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