Add file MipsLongBranch.cpp.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158436 91177308-0d34-0410-b5e6-96231b3b80d8
2024-12-27 14:45:50 +00:00 · 2012-06-14 01:22:24 +00:00 · 2012-06-14 01:22:24 +00:00 · a32ccf92c1
commit a32ccf92c1
parent 163d706c46
1 changed files with 416 additions and 0 deletions
--- a/lib/Target/Mips/MipsLongBranch.cpp
+++ b/lib/Target/Mips/MipsLongBranch.cpp
@ -0,0 +1,416 @@
+//===-- MipsLongBranch.cpp - Emit long branches ---------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass expands a branch or jump instruction into a long branch if its
+// offset is too large to fit into its immediate field.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "mips-long-branch"
+
+#include "Mips.h"
+#include "MipsTargetMachine.h"
+#include "MCTargetDesc/MipsBaseInfo.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/Function.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+
+using namespace llvm;
+
+STATISTIC(LongBranches, "Number of long branches.");
+
+static cl::opt<bool> SkipLongBranch(
+  "skip-mips-long-branch",
+  cl::init(false),
+  cl::desc("MIPS: Skip long branch pass."),
+  cl::Hidden);
+
+static cl::opt<bool> ForceLongBranch(
+  "force-mips-long-branch",
+  cl::init(false),
+  cl::desc("MIPS: Expand all branches to long format."),
+  cl::Hidden);
+
+namespace {
+  typedef MachineBasicBlock::iterator Iter;
+  typedef MachineBasicBlock::reverse_iterator ReverseIter;
+
+  struct MBBInfo {
+    uint64_t Size;
+    bool HasLongBranch;
+    MachineInstr *Br;
+
+    MBBInfo() : Size(0), HasLongBranch(false), Br(0) {}
+  };
+
+  class MipsLongBranch : public MachineFunctionPass {
+
+  public:
+    static char ID;
+    MipsLongBranch(TargetMachine &tm)
+      : MachineFunctionPass(ID), TM(tm),
+        TII(static_cast<const MipsInstrInfo*>(tm.getInstrInfo())) {}
+
+    virtual const char *getPassName() const {
+      return "Mips Long Branch";
+    }
+
+    bool runOnMachineFunction(MachineFunction &F);
+
+  private:
+    void splitMBB(MachineBasicBlock *MBB);
+    void initMBBInfo();
+    int64_t computeOffset(const MachineInstr *Br);
+    bool offsetFitsIntoField(const MachineInstr *Br);
+    unsigned addLongBranch(MachineBasicBlock &MBB, Iter Pos,
+                           MachineBasicBlock *Tgt, DebugLoc DL, bool Nop);
+    void replaceBranch(MachineBasicBlock &MBB, Iter Br, DebugLoc DL,
+                       MachineBasicBlock *MBBOpnd);
+    void expandToLongBranch(MBBInfo &Info);
+
+    const TargetMachine &TM;
+    const MipsInstrInfo *TII;
+    MachineFunction *MF;
+    SmallVector<MBBInfo, 16> MBBInfos;
+  };
+
+  char MipsLongBranch::ID = 0;
+} // end of anonymous namespace
+
+/// createMipsLongBranchPass - Returns a pass that converts branches to long
+/// branches.
+FunctionPass *llvm::createMipsLongBranchPass(MipsTargetMachine &tm) {
+  return new MipsLongBranch(tm);
+}
+
+/// Iterate over list of Br's operands and search for a MachineBasicBlock
+/// operand.
+static MachineBasicBlock *getTargetMBB(const MachineInstr &Br) {
+  for (unsigned I = 0, E = Br.getDesc().getNumOperands(); I < E; ++I) {
+    const MachineOperand &MO = Br.getOperand(I);
+
+    if (MO.isMBB())
+      return MO.getMBB();
+  }
+
+  assert(false && "This instruction does not have an MBB operand.");
+  return 0;
+}
+
+// Traverse the list of instructions backwards until a non-debug instruction is
+// found or it reaches E.
+static ReverseIter getNonDebugInstr(ReverseIter B, ReverseIter E) {
+  for (; B != E; ++B)
+    if (!B->isDebugValue())
+      return B;
+
+  return E;
+}
+
+// Split MBB if it has two direct jumps/branches.
+void MipsLongBranch::splitMBB(MachineBasicBlock *MBB) {
+  ReverseIter End = MBB->rend();
+  ReverseIter LastBr = getNonDebugInstr(MBB->rbegin(), End);
+
+  // Return if MBB has no branch instructions.
+  if ((LastBr == End) ||
+      (!LastBr->isConditionalBranch() && !LastBr->isUnconditionalBranch()))
+    return;
+
+  ReverseIter FirstBr = getNonDebugInstr(next(LastBr), End);
+
+  // MBB has only one branch instruction if FirstBr is not a branch
+  // instruction.
+  if ((FirstBr == End) ||
+      (!FirstBr->isConditionalBranch() && !FirstBr->isUnconditionalBranch()))
+    return;
+
+  assert(!FirstBr->isIndirectBranch() && "Unexpected indirect branch found.");
+
+  // Create a new MBB. Move instructions in MBB to the newly created MBB.
+  MachineBasicBlock *NewMBB =
+    MF->CreateMachineBasicBlock(MBB->getBasicBlock());
+
+  // Insert NewMBB and fix control flow.
+  MachineBasicBlock *Tgt = getTargetMBB(*FirstBr);
+  NewMBB->transferSuccessors(MBB);
+  NewMBB->removeSuccessor(Tgt);
+  MBB->addSuccessor(NewMBB);
+  MBB->addSuccessor(Tgt);
+  MF->insert(next(MachineFunction::iterator(MBB)), NewMBB);
+
+  NewMBB->splice(NewMBB->end(), MBB, (++LastBr).base(), MBB->end());
+}
+
+// Fill MBBInfos.
+void MipsLongBranch::initMBBInfo() {
+  // Split the MBBs if they have two branches. Each basic block should have at
+  // most one branch after this loop is executed.
+  for (MachineFunction::iterator I = MF->begin(), E = MF->end(); I != E;)
+    splitMBB(I++);
+
+  MF->RenumberBlocks();
+  MBBInfos.clear();
+  MBBInfos.resize(MF->size());
+
+  for (unsigned I = 0, E = MBBInfos.size(); I < E; ++I) {
+    MachineBasicBlock *MBB = MF->getBlockNumbered(I);
+
+    // Compute size of MBB.
+    for (MachineBasicBlock::instr_iterator MI = MBB->instr_begin();
+         MI != MBB->instr_end(); ++MI)
+      MBBInfos[I].Size += TII->GetInstSizeInBytes(&*MI);
+
+    // Search for MBB's branch instruction.
+    ReverseIter End = MBB->rend();
+    ReverseIter Br = getNonDebugInstr(MBB->rbegin(), End);
+
+    if ((Br != End) && !Br->isIndirectBranch() &&
+        (Br->isConditionalBranch() || Br->isUnconditionalBranch()))
+      MBBInfos[I].Br = (++Br).base();
+  }
+}
+
+// Compute offset of branch in number of bytes.
+int64_t MipsLongBranch::computeOffset(const MachineInstr *Br) {
+  int64_t Offset = 0;
+  int ThisMBB = Br->getParent()->getNumber();
+  int TargetMBB = getTargetMBB(*Br)->getNumber();
+
+  // Compute offset of a forward branch.
+  if (ThisMBB < TargetMBB) {
+    for (int N = ThisMBB + 1; N < TargetMBB; ++N)
+      Offset += MBBInfos[N].Size;
+
+    return Offset + 4;
+  }
+
+  // Compute offset of a backward branch.
+  for (int N = ThisMBB; N >= TargetMBB; --N)
+    Offset += MBBInfos[N].Size;
+
+  return -Offset + 4;
+}
+
+// Insert the following sequence:
+// (pic or N64)
+//  lw $at, global_reg_slot
+//  lw $at, got($L1)($at)
+//  addiu $at, $at, lo($L1)
+//  jr $at
+//  noop
+// (static and !N64)
+//  lui $at, hi($L1)
+//  addiu $at, $at, lo($L1)
+//  jr $at
+//  noop
+unsigned MipsLongBranch::addLongBranch(MachineBasicBlock &MBB, Iter Pos,
+                                       MachineBasicBlock *Tgt, DebugLoc DL,
+                                       bool Nop) {
+  MF->getInfo<MipsFunctionInfo>()->setEmitNOAT();
+  bool IsPIC = (TM.getRelocationModel() == Reloc::PIC_);
+  unsigned ABI = TM.getSubtarget<MipsSubtarget>().getTargetABI();
+  bool N64 = (ABI == MipsSubtarget::N64);
+  unsigned NumInstrs;
+
+  if (IsPIC || N64) {
+    bool HasMips64 = TM.getSubtarget<MipsSubtarget>().hasMips64();
+    unsigned AT = N64 ? Mips::AT_64 : Mips::AT;
+    unsigned Load = N64 ? Mips::LD_P8 : Mips::LW;
+    unsigned ADDiu = N64 ? Mips::DADDiu : Mips::ADDiu;
+    unsigned JR = N64 ? Mips::JR64 : Mips::JR;
+    unsigned GOTFlag = HasMips64 ? MipsII::MO_GOT_PAGE : MipsII::MO_GOT;
+    unsigned OFSTFlag = HasMips64 ? MipsII::MO_GOT_OFST : MipsII::MO_ABS_LO;
+    const MipsRegisterInfo *MRI =
+      static_cast<const MipsRegisterInfo*>(TM.getRegisterInfo());
+    unsigned SP = MRI->getFrameRegister(*MF);
+    unsigned GlobalRegFI = MF->getInfo<MipsFunctionInfo>()->getGlobalRegFI();
+    int64_t Offset = MF->getFrameInfo()->getObjectOffset(GlobalRegFI);
+
+    if (isInt<16>(Offset)) {
+      BuildMI(MBB, Pos, DL, TII->get(Load), AT).addReg(SP).addImm(Offset);
+      NumInstrs = 1;
+    } else {
+      unsigned ADDu = N64 ? Mips::DADDu : Mips::ADDu;
+      MipsAnalyzeImmediate::Inst LastInst(0, 0);
+
+      MF->getInfo<MipsFunctionInfo>()->setEmitNOAT();
+      NumInstrs = Mips::loadImmediate(Offset, N64, *TII, MBB, Pos, DL, true,
+                                      &LastInst) + 2;
+      BuildMI(MBB, Pos, DL, TII->get(ADDu), AT).addReg(SP).addReg(AT);
+      BuildMI(MBB, Pos, DL, TII->get(Load), AT).addReg(AT)
+        .addImm(SignExtend64<16>(LastInst.ImmOpnd));
+    }
+
+    BuildMI(MBB, Pos, DL, TII->get(Load), AT).addReg(AT).addMBB(Tgt, GOTFlag);
+    BuildMI(MBB, Pos, DL, TII->get(ADDiu), AT).addReg(AT).addMBB(Tgt, OFSTFlag);
+    BuildMI(MBB, Pos, DL, TII->get(JR)).addReg(Mips::AT, RegState::Kill);
+    NumInstrs += 3;
+  } else {
+    BuildMI(MBB, Pos, DL, TII->get(Mips::LUi), Mips::AT)
+      .addMBB(Tgt, MipsII::MO_ABS_HI);
+    BuildMI(MBB, Pos, DL, TII->get(Mips::ADDiu), Mips::AT)
+      .addReg(Mips::AT).addMBB(Tgt, MipsII::MO_ABS_LO);
+    BuildMI(MBB, Pos, DL, TII->get(Mips::JR)).addReg(Mips::AT, RegState::Kill);
+    NumInstrs = 3;
+  }
+
+  if (Nop) {
+    BuildMI(MBB, Pos, DL, TII->get(Mips::NOP))->setIsInsideBundle();
+    ++NumInstrs;
+  }
+
+  return NumInstrs;
+}
+
+// Replace Br with a branch which has the opposite condition code and a
+// MachineBasicBlock operand MBBOpnd.
+void MipsLongBranch::replaceBranch(MachineBasicBlock &MBB, Iter Br,
+                                   DebugLoc DL, MachineBasicBlock *MBBOpnd) {
+  unsigned NewOpc = Mips::GetOppositeBranchOpc(Br->getOpcode());
+  const MCInstrDesc &NewDesc = TII->get(NewOpc);
+
+  MachineInstrBuilder MIB = BuildMI(MBB, Br, DL, NewDesc);
+
+  for (unsigned I = 0, E = Br->getDesc().getNumOperands(); I < E; ++I) {
+    MachineOperand &MO = Br->getOperand(I);
+
+    if (!MO.isReg()) {
+      assert(MO.isMBB() && "MBB operand expected.");
+      break;
+    }
+
+    MIB.addReg(MO.getReg());
+  }
+
+  MIB.addMBB(MBBOpnd);
+
+  Br->eraseFromParent();
+}
+
+// Expand branch instructions to long branches.
+void MipsLongBranch::expandToLongBranch(MBBInfo &I) {
+  I.HasLongBranch = true;
+
+  MachineBasicBlock *MBB = I.Br->getParent(), *Tgt = getTargetMBB(*I.Br);
+  DebugLoc DL = I.Br->getDebugLoc();
+
+  if (I.Br->isUnconditionalBranch()) {
+    // Unconditional branch before transformation:
+    //   b $tgt
+    //   delay-slot-instr
+    //
+    // after transformation:
+    //   delay-slot-instr
+    //   lw $at, global_reg_slot
+    //   lw $at, %got($tgt)($at)
+    //   addiu $at, $at, %lo($tgt)
+    //   jr $at
+    //   nop
+    I.Size += (addLongBranch(*MBB, next(Iter(I.Br)), Tgt, DL, true) - 1) * 4;
+
+    // Remove branch and clear InsideBundle bit of the next instruction.
+    next(MachineBasicBlock::instr_iterator(I.Br))->setIsInsideBundle(false);
+    I.Br->eraseFromParent();
+    return;
+  }
+
+  assert(I.Br->isConditionalBranch() && "Conditional branch expected.");
+
+  // Conditional branch before transformation:
+  //   b cc, $tgt
+  //   delay-slot-instr
+  //  FallThrough:
+  //
+  // after transformation:
+  //   b !cc, FallThrough
+  //   delay-slot-instr
+  //  NewMBB:
+  //   lw $at, global_reg_slot
+  //   lw $at, %got($tgt)($at)
+  //   addiu $at, $at, %lo($tgt)
+  //   jr $at
+  //   noop
+  //  FallThrough:
+
+  MachineBasicBlock *NewMBB = MF->CreateMachineBasicBlock(MBB->getBasicBlock());
+  MF->insert(next(MachineFunction::iterator(MBB)), NewMBB);
+  MBB->removeSuccessor(Tgt);
+  MBB->addSuccessor(NewMBB);
+  NewMBB->addSuccessor(Tgt);
+
+  I.Size += addLongBranch(*NewMBB, NewMBB->begin(), Tgt, DL, true) * 4;
+  replaceBranch(*MBB, I.Br, DL, *MBB->succ_begin());
+}
+
+static void emitGPDisp(MachineFunction &F, const MipsInstrInfo *TII) {
+  MachineBasicBlock &MBB = F.front();
+  MachineBasicBlock::iterator I = MBB.begin();
+  DebugLoc DL = MBB.findDebugLoc(MBB.begin());
+  BuildMI(MBB, I, DL, TII->get(Mips::LUi), Mips::V0)
+    .addExternalSymbol("_gp_disp", MipsII::MO_ABS_HI);
+  BuildMI(MBB, I, DL, TII->get(Mips::ADDiu), Mips::V0)
+    .addReg(Mips::V0).addExternalSymbol("_gp_disp", MipsII::MO_ABS_LO);
+  MBB.removeLiveIn(Mips::V0);
+}
+
+bool MipsLongBranch::runOnMachineFunction(MachineFunction &F) {
+  if ((TM.getRelocationModel() == Reloc::PIC_) &&
+      TM.getSubtarget<MipsSubtarget>().isABI_O32() &&
+      F.getInfo<MipsFunctionInfo>()->globalBaseRegSet())
+    emitGPDisp(F, TII);
+
+  if (SkipLongBranch)
+    return false;
+
+  MF = &F;
+  initMBBInfo();
+
+  bool IsPIC = (TM.getRelocationModel() == Reloc::PIC_);
+  SmallVector<MBBInfo, 16>::iterator I, E = MBBInfos.end();
+  bool EverMadeChange = false, MadeChange = true;
+
+  while (MadeChange) {
+    MadeChange = false;
+
+    for (I = MBBInfos.begin(); I != E; ++I) {
+      // Skip if this MBB doesn't have a branch or the branch has already been
+      // converted to a long branch.
+      if (!I->Br || I->HasLongBranch)
+        continue;
+
+      int64_t Offset = computeOffset(I->Br);
+
+      if (!ForceLongBranch) {
+        // Check if offset fits into 16-bit immediate field of branches.
+        if ((I->Br->isConditionalBranch() || IsPIC) && isInt<16>(Offset / 4))
+          continue;
+
+        // Check if offset fits into 26-bit immediate field of jumps (J).
+        if (I->Br->isUnconditionalBranch() && !IsPIC && isInt<26>(Offset / 4))
+          continue;
+      }
+
+      expandToLongBranch(*I);
+      ++LongBranches;
+      EverMadeChange = MadeChange = true;
+    }
+  }
+
+  if (EverMadeChange)
+    MF->RenumberBlocks();
+
+  return EverMadeChange;
+}