1 //===-- LibCxxSpan.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 #include "LibCxx.h"
10 
11 #include "lldb/Core/ValueObject.h"
12 #include "lldb/DataFormatters/FormattersHelpers.h"
13 #include "lldb/Utility/ConstString.h"
14 #include "llvm/ADT/APSInt.h"
15 
16 using namespace lldb;
17 using namespace lldb_private;
18 using namespace lldb_private::formatters;
19 
20 namespace lldb_private {
21 namespace formatters {
22 
23 class LibcxxStdSpanSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
24 public:
25   LibcxxStdSpanSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp);
26 
27   ~LibcxxStdSpanSyntheticFrontEnd() override = default;
28 
29   size_t CalculateNumChildren() override;
30 
31   lldb::ValueObjectSP GetChildAtIndex(size_t idx) override;
32 
33   /// Determines properties of the std::span<> associated with this object
34   //
35   // std::span can either be instantiated with a compile-time known
36   // extent or a std::dynamic_extent (this is the default if only the
37   // type template argument is provided). The layout of std::span
38   // depends on whether the extent is dynamic or not. For static
39   // extents (e.g., std::span<int, 9>):
40   //
41   // (std::__1::span<const int, 9>) s = {
42   //   __data = 0x000000016fdff494
43   // }
44   //
45   // For dynamic extents, e.g., std::span<int>, the layout is:
46   //
47   // (std::__1::span<const int, 18446744073709551615>) s = {
48   //   __data = 0x000000016fdff494
49   //   __size = 6
50   // }
51   //
52   // This function checks for a '__size' member to determine the number
53   // of elements in the span. If no such member exists, we get the size
54   // from the only other place it can be: the template argument.
55   bool Update() override;
56 
57   bool MightHaveChildren() override;
58 
59   size_t GetIndexOfChildWithName(ConstString name) override;
60 
61 private:
62   ValueObject *m_start = nullptr; ///< First element of span. Held, not owned.
63   CompilerType m_element_type{};  ///< Type of span elements.
64   size_t m_num_elements = 0;      ///< Number of elements in span.
65   uint32_t m_element_size = 0;    ///< Size in bytes of each span element.
66 };
67 
68 lldb_private::formatters::LibcxxStdSpanSyntheticFrontEnd::
69     LibcxxStdSpanSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp)
70     : SyntheticChildrenFrontEnd(*valobj_sp) {
71   if (valobj_sp)
72     Update();
73 }
74 
75 size_t lldb_private::formatters::LibcxxStdSpanSyntheticFrontEnd::
76     CalculateNumChildren() {
77   return m_num_elements;
78 }
79 
80 lldb::ValueObjectSP
81 lldb_private::formatters::LibcxxStdSpanSyntheticFrontEnd::GetChildAtIndex(
82     size_t idx) {
83   if (!m_start)
84     return {};
85 
86   uint64_t offset = idx * m_element_size;
87   offset = offset + m_start->GetValueAsUnsigned(0);
88   StreamString name;
89   name.Printf("[%" PRIu64 "]", (uint64_t)idx);
90   return CreateValueObjectFromAddress(name.GetString(), offset,
91                                       m_backend.GetExecutionContextRef(),
92                                       m_element_type);
93 }
94 
95 bool lldb_private::formatters::LibcxxStdSpanSyntheticFrontEnd::Update() {
96   // Get element type.
97   ValueObjectSP data_type_finder_sp(
98       m_backend.GetChildMemberWithName(ConstString("__data"), true));
99   if (!data_type_finder_sp)
100     return false;
101 
102   m_element_type = data_type_finder_sp->GetCompilerType().GetPointeeType();
103 
104   // Get element size.
105   if (llvm::Optional<uint64_t> size = m_element_type.GetByteSize(nullptr)) {
106     m_element_size = *size;
107 
108     // Get data.
109     if (m_element_size > 0) {
110       m_start = data_type_finder_sp.get();
111     }
112 
113     // Get number of elements.
114     if (auto size_sp =
115             m_backend.GetChildMemberWithName(ConstString("__size"), true)) {
116       m_num_elements = size_sp->GetValueAsUnsigned(0);
117     } else if (auto arg =
118                    m_backend.GetCompilerType().GetIntegralTemplateArgument(1)) {
119 
120       m_num_elements = arg->value.getLimitedValue();
121     }
122   }
123 
124   return true;
125 }
126 
127 bool lldb_private::formatters::LibcxxStdSpanSyntheticFrontEnd::
128     MightHaveChildren() {
129   return true;
130 }
131 
132 size_t lldb_private::formatters::LibcxxStdSpanSyntheticFrontEnd::
133     GetIndexOfChildWithName(ConstString name) {
134   if (!m_start)
135     return UINT32_MAX;
136   return ExtractIndexFromString(name.GetCString());
137 }
138 
139 lldb_private::SyntheticChildrenFrontEnd *
140 LibcxxStdSpanSyntheticFrontEndCreator(CXXSyntheticChildren *,
141                                       lldb::ValueObjectSP valobj_sp) {
142   if (!valobj_sp)
143     return nullptr;
144   CompilerType type = valobj_sp->GetCompilerType();
145   if (!type.IsValid() || type.GetNumTemplateArguments() != 2)
146     return nullptr;
147   return new LibcxxStdSpanSyntheticFrontEnd(valobj_sp);
148 }
149 
150 } // namespace formatters
151 } // namespace lldb_private
152