//===- MachineSSAUpdater.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 MachineSSAUpdater class.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_CODEGEN_MACHINESSAUPDATER_H
#define LLVM_CODEGEN_MACHINESSAUPDATER_H
#include "llvm/CodeGen/Register.h"
namespace llvm {
class MachineBasicBlock;
class MachineFunction;
class MachineInstr;
class MachineOperand;
class MachineRegisterInfo;
class TargetInstrInfo;
class TargetRegisterClass;
template<typename T> class SmallVectorImpl;
template<typename T> class SSAUpdaterTraits;
/// MachineSSAUpdater - This class updates SSA form for a set of virtual
/// registers defined in multiple blocks. This is used when code duplication
/// or another unstructured transformation wants to rewrite a set of uses of one
/// vreg with uses of a set of vregs.
class MachineSSAUpdater {
friend class SSAUpdaterTraits<MachineSSAUpdater>;
private:
/// AvailableVals - This keeps track of which value to use on a per-block
/// basis. When we insert PHI nodes, we keep track of them here.
//typedef DenseMap<MachineBasicBlock*, Register> AvailableValsTy;
void *AV = nullptr;
/// VRC - Register class of the current virtual register.
const TargetRegisterClass *VRC;
/// InsertedPHIs - If this is non-null, the MachineSSAUpdater adds all PHI
/// nodes that it creates to the vector.
SmallVectorImpl<MachineInstr*> *InsertedPHIs;
const TargetInstrInfo *TII;
MachineRegisterInfo *MRI;
public:
/// MachineSSAUpdater constructor. If InsertedPHIs is specified, it will be
/// filled in with all PHI Nodes created by rewriting.
explicit MachineSSAUpdater(MachineFunction &MF,
SmallVectorImpl<MachineInstr*> *NewPHI = nullptr);
MachineSSAUpdater(const MachineSSAUpdater &) = delete;
MachineSSAUpdater &operator=(const MachineSSAUpdater &) = delete;
~MachineSSAUpdater();
/// Initialize - Reset this object to get ready for a new set of SSA
/// updates.
void Initialize(Register V);
void Initialize(const TargetRegisterClass *RC);
/// AddAvailableValue - Indicate that a rewritten value is available at the
/// end of the specified block with the specified value.
void AddAvailableValue(MachineBasicBlock *BB, Register V);
/// HasValueForBlock - Return true if the MachineSSAUpdater already has a
/// value for the specified block.
bool HasValueForBlock(MachineBasicBlock *BB) const;
/// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
/// live at the end of the specified block.
Register GetValueAtEndOfBlock(MachineBasicBlock *BB);
/// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
/// is live in the middle of the specified block. If ExistingValueOnly is
/// true then this will only return an existing value or $noreg; otherwise new
/// instructions may be inserted to materialize a value.
///
/// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
/// important case: if there is a definition of the rewritten value after the
/// 'use' in BB. Consider code like this:
///
/// X1 = ...
/// SomeBB:
/// use(X)
/// X2 = ...
/// br Cond, SomeBB, OutBB
///
/// 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.
Register GetValueInMiddleOfBlock(MachineBasicBlock *BB,
bool ExistingValueOnly = false);
/// RewriteUse - 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(MachineOperand &U);
private:
// If ExistingValueOnly is true, will not create any new instructions. Used
// for debug values, which cannot modify Codegen.
Register GetValueAtEndOfBlockInternal(MachineBasicBlock *BB,
bool ExistingValueOnly = false);
};
} // end namespace llvm
#endif // LLVM_CODEGEN_MACHINESSAUPDATER_H