llvm/llvm/lib/Target/BPF/BPFMIPeephole.cpp

//===-------------- BPFMIPeephole.cpp - MI Peephole Cleanups  -------------===//
//
// 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 pass performs peephole optimizations to cleanup ugly code sequences at
// MachineInstruction layer.
//
// Currently, there are two optimizations implemented:
//  - One pre-RA MachineSSA pass to eliminate type promotion sequences, those
//    zero extend 32-bit subregisters to 64-bit registers, if the compiler
//    could prove the subregisters is defined by 32-bit operations in which
//    case the upper half of the underlying 64-bit registers were zeroed
//    implicitly.
//
//  - One post-RA PreEmit pass to do final cleanup on some redundant
//    instructions generated due to bad RA on subregister.
//===----------------------------------------------------------------------===//

#include "BPF.h"
#include "BPFInstrInfo.h"
#include "BPFTargetMachine.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/LivePhysRegs.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/Debug.h"
#include <set>

usingnamespacellvm;

#define DEBUG_TYPE …

static cl::opt<int> GotolAbsLowBound("gotol-abs-low-bound", cl::Hidden,
  cl::init(INT16_MAX >> 1), cl::desc("Specify gotol lower bound"));

STATISTIC(ZExtElemNum, "Number of zero extension shifts eliminated");

namespace {

struct BPFMIPeephole : public MachineFunctionPass { … };

// Initialize class variables.
void BPFMIPeephole::initialize(MachineFunction &MFParm) { … }

bool BPFMIPeephole::isCopyFrom32Def(MachineInstr *CopyMI)
{ … }

bool BPFMIPeephole::isPhiFrom32Def(MachineInstr *PhiMI)
{ … }

// The \p DefInsn instruction defines a virtual register.
bool BPFMIPeephole::isInsnFrom32Def(MachineInstr *DefInsn)
{ … }

bool BPFMIPeephole::isMovFrom32Def(MachineInstr *MovMI)
{ … }

bool BPFMIPeephole::eliminateZExtSeq() { … }

bool BPFMIPeephole::eliminateZExt() { … }

} // end default namespace

INITIALIZE_PASS(…)

char BPFMIPeephole::ID = …;
FunctionPass* llvm::createBPFMIPeepholePass() { … }

STATISTIC(RedundantMovElemNum, "Number of redundant moves eliminated");

namespace {

struct BPFMIPreEmitPeephole : public MachineFunctionPass { … };

// Initialize class variables.
void BPFMIPreEmitPeephole::initialize(MachineFunction &MFParm) { … }

bool BPFMIPreEmitPeephole::eliminateRedundantMov() { … }

bool BPFMIPreEmitPeephole::in16BitRange(int Num) { … }

// Before cpu=v4, only 16bit branch target offset (-0x8000 to 0x7fff)
// is supported for both unconditional (JMP) and condition (JEQ, JSGT,
// etc.) branches. In certain cases, e.g., full unrolling, the branch
// target offset might exceed 16bit range. If this happens, the llvm
// will generate incorrect code as the offset is truncated to 16bit.
//
// To fix this rare case, a new insn JMPL is introduced. This new
// insn supports supports 32bit branch target offset. The compiler
// does not use this insn during insn selection. Rather, BPF backend
// will estimate the branch target offset and do JMP -> JMPL and
// JEQ -> JEQ + JMPL conversion if the estimated branch target offset
// is beyond 16bit.
bool BPFMIPreEmitPeephole::adjustBranch() { … }

static const unsigned CallerSavedRegs[] = …;

struct BPFFastCall { … };

static void collectBPFFastCalls(const TargetRegisterInfo *TRI,
                                LivePhysRegs &LiveRegs, MachineBasicBlock &BB,
                                SmallVectorImpl<BPFFastCall> &Calls) { … }

static int64_t computeMinFixedObjOffset(MachineFrameInfo &MFI,
                                        unsigned SlotSize) { … }

bool BPFMIPreEmitPeephole::insertMissingCallerSavedSpills() { … }

} // end default namespace

INITIALIZE_PASS(…)

char BPFMIPreEmitPeephole::ID = …;
FunctionPass* llvm::createBPFMIPreEmitPeepholePass()
{ … }