lib/CodeGen/ConstantBuilder.h - third_party/swift-clang - Git at Google

 //===----- ConstantBuilder.h - Builder for LLVM IR constants ----*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This class provides a convenient interface for building complex
 // global initializers.
 //
 //===----------------------------------------------------------------------===//

 #ifndef LLVM_CLANG_LIB_CODEGEN_CONSTANTBUILDER_H
 #define LLVM_CLANG_LIB_CODEGEN_CONSTANTBUILDER_H

 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/IR/Constants.h"

 #include "CodeGenModule.h"

 #include <vector>

 namespace clang {
 namespace CodeGen {

 class ConstantStructBuilder;
 class ConstantArrayBuilder;

 /// A convenience builder class for complex constant initializers,
 /// especially for anonymous global structures used by various language
 /// runtimes.
 ///
 /// The basic usage pattern is expected to be something like:
 ///    ConstantInitBuilder builder(CGM);
 ///    auto toplevel = builder.beginStruct();
 ///    toplevel.addInt(CGM.SizeTy, widgets.size());
 ///    auto widgetArray = builder.beginArray();
 ///    for (auto &widget : widgets) {
 ///      auto widgetDesc = widgetArray.beginStruct();
 ///      widgetDesc.addInt(CGM.SizeTy, widget.getPower());
 ///      widgetDesc.add(CGM.GetAddrOfConstantString(widget.getName()));
 ///      widgetDesc.add(CGM.GetAddrOfGlobal(widget.getInitializerDecl()));
 ///      widgetArray.add(widgetDesc.finish());
 ///    }
 ///    toplevel.add(widgetArray.finish());
 ///    auto global = toplevel.finishAndCreateGlobal("WIDGET_LIST", Align,
 ///                                                 /*constant*/ true);
 class ConstantInitBuilder {
   struct SelfReference {
     llvm::GlobalVariable *Dummy;
     llvm::SmallVector<llvm::Constant*, 4> Indices;

     SelfReference(llvm::GlobalVariable *dummy) : Dummy(dummy) {}
   };
   CodeGenModule &CGM;
   llvm::SmallVector<llvm::Constant*, 16> Buffer;
   std::vector<SelfReference> SelfReferences;
   bool Frozen = false;

 public:
   explicit ConstantInitBuilder(CodeGenModule &CGM) : CGM(CGM) {}

   ~ConstantInitBuilder() {
     assert(Buffer.empty() && "didn't claim all values out of buffer");
   }

   class AggregateBuilderBase {
   protected:
     ConstantInitBuilder &Builder;
     AggregateBuilderBase *Parent;
     size_t Begin;
     bool Finished = false;
     bool Frozen = false;

     llvm::SmallVectorImpl<llvm::Constant*> &getBuffer() {
       return Builder.Buffer;
     }

     const llvm::SmallVectorImpl<llvm::Constant*> &getBuffer() const {
       return Builder.Buffer;
     }

     AggregateBuilderBase(ConstantInitBuilder &builder,
                          AggregateBuilderBase *parent)
         : Builder(builder), Parent(parent), Begin(builder.Buffer.size()) {
       if (parent) {
         assert(!parent->Frozen && "parent already has child builder active");
         parent->Frozen = true;
       } else {
         assert(!builder.Frozen && "builder already has child builder active");
         builder.Frozen = true;
       }
     }

     ~AggregateBuilderBase() {
       assert(Finished && "didn't finish aggregate builder");
     }

     void markFinished() {
       assert(!Frozen && "child builder still active");
       assert(!Finished && "builder already finished");
       Finished = true;
       if (Parent) {
         assert(Parent->Frozen &&
                "parent not frozen while child builder active");
         Parent->Frozen = false;
       } else {
         assert(Builder.Frozen &&
                "builder not frozen while child builder active");
         Builder.Frozen = false;
       }
     }

   public:
     // Not copyable.
     AggregateBuilderBase(const AggregateBuilderBase &) = delete;
     AggregateBuilderBase &operator=(const AggregateBuilderBase &) = delete;

     // Movable, mostly to allow returning.  But we have to write this out
     // properly to satisfy the assert in the destructor.
     AggregateBuilderBase(AggregateBuilderBase &&other)
       : Builder(other.Builder), Parent(other.Parent), Begin(other.Begin),
         Finished(other.Finished), Frozen(other.Frozen) {
       other.Finished = false;
     }
     AggregateBuilderBase &operator=(AggregateBuilderBase &&other) = delete;

     /// Abandon this builder completely.
     void abandon() {
       markFinished();
       auto &buffer = Builder.Buffer;
       buffer.erase(buffer.begin() + Begin, buffer.end());
     }

     /// Add a new value to this initializer.
     void add(llvm::Constant *value) {
       assert(value && "adding null value to constant initializer");
       assert(!Finished && "cannot add more values after finishing builder");
       assert(!Frozen && "cannot add values while subbuilder is active");
       Builder.Buffer.push_back(value);
     }

     /// Add an integer value of type size_t.
     void addSize(CharUnits size) {
       add(Builder.CGM.getSize(size));
     }

     /// Add an integer value of a specific type.
     void addInt(llvm::IntegerType *intTy, uint64_t value,
                 bool isSigned = false) {
       add(llvm::ConstantInt::get(intTy, value, isSigned));
     }

     /// Add a null pointer of a specific type.
     void addNullPointer(llvm::PointerType *ptrTy) {
       add(llvm::ConstantPointerNull::get(ptrTy));
     }

     /// Add a bitcast of a value to a specific type.
     void addBitCast(llvm::Constant *value, llvm::Type *type) {
       add(llvm::ConstantExpr::getBitCast(value, type));
     }

     /// Add a bunch of new values to this initializer.
     void addAll(ArrayRef<llvm::Constant *> values) {
       assert(!Finished && "cannot add more values after finishing builder");
       assert(!Frozen && "cannot add values while subbuilder is active");
       Builder.Buffer.append(values.begin(), values.end());
     }

     /// An opaque class to hold the abstract position of a placeholder.
     class PlaceholderPosition {
       size_t Index;
       friend class AggregateBuilderBase;
       PlaceholderPosition(size_t index) : Index(index) {}
     };

     /// Add a placeholder value to the structure.  The returned position
     /// can be used to set the value later; it will not be invalidated by
     /// any intermediate operations except (1) filling the same position or
     /// (2) finishing the entire builder.
     ///
     /// This is useful for emitting certain kinds of structure which
     /// contain some sort of summary field, generaly a count, before any
     /// of the data.  By emitting a placeholder first, the structure can
     /// be emitted eagerly.
     PlaceholderPosition addPlaceholder() {
       assert(!Finished && "cannot add more values after finishing builder");
       assert(!Frozen && "cannot add values while subbuilder is active");
       Builder.Buffer.push_back(nullptr);
       return Builder.Buffer.size() - 1;
     }

     /// Fill a previously-added placeholder.
     void fillPlaceholderWithInt(PlaceholderPosition position,
                                 llvm::IntegerType *type, uint64_t value,
                                 bool isSigned = false) {
       fillPlaceholder(position, llvm::ConstantInt::get(type, value, isSigned));
     }

     /// Fill a previously-added placeholder.
     void fillPlaceholder(PlaceholderPosition position, llvm::Constant *value) {
       assert(!Finished && "cannot change values after finishing builder");
       assert(!Frozen && "cannot add values while subbuilder is active");
       llvm::Constant *&slot = Builder.Buffer[position.Index];
       assert(slot == nullptr && "placeholder already filled");
       slot = value;
     }

     /// Produce an address which will eventually point to the the next
     /// position to be filled.  This is computed with an indexed
     /// getelementptr rather than by computing offsets.
     ///
     /// The returned pointer will have type T*, where T is the given
     /// position.
     llvm::Constant *getAddrOfCurrentPosition(llvm::Type *type) {
       // Make a global variable.  We will replace this with a GEP to this
       // position after installing the initializer.
       auto dummy =
         new llvm::GlobalVariable(Builder.CGM.getModule(), type, true,
                                  llvm::GlobalVariable::PrivateLinkage,
                                  nullptr, "");
       Builder.SelfReferences.emplace_back(dummy);
       auto &entry = Builder.SelfReferences.back();
       (void) getGEPIndicesToCurrentPosition(entry.Indices);
       return dummy;
     }

     ArrayRef<llvm::Constant*> getGEPIndicesToCurrentPosition(
                              llvm::SmallVectorImpl<llvm::Constant*> &indices) {
       getGEPIndicesTo(indices, Builder.Buffer.size());
       return indices;
     }

     ConstantArrayBuilder beginArray(llvm::Type *eltTy = nullptr);
     ConstantStructBuilder beginStruct(llvm::StructType *structTy = nullptr);

   private:
     void getGEPIndicesTo(llvm::SmallVectorImpl<llvm::Constant*> &indices,
                          size_t position) const {
       // Recurse on the parent builder if present.
       if (Parent) {
         Parent->getGEPIndicesTo(indices, Begin);

       // Otherwise, add an index to drill into the first level of pointer.
       } else {
         assert(indices.empty());
         indices.push_back(llvm::ConstantInt::get(Builder.CGM.Int32Ty, 0));
       }

       assert(position >= Begin);
       // We have to use i32 here because struct GEPs demand i32 indices.
       // It's rather unlikely to matter in practice.
       indices.push_back(llvm::ConstantInt::get(Builder.CGM.Int32Ty,
                                                position - Begin));
     }
   };

   template <class Impl>
   class AggregateBuilder : public AggregateBuilderBase {
   protected:
     AggregateBuilder(ConstantInitBuilder &builder,
                      AggregateBuilderBase *parent)
       : AggregateBuilderBase(builder, parent) {}

     Impl &asImpl() { return *static_cast<Impl*>(this); }

   public:
     /// Given that this builder was created by beginning an array or struct
     /// component on the given parent builder, finish the array/struct
     /// component and add it to the parent.
     ///
     /// It is an intentional choice that the parent is passed in explicitly
     /// despite it being redundant with information already kept in the
     /// builder.  This aids in readability by making it easier to find the
     /// places that add components to a builder, as well as "bookending"
     /// the sub-builder more explicitly.
     void finishAndAddTo(AggregateBuilderBase &parent) {
       assert(Parent == &parent && "adding to non-parent builder");
       parent.add(asImpl().finishImpl());
     }

     /// Given that this builder was created by beginning an array or struct
     /// directly on a ConstantInitBuilder, finish the array/struct and
     /// create a global variable with it as the initializer.
     template <class... As>
     llvm::GlobalVariable *finishAndCreateGlobal(As &&...args) {
       assert(!Parent && "finishing non-root builder");
       return Builder.createGlobal(asImpl().finishImpl(),
                                   std::forward<As>(args)...);
     }

     /// Given that this builder was created by beginning an array or struct
     /// directly on a ConstantInitBuilder, finish the array/struct and
     /// set it as the initializer of the given global variable.
     void finishAndSetAsInitializer(llvm::GlobalVariable *global) {
       assert(!Parent && "finishing non-root builder");
       return Builder.setGlobalInitializer(global, asImpl().finishImpl());
     }
   };

   ConstantArrayBuilder beginArray(llvm::Type *eltTy = nullptr);

   ConstantStructBuilder beginStruct(llvm::StructType *structTy = nullptr);

 private:
   llvm::GlobalVariable *createGlobal(llvm::Constant *initializer,
                                      const llvm::Twine &name,
                                      CharUnits alignment,
                                      bool constant = false,
                                      llvm::GlobalValue::LinkageTypes linkage
                                        = llvm::GlobalValue::InternalLinkage,
                                      unsigned addressSpace = 0) {
     auto GV = new llvm::GlobalVariable(CGM.getModule(),
                                        initializer->getType(),
                                        constant,
                                        linkage,
                                        initializer,
                                        name,
                                        /*insert before*/ nullptr,
                                        llvm::GlobalValue::NotThreadLocal,
                                        addressSpace);
     GV->setAlignment(alignment.getQuantity());
     resolveSelfReferences(GV);
     return GV;
   }

   void setGlobalInitializer(llvm::GlobalVariable *GV,
                             llvm::Constant *initializer) {
     GV->setInitializer(initializer);
     resolveSelfReferences(GV);
   }

   void resolveSelfReferences(llvm::GlobalVariable *GV) {
     for (auto &entry : SelfReferences) {
       llvm::Constant *resolvedReference =
         llvm::ConstantExpr::getInBoundsGetElementPtr(
           GV->getValueType(), GV, entry.Indices);
       entry.Dummy->replaceAllUsesWith(resolvedReference);
       entry.Dummy->eraseFromParent();
     }
   }
 };

 /// A helper class of ConstantInitBuilder, used for building constant
 /// array initializers.
 class ConstantArrayBuilder
     : public ConstantInitBuilder::AggregateBuilder<ConstantArrayBuilder> {
   llvm::Type *EltTy;
   friend class ConstantInitBuilder;
   template <class Impl> friend class ConstantInitBuilder::AggregateBuilder;
   ConstantArrayBuilder(ConstantInitBuilder &builder,
                        AggregateBuilderBase *parent, llvm::Type *eltTy)
     : AggregateBuilder(builder, parent), EltTy(eltTy) {}
 public:
   size_t size() const {
     assert(!Finished);
     assert(!Frozen);
     assert(Begin <= getBuffer().size());
     return getBuffer().size() - Begin;
   }

   bool empty() const {
     return size() == 0;
   }

 private:
   /// Form an array constant from the values that have been added to this
   /// builder.
   llvm::Constant *finishImpl() {
     markFinished();

     auto &buffer = getBuffer();
     assert((Begin < buffer.size() ||
             (Begin == buffer.size() && EltTy))
            && "didn't add any array elements without element type");
     auto elts = llvm::makeArrayRef(buffer).slice(Begin);
     auto eltTy = EltTy ? EltTy : elts[0]->getType();
     auto type = llvm::ArrayType::get(eltTy, elts.size());
     auto constant = llvm::ConstantArray::get(type, elts);
     buffer.erase(buffer.begin() + Begin, buffer.end());
     return constant;
   }
 };

 inline ConstantArrayBuilder
 ConstantInitBuilder::beginArray(llvm::Type *eltTy) {
   return ConstantArrayBuilder(*this, nullptr, eltTy);
 }

 inline ConstantArrayBuilder
 ConstantInitBuilder::AggregateBuilderBase::beginArray(llvm::Type *eltTy) {
   return ConstantArrayBuilder(Builder, this, eltTy);
 }

 /// A helper class of ConstantInitBuilder, used for building constant
 /// struct initializers.
 class ConstantStructBuilder
     : public ConstantInitBuilder::AggregateBuilder<ConstantStructBuilder> {
   llvm::StructType *Ty;
   friend class ConstantInitBuilder;
   template <class Impl> friend class ConstantInitBuilder::AggregateBuilder;
   ConstantStructBuilder(ConstantInitBuilder &builder,
                         AggregateBuilderBase *parent, llvm::StructType *ty)
     : AggregateBuilder(builder, parent), Ty(ty) {}

   /// Finish the struct.
   llvm::Constant *finishImpl() {
     markFinished();

     auto &buffer = getBuffer();
     assert(Begin < buffer.size() && "didn't add any struct elements?");
     auto elts = llvm::makeArrayRef(buffer).slice(Begin);

     llvm::Constant *constant;
     if (Ty) {
       constant = llvm::ConstantStruct::get(Ty, elts);
     } else {
       constant = llvm::ConstantStruct::getAnon(elts, /*packed*/ false);
     }

     buffer.erase(buffer.begin() + Begin, buffer.end());
     return constant;
   }
 };

 inline ConstantStructBuilder
 ConstantInitBuilder::beginStruct(llvm::StructType *structTy) {
   return ConstantStructBuilder(*this, nullptr, structTy);
 }

 inline ConstantStructBuilder
 ConstantInitBuilder::AggregateBuilderBase::beginStruct(
                                                   llvm::StructType *structTy) {
   return ConstantStructBuilder(Builder, this, structTy);
 }

 }  // end namespace CodeGen
 }  // end namespace clang

 #endif
	//===----- ConstantBuilder.h - Builder for LLVM IR constants ----- C++ --===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This class provides a convenient interface for building complex
	// global initializers.
	//
	//===----------------------------------------------------------------------===//

	#ifndef LLVM_CLANG_LIB_CODEGEN_CONSTANTBUILDER_H
	#define LLVM_CLANG_LIB_CODEGEN_CONSTANTBUILDER_H

	#include "llvm/ADT/ArrayRef.h"
	#include "llvm/ADT/SmallVector.h"
	#include "llvm/IR/Constants.h"

	#include "CodeGenModule.h"

	#include <vector>

	namespace clang {
	namespace CodeGen {

	class ConstantStructBuilder;
	class ConstantArrayBuilder;

	/// A convenience builder class for complex constant initializers,
	/// especially for anonymous global structures used by various language
	/// runtimes.
	///
	/// The basic usage pattern is expected to be something like:
	/// ConstantInitBuilder builder(CGM);
	/// auto toplevel = builder.beginStruct();
	/// toplevel.addInt(CGM.SizeTy, widgets.size());
	/// auto widgetArray = builder.beginArray();
	/// for (auto &widget : widgets) {
	/// auto widgetDesc = widgetArray.beginStruct();
	/// widgetDesc.addInt(CGM.SizeTy, widget.getPower());
	/// widgetDesc.add(CGM.GetAddrOfConstantString(widget.getName()));
	/// widgetDesc.add(CGM.GetAddrOfGlobal(widget.getInitializerDecl()));
	/// widgetArray.add(widgetDesc.finish());
	/// }
	/// toplevel.add(widgetArray.finish());
	/// auto global = toplevel.finishAndCreateGlobal("WIDGET_LIST", Align,
	/// /constant/ true);
	class ConstantInitBuilder {
	struct SelfReference {
	llvm::GlobalVariable *Dummy;
	llvm::SmallVector<llvm::Constant*, 4> Indices;

	SelfReference(llvm::GlobalVariable *dummy) : Dummy(dummy) {}
	};
	CodeGenModule &CGM;
	llvm::SmallVector<llvm::Constant*, 16> Buffer;
	std::vector<SelfReference> SelfReferences;
	bool Frozen = false;

	public:
	explicit ConstantInitBuilder(CodeGenModule &CGM) : CGM(CGM) {}

	~ConstantInitBuilder() {
	assert(Buffer.empty() && "didn't claim all values out of buffer");
	}

	class AggregateBuilderBase {
	protected:
	ConstantInitBuilder &Builder;
	AggregateBuilderBase *Parent;
	size_t Begin;
	bool Finished = false;
	bool Frozen = false;

	llvm::SmallVectorImpl<llvm::Constant*> &getBuffer() {
	return Builder.Buffer;
	}

	const llvm::SmallVectorImpl<llvm::Constant*> &getBuffer() const {
	return Builder.Buffer;
	}

	AggregateBuilderBase(ConstantInitBuilder &builder,
	AggregateBuilderBase *parent)
	: Builder(builder), Parent(parent), Begin(builder.Buffer.size()) {
	if (parent) {
	assert(!parent->Frozen && "parent already has child builder active");
	parent->Frozen = true;
	} else {
	assert(!builder.Frozen && "builder already has child builder active");
	builder.Frozen = true;
	}
	}

	~AggregateBuilderBase() {
	assert(Finished && "didn't finish aggregate builder");
	}

	void markFinished() {
	assert(!Frozen && "child builder still active");
	assert(!Finished && "builder already finished");
	Finished = true;
	if (Parent) {
	assert(Parent->Frozen &&
	"parent not frozen while child builder active");
	Parent->Frozen = false;
	} else {
	assert(Builder.Frozen &&
	"builder not frozen while child builder active");
	Builder.Frozen = false;
	}
	}

	public:
	// Not copyable.
	AggregateBuilderBase(const AggregateBuilderBase &) = delete;
	AggregateBuilderBase &operator=(const AggregateBuilderBase &) = delete;

	// Movable, mostly to allow returning. But we have to write this out
	// properly to satisfy the assert in the destructor.
	AggregateBuilderBase(AggregateBuilderBase &&other)
	: Builder(other.Builder), Parent(other.Parent), Begin(other.Begin),
	Finished(other.Finished), Frozen(other.Frozen) {
	other.Finished = false;
	}
	AggregateBuilderBase &operator=(AggregateBuilderBase &&other) = delete;

	/// Abandon this builder completely.
	void abandon() {
	markFinished();
	auto &buffer = Builder.Buffer;
	buffer.erase(buffer.begin() + Begin, buffer.end());
	}

	/// Add a new value to this initializer.
	void add(llvm::Constant *value) {
	assert(value && "adding null value to constant initializer");
	assert(!Finished && "cannot add more values after finishing builder");
	assert(!Frozen && "cannot add values while subbuilder is active");
	Builder.Buffer.push_back(value);
	}

	/// Add an integer value of type size_t.
	void addSize(CharUnits size) {
	add(Builder.CGM.getSize(size));
	}

	/// Add an integer value of a specific type.
	void addInt(llvm::IntegerType *intTy, uint64_t value,
	bool isSigned = false) {
	add(llvm::ConstantInt::get(intTy, value, isSigned));
	}

	/// Add a null pointer of a specific type.
	void addNullPointer(llvm::PointerType *ptrTy) {
	add(llvm::ConstantPointerNull::get(ptrTy));
	}

	/// Add a bitcast of a value to a specific type.
	void addBitCast(llvm::Constant value, llvm::Type type) {
	add(llvm::ConstantExpr::getBitCast(value, type));
	}

	/// Add a bunch of new values to this initializer.
	void addAll(ArrayRef<llvm::Constant *> values) {
	assert(!Finished && "cannot add more values after finishing builder");
	assert(!Frozen && "cannot add values while subbuilder is active");
	Builder.Buffer.append(values.begin(), values.end());
	}

	/// An opaque class to hold the abstract position of a placeholder.
	class PlaceholderPosition {
	size_t Index;
	friend class AggregateBuilderBase;
	PlaceholderPosition(size_t index) : Index(index) {}
	};

	/// Add a placeholder value to the structure. The returned position
	/// can be used to set the value later; it will not be invalidated by
	/// any intermediate operations except (1) filling the same position or
	/// (2) finishing the entire builder.
	///
	/// This is useful for emitting certain kinds of structure which
	/// contain some sort of summary field, generaly a count, before any
	/// of the data. By emitting a placeholder first, the structure can
	/// be emitted eagerly.
	PlaceholderPosition addPlaceholder() {
	assert(!Finished && "cannot add more values after finishing builder");
	assert(!Frozen && "cannot add values while subbuilder is active");
	Builder.Buffer.push_back(nullptr);
	return Builder.Buffer.size() - 1;
	}

	/// Fill a previously-added placeholder.
	void fillPlaceholderWithInt(PlaceholderPosition position,
	llvm::IntegerType *type, uint64_t value,
	bool isSigned = false) {
	fillPlaceholder(position, llvm::ConstantInt::get(type, value, isSigned));
	}

	/// Fill a previously-added placeholder.
	void fillPlaceholder(PlaceholderPosition position, llvm::Constant *value) {
	assert(!Finished && "cannot change values after finishing builder");
	assert(!Frozen && "cannot add values while subbuilder is active");
	llvm::Constant *&slot = Builder.Buffer[position.Index];
	assert(slot == nullptr && "placeholder already filled");
	slot = value;
	}

	/// Produce an address which will eventually point to the the next
	/// position to be filled. This is computed with an indexed
	/// getelementptr rather than by computing offsets.
	///
	/// The returned pointer will have type T*, where T is the given
	/// position.
	llvm::Constant getAddrOfCurrentPosition(llvm::Type type) {
	// Make a global variable. We will replace this with a GEP to this
	// position after installing the initializer.
	auto dummy =
	new llvm::GlobalVariable(Builder.CGM.getModule(), type, true,
	llvm::GlobalVariable::PrivateLinkage,
	nullptr, "");
	Builder.SelfReferences.emplace_back(dummy);
	auto &entry = Builder.SelfReferences.back();
	(void) getGEPIndicesToCurrentPosition(entry.Indices);
	return dummy;
	}

	ArrayRef<llvm::Constant*> getGEPIndicesToCurrentPosition(
	llvm::SmallVectorImpl<llvm::Constant*> &indices) {
	getGEPIndicesTo(indices, Builder.Buffer.size());
	return indices;
	}

	ConstantArrayBuilder beginArray(llvm::Type *eltTy = nullptr);
	ConstantStructBuilder beginStruct(llvm::StructType *structTy = nullptr);

	private:
	void getGEPIndicesTo(llvm::SmallVectorImpl<llvm::Constant*> &indices,
	size_t position) const {
	// Recurse on the parent builder if present.
	if (Parent) {
	Parent->getGEPIndicesTo(indices, Begin);

	// Otherwise, add an index to drill into the first level of pointer.
	} else {
	assert(indices.empty());
	indices.push_back(llvm::ConstantInt::get(Builder.CGM.Int32Ty, 0));
	}

	assert(position >= Begin);
	// We have to use i32 here because struct GEPs demand i32 indices.
	// It's rather unlikely to matter in practice.
	indices.push_back(llvm::ConstantInt::get(Builder.CGM.Int32Ty,
	position - Begin));
	}
	};

	template <class Impl>
	class AggregateBuilder : public AggregateBuilderBase {
	protected:
	AggregateBuilder(ConstantInitBuilder &builder,
	AggregateBuilderBase *parent)
	: AggregateBuilderBase(builder, parent) {}

	Impl &asImpl() { return static_cast<Impl>(this); }

	public:
	/// Given that this builder was created by beginning an array or struct
	/// component on the given parent builder, finish the array/struct
	/// component and add it to the parent.
	///
	/// It is an intentional choice that the parent is passed in explicitly
	/// despite it being redundant with information already kept in the
	/// builder. This aids in readability by making it easier to find the
	/// places that add components to a builder, as well as "bookending"
	/// the sub-builder more explicitly.
	void finishAndAddTo(AggregateBuilderBase &parent) {
	assert(Parent == &parent && "adding to non-parent builder");
	parent.add(asImpl().finishImpl());
	}

	/// Given that this builder was created by beginning an array or struct
	/// directly on a ConstantInitBuilder, finish the array/struct and
	/// create a global variable with it as the initializer.
	template <class... As>
	llvm::GlobalVariable *finishAndCreateGlobal(As &&...args) {
	assert(!Parent && "finishing non-root builder");
	return Builder.createGlobal(asImpl().finishImpl(),
	std::forward<As>(args)...);
	}

	/// Given that this builder was created by beginning an array or struct
	/// directly on a ConstantInitBuilder, finish the array/struct and
	/// set it as the initializer of the given global variable.
	void finishAndSetAsInitializer(llvm::GlobalVariable *global) {
	assert(!Parent && "finishing non-root builder");
	return Builder.setGlobalInitializer(global, asImpl().finishImpl());
	}
	};

	ConstantArrayBuilder beginArray(llvm::Type *eltTy = nullptr);

	ConstantStructBuilder beginStruct(llvm::StructType *structTy = nullptr);

	private:
	llvm::GlobalVariable createGlobal(llvm::Constant initializer,
	const llvm::Twine &name,
	CharUnits alignment,
	bool constant = false,
	llvm::GlobalValue::LinkageTypes linkage
	= llvm::GlobalValue::InternalLinkage,
	unsigned addressSpace = 0) {
	auto GV = new llvm::GlobalVariable(CGM.getModule(),
	initializer->getType(),
	constant,
	linkage,
	initializer,
	name,
	/insert before/ nullptr,
	llvm::GlobalValue::NotThreadLocal,
	addressSpace);
	GV->setAlignment(alignment.getQuantity());
	resolveSelfReferences(GV);
	return GV;
	}

	void setGlobalInitializer(llvm::GlobalVariable *GV,
	llvm::Constant *initializer) {
	GV->setInitializer(initializer);
	resolveSelfReferences(GV);
	}

	void resolveSelfReferences(llvm::GlobalVariable *GV) {
	for (auto &entry : SelfReferences) {
	llvm::Constant *resolvedReference =
	llvm::ConstantExpr::getInBoundsGetElementPtr(
	GV->getValueType(), GV, entry.Indices);
	entry.Dummy->replaceAllUsesWith(resolvedReference);
	entry.Dummy->eraseFromParent();
	}
	}
	};

	/// A helper class of ConstantInitBuilder, used for building constant
	/// array initializers.
	class ConstantArrayBuilder
	: public ConstantInitBuilder::AggregateBuilder<ConstantArrayBuilder> {
	llvm::Type *EltTy;
	friend class ConstantInitBuilder;
	template <class Impl> friend class ConstantInitBuilder::AggregateBuilder;
	ConstantArrayBuilder(ConstantInitBuilder &builder,
	AggregateBuilderBase parent, llvm::Type eltTy)
	: AggregateBuilder(builder, parent), EltTy(eltTy) {}
	public:
	size_t size() const {
	assert(!Finished);
	assert(!Frozen);
	assert(Begin <= getBuffer().size());
	return getBuffer().size() - Begin;
	}

	bool empty() const {
	return size() == 0;
	}

	private:
	/// Form an array constant from the values that have been added to this
	/// builder.
	llvm::Constant *finishImpl() {
	markFinished();

	auto &buffer = getBuffer();
	assert((Begin < buffer.size() \|\|
	(Begin == buffer.size() && EltTy))
	&& "didn't add any array elements without element type");
	auto elts = llvm::makeArrayRef(buffer).slice(Begin);
	auto eltTy = EltTy ? EltTy : elts[0]->getType();
	auto type = llvm::ArrayType::get(eltTy, elts.size());
	auto constant = llvm::ConstantArray::get(type, elts);
	buffer.erase(buffer.begin() + Begin, buffer.end());
	return constant;
	}
	};

	inline ConstantArrayBuilder
	ConstantInitBuilder::beginArray(llvm::Type *eltTy) {
	return ConstantArrayBuilder(*this, nullptr, eltTy);
	}

	inline ConstantArrayBuilder
	ConstantInitBuilder::AggregateBuilderBase::beginArray(llvm::Type *eltTy) {
	return ConstantArrayBuilder(Builder, this, eltTy);
	}

	/// A helper class of ConstantInitBuilder, used for building constant
	/// struct initializers.
	class ConstantStructBuilder
	: public ConstantInitBuilder::AggregateBuilder<ConstantStructBuilder> {
	llvm::StructType *Ty;
	friend class ConstantInitBuilder;
	template <class Impl> friend class ConstantInitBuilder::AggregateBuilder;
	ConstantStructBuilder(ConstantInitBuilder &builder,
	AggregateBuilderBase parent, llvm::StructType ty)
	: AggregateBuilder(builder, parent), Ty(ty) {}

	/// Finish the struct.
	llvm::Constant *finishImpl() {
	markFinished();

	auto &buffer = getBuffer();
	assert(Begin < buffer.size() && "didn't add any struct elements?");
	auto elts = llvm::makeArrayRef(buffer).slice(Begin);

	llvm::Constant *constant;
	if (Ty) {
	constant = llvm::ConstantStruct::get(Ty, elts);
	} else {
	constant = llvm::ConstantStruct::getAnon(elts, /packed/ false);
	}

	buffer.erase(buffer.begin() + Begin, buffer.end());
	return constant;
	}
	};

	inline ConstantStructBuilder
	ConstantInitBuilder::beginStruct(llvm::StructType *structTy) {
	return ConstantStructBuilder(*this, nullptr, structTy);
	}

	inline ConstantStructBuilder
	ConstantInitBuilder::AggregateBuilderBase::beginStruct(
	llvm::StructType *structTy) {
	return ConstantStructBuilder(Builder, this, structTy);
	}

	} // end namespace CodeGen
	} // end namespace clang

	#endif