS = dyn_cast<DeclStmt>(S)) {
50       assert(TopLayer->isLast());
51       return create<SimpleVariableConstructionContext>(C, DS);
52     }
53     if (const auto *NE = dyn_cast<CXXNewExpr>(S)) {
54       assert(TopLayer->isLast());
55       return create<NewAllocatedObjectConstructionContext>(C, NE);
56     }
57     if (const auto *BTE = dyn_cast<CXXBindTemporaryExpr>(S)) {
58       const MaterializeTemporaryExpr *MTE = nullptr;
59       assert(BTE->getType().getCanonicalType()
60                 ->getAsCXXRecordDecl()->hasNonTrivialDestructor());
61       // For temporaries with destructors, there may or may not be
62       // lifetime extension on the parent layer.
63       if (const ConstructionContextLayer *ParentLayer = TopLayer->getParent()) {
64         assert(ParentLayer->isLast());
65         if ((MTE = dyn_cast<MaterializeTemporaryExpr>(
66                  ParentLayer->getTriggerStmt()))) {
67           // A temporary object which has both destruction and
68           // materialization info.
69           return create<TemporaryObjectConstructionContext>(C, BTE, MTE);
70         }
71         // C++17 *requires* elision of the constructor at the return site
72         // and at variable initialization site, while previous standards
73         // were allowing an optional elidable constructor.
74         if (auto *RS = dyn_cast<ReturnStmt>(ParentLayer->getTriggerStmt())) {
75           assert(!RS->getRetValue()->getType().getCanonicalType()
76                     ->getAsCXXRecordDecl()->hasTrivialDestructor());
77           return create<CXX17ElidedCopyReturnedValueConstructionContext>(C,
78                                                                        RS, BTE);
79         }
80         if (auto *DS = dyn_cast<DeclStmt>(ParentLayer->getTriggerStmt())) {
81           assert(!cast<VarDecl>(DS->getSingleDecl())->getType()
82                       .getCanonicalType()->getAsCXXRecordDecl()
83                       ->hasTrivialDestructor());
84           return create<CXX17ElidedCopyVariableConstructionContext>(C, DS, BTE);
85         }
86         llvm_unreachable("Unexpected construction context with destructor!");
87       }
88       // A temporary object that doesn't require materialization.
89       return create<TemporaryObjectConstructionContext>(C, BTE, /*MTE=*/nullptr);
90     }
91     if (const auto *MTE = dyn_cast<MaterializeTemporaryExpr>(S)) {
92       // If the object requires destruction and is not lifetime-extended,
93       // then it must have a BTE within its MTE.
94       assert(MTE->getType().getCanonicalType()
95                 ->getAsCXXRecordDecl()->hasTrivialDestructor() ||
96              MTE->getStorageDuration() != SD_FullExpression);
97       assert(TopLayer->isLast());
98       return create<TemporaryObjectConstructionContext>(C, nullptr, MTE);
99     }
100     if (const auto *RS = dyn_cast<ReturnStmt>(S)) {
101       assert(TopLayer->isLast());
102       return create<SimpleReturnedValueConstructionContext>(C, RS);
103     }
104     llvm_unreachable("Unexpected construction context with statement!");
105   } else if (const CXXCtorInitializer *I = TopLayer->getTriggerInit()) {
106     assert(TopLayer->isLast());
107     return create<ConstructorInitializerConstructionContext>(C, I);
108   }
109   llvm_unreachable("Unexpected construction context!");
110 }
111