322 lines
9.6 KiB
C++
322 lines
9.6 KiB
C++
//===-- Thumb2ITBlockPass.cpp - Insert Thumb-2 IT blocks ------------------===//
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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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#include "ARM.h"
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#include "ARMMachineFunctionInfo.h"
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#include "ARMSubtarget.h"
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#include "MCTargetDesc/ARMBaseInfo.h"
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#include "Thumb2InstrInfo.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/CodeGen/MachineBasicBlock.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstr.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/MachineInstrBundle.h"
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#include "llvm/CodeGen/MachineOperand.h"
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#include "llvm/IR/DebugLoc.h"
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#include "llvm/MC/MCInstrDesc.h"
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#include "llvm/MC/MCRegisterInfo.h"
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#include <cassert>
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#include <new>
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using namespace llvm;
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#define DEBUG_TYPE "thumb2-it"
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STATISTIC(NumITs, "Number of IT blocks inserted");
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STATISTIC(NumMovedInsts, "Number of predicated instructions moved");
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namespace {
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class Thumb2ITBlockPass : public MachineFunctionPass {
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public:
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static char ID;
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bool restrictIT;
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const Thumb2InstrInfo *TII;
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const TargetRegisterInfo *TRI;
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ARMFunctionInfo *AFI;
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Thumb2ITBlockPass() : MachineFunctionPass(ID) {}
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bool runOnMachineFunction(MachineFunction &Fn) override;
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MachineFunctionProperties getRequiredProperties() const override {
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return MachineFunctionProperties().set(
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MachineFunctionProperties::Property::NoVRegs);
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}
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StringRef getPassName() const override {
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return "Thumb IT blocks insertion pass";
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}
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private:
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bool MoveCopyOutOfITBlock(MachineInstr *MI,
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ARMCC::CondCodes CC, ARMCC::CondCodes OCC,
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SmallSet<unsigned, 4> &Defs,
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SmallSet<unsigned, 4> &Uses);
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bool InsertITInstructions(MachineBasicBlock &MBB);
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};
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char Thumb2ITBlockPass::ID = 0;
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} // end anonymous namespace
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/// TrackDefUses - Tracking what registers are being defined and used by
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/// instructions in the IT block. This also tracks "dependencies", i.e. uses
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/// in the IT block that are defined before the IT instruction.
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static void TrackDefUses(MachineInstr *MI,
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SmallSet<unsigned, 4> &Defs,
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SmallSet<unsigned, 4> &Uses,
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const TargetRegisterInfo *TRI) {
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SmallVector<unsigned, 4> LocalDefs;
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SmallVector<unsigned, 4> LocalUses;
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for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
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MachineOperand &MO = MI->getOperand(i);
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if (!MO.isReg())
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continue;
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unsigned Reg = MO.getReg();
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if (!Reg || Reg == ARM::ITSTATE || Reg == ARM::SP)
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continue;
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if (MO.isUse())
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LocalUses.push_back(Reg);
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else
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LocalDefs.push_back(Reg);
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}
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for (unsigned i = 0, e = LocalUses.size(); i != e; ++i) {
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unsigned Reg = LocalUses[i];
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for (MCSubRegIterator Subreg(Reg, TRI, /*IncludeSelf=*/true);
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Subreg.isValid(); ++Subreg)
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Uses.insert(*Subreg);
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}
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for (unsigned i = 0, e = LocalDefs.size(); i != e; ++i) {
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unsigned Reg = LocalDefs[i];
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for (MCSubRegIterator Subreg(Reg, TRI, /*IncludeSelf=*/true);
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Subreg.isValid(); ++Subreg)
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Defs.insert(*Subreg);
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if (Reg == ARM::CPSR)
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continue;
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}
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}
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/// Clear kill flags for any uses in the given set. This will likely
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/// conservatively remove more kill flags than are necessary, but removing them
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/// is safer than incorrect kill flags remaining on instructions.
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static void ClearKillFlags(MachineInstr *MI, SmallSet<unsigned, 4> &Uses) {
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for (MachineOperand &MO : MI->operands()) {
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if (!MO.isReg() || MO.isDef() || !MO.isKill())
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continue;
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if (!Uses.count(MO.getReg()))
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continue;
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MO.setIsKill(false);
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}
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}
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static bool isCopy(MachineInstr *MI) {
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switch (MI->getOpcode()) {
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default:
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return false;
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case ARM::MOVr:
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case ARM::MOVr_TC:
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case ARM::tMOVr:
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case ARM::t2MOVr:
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return true;
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}
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}
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bool
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Thumb2ITBlockPass::MoveCopyOutOfITBlock(MachineInstr *MI,
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ARMCC::CondCodes CC, ARMCC::CondCodes OCC,
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SmallSet<unsigned, 4> &Defs,
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SmallSet<unsigned, 4> &Uses) {
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if (!isCopy(MI))
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return false;
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// llvm models select's as two-address instructions. That means a copy
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// is inserted before a t2MOVccr, etc. If the copy is scheduled in
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// between selects we would end up creating multiple IT blocks.
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assert(MI->getOperand(0).getSubReg() == 0 &&
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MI->getOperand(1).getSubReg() == 0 &&
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"Sub-register indices still around?");
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unsigned DstReg = MI->getOperand(0).getReg();
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unsigned SrcReg = MI->getOperand(1).getReg();
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// First check if it's safe to move it.
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if (Uses.count(DstReg) || Defs.count(SrcReg))
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return false;
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// If the CPSR is defined by this copy, then we don't want to move it. E.g.,
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// if we have:
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//
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// movs r1, r1
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// rsb r1, 0
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// movs r2, r2
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// rsb r2, 0
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//
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// we don't want this to be converted to:
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//
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// movs r1, r1
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// movs r2, r2
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// itt mi
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// rsb r1, 0
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// rsb r2, 0
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//
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const MCInstrDesc &MCID = MI->getDesc();
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if (MI->hasOptionalDef() &&
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MI->getOperand(MCID.getNumOperands() - 1).getReg() == ARM::CPSR)
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return false;
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// Then peek at the next instruction to see if it's predicated on CC or OCC.
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// If not, then there is nothing to be gained by moving the copy.
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MachineBasicBlock::iterator I = MI; ++I;
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MachineBasicBlock::iterator E = MI->getParent()->end();
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while (I != E && I->isDebugValue())
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++I;
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if (I != E) {
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unsigned NPredReg = 0;
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ARMCC::CondCodes NCC = getITInstrPredicate(*I, NPredReg);
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if (NCC == CC || NCC == OCC)
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return true;
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}
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return false;
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}
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bool Thumb2ITBlockPass::InsertITInstructions(MachineBasicBlock &MBB) {
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bool Modified = false;
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SmallSet<unsigned, 4> Defs;
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SmallSet<unsigned, 4> Uses;
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MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end();
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while (MBBI != E) {
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MachineInstr *MI = &*MBBI;
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DebugLoc dl = MI->getDebugLoc();
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unsigned PredReg = 0;
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ARMCC::CondCodes CC = getITInstrPredicate(*MI, PredReg);
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if (CC == ARMCC::AL) {
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++MBBI;
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continue;
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}
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Defs.clear();
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Uses.clear();
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TrackDefUses(MI, Defs, Uses, TRI);
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// Insert an IT instruction.
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MachineInstrBuilder MIB = BuildMI(MBB, MBBI, dl, TII->get(ARM::t2IT))
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.addImm(CC);
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// Add implicit use of ITSTATE to IT block instructions.
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MI->addOperand(MachineOperand::CreateReg(ARM::ITSTATE, false/*ifDef*/,
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true/*isImp*/, false/*isKill*/));
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MachineInstr *LastITMI = MI;
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MachineBasicBlock::iterator InsertPos = MIB.getInstr();
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++MBBI;
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// Form IT block.
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ARMCC::CondCodes OCC = ARMCC::getOppositeCondition(CC);
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unsigned Mask = 0, Pos = 3;
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// v8 IT blocks are limited to one conditional op unless -arm-no-restrict-it
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// is set: skip the loop
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if (!restrictIT) {
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// Branches, including tricky ones like LDM_RET, need to end an IT
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// block so check the instruction we just put in the block.
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for (; MBBI != E && Pos &&
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(!MI->isBranch() && !MI->isReturn()) ; ++MBBI) {
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if (MBBI->isDebugValue())
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continue;
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MachineInstr *NMI = &*MBBI;
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MI = NMI;
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unsigned NPredReg = 0;
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ARMCC::CondCodes NCC = getITInstrPredicate(*NMI, NPredReg);
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if (NCC == CC || NCC == OCC) {
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Mask |= (NCC & 1) << Pos;
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// Add implicit use of ITSTATE.
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NMI->addOperand(MachineOperand::CreateReg(ARM::ITSTATE, false/*ifDef*/,
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true/*isImp*/, false/*isKill*/));
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LastITMI = NMI;
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} else {
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if (NCC == ARMCC::AL &&
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MoveCopyOutOfITBlock(NMI, CC, OCC, Defs, Uses)) {
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--MBBI;
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MBB.remove(NMI);
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MBB.insert(InsertPos, NMI);
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ClearKillFlags(MI, Uses);
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++NumMovedInsts;
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continue;
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}
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break;
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}
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TrackDefUses(NMI, Defs, Uses, TRI);
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--Pos;
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}
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}
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// Finalize IT mask.
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Mask |= (1 << Pos);
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// Tag along (firstcond[0] << 4) with the mask.
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Mask |= (CC & 1) << 4;
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MIB.addImm(Mask);
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// Last instruction in IT block kills ITSTATE.
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LastITMI->findRegisterUseOperand(ARM::ITSTATE)->setIsKill();
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// Finalize the bundle.
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finalizeBundle(MBB, InsertPos.getInstrIterator(),
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++LastITMI->getIterator());
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Modified = true;
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++NumITs;
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}
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return Modified;
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}
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bool Thumb2ITBlockPass::runOnMachineFunction(MachineFunction &Fn) {
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const ARMSubtarget &STI =
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static_cast<const ARMSubtarget &>(Fn.getSubtarget());
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if (!STI.isThumb2())
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return false;
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AFI = Fn.getInfo<ARMFunctionInfo>();
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TII = static_cast<const Thumb2InstrInfo *>(STI.getInstrInfo());
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TRI = STI.getRegisterInfo();
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restrictIT = STI.restrictIT();
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if (!AFI->isThumbFunction())
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return false;
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bool Modified = false;
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for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E; ) {
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MachineBasicBlock &MBB = *MFI;
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++MFI;
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Modified |= InsertITInstructions(MBB);
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}
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if (Modified)
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AFI->setHasITBlocks(true);
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return Modified;
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}
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/// createThumb2ITBlockPass - Returns an instance of the Thumb2 IT blocks
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/// insertion pass.
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FunctionPass *llvm::createThumb2ITBlockPass() {
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return new Thumb2ITBlockPass();
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}
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