MachineSSAUpdater.cpp | Explore in Territory

//===- MachineSSAUpdater.cpp - Unstructured SSA Update Tool ---------------===//
//
// 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 implements the MachineSSAUpdater class. It's based on SSAUpdater
// class in lib/Transforms/Utils.
//
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/MachineSSAUpdater.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetOpcodes.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
#include <utility>

usingnamespacellvm;

#define DEBUG_TYPE …

AvailableValsTy;

static AvailableValsTy &getAvailableVals(void *AV) { … }

MachineSSAUpdater::MachineSSAUpdater(MachineFunction &MF,
                                     SmallVectorImpl<MachineInstr*> *NewPHI)
  : … { … }

MachineSSAUpdater::~MachineSSAUpdater() { … }

/// Initialize - Reset this object to get ready for a new set of SSA
/// updates.
void MachineSSAUpdater::Initialize(Register V) { … }

/// HasValueForBlock - Return true if the MachineSSAUpdater already has a value for
/// the specified block.
bool MachineSSAUpdater::HasValueForBlock(MachineBasicBlock *BB) const { … }

/// AddAvailableValue - Indicate that a rewritten value is available in the
/// specified block with the specified value.
void MachineSSAUpdater::AddAvailableValue(MachineBasicBlock *BB, Register V) { … }

/// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
/// live at the end of the specified block.
Register MachineSSAUpdater::GetValueAtEndOfBlock(MachineBasicBlock *BB) { … }

static
Register LookForIdenticalPHI(MachineBasicBlock *BB,
        SmallVectorImpl<std::pair<MachineBasicBlock *, Register>> &PredValues) { … }

/// InsertNewDef - Insert an empty PHI or IMPLICIT_DEF instruction which define
/// a value of the given register class at the start of the specified basic
/// block. It returns the virtual register defined by the instruction.
static MachineInstrBuilder InsertNewDef(unsigned Opcode, MachineBasicBlock *BB,
                                        MachineBasicBlock::iterator I,
                                        MachineRegisterInfo::VRegAttrs RegAttrs,
                                        MachineRegisterInfo *MRI,
                                        const TargetInstrInfo *TII) { … }

/// 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 MachineSSAUpdater::GetValueInMiddleOfBlock(MachineBasicBlock *BB,
                                                    bool ExistingValueOnly) { … }

static
MachineBasicBlock *findCorrespondingPred(const MachineInstr *MI,
                                         MachineOperand *U) { … }

/// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
/// which use their value in the corresponding predecessor.
void MachineSSAUpdater::RewriteUse(MachineOperand &U) { … }

namespace llvm {

/// SSAUpdaterTraits<MachineSSAUpdater> - Traits for the SSAUpdaterImpl
/// template, specialized for MachineSSAUpdater.
template<>
class SSAUpdaterTraits<MachineSSAUpdater> { … };

} // end namespace llvm

/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
/// for the specified BB and if so, return it.  If not, construct SSA form by
/// first calculating the required placement of PHIs and then inserting new
/// PHIs where needed.
Register
MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB,
                                                bool ExistingValueOnly) { … }
llvm/llvm/lib/CodeGen/MachineSSAUpdater.cpp
