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 
18 using namespace clang;
19 using namespace CodeGen;
20 
21 llvm::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 
30 void 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 
38 void 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 
51 ConstantInitFuture
52 ConstantInitBuilderBase::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.
59 inline 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 
66 llvm::GlobalVariable *
67 ConstantInitBuilderBase::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 
87 void ConstantInitBuilderBase::setGlobalInitializer(llvm::GlobalVariable *GV,
88                                                    llvm::Constant *initializer){
89   GV->setInitializer(initializer);
90 
91   if (!SelfReferences.empty())
92     resolveSelfReferences(GV);
93 }
94 
95 void 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 
107 void 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::PoisonValue::get(dummy->getType()));
118       dummy->eraseFromParent();
119     }
120     SelfReferences.clear();
121   }
122 }
123 
124 void ConstantAggregateBuilderBase::addSize(CharUnits size) {
125   add(Builder.CGM.getSize(size));
126 }
127 
128 llvm::Constant *
129 ConstantAggregateBuilderBase::getRelativeOffset(llvm::IntegerType *offsetType,
130                                                 llvm::Constant *target) {
131   return getRelativeOffsetToPosition(offsetType, target,
132                                      Builder.Buffer.size() - Begin);
133 }
134 
135 llvm::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 
153 llvm::Constant *
154 ConstantAggregateBuilderBase::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 
167 llvm::Constant *
168 ConstantAggregateBuilderBase::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 
181 void 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 
201 ConstantAggregateBuilderBase::PlaceholderPosition
202 ConstantAggregateBuilderBase::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(layout.getABITypeAlign(type)));
213   offset += CharUnits::fromQuantity(layout.getTypeStoreSize(type));
214 
215   CachedOffsetEnd = Builder.Buffer.size();
216   CachedOffsetFromGlobal = offset;
217 
218   return position;
219 }
220 
221 CharUnits ConstantAggregateBuilderBase::getOffsetFromGlobalTo(size_t end) const{
222   size_t cacheEnd = CachedOffsetEnd;
223   assert(cacheEnd <= end);
224 
225   // Fast path: if the cache is valid, just use it.
226   if (cacheEnd == end) {
227     return CachedOffsetFromGlobal;
228   }
229 
230   // If the cached range ends before the index at which the current
231   // aggregate starts, recurse for the parent.
232   CharUnits offset;
233   if (cacheEnd < Begin) {
234     assert(cacheEnd == 0);
235     assert(Parent && "Begin != 0 for root builder");
236     cacheEnd = Begin;
237     offset = Parent->getOffsetFromGlobalTo(Begin);
238   } else {
239     offset = CachedOffsetFromGlobal;
240   }
241 
242   // Perform simple layout on the elements in cacheEnd..<end.
243   if (cacheEnd != end) {
244     auto &layout = Builder.CGM.getDataLayout();
245     do {
246       llvm::Constant *element = Builder.Buffer[cacheEnd];
247       assert(element != nullptr &&
248              "cannot compute offset when a placeholder is present");
249       llvm::Type *elementType = element->getType();
250       if (!Packed)
251         offset = offset.alignTo(
252             CharUnits::fromQuantity(layout.getABITypeAlign(elementType)));
253       offset += CharUnits::fromQuantity(layout.getTypeStoreSize(elementType));
254     } while (++cacheEnd != end);
255   }
256 
257   // Cache and return.
258   CachedOffsetEnd = cacheEnd;
259   CachedOffsetFromGlobal = offset;
260   return offset;
261 }
262 
263 llvm::Constant *ConstantAggregateBuilderBase::finishArray(llvm::Type *eltTy) {
264   markFinished();
265 
266   auto &buffer = getBuffer();
267   assert((Begin < buffer.size() ||
268           (Begin == buffer.size() && eltTy))
269          && "didn't add any array elements without element type");
270   auto elts = llvm::ArrayRef(buffer).slice(Begin);
271   if (!eltTy) eltTy = elts[0]->getType();
272   auto type = llvm::ArrayType::get(eltTy, elts.size());
273   auto constant = llvm::ConstantArray::get(type, elts);
274   buffer.erase(buffer.begin() + Begin, buffer.end());
275   return constant;
276 }
277 
278 llvm::Constant *
279 ConstantAggregateBuilderBase::finishStruct(llvm::StructType *ty) {
280   markFinished();
281 
282   auto &buffer = getBuffer();
283   auto elts = llvm::ArrayRef(buffer).slice(Begin);
284 
285   if (ty == nullptr && elts.empty())
286     ty = llvm::StructType::get(Builder.CGM.getLLVMContext(), {}, Packed);
287 
288   llvm::Constant *constant;
289   if (ty) {
290     assert(ty->isPacked() == Packed);
291     constant = llvm::ConstantStruct::get(ty, elts);
292   } else {
293     constant = llvm::ConstantStruct::getAnon(elts, Packed);
294   }
295 
296   buffer.erase(buffer.begin() + Begin, buffer.end());
297   return constant;
298 }
299