//===- SSAUpdater.h - Unstructured SSA Update Tool --------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file declares the SSAUpdater class.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_TRANSFORMS_UTILS_SSAUPDATER_H
#define LLVM_TRANSFORMS_UTILS_SSAUPDATER_H
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/StringRef.h"
#include <string>
namespace llvm {
class BasicBlock;
class Instruction;
class LoadInst;
class PHINode;
template <typename T> class SmallVectorImpl;
template <typename T> class SSAUpdaterTraits;
class Type;
class Use;
class Value;
/// Helper class for SSA formation on a set of values defined in
/// multiple blocks.
///
/// This is used when code duplication or another unstructured
/// transformation wants to rewrite a set of uses of one value with uses of a
/// set of values.
class SSAUpdater {
friend class SSAUpdaterTraits<SSAUpdater>;
private:
/// This keeps track of which value to use on a per-block basis. When we
/// insert PHI nodes, we keep track of them here.
void *AV = nullptr;
/// ProtoType holds the type of the values being rewritten.
Type *ProtoType = nullptr;
/// PHI nodes are given a name based on ProtoName.
std::string ProtoName;
/// If this is non-null, the SSAUpdater adds all PHI nodes that it creates to
/// the vector.
SmallVectorImpl<PHINode *> *InsertedPHIs;
public:
/// If InsertedPHIs is specified, it will be filled
/// in with all PHI Nodes created by rewriting.
explicit SSAUpdater(SmallVectorImpl<PHINode *> *InsertedPHIs = nullptr);
SSAUpdater(const SSAUpdater &) = delete;
SSAUpdater &operator=(const SSAUpdater &) = delete;
~SSAUpdater();
/// Reset this object to get ready for a new set of SSA updates with
/// type 'Ty'.
///
/// PHI nodes get a name based on 'Name'.
void Initialize(Type *Ty, StringRef Name);
/// Indicate that a rewritten value is available in the specified block
/// with the specified value.
void AddAvailableValue(BasicBlock *BB, Value *V);
/// Return true if the SSAUpdater already has a value for the specified
/// block.
bool HasValueForBlock(BasicBlock *BB) const;
/// Return the value for the specified block if the SSAUpdater has one,
/// otherwise return nullptr.
Value *FindValueForBlock(BasicBlock *BB) const;
/// Construct SSA form, materializing a value that is live at the end
/// of the specified block.
Value *GetValueAtEndOfBlock(BasicBlock *BB);
/// Construct SSA form, materializing a value that is live in the
/// middle of the specified block.
///
/// \c GetValueInMiddleOfBlock is the same as \c GetValueAtEndOfBlock except
/// in one important case: if there is a definition of the rewritten value
/// after the 'use' in BB. Consider code like this:
///
/// \code
/// X1 = ...
/// SomeBB:
/// use(X)
/// X2 = ...
/// br Cond, SomeBB, OutBB
/// \endcode
///
/// In this case, there are two values (X1 and X2) added to the AvailableVals
/// set by the client of the rewriter, and those values are both live out of
/// their respective blocks. However, the use of X happens in the *middle* of
/// a block. Because of this, we need to insert a new PHI node in SomeBB to
/// merge the appropriate values, and this value isn't live out of the block.
Value *GetValueInMiddleOfBlock(BasicBlock *BB);
/// Rewrite a use of the symbolic value.
///
/// This handles PHI nodes, which use their value in the corresponding
/// predecessor. Note that this will not work if the use is supposed to be
/// rewritten to a value defined in the same block as the use, but above it.
/// Any 'AddAvailableValue's added for the use's block will be considered to
/// be below it.
void RewriteUse(Use &U);
/// Rewrite a use like \c RewriteUse but handling in-block definitions.
///
/// This version of the method can rewrite uses in the same block as
/// a definition, because it assumes that all uses of a value are below any
/// inserted values.
void RewriteUseAfterInsertions(Use &U);
private:
Value *GetValueAtEndOfBlockInternal(BasicBlock *BB);
};
/// Helper class for promoting a collection of loads and stores into SSA
/// Form using the SSAUpdater.
///
/// This handles complexities that SSAUpdater doesn't, such as multiple loads
/// and stores in one block.
///
/// Clients of this class are expected to subclass this and implement the
/// virtual methods.
class LoadAndStorePromoter {
protected:
SSAUpdater &SSA;
public:
LoadAndStorePromoter(ArrayRef<const Instruction *> Insts,
SSAUpdater &S, StringRef Name = StringRef());
virtual ~LoadAndStorePromoter() = default;
/// This does the promotion.
///
/// Insts is a list of loads and stores to promote, and Name is the basename
/// for the PHIs to insert. After this is complete, the loads and stores are
/// removed from the code.
void run(const SmallVectorImpl<Instruction *> &Insts);
/// Return true if the specified instruction is in the Inst list.
///
/// The Insts list is the one passed into the constructor. Clients should
/// implement this with a more efficient version if possible.
virtual bool isInstInList(Instruction *I,
const SmallVectorImpl<Instruction *> &Insts) const;
/// This hook is invoked after all the stores are found and inserted as
/// available values.
virtual void doExtraRewritesBeforeFinalDeletion() {}
/// Clients can choose to implement this to get notified right before
/// a load is RAUW'd another value.
virtual void replaceLoadWithValue(LoadInst *LI, Value *V) const {}
/// Called before each instruction is deleted.
virtual void instructionDeleted(Instruction *I) const {}
/// Called to update debug info associated with the instruction.
virtual void updateDebugInfo(Instruction *I) const {}
/// Return false if a sub-class wants to keep one of the loads/stores
/// after the SSA construction.
virtual bool shouldDelete(Instruction *I) const { return true; }
};
} // end namespace llvm
#endif // LLVM_TRANSFORMS_UTILS_SSAUPDATER_H