1 //===- llvm/ADT/SmallVector.cpp - 'Normally small' vectors ----------------===//
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 // This file implements the SmallVector class.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/ADT/SmallVector.h"
14 #include "llvm/ADT/Twine.h"
15 #include "llvm/Support/MemAlloc.h"
16 #include <cstdint>
17 #ifdef LLVM_ENABLE_EXCEPTIONS
18 #include <stdexcept>
19 #endif
20 using namespace llvm;
21 
22 // Check that no bytes are wasted and everything is well-aligned.
23 namespace {
24 // These structures may cause binary compat warnings on AIX. Suppress the
25 // warning since we are only using these types for the static assertions below.
26 #if defined(_AIX)
27 #pragma GCC diagnostic push
28 #pragma GCC diagnostic ignored "-Waix-compat"
29 #endif
30 struct Struct16B {
31   alignas(16) void *X;
32 };
33 struct Struct32B {
34   alignas(32) void *X;
35 };
36 #if defined(_AIX)
37 #pragma GCC diagnostic pop
38 #endif
39 }
40 static_assert(sizeof(SmallVector<void *, 0>) ==
41                   sizeof(unsigned) * 2 + sizeof(void *),
42               "wasted space in SmallVector size 0");
43 static_assert(alignof(SmallVector<Struct16B, 0>) >= alignof(Struct16B),
44               "wrong alignment for 16-byte aligned T");
45 static_assert(alignof(SmallVector<Struct32B, 0>) >= alignof(Struct32B),
46               "wrong alignment for 32-byte aligned T");
47 static_assert(sizeof(SmallVector<Struct16B, 0>) >= alignof(Struct16B),
48               "missing padding for 16-byte aligned T");
49 static_assert(sizeof(SmallVector<Struct32B, 0>) >= alignof(Struct32B),
50               "missing padding for 32-byte aligned T");
51 static_assert(sizeof(SmallVector<void *, 1>) ==
52                   sizeof(unsigned) * 2 + sizeof(void *) * 2,
53               "wasted space in SmallVector size 1");
54 
55 static_assert(sizeof(SmallVector<char, 0>) ==
56                   sizeof(void *) * 2 + sizeof(void *),
57               "1 byte elements have word-sized type for size and capacity");
58 
59 /// Report that MinSize doesn't fit into this vector's size type. Throws
60 /// std::length_error or calls report_fatal_error.
61 [[noreturn]] static void report_size_overflow(size_t MinSize, size_t MaxSize);
62 static void report_size_overflow(size_t MinSize, size_t MaxSize) {
63   std::string Reason = "SmallVector unable to grow. Requested capacity (" +
64                        std::to_string(MinSize) +
65                        ") is larger than maximum value for size type (" +
66                        std::to_string(MaxSize) + ")";
67 #ifdef LLVM_ENABLE_EXCEPTIONS
68   throw std::length_error(Reason);
69 #else
70   report_fatal_error(Twine(Reason));
71 #endif
72 }
73 
74 /// Report that this vector is already at maximum capacity. Throws
75 /// std::length_error or calls report_fatal_error.
76 [[noreturn]] static void report_at_maximum_capacity(size_t MaxSize);
77 static void report_at_maximum_capacity(size_t MaxSize) {
78   std::string Reason =
79       "SmallVector capacity unable to grow. Already at maximum size " +
80       std::to_string(MaxSize);
81 #ifdef LLVM_ENABLE_EXCEPTIONS
82   throw std::length_error(Reason);
83 #else
84   report_fatal_error(Twine(Reason));
85 #endif
86 }
87 
88 // Note: Moving this function into the header may cause performance regression.
89 template <class Size_T>
90 static size_t getNewCapacity(size_t MinSize, size_t TSize, size_t OldCapacity) {
91   constexpr size_t MaxSize = std::numeric_limits<Size_T>::max();
92 
93   // Ensure we can fit the new capacity.
94   // This is only going to be applicable when the capacity is 32 bit.
95   if (MinSize > MaxSize)
96     report_size_overflow(MinSize, MaxSize);
97 
98   // Ensure we can meet the guarantee of space for at least one more element.
99   // The above check alone will not catch the case where grow is called with a
100   // default MinSize of 0, but the current capacity cannot be increased.
101   // This is only going to be applicable when the capacity is 32 bit.
102   if (OldCapacity == MaxSize)
103     report_at_maximum_capacity(MaxSize);
104 
105   // In theory 2*capacity can overflow if the capacity is 64 bit, but the
106   // original capacity would never be large enough for this to be a problem.
107   size_t NewCapacity = 2 * OldCapacity + 1; // Always grow.
108   return std::clamp(NewCapacity, MinSize, MaxSize);
109 }
110 
111 template <class Size_T>
112 void *SmallVectorBase<Size_T>::replaceAllocation(void *NewElts, size_t TSize,
113                                                  size_t NewCapacity,
114                                                  size_t VSize) {
115   void *NewEltsReplace = llvm::safe_malloc(NewCapacity * TSize);
116   if (VSize)
117     memcpy(NewEltsReplace, NewElts, VSize * TSize);
118   free(NewElts);
119   return NewEltsReplace;
120 }
121 
122 // Note: Moving this function into the header may cause performance regression.
123 template <class Size_T>
124 void *SmallVectorBase<Size_T>::mallocForGrow(void *FirstEl, size_t MinSize,
125                                              size_t TSize,
126                                              size_t &NewCapacity) {
127   NewCapacity = getNewCapacity<Size_T>(MinSize, TSize, this->capacity());
128   // Even if capacity is not 0 now, if the vector was originally created with
129   // capacity 0, it's possible for the malloc to return FirstEl.
130   void *NewElts = llvm::safe_malloc(NewCapacity * TSize);
131   if (NewElts == FirstEl)
132     NewElts = replaceAllocation(NewElts, TSize, NewCapacity);
133   return NewElts;
134 }
135 
136 // Note: Moving this function into the header may cause performance regression.
137 template <class Size_T>
138 void SmallVectorBase<Size_T>::grow_pod(void *FirstEl, size_t MinSize,
139                                        size_t TSize) {
140   size_t NewCapacity = getNewCapacity<Size_T>(MinSize, TSize, this->capacity());
141   void *NewElts;
142   if (BeginX == FirstEl) {
143     NewElts = llvm::safe_malloc(NewCapacity * TSize);
144     if (NewElts == FirstEl)
145       NewElts = replaceAllocation(NewElts, TSize, NewCapacity);
146 
147     // Copy the elements over.  No need to run dtors on PODs.
148     memcpy(NewElts, this->BeginX, size() * TSize);
149   } else {
150     // If this wasn't grown from the inline copy, grow the allocated space.
151     NewElts = llvm::safe_realloc(this->BeginX, NewCapacity * TSize);
152     if (NewElts == FirstEl)
153       NewElts = replaceAllocation(NewElts, TSize, NewCapacity, size());
154   }
155 
156   this->set_allocation_range(NewElts, NewCapacity);
157 }
158 
159 template class llvm::SmallVectorBase<uint32_t>;
160 
161 // Disable the uint64_t instantiation for 32-bit builds.
162 // Both uint32_t and uint64_t instantiations are needed for 64-bit builds.
163 // This instantiation will never be used in 32-bit builds, and will cause
164 // warnings when sizeof(Size_T) > sizeof(size_t).
165 #if SIZE_MAX > UINT32_MAX
166 template class llvm::SmallVectorBase<uint64_t>;
167 
168 // Assertions to ensure this #if stays in sync with SmallVectorSizeType.
169 static_assert(sizeof(SmallVectorSizeType<char>) == sizeof(uint64_t),
170               "Expected SmallVectorBase<uint64_t> variant to be in use.");
171 #else
172 static_assert(sizeof(SmallVectorSizeType<char>) == sizeof(uint32_t),
173               "Expected SmallVectorBase<uint32_t> variant to be in use.");
174 #endif
175