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         // C++17 *requires* elision of the constructor at the return site
66         // and at variable/member initialization site, while previous standards
67         // were allowing an optional elidable constructor.
68         // This is the C++17 copy-elided construction into a ctor initializer.
69         if (const CXXCtorInitializer *I = ParentLayer->getTriggerInit()) {
70           return create<
71               CXX17ElidedCopyConstructorInitializerConstructionContext>(C,
72                                                                         I, BTE);
73         }
74         assert(ParentLayer->getTriggerStmt() &&
75                "Non-statement-based layers have been handled above!");
76         // This is the normal, non-C++17 case: a temporary object which has
77         // both destruction and materialization info attached to it in the AST.
78         if ((MTE = dyn_cast<MaterializeTemporaryExpr>(
79                  ParentLayer->getTriggerStmt()))) {
80           return create<TemporaryObjectConstructionContext>(C, BTE, MTE);
81         }
82         // This is a constructor into a function argument. Not implemented yet.
83         if (isa<CallExpr>(ParentLayer->getTriggerStmt()))
84           return nullptr;
85         // This is C++17 copy-elided construction into return statement.
86         if (auto *RS = dyn_cast<ReturnStmt>(ParentLayer->getTriggerStmt())) {
87           assert(!RS->getRetValue()->getType().getCanonicalType()
88                     ->getAsCXXRecordDecl()->hasTrivialDestructor());
89           return create<CXX17ElidedCopyReturnedValueConstructionContext>(C,
90                                                                        RS, BTE);
91         }
92         // This is C++17 copy-elided construction into a simple variable.
93         if (auto *DS = dyn_cast<DeclStmt>(ParentLayer->getTriggerStmt())) {
94           assert(!cast<VarDecl>(DS->getSingleDecl())->getType()
95                       .getCanonicalType()->getAsCXXRecordDecl()
96                       ->hasTrivialDestructor());
97           return create<CXX17ElidedCopyVariableConstructionContext>(C, DS, BTE);
98         }
99         llvm_unreachable("Unexpected construction context with destructor!");
100       }
101       // A temporary object that doesn't require materialization.
102       return create<TemporaryObjectConstructionContext>(C, BTE, /*MTE=*/nullptr);
103     }
104     if (const auto *MTE = dyn_cast<MaterializeTemporaryExpr>(S)) {
105       // If the object requires destruction and is not lifetime-extended,
106       // then it must have a BTE within its MTE.
107       // FIXME: This should be an assertion.
108       if (!(MTE->getType().getCanonicalType()
109                 ->getAsCXXRecordDecl()->hasTrivialDestructor() ||
110              MTE->getStorageDuration() != SD_FullExpression))
111         return nullptr;
112 
113       assert(TopLayer->isLast());
114       return create<TemporaryObjectConstructionContext>(C, nullptr, MTE);
115     }
116     if (const auto *RS = dyn_cast<ReturnStmt>(S)) {
117       assert(TopLayer->isLast());
118       return create<SimpleReturnedValueConstructionContext>(C, RS);
119     }
120     // This is a constructor into a function argument. Not implemented yet.
121     if (isa<CallExpr>(TopLayer->getTriggerStmt()))
122       return nullptr;
123     llvm_unreachable("Unexpected construction context with statement!");
124   } else if (const CXXCtorInitializer *I = TopLayer->getTriggerInit()) {
125     assert(TopLayer->isLast());
126     return create<SimpleConstructorInitializerConstructionContext>(C, I);
127   }
128   llvm_unreachable("Unexpected construction context!");
129 }
130