1//===--- ConstantInitBuilder.cpp - Global initializer builder -------------===//
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 defines out-of-line routines for building initializers for
10// global variables, in particular the kind of globals that are implicitly
11// introduced by various language ABIs.
12//
13//===----------------------------------------------------------------------===//
14
15#include "clang/CodeGen/ConstantInitBuilder.h"
16#include "CodeGenModule.h"
17
18using namespace clang;
19using namespace CodeGen;
20
21llvm::Type *ConstantInitFuture::getType() const {
22  assert(Data && "dereferencing null future");
23  if (Data.is<llvm::Constant*>()) {
24    return Data.get<llvm::Constant*>()->getType();
25  } else {
26    return Data.get<ConstantInitBuilderBase*>()->Buffer[0]->getType();
27  }
28}
29
30void ConstantInitFuture::abandon() {
31  assert(Data && "abandoning null future");
32  if (auto builder = Data.dyn_cast<ConstantInitBuilderBase*>()) {
33    builder->abandon(0);
34  }
35  Data = nullptr;
36}
37
38void ConstantInitFuture::installInGlobal(llvm::GlobalVariable *GV) {
39  assert(Data && "installing null future");
40  if (Data.is<llvm::Constant*>()) {
41    GV->setInitializer(Data.get<llvm::Constant*>());
42  } else {
43    auto &builder = *Data.get<ConstantInitBuilderBase*>();
44    assert(builder.Buffer.size() == 1);
45    builder.setGlobalInitializer(GV, builder.Buffer[0]);
46    builder.Buffer.clear();
47    Data = nullptr;
48  }
49}
50
51ConstantInitFuture
52ConstantInitBuilderBase::createFuture(llvm::Constant *initializer) {
53  assert(Buffer.empty() && "buffer not current empty");
54  Buffer.push_back(initializer);
55  return ConstantInitFuture(this);
56}
57
58// Only used in this file.
59inline ConstantInitFuture::ConstantInitFuture(ConstantInitBuilderBase *builder)
60    : Data(builder) {
61  assert(!builder->Frozen);
62  assert(builder->Buffer.size() == 1);
63  assert(builder->Buffer[0] != nullptr);
64}
65
66llvm::GlobalVariable *
67ConstantInitBuilderBase::createGlobal(llvm::Constant *initializer,
68                                      const llvm::Twine &name,
69                                      CharUnits alignment,
70                                      bool constant,
71                                      llvm::GlobalValue::LinkageTypes linkage,
72                                      unsigned addressSpace) {
73  auto GV = new llvm::GlobalVariable(CGM.getModule(),
74                                     initializer->getType(),
75                                     constant,
76                                     linkage,
77                                     initializer,
78                                     name,
79                                     /*insert before*/ nullptr,
80                                     llvm::GlobalValue::NotThreadLocal,
81                                     addressSpace);
82  GV->setAlignment(alignment.getAsAlign());
83  resolveSelfReferences(GV);
84  return GV;
85}
86
87void ConstantInitBuilderBase::setGlobalInitializer(llvm::GlobalVariable *GV,
88                                                   llvm::Constant *initializer){
89  GV->setInitializer(initializer);
90
91  if (!SelfReferences.empty())
92    resolveSelfReferences(GV);
93}
94
95void ConstantInitBuilderBase::resolveSelfReferences(llvm::GlobalVariable *GV) {
96  for (auto &entry : SelfReferences) {
97    llvm::Constant *resolvedReference =
98      llvm::ConstantExpr::getInBoundsGetElementPtr(
99        GV->getValueType(), GV, entry.Indices);
100    auto dummy = entry.Dummy;
101    dummy->replaceAllUsesWith(resolvedReference);
102    dummy->eraseFromParent();
103  }
104  SelfReferences.clear();
105}
106
107void ConstantInitBuilderBase::abandon(size_t newEnd) {
108  // Remove all the entries we've added.
109  Buffer.erase(Buffer.begin() + newEnd, Buffer.end());
110
111  // If we're abandoning all the way to the beginning, destroy
112  // all the self-references, because we might not get another
113  // opportunity.
114  if (newEnd == 0) {
115    for (auto &entry : SelfReferences) {
116      auto dummy = entry.Dummy;
117      dummy->replaceAllUsesWith(llvm::UndefValue::get(dummy->getType()));
118      dummy->eraseFromParent();
119    }
120    SelfReferences.clear();
121  }
122}
123
124void ConstantAggregateBuilderBase::addSize(CharUnits size) {
125  add(Builder.CGM.getSize(size));
126}
127
128llvm::Constant *
129ConstantAggregateBuilderBase::getRelativeOffset(llvm::IntegerType *offsetType,
130                                                llvm::Constant *target) {
131  return getRelativeOffsetToPosition(offsetType, target,
132                                     Builder.Buffer.size() - Begin);
133}
134
135llvm::Constant *ConstantAggregateBuilderBase::getRelativeOffsetToPosition(
136    llvm::IntegerType *offsetType, llvm::Constant *target, size_t position) {
137  // Compute the address of the relative-address slot.
138  auto base = getAddrOfPosition(offsetType, position);
139
140  // Subtract.
141  base = llvm::ConstantExpr::getPtrToInt(base, Builder.CGM.IntPtrTy);
142  target = llvm::ConstantExpr::getPtrToInt(target, Builder.CGM.IntPtrTy);
143  llvm::Constant *offset = llvm::ConstantExpr::getSub(target, base);
144
145  // Truncate to the relative-address type if necessary.
146  if (Builder.CGM.IntPtrTy != offsetType) {
147    offset = llvm::ConstantExpr::getTrunc(offset, offsetType);
148  }
149
150  return offset;
151}
152
153llvm::Constant *
154ConstantAggregateBuilderBase::getAddrOfPosition(llvm::Type *type,
155                                                size_t position) {
156  // Make a global variable.  We will replace this with a GEP to this
157  // position after installing the initializer.
158  auto dummy = new llvm::GlobalVariable(Builder.CGM.getModule(), type, true,
159                                        llvm::GlobalVariable::PrivateLinkage,
160                                        nullptr, "");
161  Builder.SelfReferences.emplace_back(dummy);
162  auto &entry = Builder.SelfReferences.back();
163  (void)getGEPIndicesTo(entry.Indices, position + Begin);
164  return dummy;
165}
166
167llvm::Constant *
168ConstantAggregateBuilderBase::getAddrOfCurrentPosition(llvm::Type *type) {
169  // Make a global variable.  We will replace this with a GEP to this
170  // position after installing the initializer.
171  auto dummy =
172    new llvm::GlobalVariable(Builder.CGM.getModule(), type, true,
173                             llvm::GlobalVariable::PrivateLinkage,
174                             nullptr, "");
175  Builder.SelfReferences.emplace_back(dummy);
176  auto &entry = Builder.SelfReferences.back();
177  (void) getGEPIndicesToCurrentPosition(entry.Indices);
178  return dummy;
179}
180
181void ConstantAggregateBuilderBase::getGEPIndicesTo(
182                               llvm::SmallVectorImpl<llvm::Constant*> &indices,
183                               size_t position) const {
184  // Recurse on the parent builder if present.
185  if (Parent) {
186    Parent->getGEPIndicesTo(indices, Begin);
187
188  // Otherwise, add an index to drill into the first level of pointer.
189  } else {
190    assert(indices.empty());
191    indices.push_back(llvm::ConstantInt::get(Builder.CGM.Int32Ty, 0));
192  }
193
194  assert(position >= Begin);
195  // We have to use i32 here because struct GEPs demand i32 indices.
196  // It's rather unlikely to matter in practice.
197  indices.push_back(llvm::ConstantInt::get(Builder.CGM.Int32Ty,
198                                           position - Begin));
199}
200
201ConstantAggregateBuilderBase::PlaceholderPosition
202ConstantAggregateBuilderBase::addPlaceholderWithSize(llvm::Type *type) {
203  // Bring the offset up to the last field.
204  CharUnits offset = getNextOffsetFromGlobal();
205
206  // Create the placeholder.
207  auto position = addPlaceholder();
208
209  // Advance the offset past that field.
210  auto &layout = Builder.CGM.getDataLayout();
211  if (!Packed)
212    offset = offset.alignTo(CharUnits::fromQuantity(
213                                layout.getABITypeAlignment(type)));
214  offset += CharUnits::fromQuantity(layout.getTypeStoreSize(type));
215
216  CachedOffsetEnd = Builder.Buffer.size();
217  CachedOffsetFromGlobal = offset;
218
219  return position;
220}
221
222CharUnits ConstantAggregateBuilderBase::getOffsetFromGlobalTo(size_t end) const{
223  size_t cacheEnd = CachedOffsetEnd;
224  assert(cacheEnd <= end);
225
226  // Fast path: if the cache is valid, just use it.
227  if (cacheEnd == end) {
228    return CachedOffsetFromGlobal;
229  }
230
231  // If the cached range ends before the index at which the current
232  // aggregate starts, recurse for the parent.
233  CharUnits offset;
234  if (cacheEnd < Begin) {
235    assert(cacheEnd == 0);
236    assert(Parent && "Begin != 0 for root builder");
237    cacheEnd = Begin;
238    offset = Parent->getOffsetFromGlobalTo(Begin);
239  } else {
240    offset = CachedOffsetFromGlobal;
241  }
242
243  // Perform simple layout on the elements in cacheEnd..<end.
244  if (cacheEnd != end) {
245    auto &layout = Builder.CGM.getDataLayout();
246    do {
247      llvm::Constant *element = Builder.Buffer[cacheEnd];
248      assert(element != nullptr &&
249             "cannot compute offset when a placeholder is present");
250      llvm::Type *elementType = element->getType();
251      if (!Packed)
252        offset = offset.alignTo(CharUnits::fromQuantity(
253                                  layout.getABITypeAlignment(elementType)));
254      offset += CharUnits::fromQuantity(layout.getTypeStoreSize(elementType));
255    } while (++cacheEnd != end);
256  }
257
258  // Cache and return.
259  CachedOffsetEnd = cacheEnd;
260  CachedOffsetFromGlobal = offset;
261  return offset;
262}
263
264llvm::Constant *ConstantAggregateBuilderBase::finishArray(llvm::Type *eltTy) {
265  markFinished();
266
267  auto &buffer = getBuffer();
268  assert((Begin < buffer.size() ||
269          (Begin == buffer.size() && eltTy))
270         && "didn't add any array elements without element type");
271  auto elts = llvm::makeArrayRef(buffer).slice(Begin);
272  if (!eltTy) eltTy = elts[0]->getType();
273  auto type = llvm::ArrayType::get(eltTy, elts.size());
274  auto constant = llvm::ConstantArray::get(type, elts);
275  buffer.erase(buffer.begin() + Begin, buffer.end());
276  return constant;
277}
278
279llvm::Constant *
280ConstantAggregateBuilderBase::finishStruct(llvm::StructType *ty) {
281  markFinished();
282
283  auto &buffer = getBuffer();
284  auto elts = llvm::makeArrayRef(buffer).slice(Begin);
285
286  if (ty == nullptr && elts.empty())
287    ty = llvm::StructType::get(Builder.CGM.getLLVMContext(), {}, Packed);
288
289  llvm::Constant *constant;
290  if (ty) {
291    assert(ty->isPacked() == Packed);
292    constant = llvm::ConstantStruct::get(ty, elts);
293  } else {
294    constant = llvm::ConstantStruct::getAnon(elts, Packed);
295  }
296
297  buffer.erase(buffer.begin() + Begin, buffer.end());
298  return constant;
299}
300