PPCTargetMachine.cpp

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//===-- PPCTargetMachine.cpp - Define TargetMachine for PowerPC -----------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Top-level implementation for the PowerPC target.
//
//===----------------------------------------------------------------------===//
 
#include "PPCTargetMachine.h"
#include "MCTargetDesc/PPCMCTargetDesc.h"
#include "PPC.h"
#include "PPCMachineFunctionInfo.h"
#include "PPCMachineScheduler.h"
#include "PPCMacroFusion.h"
#include "PPCSubtarget.h"
#include "PPCTargetObjectFile.h"
#include "PPCTargetTransformInfo.h"
#include "TargetInfo/PowerPCTargetInfo.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/CodeGen/GlobalISel/IRTranslator.h"
#include "llvm/CodeGen/GlobalISel/InstructionSelect.h"
#include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
#include "llvm/CodeGen/GlobalISel/Legalizer.h"
#include "llvm/CodeGen/GlobalISel/Localizer.h"
#include "llvm/CodeGen/GlobalISel/RegBankSelect.h"
#include "llvm/CodeGen/MachineScheduler.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Function.h"
#include "llvm/InitializePasses.h"
#include "llvm/MC/TargetRegistry.h"
#include "llvm/Pass.h"
#include "llvm/Support/CodeGen.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Target/TargetLoweringObjectFile.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/TargetParser/Triple.h"
#include "llvm/Transforms/Scalar.h"
#include <cassert>
#include <memory>
#include <optional>
#include <string>
 
using namespace llvm;
 
 
static cl::opt<bool>
    EnableBranchCoalescing("enable-ppc-branch-coalesce", cl::Hidden,
                           cl::desc("enable coalescing of duplicate branches for PPC"));
static cl::
opt<bool> DisableCTRLoops("disable-ppc-ctrloops", cl::Hidden,
                        cl::desc("Disable CTR loops for PPC"));
 
static cl::
opt<bool> DisableInstrFormPrep("disable-ppc-instr-form-prep", cl::Hidden,
                            cl::desc("Disable PPC loop instr form prep"));
 
static cl::opt<bool>
VSXFMAMutateEarly("schedule-ppc-vsx-fma-mutation-early",
  cl::Hidden, cl::desc("Schedule VSX FMA instruction mutation early"));
 
static cl::
opt<bool> DisableVSXSwapRemoval("disable-ppc-vsx-swap-removal", cl::Hidden,
                                cl::desc("Disable VSX Swap Removal for PPC"));
 
static cl::
opt<bool> DisableMIPeephole("disable-ppc-peephole", cl::Hidden,
                            cl::desc("Disable machine peepholes for PPC"));
 
static cl::opt<bool>
EnableGEPOpt("ppc-gep-opt", cl::Hidden,
             cl::desc("Enable optimizations on complex GEPs"),
             cl::init(true));
 
static cl::opt<bool>
EnablePrefetch("enable-ppc-prefetching",
                  cl::desc("enable software prefetching on PPC"),
                  cl::init(false), cl::Hidden);
 
static cl::opt<bool>
EnableExtraTOCRegDeps("enable-ppc-extra-toc-reg-deps",
                      cl::desc("Add extra TOC register dependencies"),
                      cl::init(true), cl::Hidden);
 
static cl::opt<bool>
EnableMachineCombinerPass("ppc-machine-combiner",
                          cl::desc("Enable the machine combiner pass"),
                          cl::init(true), cl::Hidden);
 
static cl::opt<bool>
  ReduceCRLogical("ppc-reduce-cr-logicals",
                  cl::desc("Expand eligible cr-logical binary ops to branches"),
                  cl::init(true), cl::Hidden);
 
static cl::opt<bool> EnablePPCGenScalarMASSEntries(
    "enable-ppc-gen-scalar-mass", cl::init(false),
    cl::desc("Enable lowering math functions to their corresponding MASS "
             "(scalar) entries"),
    cl::Hidden);
 
extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializePowerPCTarget() {
  // Register the targets
  RegisterTargetMachine<PPCTargetMachine> A(getThePPC32Target());
  RegisterTargetMachine<PPCTargetMachine> B(getThePPC32LETarget());
  RegisterTargetMachine<PPCTargetMachine> C(getThePPC64Target());
  RegisterTargetMachine<PPCTargetMachine> D(getThePPC64LETarget());
 
  PassRegistry &PR = *PassRegistry::getPassRegistry();
#ifndef NDEBUG
  initializePPCCTRLoopsVerifyPass(PR);
#endif
  initializePPCLoopInstrFormPrepPass(PR);
  initializePPCTOCRegDepsPass(PR);
  initializePPCEarlyReturnPass(PR);
  initializePPCVSXCopyPass(PR);
  initializePPCVSXFMAMutatePass(PR);
  initializePPCVSXSwapRemovalPass(PR);
  initializePPCReduceCRLogicalsPass(PR);
  initializePPCBSelPass(PR);
  initializePPCBranchCoalescingPass(PR);
  initializePPCBoolRetToIntPass(PR);
  initializePPCExpandISELPass(PR);
  initializePPCPreEmitPeepholePass(PR);
  initializePPCTLSDynamicCallPass(PR);
  initializePPCMIPeepholePass(PR);
  initializePPCLowerMASSVEntriesPass(PR);
  initializePPCGenScalarMASSEntriesPass(PR);
  initializePPCExpandAtomicPseudoPass(PR);
  initializeGlobalISel(PR);
  initializePPCCTRLoopsPass(PR);
  initializePPCDAGToDAGISelPass(PR);
}
 
static bool isLittleEndianTriple(const Triple &T) {
  return T.getArch() == Triple::ppc64le || T.getArch() == Triple::ppcle;
}
 
/// Return the datalayout string of a subtarget.
static std::string getDataLayoutString(const Triple &T) {
  bool is64Bit = T.getArch() == Triple::ppc64 || T.getArch() == Triple::ppc64le;
  std::string Ret;
 
  // Most PPC* platforms are big endian, PPC(64)LE is little endian.
  if (isLittleEndianTriple(T))
    Ret = "e";
  else
    Ret = "E";
 
  Ret += DataLayout::getManglingComponent(T);
 
  // PPC32 has 32 bit pointers. The PS3 (OS Lv2) is a PPC64 machine with 32 bit
  // pointers.
  if (!is64Bit || T.getOS() == Triple::Lv2)
    Ret += "-p:32:32";
 
  // Note, the alignment values for f64 and i64 on ppc64 in Darwin
  // documentation are wrong; these are correct (i.e. "what gcc does").
  Ret += "-i64:64";
 
  // PPC64 has 32 and 64 bit registers, PPC32 has only 32 bit ones.
  if (is64Bit)
    Ret += "-n32:64";
  else
    Ret += "-n32";
 
  // Specify the vector alignment explicitly. For v256i1 and v512i1, the
  // calculated alignment would be 256*alignment(i1) and 512*alignment(i1),
  // which is 256 and 512 bytes - way over aligned.
  if (is64Bit && (T.isOSAIX() || T.isOSLinux()))
    Ret += "-S128-v256:256:256-v512:512:512";
 
  return Ret;
}
 
static std::string computeFSAdditions(StringRef FS, CodeGenOpt::Level OL,
                                      const Triple &TT) {
  std::string FullFS = std::string(FS);
 
  // Make sure 64-bit features are available when CPUname is generic
  if (TT.getArch() == Triple::ppc64 || TT.getArch() == Triple::ppc64le) {
    if (!FullFS.empty())
      FullFS = "+64bit," + FullFS;
    else
      FullFS = "+64bit";
  }
 
  if (OL >= CodeGenOpt::Default) {
    if (!FullFS.empty())
      FullFS = "+crbits," + FullFS;
    else
      FullFS = "+crbits";
  }
 
  if (OL != CodeGenOpt::None) {
    if (!FullFS.empty())
      FullFS = "+invariant-function-descriptors," + FullFS;
    else
      FullFS = "+invariant-function-descriptors";
  }
 
  if (TT.isOSAIX()) {
    if (!FullFS.empty())
      FullFS = "+aix," + FullFS;
    else
      FullFS = "+aix";
  }
 
  return FullFS;
}
 
static std::unique_ptr<TargetLoweringObjectFile> createTLOF(const Triple &TT) {
  if (TT.isOSAIX())
    return std::make_unique<TargetLoweringObjectFileXCOFF>();
 
  return std::make_unique<PPC64LinuxTargetObjectFile>();
}
 
static PPCTargetMachine::PPCABI computeTargetABI(const Triple &TT,
                                                 const TargetOptions &Options) {
  if (Options.MCOptions.getABIName().startswith("elfv1"))
    return PPCTargetMachine::PPC_ABI_ELFv1;
  else if (Options.MCOptions.getABIName().startswith("elfv2"))
    return PPCTargetMachine::PPC_ABI_ELFv2;
 
  assert(Options.MCOptions.getABIName().empty() &&
         "Unknown target-abi option!");
 
  switch (TT.getArch()) {
  case Triple::ppc64le:
    return PPCTargetMachine::PPC_ABI_ELFv2;
  case Triple::ppc64:
    if (TT.isPPC64ELFv2ABI())
      return PPCTargetMachine::PPC_ABI_ELFv2;
    else
      return PPCTargetMachine::PPC_ABI_ELFv1;
  default:
    return PPCTargetMachine::PPC_ABI_UNKNOWN;
  }
}
 
static Reloc::Model getEffectiveRelocModel(const Triple &TT,
                                           std::optional<Reloc::Model> RM) {
  assert((!TT.isOSAIX() || !RM || *RM == Reloc::PIC_) &&
         "Invalid relocation model for AIX.");
 
  if (RM)
    return *RM;
 
  // Big Endian PPC and AIX default to PIC.
  if (TT.getArch() == Triple::ppc64 || TT.isOSAIX())
    return Reloc::PIC_;
 
  // Rest are static by default.
  return Reloc::Static;
}
 
static CodeModel::Model
getEffectivePPCCodeModel(const Triple &TT, std::optional<CodeModel::Model> CM,
                         bool JIT) {
  if (CM) {
    if (*CM == CodeModel::Tiny)
      report_fatal_error("Target does not support the tiny CodeModel", false);
    if (*CM == CodeModel::Kernel)
      report_fatal_error("Target does not support the kernel CodeModel", false);
    return *CM;
  }
 
  if (JIT)
    return CodeModel::Small;
  if (TT.isOSAIX())
    return CodeModel::Small;
 
  assert(TT.isOSBinFormatELF() && "All remaining PPC OSes are ELF based.");
 
  if (TT.isArch32Bit())
    return CodeModel::Small;
 
  assert(TT.isArch64Bit() && "Unsupported PPC architecture.");
  return CodeModel::Medium;
}
 
 
static ScheduleDAGInstrs *createPPCMachineScheduler(MachineSchedContext *C) {
  const PPCSubtarget &ST = C->MF->getSubtarget<PPCSubtarget>();
  ScheduleDAGMILive *DAG =
    new ScheduleDAGMILive(C, ST.usePPCPreRASchedStrategy() ?
                          std::make_unique<PPCPreRASchedStrategy>(C) :
                          std::make_unique<GenericScheduler>(C));
  // add DAG Mutations here.
  DAG->addMutation(createCopyConstrainDAGMutation(DAG->TII, DAG->TRI));
  if (ST.hasStoreFusion())
    DAG->addMutation(createStoreClusterDAGMutation(DAG->TII, DAG->TRI));
  if (ST.hasFusion())
    DAG->addMutation(createPowerPCMacroFusionDAGMutation());
 
  return DAG;
}
 
static ScheduleDAGInstrs *createPPCPostMachineScheduler(
  MachineSchedContext *C) {
  const PPCSubtarget &ST = C->MF->getSubtarget<PPCSubtarget>();
  ScheduleDAGMI *DAG =
    new ScheduleDAGMI(C, ST.usePPCPostRASchedStrategy() ?
                      std::make_unique<PPCPostRASchedStrategy>(C) :
                      std::make_unique<PostGenericScheduler>(C), true);
  // add DAG Mutations here.
  if (ST.hasStoreFusion())
    DAG->addMutation(createStoreClusterDAGMutation(DAG->TII, DAG->TRI));
  if (ST.hasFusion())
    DAG->addMutation(createPowerPCMacroFusionDAGMutation());
  return DAG;
}
 
// The FeatureString here is a little subtle. We are modifying the feature
// string with what are (currently) non-function specific overrides as it goes
// into the LLVMTargetMachine constructor and then using the stored value in the
// Subtarget constructor below it.
PPCTargetMachine::PPCTargetMachine(const Target &T, const Triple &TT,
                                   StringRef CPU, StringRef FS,
                                   const TargetOptions &Options,
                                   std::optional<Reloc::Model> RM,
                                   std::optional<CodeModel::Model> CM,
                                   CodeGenOpt::Level OL, bool JIT)
    : LLVMTargetMachine(T, getDataLayoutString(TT), TT, CPU,
                        computeFSAdditions(FS, OL, TT), Options,
                        getEffectiveRelocModel(TT, RM),
                        getEffectivePPCCodeModel(TT, CM, JIT), OL),
      TLOF(createTLOF(getTargetTriple())),
      TargetABI(computeTargetABI(TT, Options)),
      Endianness(isLittleEndianTriple(TT) ? Endian::LITTLE : Endian::BIG) {
  initAsmInfo();
}
 
PPCTargetMachine::~PPCTargetMachine() = default;
 
const PPCSubtarget *
PPCTargetMachine::getSubtargetImpl(const Function &F) const {
  Attribute CPUAttr = F.getFnAttribute("target-cpu");
  Attribute TuneAttr = F.getFnAttribute("tune-cpu");
  Attribute FSAttr = F.getFnAttribute("target-features");
 
  std::string CPU =
      CPUAttr.isValid() ? CPUAttr.getValueAsString().str() : TargetCPU;
  std::string TuneCPU =
      TuneAttr.isValid() ? TuneAttr.getValueAsString().str() : CPU;
  std::string FS =
      FSAttr.isValid() ? FSAttr.getValueAsString().str() : TargetFS;
 
  // FIXME: This is related to the code below to reset the target options,
  // we need to know whether or not the soft float flag is set on the
  // function before we can generate a subtarget. We also need to use
  // it as a key for the subtarget since that can be the only difference
  // between two functions.
  bool SoftFloat = F.getFnAttribute("use-soft-float").getValueAsBool();
  // If the soft float attribute is set on the function turn on the soft float
  // subtarget feature.
  if (SoftFloat)
    FS += FS.empty() ? "-hard-float" : ",-hard-float";
 
  auto &I = SubtargetMap[CPU + TuneCPU + FS];
  if (!I) {
    // This needs to be done before we create a new subtarget since any
    // creation will depend on the TM and the code generation flags on the
    // function that reside in TargetOptions.
    resetTargetOptions(F);
    I = std::make_unique<PPCSubtarget>(
        TargetTriple, CPU, TuneCPU,
        // FIXME: It would be good to have the subtarget additions here
        // not necessary. Anything that turns them on/off (overrides) ends
        // up being put at the end of the feature string, but the defaults
        // shouldn't require adding them. Fixing this means pulling Feature64Bit
        // out of most of the target cpus in the .td file and making it set only
        // as part of initialization via the TargetTriple.
        computeFSAdditions(FS, getOptLevel(), getTargetTriple()), *this);
  }
  return I.get();
}
 
//===----------------------------------------------------------------------===//
// Pass Pipeline Configuration
//===----------------------------------------------------------------------===//
 
namespace {
 
/// PPC Code Generator Pass Configuration Options.
class PPCPassConfig : public TargetPassConfig {
public:
  PPCPassConfig(PPCTargetMachine &TM, PassManagerBase &PM)
    : TargetPassConfig(TM, PM) {
    // At any optimization level above -O0 we use the Machine Scheduler and not
    // the default Post RA List Scheduler.
    if (TM.getOptLevel() != CodeGenOpt::None)
      substitutePass(&PostRASchedulerID, &PostMachineSchedulerID);
  }
 
  PPCTargetMachine &getPPCTargetMachine() const {
    return getTM<PPCTargetMachine>();
  }
 
  void addIRPasses() override;
  bool addPreISel() override;
  bool addILPOpts() override;
  bool addInstSelector() override;
  void addMachineSSAOptimization() override;
  void addPreRegAlloc() override;
  void addPreSched2() override;
  void addPreEmitPass() override;
  void addPreEmitPass2() override;
  // GlobalISEL
  bool addIRTranslator() override;
  bool addLegalizeMachineIR() override;
  bool addRegBankSelect() override;
  bool addGlobalInstructionSelect() override;
 
  ScheduleDAGInstrs *
  createMachineScheduler(MachineSchedContext *C) const override {
    return createPPCMachineScheduler(C);
  }
  ScheduleDAGInstrs *
  createPostMachineScheduler(MachineSchedContext *C) const override {
    return createPPCPostMachineScheduler(C);
  }
};
 
} // end anonymous namespace
 
TargetPassConfig *PPCTargetMachine::createPassConfig(PassManagerBase &PM) {
  return new PPCPassConfig(*this, PM);
}
 
void PPCPassConfig::addIRPasses() {
  if (TM->getOptLevel() != CodeGenOpt::None)
    addPass(createPPCBoolRetToIntPass());
  addPass(createAtomicExpandPass());
 
  // Lower generic MASSV routines to PowerPC subtarget-specific entries.
  addPass(createPPCLowerMASSVEntriesPass());
 
  // Generate PowerPC target-specific entries for scalar math functions
  // that are available in IBM MASS (scalar) library.
  if (TM->getOptLevel() == CodeGenOpt::Aggressive &&
      EnablePPCGenScalarMASSEntries) {
    TM->Options.PPCGenScalarMASSEntries = EnablePPCGenScalarMASSEntries;
    addPass(createPPCGenScalarMASSEntriesPass());
  }
 
  // If explicitly requested, add explicit data prefetch intrinsics.
  if (EnablePrefetch.getNumOccurrences() > 0)
    addPass(createLoopDataPrefetchPass());
 
  if (TM->getOptLevel() >= CodeGenOpt::Default && EnableGEPOpt) {
    // Call SeparateConstOffsetFromGEP pass to extract constants within indices
    // and lower a GEP with multiple indices to either arithmetic operations or
    // multiple GEPs with single index.
    addPass(createSeparateConstOffsetFromGEPPass(true));
    // Call EarlyCSE pass to find and remove subexpressions in the lowered
    // result.
    addPass(createEarlyCSEPass());
    // Do loop invariant code motion in case part of the lowered result is
    // invariant.
    addPass(createLICMPass());
  }
 
  TargetPassConfig::addIRPasses();
}
 
bool PPCPassConfig::addPreISel() {
  if (!DisableInstrFormPrep && getOptLevel() != CodeGenOpt::None)
    addPass(createPPCLoopInstrFormPrepPass(getPPCTargetMachine()));
 
  if (!DisableCTRLoops && getOptLevel() != CodeGenOpt::None)
    addPass(createHardwareLoopsLegacyPass());
 
  return false;
}
 
bool PPCPassConfig::addILPOpts() {
  addPass(&EarlyIfConverterID);
 
  if (EnableMachineCombinerPass)
    addPass(&MachineCombinerID);
 
  return true;
}
 
bool PPCPassConfig::addInstSelector() {
  // Install an instruction selector.
  addPass(createPPCISelDag(getPPCTargetMachine(), getOptLevel()));
 
#ifndef NDEBUG
  if (!DisableCTRLoops && getOptLevel() != CodeGenOpt::None)
    addPass(createPPCCTRLoopsVerify());
#endif
 
  addPass(createPPCVSXCopyPass());
  return false;
}
 
void PPCPassConfig::addMachineSSAOptimization() {
  // Run CTR loops pass before any cfg modification pass to prevent the
  // canonical form of hardware loop from being destroied.
  if (!DisableCTRLoops && getOptLevel() != CodeGenOpt::None)
    addPass(createPPCCTRLoopsPass());
 
  // PPCBranchCoalescingPass need to be done before machine sinking
  // since it merges empty blocks.
  if (EnableBranchCoalescing && getOptLevel() != CodeGenOpt::None)
    addPass(createPPCBranchCoalescingPass());
  TargetPassConfig::addMachineSSAOptimization();
  // For little endian, remove where possible the vector swap instructions
  // introduced at code generation to normalize vector element order.
  if (TM->getTargetTriple().getArch() == Triple::ppc64le &&
      !DisableVSXSwapRemoval)
    addPass(createPPCVSXSwapRemovalPass());
  // Reduce the number of cr-logical ops.
  if (ReduceCRLogical && getOptLevel() != CodeGenOpt::None)
    addPass(createPPCReduceCRLogicalsPass());
  // Target-specific peephole cleanups performed after instruction
  // selection.
  if (!DisableMIPeephole) {
    addPass(createPPCMIPeepholePass());
    addPass(&DeadMachineInstructionElimID);
  }
}
 
void PPCPassConfig::addPreRegAlloc() {
  if (getOptLevel() != CodeGenOpt::None) {
    initializePPCVSXFMAMutatePass(*PassRegistry::getPassRegistry());
    insertPass(VSXFMAMutateEarly ? &RegisterCoalescerID : &MachineSchedulerID,
               &PPCVSXFMAMutateID);
  }
 
  // FIXME: We probably don't need to run these for -fPIE.
  if (getPPCTargetMachine().isPositionIndependent()) {
    // FIXME: LiveVariables should not be necessary here!
    // PPCTLSDynamicCallPass uses LiveIntervals which previously dependent on
    // LiveVariables. This (unnecessary) dependency has been removed now,
    // however a stage-2 clang build fails without LiveVariables computed here.
    addPass(&LiveVariablesID);
    addPass(createPPCTLSDynamicCallPass());
  }
  if (EnableExtraTOCRegDeps)
    addPass(createPPCTOCRegDepsPass());
 
  if (getOptLevel() != CodeGenOpt::None)
    addPass(&MachinePipelinerID);
}
 
void PPCPassConfig::addPreSched2() {
  if (getOptLevel() != CodeGenOpt::None)
    addPass(&IfConverterID);
}
 
void PPCPassConfig::addPreEmitPass() {
  addPass(createPPCPreEmitPeepholePass());
  addPass(createPPCExpandISELPass());
 
  if (getOptLevel() != CodeGenOpt::None)
    addPass(createPPCEarlyReturnPass());
}
 
void PPCPassConfig::addPreEmitPass2() {
  // Schedule the expansion of AMOs at the last possible moment, avoiding the
  // possibility for other passes to break the requirements for forward
  // progress in the LL/SC block.
  addPass(createPPCExpandAtomicPseudoPass());
  // Must run branch selection immediately preceding the asm printer.
  addPass(createPPCBranchSelectionPass());
}
 
TargetTransformInfo
PPCTargetMachine::getTargetTransformInfo(const Function &F) const {
  return TargetTransformInfo(PPCTTIImpl(this, F));
}
 
bool PPCTargetMachine::isLittleEndian() const {
  assert(Endianness != Endian::NOT_DETECTED &&
         "Unable to determine endianness");
  return Endianness == Endian::LITTLE;
}
 
MachineFunctionInfo *PPCTargetMachine::createMachineFunctionInfo(
    BumpPtrAllocator &Allocator, const Function &F,
    const TargetSubtargetInfo *STI) const {
  return PPCFunctionInfo::create<PPCFunctionInfo>(Allocator, F, STI);
}
 
static MachineSchedRegistry
PPCPreRASchedRegistry("ppc-prera",
                      "Run PowerPC PreRA specific scheduler",
                      createPPCMachineScheduler);
 
static MachineSchedRegistry
PPCPostRASchedRegistry("ppc-postra",
                       "Run PowerPC PostRA specific scheduler",
                       createPPCPostMachineScheduler);
 
// Global ISEL
bool PPCPassConfig::addIRTranslator() {
  addPass(new IRTranslator());
  return false;
}
 
bool PPCPassConfig::addLegalizeMachineIR() {
  addPass(new Legalizer());
  return false;
}
 
bool PPCPassConfig::addRegBankSelect() {
  addPass(new RegBankSelect());
  return false;
}
 
bool PPCPassConfig::addGlobalInstructionSelect() {
  addPass(new InstructionSelect(getOptLevel()));
  return false;
}