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llvm-project/llvm/lib/Target/PowerPC/PPCMIPeephole.cpp

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//===-------------- PPCMIPeephole.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 clean up ugly code
// sequences at the MachineInstruction layer. It runs at the end of
// the SSA phases, following VSX swap removal. A pass of dead code
// elimination follows this one for quick clean-up of any dead
// instructions introduced here. Although we could do this as callbacks
// from the generic peephole pass, this would have a couple of bad
// effects: it might remove optimization opportunities for VSX swap
// removal, and it would miss cleanups made possible following VSX
// swap removal.
//
//===---------------------------------------------------------------------===//
#include "MCTargetDesc/PPCMCTargetDesc.h"
#include "MCTargetDesc/PPCPredicates.h"
#include "PPC.h"
#include "PPCInstrBuilder.h"
#include "PPCInstrInfo.h"
#include "PPCMachineFunctionInfo.h"
#include "PPCTargetMachine.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachinePostDominators.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/Debug.h"
using namespace llvm;
#define DEBUG_TYPE "ppc-mi-peepholes"
STATISTIC(RemoveTOCSave, "Number of TOC saves removed");
STATISTIC(MultiTOCSaves,
"Number of functions with multiple TOC saves that must be kept");
STATISTIC(NumTOCSavesInPrologue, "Number of TOC saves placed in the prologue");
STATISTIC(NumEliminatedSExt, "Number of eliminated sign-extensions");
STATISTIC(NumEliminatedZExt, "Number of eliminated zero-extensions");
STATISTIC(NumOptADDLIs, "Number of optimized ADD instruction fed by LI");
STATISTIC(NumConvertedToImmediateForm,
"Number of instructions converted to their immediate form");
STATISTIC(NumFunctionsEnteredInMIPeephole,
"Number of functions entered in PPC MI Peepholes");
STATISTIC(NumFixedPointIterations,
"Number of fixed-point iterations converting reg-reg instructions "
"to reg-imm ones");
STATISTIC(NumRotatesCollapsed,
"Number of pairs of rotate left, clear left/right collapsed");
STATISTIC(NumEXTSWAndSLDICombined,
"Number of pairs of EXTSW and SLDI combined as EXTSWSLI");
STATISTIC(NumLoadImmZeroFoldedAndRemoved,
"Number of LI(8) reg, 0 that are folded to r0 and removed");
static cl::opt<bool>
FixedPointRegToImm("ppc-reg-to-imm-fixed-point", cl::Hidden, cl::init(true),
cl::desc("Iterate to a fixed point when attempting to "
"convert reg-reg instructions to reg-imm"));
static cl::opt<bool>
ConvertRegReg("ppc-convert-rr-to-ri", cl::Hidden, cl::init(true),
cl::desc("Convert eligible reg+reg instructions to reg+imm"));
static cl::opt<bool>
EnableSExtElimination("ppc-eliminate-signext",
cl::desc("enable elimination of sign-extensions"),
cl::init(false), cl::Hidden);
static cl::opt<bool>
EnableZExtElimination("ppc-eliminate-zeroext",
cl::desc("enable elimination of zero-extensions"),
cl::init(false), cl::Hidden);
namespace {
struct PPCMIPeephole : public MachineFunctionPass {
static char ID;
const PPCInstrInfo *TII;
MachineFunction *MF;
MachineRegisterInfo *MRI;
PPCMIPeephole() : MachineFunctionPass(ID) {
initializePPCMIPeepholePass(*PassRegistry::getPassRegistry());
}
private:
MachineDominatorTree *MDT;
MachinePostDominatorTree *MPDT;
MachineBlockFrequencyInfo *MBFI;
uint64_t EntryFreq;
// Initialize class variables.
void initialize(MachineFunction &MFParm);
// Perform peepholes.
bool simplifyCode(void);
// Perform peepholes.
bool eliminateRedundantCompare(void);
bool eliminateRedundantTOCSaves(std::map<MachineInstr *, bool> &TOCSaves);
bool combineSEXTAndSHL(MachineInstr &MI, MachineInstr *&ToErase);
bool emitRLDICWhenLoweringJumpTables(MachineInstr &MI);
void UpdateTOCSaves(std::map<MachineInstr *, bool> &TOCSaves,
MachineInstr *MI);
public:
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<MachineDominatorTree>();
AU.addRequired<MachinePostDominatorTree>();
AU.addRequired<MachineBlockFrequencyInfo>();
AU.addPreserved<MachineDominatorTree>();
AU.addPreserved<MachinePostDominatorTree>();
AU.addPreserved<MachineBlockFrequencyInfo>();
MachineFunctionPass::getAnalysisUsage(AU);
}
// Main entry point for this pass.
bool runOnMachineFunction(MachineFunction &MF) override {
initialize(MF);
// At this point, TOC pointer should not be used in a function that uses
// PC-Relative addressing.
assert((MF.getRegInfo().use_empty(PPC::X2) ||
!MF.getSubtarget<PPCSubtarget>().isUsingPCRelativeCalls()) &&
"TOC pointer used in a function using PC-Relative addressing!");
if (skipFunction(MF.getFunction()))
return false;
return simplifyCode();
}
};
// Initialize class variables.
void PPCMIPeephole::initialize(MachineFunction &MFParm) {
MF = &MFParm;
MRI = &MF->getRegInfo();
MDT = &getAnalysis<MachineDominatorTree>();
MPDT = &getAnalysis<MachinePostDominatorTree>();
MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
EntryFreq = MBFI->getEntryFreq();
TII = MF->getSubtarget<PPCSubtarget>().getInstrInfo();
LLVM_DEBUG(dbgs() << "*** PowerPC MI peephole pass ***\n\n");
LLVM_DEBUG(MF->dump());
}
static MachineInstr *getVRegDefOrNull(MachineOperand *Op,
MachineRegisterInfo *MRI) {
assert(Op && "Invalid Operand!");
if (!Op->isReg())
return nullptr;
Register Reg = Op->getReg();
if (!Register::isVirtualRegister(Reg))
return nullptr;
return MRI->getVRegDef(Reg);
}
// This function returns number of known zero bits in output of MI
// starting from the most significant bit.
static unsigned
getKnownLeadingZeroCount(MachineInstr *MI, const PPCInstrInfo *TII) {
unsigned Opcode = MI->getOpcode();
if (Opcode == PPC::RLDICL || Opcode == PPC::RLDICL_rec ||
Opcode == PPC::RLDCL || Opcode == PPC::RLDCL_rec)
return MI->getOperand(3).getImm();
if ((Opcode == PPC::RLDIC || Opcode == PPC::RLDIC_rec) &&
MI->getOperand(3).getImm() <= 63 - MI->getOperand(2).getImm())
return MI->getOperand(3).getImm();
if ((Opcode == PPC::RLWINM || Opcode == PPC::RLWINM_rec ||
Opcode == PPC::RLWNM || Opcode == PPC::RLWNM_rec ||
Opcode == PPC::RLWINM8 || Opcode == PPC::RLWNM8) &&
MI->getOperand(3).getImm() <= MI->getOperand(4).getImm())
return 32 + MI->getOperand(3).getImm();
if (Opcode == PPC::ANDI_rec) {
uint16_t Imm = MI->getOperand(2).getImm();
return 48 + countLeadingZeros(Imm);
}
if (Opcode == PPC::CNTLZW || Opcode == PPC::CNTLZW_rec ||
Opcode == PPC::CNTTZW || Opcode == PPC::CNTTZW_rec ||
Opcode == PPC::CNTLZW8 || Opcode == PPC::CNTTZW8)
// The result ranges from 0 to 32.
return 58;
if (Opcode == PPC::CNTLZD || Opcode == PPC::CNTLZD_rec ||
Opcode == PPC::CNTTZD || Opcode == PPC::CNTTZD_rec)
// The result ranges from 0 to 64.
return 57;
if (Opcode == PPC::LHZ || Opcode == PPC::LHZX ||
Opcode == PPC::LHZ8 || Opcode == PPC::LHZX8 ||
Opcode == PPC::LHZU || Opcode == PPC::LHZUX ||
Opcode == PPC::LHZU8 || Opcode == PPC::LHZUX8)
return 48;
if (Opcode == PPC::LBZ || Opcode == PPC::LBZX ||
Opcode == PPC::LBZ8 || Opcode == PPC::LBZX8 ||
Opcode == PPC::LBZU || Opcode == PPC::LBZUX ||
Opcode == PPC::LBZU8 || Opcode == PPC::LBZUX8)
return 56;
if (TII->isZeroExtended(*MI))
return 32;
return 0;
}
// This function maintains a map for the pairs <TOC Save Instr, Keep>
// Each time a new TOC save is encountered, it checks if any of the existing
// ones are dominated by the new one. If so, it marks the existing one as
// redundant by setting it's entry in the map as false. It then adds the new
// instruction to the map with either true or false depending on if any
// existing instructions dominated the new one.
void PPCMIPeephole::UpdateTOCSaves(
std::map<MachineInstr *, bool> &TOCSaves, MachineInstr *MI) {
assert(TII->isTOCSaveMI(*MI) && "Expecting a TOC save instruction here");
assert(MF->getSubtarget<PPCSubtarget>().isELFv2ABI() &&
"TOC-save removal only supported on ELFv2");
PPCFunctionInfo *FI = MF->getInfo<PPCFunctionInfo>();
MachineBasicBlock *Entry = &MF->front();
uint64_t CurrBlockFreq = MBFI->getBlockFreq(MI->getParent()).getFrequency();
// If the block in which the TOC save resides is in a block that
// post-dominates Entry, or a block that is hotter than entry (keep in mind
// that early MachineLICM has already run so the TOC save won't be hoisted)
// we can just do the save in the prologue.
if (CurrBlockFreq > EntryFreq || MPDT->dominates(MI->getParent(), Entry))
FI->setMustSaveTOC(true);
// If we are saving the TOC in the prologue, all the TOC saves can be removed
// from the code.
if (FI->mustSaveTOC()) {
for (auto &TOCSave : TOCSaves)
TOCSave.second = false;
// Add new instruction to map.
TOCSaves[MI] = false;
return;
}
bool Keep = true;
for (auto It = TOCSaves.begin(); It != TOCSaves.end(); It++ ) {
MachineInstr *CurrInst = It->first;
// If new instruction dominates an existing one, mark existing one as
// redundant.
if (It->second && MDT->dominates(MI, CurrInst))
It->second = false;
// Check if the new instruction is redundant.
if (MDT->dominates(CurrInst, MI)) {
Keep = false;
break;
}
}
// Add new instruction to map.
TOCSaves[MI] = Keep;
}
// This function returns a list of all PHI nodes in the tree starting from
// the RootPHI node. We perform a BFS traversal to get an ordered list of nodes.
// The list initially only contains the root PHI. When we visit a PHI node, we
// add it to the list. We continue to look for other PHI node operands while
// there are nodes to visit in the list. The function returns false if the
// optimization cannot be applied on this tree.
static bool collectUnprimedAccPHIs(MachineRegisterInfo *MRI,
MachineInstr *RootPHI,
SmallVectorImpl<MachineInstr *> &PHIs) {
PHIs.push_back(RootPHI);
unsigned VisitedIndex = 0;
while (VisitedIndex < PHIs.size()) {
MachineInstr *VisitedPHI = PHIs[VisitedIndex];
for (unsigned PHIOp = 1, NumOps = VisitedPHI->getNumOperands();
PHIOp != NumOps; PHIOp += 2) {
Register RegOp = VisitedPHI->getOperand(PHIOp).getReg();
if (!Register::isVirtualRegister(RegOp))
return false;
MachineInstr *Instr = MRI->getVRegDef(RegOp);
// While collecting the PHI nodes, we check if they can be converted (i.e.
// all the operands are either copies, implicit defs or PHI nodes).
unsigned Opcode = Instr->getOpcode();
if (Opcode == PPC::COPY) {
Register Reg = Instr->getOperand(1).getReg();
if (!Register::isVirtualRegister(Reg) ||
MRI->getRegClass(Reg) != &PPC::ACCRCRegClass)
return false;
} else if (Opcode != PPC::IMPLICIT_DEF && Opcode != PPC::PHI)
return false;
// If we detect a cycle in the PHI nodes, we exit. It would be
// possible to change cycles as well, but that would add a lot
// of complexity for a case that is unlikely to occur with MMA
// code.
if (Opcode != PPC::PHI)
continue;
if (llvm::is_contained(PHIs, Instr))
return false;
PHIs.push_back(Instr);
}
VisitedIndex++;
}
return true;
}
// This function changes the unprimed accumulator PHI nodes in the PHIs list to
// primed accumulator PHI nodes. The list is traversed in reverse order to
// change all the PHI operands of a PHI node before changing the node itself.
// We keep a map to associate each changed PHI node to its non-changed form.
static void convertUnprimedAccPHIs(const PPCInstrInfo *TII,
MachineRegisterInfo *MRI,
SmallVectorImpl<MachineInstr *> &PHIs,
Register Dst) {
DenseMap<MachineInstr *, MachineInstr *> ChangedPHIMap;
for (auto It = PHIs.rbegin(), End = PHIs.rend(); It != End; ++It) {
MachineInstr *PHI = *It;
SmallVector<std::pair<MachineOperand, MachineOperand>, 4> PHIOps;
// We check if the current PHI node can be changed by looking at its
// operands. If all the operands are either copies from primed
// accumulators, implicit definitions or other unprimed accumulator
// PHI nodes, we change it.
for (unsigned PHIOp = 1, NumOps = PHI->getNumOperands(); PHIOp != NumOps;
PHIOp += 2) {
Register RegOp = PHI->getOperand(PHIOp).getReg();
MachineInstr *PHIInput = MRI->getVRegDef(RegOp);
unsigned Opcode = PHIInput->getOpcode();
assert((Opcode == PPC::COPY || Opcode == PPC::IMPLICIT_DEF ||
Opcode == PPC::PHI) &&
"Unexpected instruction");
if (Opcode == PPC::COPY) {
assert(MRI->getRegClass(PHIInput->getOperand(1).getReg()) ==
&PPC::ACCRCRegClass &&
"Unexpected register class");
PHIOps.push_back({PHIInput->getOperand(1), PHI->getOperand(PHIOp + 1)});
} else if (Opcode == PPC::IMPLICIT_DEF) {
Register AccReg = MRI->createVirtualRegister(&PPC::ACCRCRegClass);
BuildMI(*PHIInput->getParent(), PHIInput, PHIInput->getDebugLoc(),
TII->get(PPC::IMPLICIT_DEF), AccReg);
PHIOps.push_back({MachineOperand::CreateReg(AccReg, false),
PHI->getOperand(PHIOp + 1)});
} else if (Opcode == PPC::PHI) {
// We found a PHI operand. At this point we know this operand
// has already been changed so we get its associated changed form
// from the map.
assert(ChangedPHIMap.count(PHIInput) == 1 &&
"This PHI node should have already been changed.");
MachineInstr *PrimedAccPHI = ChangedPHIMap.lookup(PHIInput);
PHIOps.push_back({MachineOperand::CreateReg(
PrimedAccPHI->getOperand(0).getReg(), false),
PHI->getOperand(PHIOp + 1)});
}
}
Register AccReg = Dst;
// If the PHI node we are changing is the root node, the register it defines
// will be the destination register of the original copy (of the PHI def).
// For all other PHI's in the list, we need to create another primed
// accumulator virtual register as the PHI will no longer define the
// unprimed accumulator.
if (PHI != PHIs[0])
AccReg = MRI->createVirtualRegister(&PPC::ACCRCRegClass);
MachineInstrBuilder NewPHI = BuildMI(
*PHI->getParent(), PHI, PHI->getDebugLoc(), TII->get(PPC::PHI), AccReg);
for (auto RegMBB : PHIOps)
NewPHI.add(RegMBB.first).add(RegMBB.second);
ChangedPHIMap[PHI] = NewPHI.getInstr();
}
}
// Perform peephole optimizations.
bool PPCMIPeephole::simplifyCode(void) {
bool Simplified = false;
MachineInstr* ToErase = nullptr;
std::map<MachineInstr *, bool> TOCSaves;
const TargetRegisterInfo *TRI = &TII->getRegisterInfo();
NumFunctionsEnteredInMIPeephole++;
if (ConvertRegReg) {
// Fixed-point conversion of reg/reg instructions fed by load-immediate
// into reg/imm instructions. FIXME: This is expensive, control it with
// an option.
bool SomethingChanged = false;
do {
NumFixedPointIterations++;
SomethingChanged = false;
for (MachineBasicBlock &MBB : *MF) {
for (MachineInstr &MI : MBB) {
if (MI.isDebugInstr())
continue;
if (TII->convertToImmediateForm(MI)) {
// We don't erase anything in case the def has other uses. Let DCE
// remove it if it can be removed.
LLVM_DEBUG(dbgs() << "Converted instruction to imm form: ");
LLVM_DEBUG(MI.dump());
NumConvertedToImmediateForm++;
SomethingChanged = true;
Simplified = true;
continue;
}
}
}
} while (SomethingChanged && FixedPointRegToImm);
}
for (MachineBasicBlock &MBB : *MF) {
for (MachineInstr &MI : MBB) {
// If the previous instruction was marked for elimination,
// remove it now.
if (ToErase) {
ToErase->eraseFromParent();
ToErase = nullptr;
}
// Ignore debug instructions.
if (MI.isDebugInstr())
continue;
// Per-opcode peepholes.
switch (MI.getOpcode()) {
default:
break;
case PPC::COPY: {
Register Src = MI.getOperand(1).getReg();
Register Dst = MI.getOperand(0).getReg();
if (!Register::isVirtualRegister(Src) ||
!Register::isVirtualRegister(Dst))
break;
if (MRI->getRegClass(Src) != &PPC::UACCRCRegClass ||
MRI->getRegClass(Dst) != &PPC::ACCRCRegClass)
break;
// We are copying an unprimed accumulator to a primed accumulator.
// If the input to the copy is a PHI that is fed only by (i) copies in
// the other direction (ii) implicitly defined unprimed accumulators or
// (iii) other PHI nodes satisfying (i) and (ii), we can change
// the PHI to a PHI on primed accumulators (as long as we also change
// its operands). To detect and change such copies, we first get a list
// of all the PHI nodes starting from the root PHI node in BFS order.
// We then visit all these PHI nodes to check if they can be changed to
// primed accumulator PHI nodes and if so, we change them.
MachineInstr *RootPHI = MRI->getVRegDef(Src);
if (RootPHI->getOpcode() != PPC::PHI)
break;
SmallVector<MachineInstr *, 4> PHIs;
if (!collectUnprimedAccPHIs(MRI, RootPHI, PHIs))
break;
convertUnprimedAccPHIs(TII, MRI, PHIs, Dst);
ToErase = &MI;
break;
}
case PPC::LI:
case PPC::LI8: {
// If we are materializing a zero, look for any use operands for which
// zero means immediate zero. All such operands can be replaced with
// PPC::ZERO.
if (!MI.getOperand(1).isImm() || MI.getOperand(1).getImm() != 0)
break;
unsigned MIDestReg = MI.getOperand(0).getReg();
for (MachineInstr& UseMI : MRI->use_instructions(MIDestReg))
Simplified |= TII->onlyFoldImmediate(UseMI, MI, MIDestReg);
if (MRI->use_nodbg_empty(MIDestReg)) {
++NumLoadImmZeroFoldedAndRemoved;
ToErase = &MI;
}
break;
}
case PPC::STD: {
MachineFrameInfo &MFI = MF->getFrameInfo();
if (MFI.hasVarSizedObjects() ||
!MF->getSubtarget<PPCSubtarget>().isELFv2ABI())
break;
// When encountering a TOC save instruction, call UpdateTOCSaves
// to add it to the TOCSaves map and mark any existing TOC saves
// it dominates as redundant.
if (TII->isTOCSaveMI(MI))
UpdateTOCSaves(TOCSaves, &MI);
break;
}
case PPC::XXPERMDI: {
// Perform simplifications of 2x64 vector swaps and splats.
// A swap is identified by an immediate value of 2, and a splat
// is identified by an immediate value of 0 or 3.
int Immed = MI.getOperand(3).getImm();
if (Immed == 1)
break;
// For each of these simplifications, we need the two source
// regs to match. Unfortunately, MachineCSE ignores COPY and
// SUBREG_TO_REG, so for example we can see
// XXPERMDI t, SUBREG_TO_REG(s), SUBREG_TO_REG(s), immed.
// We have to look through chains of COPY and SUBREG_TO_REG
// to find the real source values for comparison.
unsigned TrueReg1 =
TRI->lookThruCopyLike(MI.getOperand(1).getReg(), MRI);
unsigned TrueReg2 =
TRI->lookThruCopyLike(MI.getOperand(2).getReg(), MRI);
if (!(TrueReg1 == TrueReg2 && Register::isVirtualRegister(TrueReg1)))
break;
MachineInstr *DefMI = MRI->getVRegDef(TrueReg1);
if (!DefMI)
break;
unsigned DefOpc = DefMI->getOpcode();
// If this is a splat fed by a splatting load, the splat is
// redundant. Replace with a copy. This doesn't happen directly due
// to code in PPCDAGToDAGISel.cpp, but it can happen when converting
// a load of a double to a vector of 64-bit integers.
auto isConversionOfLoadAndSplat = [=]() -> bool {
if (DefOpc != PPC::XVCVDPSXDS && DefOpc != PPC::XVCVDPUXDS)
return false;
unsigned FeedReg1 =
TRI->lookThruCopyLike(DefMI->getOperand(1).getReg(), MRI);
if (Register::isVirtualRegister(FeedReg1)) {
MachineInstr *LoadMI = MRI->getVRegDef(FeedReg1);
if (LoadMI && LoadMI->getOpcode() == PPC::LXVDSX)
return true;
}
return false;
};
if ((Immed == 0 || Immed == 3) &&
(DefOpc == PPC::LXVDSX || isConversionOfLoadAndSplat())) {
LLVM_DEBUG(dbgs() << "Optimizing load-and-splat/splat "
"to load-and-splat/copy: ");
LLVM_DEBUG(MI.dump());
BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(PPC::COPY),
MI.getOperand(0).getReg())
.add(MI.getOperand(1));
ToErase = &MI;
Simplified = true;
}
// If this is a splat or a swap fed by another splat, we
// can replace it with a copy.
if (DefOpc == PPC::XXPERMDI) {
unsigned DefReg1 = DefMI->getOperand(1).getReg();
unsigned DefReg2 = DefMI->getOperand(2).getReg();
unsigned DefImmed = DefMI->getOperand(3).getImm();
// If the two inputs are not the same register, check to see if
// they originate from the same virtual register after only
// copy-like instructions.
if (DefReg1 != DefReg2) {
unsigned FeedReg1 = TRI->lookThruCopyLike(DefReg1, MRI);
unsigned FeedReg2 = TRI->lookThruCopyLike(DefReg2, MRI);
if (!(FeedReg1 == FeedReg2 &&
Register::isVirtualRegister(FeedReg1)))
break;
}
if (DefImmed == 0 || DefImmed == 3) {
LLVM_DEBUG(dbgs() << "Optimizing splat/swap or splat/splat "
"to splat/copy: ");
LLVM_DEBUG(MI.dump());
BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(PPC::COPY),
MI.getOperand(0).getReg())
.add(MI.getOperand(1));
ToErase = &MI;
Simplified = true;
}
// If this is a splat fed by a swap, we can simplify modify
// the splat to splat the other value from the swap's input
// parameter.
else if ((Immed == 0 || Immed == 3) && DefImmed == 2) {
LLVM_DEBUG(dbgs() << "Optimizing swap/splat => splat: ");
LLVM_DEBUG(MI.dump());
MI.getOperand(1).setReg(DefReg1);
MI.getOperand(2).setReg(DefReg2);
MI.getOperand(3).setImm(3 - Immed);
Simplified = true;
}
// If this is a swap fed by a swap, we can replace it
// with a copy from the first swap's input.
else if (Immed == 2 && DefImmed == 2) {
LLVM_DEBUG(dbgs() << "Optimizing swap/swap => copy: ");
LLVM_DEBUG(MI.dump());
BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(PPC::COPY),
MI.getOperand(0).getReg())
.add(DefMI->getOperand(1));
ToErase = &MI;
Simplified = true;
}
} else if ((Immed == 0 || Immed == 3) && DefOpc == PPC::XXPERMDIs &&
(DefMI->getOperand(2).getImm() == 0 ||
DefMI->getOperand(2).getImm() == 3)) {
// Splat fed by another splat - switch the output of the first
// and remove the second.
DefMI->getOperand(0).setReg(MI.getOperand(0).getReg());
ToErase = &MI;
Simplified = true;
LLVM_DEBUG(dbgs() << "Removing redundant splat: ");
LLVM_DEBUG(MI.dump());
}
break;
}
case PPC::VSPLTB:
case PPC::VSPLTH:
case PPC::XXSPLTW: {
unsigned MyOpcode = MI.getOpcode();
unsigned OpNo = MyOpcode == PPC::XXSPLTW ? 1 : 2;
unsigned TrueReg =
TRI->lookThruCopyLike(MI.getOperand(OpNo).getReg(), MRI);
if (!Register::isVirtualRegister(TrueReg))
break;
MachineInstr *DefMI = MRI->getVRegDef(TrueReg);
if (!DefMI)
break;
unsigned DefOpcode = DefMI->getOpcode();
auto isConvertOfSplat = [=]() -> bool {
if (DefOpcode != PPC::XVCVSPSXWS && DefOpcode != PPC::XVCVSPUXWS)
return false;
Register ConvReg = DefMI->getOperand(1).getReg();
if (!Register::isVirtualRegister(ConvReg))
return false;
MachineInstr *Splt = MRI->getVRegDef(ConvReg);
return Splt && (Splt->getOpcode() == PPC::LXVWSX ||
Splt->getOpcode() == PPC::XXSPLTW);
};
bool AlreadySplat = (MyOpcode == DefOpcode) ||
(MyOpcode == PPC::VSPLTB && DefOpcode == PPC::VSPLTBs) ||
(MyOpcode == PPC::VSPLTH && DefOpcode == PPC::VSPLTHs) ||
(MyOpcode == PPC::XXSPLTW && DefOpcode == PPC::XXSPLTWs) ||
(MyOpcode == PPC::XXSPLTW && DefOpcode == PPC::LXVWSX) ||
(MyOpcode == PPC::XXSPLTW && DefOpcode == PPC::MTVSRWS)||
(MyOpcode == PPC::XXSPLTW && isConvertOfSplat());
// If the instruction[s] that feed this splat have already splat
// the value, this splat is redundant.
if (AlreadySplat) {
LLVM_DEBUG(dbgs() << "Changing redundant splat to a copy: ");
LLVM_DEBUG(MI.dump());
BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(PPC::COPY),
MI.getOperand(0).getReg())
.add(MI.getOperand(OpNo));
ToErase = &MI;
Simplified = true;
}
// Splat fed by a shift. Usually when we align value to splat into
// vector element zero.
if (DefOpcode == PPC::XXSLDWI) {
Register ShiftRes = DefMI->getOperand(0).getReg();
Register ShiftOp1 = DefMI->getOperand(1).getReg();
Register ShiftOp2 = DefMI->getOperand(2).getReg();
unsigned ShiftImm = DefMI->getOperand(3).getImm();
unsigned SplatImm = MI.getOperand(2).getImm();
if (ShiftOp1 == ShiftOp2) {
unsigned NewElem = (SplatImm + ShiftImm) & 0x3;
if (MRI->hasOneNonDBGUse(ShiftRes)) {
LLVM_DEBUG(dbgs() << "Removing redundant shift: ");
LLVM_DEBUG(DefMI->dump());
ToErase = DefMI;
}
Simplified = true;
LLVM_DEBUG(dbgs() << "Changing splat immediate from " << SplatImm
<< " to " << NewElem << " in instruction: ");
LLVM_DEBUG(MI.dump());
MI.getOperand(1).setReg(ShiftOp1);
MI.getOperand(2).setImm(NewElem);
}
}
break;
}
case PPC::XVCVDPSP: {
// If this is a DP->SP conversion fed by an FRSP, the FRSP is redundant.
unsigned TrueReg =
TRI->lookThruCopyLike(MI.getOperand(1).getReg(), MRI);
if (!Register::isVirtualRegister(TrueReg))
break;
MachineInstr *DefMI = MRI->getVRegDef(TrueReg);
// This can occur when building a vector of single precision or integer
// values.
if (DefMI && DefMI->getOpcode() == PPC::XXPERMDI) {
unsigned DefsReg1 =
TRI->lookThruCopyLike(DefMI->getOperand(1).getReg(), MRI);
unsigned DefsReg2 =
TRI->lookThruCopyLike(DefMI->getOperand(2).getReg(), MRI);
if (!Register::isVirtualRegister(DefsReg1) ||
!Register::isVirtualRegister(DefsReg2))
break;
MachineInstr *P1 = MRI->getVRegDef(DefsReg1);
MachineInstr *P2 = MRI->getVRegDef(DefsReg2);
if (!P1 || !P2)
break;
// Remove the passed FRSP/XSRSP instruction if it only feeds this MI
// and set any uses of that FRSP/XSRSP (in this MI) to the source of
// the FRSP/XSRSP.
auto removeFRSPIfPossible = [&](MachineInstr *RoundInstr) {
unsigned Opc = RoundInstr->getOpcode();
if ((Opc == PPC::FRSP || Opc == PPC::XSRSP) &&
MRI->hasOneNonDBGUse(RoundInstr->getOperand(0).getReg())) {
Simplified = true;
Register ConvReg1 = RoundInstr->getOperand(1).getReg();
Register FRSPDefines = RoundInstr->getOperand(0).getReg();
MachineInstr &Use = *(MRI->use_instr_nodbg_begin(FRSPDefines));
for (int i = 0, e = Use.getNumOperands(); i < e; ++i)
if (Use.getOperand(i).isReg() &&
Use.getOperand(i).getReg() == FRSPDefines)
Use.getOperand(i).setReg(ConvReg1);
LLVM_DEBUG(dbgs() << "Removing redundant FRSP/XSRSP:\n");
LLVM_DEBUG(RoundInstr->dump());
LLVM_DEBUG(dbgs() << "As it feeds instruction:\n");
LLVM_DEBUG(MI.dump());
LLVM_DEBUG(dbgs() << "Through instruction:\n");
LLVM_DEBUG(DefMI->dump());
RoundInstr->eraseFromParent();
}
};
// If the input to XVCVDPSP is a vector that was built (even
// partially) out of FRSP's, the FRSP(s) can safely be removed
// since this instruction performs the same operation.
if (P1 != P2) {
removeFRSPIfPossible(P1);
removeFRSPIfPossible(P2);
break;
}
removeFRSPIfPossible(P1);
}
break;
}
case PPC::EXTSH:
case PPC::EXTSH8:
case PPC::EXTSH8_32_64: {
if (!EnableSExtElimination) break;
Register NarrowReg = MI.getOperand(1).getReg();
if (!Register::isVirtualRegister(NarrowReg))
break;
MachineInstr *SrcMI = MRI->getVRegDef(NarrowReg);
// If we've used a zero-extending load that we will sign-extend,
// just do a sign-extending load.
if (SrcMI->getOpcode() == PPC::LHZ ||
SrcMI->getOpcode() == PPC::LHZX) {
if (!MRI->hasOneNonDBGUse(SrcMI->getOperand(0).getReg()))
break;
auto is64Bit = [] (unsigned Opcode) {
return Opcode == PPC::EXTSH8;
};
auto isXForm = [] (unsigned Opcode) {
return Opcode == PPC::LHZX;
};
auto getSextLoadOp = [] (bool is64Bit, bool isXForm) {
if (is64Bit)
if (isXForm) return PPC::LHAX8;
else return PPC::LHA8;
else
if (isXForm) return PPC::LHAX;
else return PPC::LHA;
};
unsigned Opc = getSextLoadOp(is64Bit(MI.getOpcode()),
isXForm(SrcMI->getOpcode()));
LLVM_DEBUG(dbgs() << "Zero-extending load\n");
LLVM_DEBUG(SrcMI->dump());
LLVM_DEBUG(dbgs() << "and sign-extension\n");
LLVM_DEBUG(MI.dump());
LLVM_DEBUG(dbgs() << "are merged into sign-extending load\n");
SrcMI->setDesc(TII->get(Opc));
SrcMI->getOperand(0).setReg(MI.getOperand(0).getReg());
ToErase = &MI;
Simplified = true;
NumEliminatedSExt++;
}
break;
}
case PPC::EXTSW:
case PPC::EXTSW_32:
case PPC::EXTSW_32_64: {
if (!EnableSExtElimination) break;
Register NarrowReg = MI.getOperand(1).getReg();
if (!Register::isVirtualRegister(NarrowReg))
break;
MachineInstr *SrcMI = MRI->getVRegDef(NarrowReg);
// If we've used a zero-extending load that we will sign-extend,
// just do a sign-extending load.
if (SrcMI->getOpcode() == PPC::LWZ ||
SrcMI->getOpcode() == PPC::LWZX) {
if (!MRI->hasOneNonDBGUse(SrcMI->getOperand(0).getReg()))
break;
auto is64Bit = [] (unsigned Opcode) {
return Opcode == PPC::EXTSW || Opcode == PPC::EXTSW_32_64;
};
auto isXForm = [] (unsigned Opcode) {
return Opcode == PPC::LWZX;
};
auto getSextLoadOp = [] (bool is64Bit, bool isXForm) {
if (is64Bit)
if (isXForm) return PPC::LWAX;
else return PPC::LWA;
else
if (isXForm) return PPC::LWAX_32;
else return PPC::LWA_32;
};
unsigned Opc = getSextLoadOp(is64Bit(MI.getOpcode()),
isXForm(SrcMI->getOpcode()));
LLVM_DEBUG(dbgs() << "Zero-extending load\n");
LLVM_DEBUG(SrcMI->dump());
LLVM_DEBUG(dbgs() << "and sign-extension\n");
LLVM_DEBUG(MI.dump());
LLVM_DEBUG(dbgs() << "are merged into sign-extending load\n");
SrcMI->setDesc(TII->get(Opc));
SrcMI->getOperand(0).setReg(MI.getOperand(0).getReg());
ToErase = &MI;
Simplified = true;
NumEliminatedSExt++;
} else if (MI.getOpcode() == PPC::EXTSW_32_64 &&
TII->isSignExtended(*SrcMI)) {
// We can eliminate EXTSW if the input is known to be already
// sign-extended.
LLVM_DEBUG(dbgs() << "Removing redundant sign-extension\n");
Register TmpReg =
MF->getRegInfo().createVirtualRegister(&PPC::G8RCRegClass);
BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(PPC::IMPLICIT_DEF),
TmpReg);
BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(PPC::INSERT_SUBREG),
MI.getOperand(0).getReg())
.addReg(TmpReg)
.addReg(NarrowReg)
.addImm(PPC::sub_32);
ToErase = &MI;
Simplified = true;
NumEliminatedSExt++;
}
break;
}
case PPC::RLDICL: {
// We can eliminate RLDICL (e.g. for zero-extension)
// if all bits to clear are already zero in the input.
// This code assume following code sequence for zero-extension.
// %6 = COPY %5:sub_32; (optional)
// %8 = IMPLICIT_DEF;
// %7<def,tied1> = INSERT_SUBREG %8<tied0>, %6, sub_32;
if (!EnableZExtElimination) break;
if (MI.getOperand(2).getImm() != 0)
break;
Register SrcReg = MI.getOperand(1).getReg();
if (!Register::isVirtualRegister(SrcReg))
break;
MachineInstr *SrcMI = MRI->getVRegDef(SrcReg);
if (!(SrcMI && SrcMI->getOpcode() == PPC::INSERT_SUBREG &&
SrcMI->getOperand(0).isReg() && SrcMI->getOperand(1).isReg()))
break;
MachineInstr *ImpDefMI, *SubRegMI;
ImpDefMI = MRI->getVRegDef(SrcMI->getOperand(1).getReg());
SubRegMI = MRI->getVRegDef(SrcMI->getOperand(2).getReg());
if (ImpDefMI->getOpcode() != PPC::IMPLICIT_DEF) break;
SrcMI = SubRegMI;
if (SubRegMI->getOpcode() == PPC::COPY) {
Register CopyReg = SubRegMI->getOperand(1).getReg();
if (Register::isVirtualRegister(CopyReg))
SrcMI = MRI->getVRegDef(CopyReg);
}
unsigned KnownZeroCount = getKnownLeadingZeroCount(SrcMI, TII);
if (MI.getOperand(3).getImm() <= KnownZeroCount) {
LLVM_DEBUG(dbgs() << "Removing redundant zero-extension\n");
BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(PPC::COPY),
MI.getOperand(0).getReg())
.addReg(SrcReg);
ToErase = &MI;
Simplified = true;
NumEliminatedZExt++;
}
break;
}
// TODO: Any instruction that has an immediate form fed only by a PHI
// whose operands are all load immediate can be folded away. We currently
// do this for ADD instructions, but should expand it to arithmetic and
// binary instructions with immediate forms in the future.
case PPC::ADD4:
case PPC::ADD8: {
auto isSingleUsePHI = [&](MachineOperand *PhiOp) {
assert(PhiOp && "Invalid Operand!");
MachineInstr *DefPhiMI = getVRegDefOrNull(PhiOp, MRI);
return DefPhiMI && (DefPhiMI->getOpcode() == PPC::PHI) &&
MRI->hasOneNonDBGUse(DefPhiMI->getOperand(0).getReg());
};
auto dominatesAllSingleUseLIs = [&](MachineOperand *DominatorOp,
MachineOperand *PhiOp) {
assert(PhiOp && "Invalid Operand!");
assert(DominatorOp && "Invalid Operand!");
MachineInstr *DefPhiMI = getVRegDefOrNull(PhiOp, MRI);
MachineInstr *DefDomMI = getVRegDefOrNull(DominatorOp, MRI);
// Note: the vregs only show up at odd indices position of PHI Node,
// the even indices position save the BB info.
for (unsigned i = 1; i < DefPhiMI->getNumOperands(); i += 2) {
MachineInstr *LiMI =
getVRegDefOrNull(&DefPhiMI->getOperand(i), MRI);
if (!LiMI ||
(LiMI->getOpcode() != PPC::LI && LiMI->getOpcode() != PPC::LI8)
|| !MRI->hasOneNonDBGUse(LiMI->getOperand(0).getReg()) ||
!MDT->dominates(DefDomMI, LiMI))
return false;
}
return true;
};
MachineOperand Op1 = MI.getOperand(1);
MachineOperand Op2 = MI.getOperand(2);
if (isSingleUsePHI(&Op2) && dominatesAllSingleUseLIs(&Op1, &Op2))
std::swap(Op1, Op2);
else if (!isSingleUsePHI(&Op1) || !dominatesAllSingleUseLIs(&Op2, &Op1))
break; // We don't have an ADD fed by LI's that can be transformed
// Now we know that Op1 is the PHI node and Op2 is the dominator
Register DominatorReg = Op2.getReg();
const TargetRegisterClass *TRC = MI.getOpcode() == PPC::ADD8
? &PPC::G8RC_and_G8RC_NOX0RegClass
: &PPC::GPRC_and_GPRC_NOR0RegClass;
MRI->setRegClass(DominatorReg, TRC);
// replace LIs with ADDIs
MachineInstr *DefPhiMI = getVRegDefOrNull(&Op1, MRI);
for (unsigned i = 1; i < DefPhiMI->getNumOperands(); i += 2) {
MachineInstr *LiMI = getVRegDefOrNull(&DefPhiMI->getOperand(i), MRI);
LLVM_DEBUG(dbgs() << "Optimizing LI to ADDI: ");
LLVM_DEBUG(LiMI->dump());
// There could be repeated registers in the PHI, e.g: %1 =
// PHI %6, <%bb.2>, %8, <%bb.3>, %8, <%bb.6>; So if we've
// already replaced the def instruction, skip.
if (LiMI->getOpcode() == PPC::ADDI || LiMI->getOpcode() == PPC::ADDI8)
continue;
assert((LiMI->getOpcode() == PPC::LI ||
LiMI->getOpcode() == PPC::LI8) &&
"Invalid Opcode!");
auto LiImm = LiMI->getOperand(1).getImm(); // save the imm of LI
LiMI->RemoveOperand(1); // remove the imm of LI
LiMI->setDesc(TII->get(LiMI->getOpcode() == PPC::LI ? PPC::ADDI
: PPC::ADDI8));
MachineInstrBuilder(*LiMI->getParent()->getParent(), *LiMI)
.addReg(DominatorReg)
.addImm(LiImm); // restore the imm of LI
LLVM_DEBUG(LiMI->dump());
}
// Replace ADD with COPY
LLVM_DEBUG(dbgs() << "Optimizing ADD to COPY: ");
LLVM_DEBUG(MI.dump());
BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(PPC::COPY),
MI.getOperand(0).getReg())
.add(Op1);
ToErase = &MI;
Simplified = true;
NumOptADDLIs++;
break;
}
case PPC::RLDICR: {
Simplified |= emitRLDICWhenLoweringJumpTables(MI) ||
combineSEXTAndSHL(MI, ToErase);
break;
}
case PPC::RLWINM:
case PPC::RLWINM_rec:
case PPC::RLWINM8:
case PPC::RLWINM8_rec: {
Simplified = TII->combineRLWINM(MI, &ToErase);
if (Simplified)
++NumRotatesCollapsed;
break;
}
}
}
// If the last instruction was marked for elimination,
// remove it now.
if (ToErase) {
ToErase->eraseFromParent();
ToErase = nullptr;
}
}
// Eliminate all the TOC save instructions which are redundant.
Simplified |= eliminateRedundantTOCSaves(TOCSaves);
PPCFunctionInfo *FI = MF->getInfo<PPCFunctionInfo>();
if (FI->mustSaveTOC())
NumTOCSavesInPrologue++;
// We try to eliminate redundant compare instruction.
Simplified |= eliminateRedundantCompare();
return Simplified;
}
// helper functions for eliminateRedundantCompare
static bool isEqOrNe(MachineInstr *BI) {
PPC::Predicate Pred = (PPC::Predicate)BI->getOperand(0).getImm();
unsigned PredCond = PPC::getPredicateCondition(Pred);
return (PredCond == PPC::PRED_EQ || PredCond == PPC::PRED_NE);
}
static bool isSupportedCmpOp(unsigned opCode) {
return (opCode == PPC::CMPLD || opCode == PPC::CMPD ||
opCode == PPC::CMPLW || opCode == PPC::CMPW ||
opCode == PPC::CMPLDI || opCode == PPC::CMPDI ||
opCode == PPC::CMPLWI || opCode == PPC::CMPWI);
}
static bool is64bitCmpOp(unsigned opCode) {
return (opCode == PPC::CMPLD || opCode == PPC::CMPD ||
opCode == PPC::CMPLDI || opCode == PPC::CMPDI);
}
static bool isSignedCmpOp(unsigned opCode) {
return (opCode == PPC::CMPD || opCode == PPC::CMPW ||
opCode == PPC::CMPDI || opCode == PPC::CMPWI);
}
static unsigned getSignedCmpOpCode(unsigned opCode) {
if (opCode == PPC::CMPLD) return PPC::CMPD;
if (opCode == PPC::CMPLW) return PPC::CMPW;
if (opCode == PPC::CMPLDI) return PPC::CMPDI;
if (opCode == PPC::CMPLWI) return PPC::CMPWI;
return opCode;
}
// We can decrement immediate x in (GE x) by changing it to (GT x-1) or
// (LT x) to (LE x-1)
static unsigned getPredicateToDecImm(MachineInstr *BI, MachineInstr *CMPI) {
uint64_t Imm = CMPI->getOperand(2).getImm();
bool SignedCmp = isSignedCmpOp(CMPI->getOpcode());
if ((!SignedCmp && Imm == 0) || (SignedCmp && Imm == 0x8000))
return 0;
PPC::Predicate Pred = (PPC::Predicate)BI->getOperand(0).getImm();
unsigned PredCond = PPC::getPredicateCondition(Pred);
unsigned PredHint = PPC::getPredicateHint(Pred);
if (PredCond == PPC::PRED_GE)
return PPC::getPredicate(PPC::PRED_GT, PredHint);
if (PredCond == PPC::PRED_LT)
return PPC::getPredicate(PPC::PRED_LE, PredHint);
return 0;
}
// We can increment immediate x in (GT x) by changing it to (GE x+1) or
// (LE x) to (LT x+1)
static unsigned getPredicateToIncImm(MachineInstr *BI, MachineInstr *CMPI) {
uint64_t Imm = CMPI->getOperand(2).getImm();
bool SignedCmp = isSignedCmpOp(CMPI->getOpcode());
if ((!SignedCmp && Imm == 0xFFFF) || (SignedCmp && Imm == 0x7FFF))
return 0;
PPC::Predicate Pred = (PPC::Predicate)BI->getOperand(0).getImm();
unsigned PredCond = PPC::getPredicateCondition(Pred);
unsigned PredHint = PPC::getPredicateHint(Pred);
if (PredCond == PPC::PRED_GT)
return PPC::getPredicate(PPC::PRED_GE, PredHint);
if (PredCond == PPC::PRED_LE)
return PPC::getPredicate(PPC::PRED_LT, PredHint);
return 0;
}
// This takes a Phi node and returns a register value for the specified BB.
static unsigned getIncomingRegForBlock(MachineInstr *Phi,
MachineBasicBlock *MBB) {
for (unsigned I = 2, E = Phi->getNumOperands() + 1; I != E; I += 2) {
MachineOperand &MO = Phi->getOperand(I);
if (MO.getMBB() == MBB)
return Phi->getOperand(I-1).getReg();
}
llvm_unreachable("invalid src basic block for this Phi node\n");
return 0;
}
// This function tracks the source of the register through register copy.
// If BB1 and BB2 are non-NULL, we also track PHI instruction in BB2
// assuming that the control comes from BB1 into BB2.
static unsigned getSrcVReg(unsigned Reg, MachineBasicBlock *BB1,
MachineBasicBlock *BB2, MachineRegisterInfo *MRI) {
unsigned SrcReg = Reg;
while (1) {
unsigned NextReg = SrcReg;
MachineInstr *Inst = MRI->getVRegDef(SrcReg);
if (BB1 && Inst->getOpcode() == PPC::PHI && Inst->getParent() == BB2) {
NextReg = getIncomingRegForBlock(Inst, BB1);
// We track through PHI only once to avoid infinite loop.
BB1 = nullptr;
}
else if (Inst->isFullCopy())
NextReg = Inst->getOperand(1).getReg();
if (NextReg == SrcReg || !Register::isVirtualRegister(NextReg))
break;
SrcReg = NextReg;
}
return SrcReg;
}
static bool eligibleForCompareElimination(MachineBasicBlock &MBB,
MachineBasicBlock *&PredMBB,
MachineBasicBlock *&MBBtoMoveCmp,
MachineRegisterInfo *MRI) {
auto isEligibleBB = [&](MachineBasicBlock &BB) {
auto BII = BB.getFirstInstrTerminator();
// We optimize BBs ending with a conditional branch.
// We check only for BCC here, not BCCLR, because BCCLR
// will be formed only later in the pipeline.
if (BB.succ_size() == 2 &&
BII != BB.instr_end() &&
(*BII).getOpcode() == PPC::BCC &&
(*BII).getOperand(1).isReg()) {
// We optimize only if the condition code is used only by one BCC.
Register CndReg = (*BII).getOperand(1).getReg();
if (!Register::isVirtualRegister(CndReg) || !MRI->hasOneNonDBGUse(CndReg))
return false;
MachineInstr *CMPI = MRI->getVRegDef(CndReg);
// We assume compare and branch are in the same BB for ease of analysis.
if (CMPI->getParent() != &BB)
return false;
// We skip this BB if a physical register is used in comparison.
for (MachineOperand &MO : CMPI->operands())
if (MO.isReg() && !Register::isVirtualRegister(MO.getReg()))
return false;
return true;
}
return false;
};
// If this BB has more than one successor, we can create a new BB and
// move the compare instruction in the new BB.
// So far, we do not move compare instruction to a BB having multiple
// successors to avoid potentially increasing code size.
auto isEligibleForMoveCmp = [](MachineBasicBlock &BB) {
return BB.succ_size() == 1;
};
if (!isEligibleBB(MBB))
return false;
unsigned NumPredBBs = MBB.pred_size();
if (NumPredBBs == 1) {
MachineBasicBlock *TmpMBB = *MBB.pred_begin();
if (isEligibleBB(*TmpMBB)) {
PredMBB = TmpMBB;
MBBtoMoveCmp = nullptr;
return true;
}
}
else if (NumPredBBs == 2) {
// We check for partially redundant case.
// So far, we support cases with only two predecessors
// to avoid increasing the number of instructions.
MachineBasicBlock::pred_iterator PI = MBB.pred_begin();
MachineBasicBlock *Pred1MBB = *PI;
MachineBasicBlock *Pred2MBB = *(PI+1);
if (isEligibleBB(*Pred1MBB) && isEligibleForMoveCmp(*Pred2MBB)) {
// We assume Pred1MBB is the BB containing the compare to be merged and
// Pred2MBB is the BB to which we will append a compare instruction.
// Hence we can proceed as is.
}
else if (isEligibleBB(*Pred2MBB) && isEligibleForMoveCmp(*Pred1MBB)) {
// We need to swap Pred1MBB and Pred2MBB to canonicalize.
std::swap(Pred1MBB, Pred2MBB);
}
else return false;
// Here, Pred2MBB is the BB to which we need to append a compare inst.
// We cannot move the compare instruction if operands are not available
// in Pred2MBB (i.e. defined in MBB by an instruction other than PHI).
MachineInstr *BI = &*MBB.getFirstInstrTerminator();
MachineInstr *CMPI = MRI->getVRegDef(BI->getOperand(1).getReg());
for (int I = 1; I <= 2; I++)
if (CMPI->getOperand(I).isReg()) {
MachineInstr *Inst = MRI->getVRegDef(CMPI->getOperand(I).getReg());
if (Inst->getParent() == &MBB && Inst->getOpcode() != PPC::PHI)
return false;
}
PredMBB = Pred1MBB;
MBBtoMoveCmp = Pred2MBB;
return true;
}
return false;
}
// This function will iterate over the input map containing a pair of TOC save
// instruction and a flag. The flag will be set to false if the TOC save is
// proven redundant. This function will erase from the basic block all the TOC
// saves marked as redundant.
bool PPCMIPeephole::eliminateRedundantTOCSaves(
std::map<MachineInstr *, bool> &TOCSaves) {
bool Simplified = false;
int NumKept = 0;
for (auto TOCSave : TOCSaves) {
if (!TOCSave.second) {
TOCSave.first->eraseFromParent();
RemoveTOCSave++;
Simplified = true;
} else {
NumKept++;
}
}
if (NumKept > 1)
MultiTOCSaves++;
return Simplified;
}
// If multiple conditional branches are executed based on the (essentially)
// same comparison, we merge compare instructions into one and make multiple
// conditional branches on this comparison.
// For example,
// if (a == 0) { ... }
// else if (a < 0) { ... }
// can be executed by one compare and two conditional branches instead of
// two pairs of a compare and a conditional branch.
//
// This method merges two compare instructions in two MBBs and modifies the
// compare and conditional branch instructions if needed.
// For the above example, the input for this pass looks like:
// cmplwi r3, 0
// beq 0, .LBB0_3
// cmpwi r3, -1
// bgt 0, .LBB0_4
// So, before merging two compares, we need to modify these instructions as
// cmpwi r3, 0 ; cmplwi and cmpwi yield same result for beq
// beq 0, .LBB0_3
// cmpwi r3, 0 ; greather than -1 means greater or equal to 0
// bge 0, .LBB0_4
bool PPCMIPeephole::eliminateRedundantCompare(void) {
bool Simplified = false;
for (MachineBasicBlock &MBB2 : *MF) {
MachineBasicBlock *MBB1 = nullptr, *MBBtoMoveCmp = nullptr;
// For fully redundant case, we select two basic blocks MBB1 and MBB2
// as an optimization target if
// - both MBBs end with a conditional branch,
// - MBB1 is the only predecessor of MBB2, and
// - compare does not take a physical register as a operand in both MBBs.
// In this case, eligibleForCompareElimination sets MBBtoMoveCmp nullptr.
//
// As partially redundant case, we additionally handle if MBB2 has one
// additional predecessor, which has only one successor (MBB2).
// In this case, we move the compare instruction originally in MBB2 into
// MBBtoMoveCmp. This partially redundant case is typically appear by
// compiling a while loop; here, MBBtoMoveCmp is the loop preheader.
//
// Overview of CFG of related basic blocks
// Fully redundant case Partially redundant case
// -------- ---------------- --------
// | MBB1 | (w/ 2 succ) | MBBtoMoveCmp | | MBB1 | (w/ 2 succ)
// -------- ---------------- --------
// | \ (w/ 1 succ) \ | \
// | \ \ | \
// | \ |
// -------- --------
// | MBB2 | (w/ 1 pred | MBB2 | (w/ 2 pred
// -------- and 2 succ) -------- and 2 succ)
// | \ | \
// | \ | \
//
if (!eligibleForCompareElimination(MBB2, MBB1, MBBtoMoveCmp, MRI))
continue;
MachineInstr *BI1 = &*MBB1->getFirstInstrTerminator();
MachineInstr *CMPI1 = MRI->getVRegDef(BI1->getOperand(1).getReg());
MachineInstr *BI2 = &*MBB2.getFirstInstrTerminator();
MachineInstr *CMPI2 = MRI->getVRegDef(BI2->getOperand(1).getReg());
bool IsPartiallyRedundant = (MBBtoMoveCmp != nullptr);
// We cannot optimize an unsupported compare opcode or
// a mix of 32-bit and 64-bit comaprisons
if (!isSupportedCmpOp(CMPI1->getOpcode()) ||
!isSupportedCmpOp(CMPI2->getOpcode()) ||
is64bitCmpOp(CMPI1->getOpcode()) != is64bitCmpOp(CMPI2->getOpcode()))
continue;
unsigned NewOpCode = 0;
unsigned NewPredicate1 = 0, NewPredicate2 = 0;
int16_t Imm1 = 0, NewImm1 = 0, Imm2 = 0, NewImm2 = 0;
bool SwapOperands = false;
if (CMPI1->getOpcode() != CMPI2->getOpcode()) {
// Typically, unsigned comparison is used for equality check, but
// we replace it with a signed comparison if the comparison
// to be merged is a signed comparison.
// In other cases of opcode mismatch, we cannot optimize this.
// We cannot change opcode when comparing against an immediate
// if the most significant bit of the immediate is one
// due to the difference in sign extension.
auto CmpAgainstImmWithSignBit = [](MachineInstr *I) {
if (!I->getOperand(2).isImm())
return false;
int16_t Imm = (int16_t)I->getOperand(2).getImm();
return Imm < 0;
};
if (isEqOrNe(BI2) && !CmpAgainstImmWithSignBit(CMPI2) &&
CMPI1->getOpcode() == getSignedCmpOpCode(CMPI2->getOpcode()))
NewOpCode = CMPI1->getOpcode();
else if (isEqOrNe(BI1) && !CmpAgainstImmWithSignBit(CMPI1) &&
getSignedCmpOpCode(CMPI1->getOpcode()) == CMPI2->getOpcode())
NewOpCode = CMPI2->getOpcode();
else continue;
}
if (CMPI1->getOperand(2).isReg() && CMPI2->getOperand(2).isReg()) {
// In case of comparisons between two registers, these two registers
// must be same to merge two comparisons.
unsigned Cmp1Operand1 = getSrcVReg(CMPI1->getOperand(1).getReg(),
nullptr, nullptr, MRI);
unsigned Cmp1Operand2 = getSrcVReg(CMPI1->getOperand(2).getReg(),
nullptr, nullptr, MRI);
unsigned Cmp2Operand1 = getSrcVReg(CMPI2->getOperand(1).getReg(),
MBB1, &MBB2, MRI);
unsigned Cmp2Operand2 = getSrcVReg(CMPI2->getOperand(2).getReg(),
MBB1, &MBB2, MRI);
if (Cmp1Operand1 == Cmp2Operand1 && Cmp1Operand2 == Cmp2Operand2) {
// Same pair of registers in the same order; ready to merge as is.
}
else if (Cmp1Operand1 == Cmp2Operand2 && Cmp1Operand2 == Cmp2Operand1) {
// Same pair of registers in different order.
// We reverse the predicate to merge compare instructions.
PPC::Predicate Pred = (PPC::Predicate)BI2->getOperand(0).getImm();
NewPredicate2 = (unsigned)PPC::getSwappedPredicate(Pred);
// In case of partial redundancy, we need to swap operands
// in another compare instruction.
SwapOperands = true;
}
else continue;
}
else if (CMPI1->getOperand(2).isImm() && CMPI2->getOperand(2).isImm()) {
// In case of comparisons between a register and an immediate,
// the operand register must be same for two compare instructions.
unsigned Cmp1Operand1 = getSrcVReg(CMPI1->getOperand(1).getReg(),
nullptr, nullptr, MRI);
unsigned Cmp2Operand1 = getSrcVReg(CMPI2->getOperand(1).getReg(),
MBB1, &MBB2, MRI);
if (Cmp1Operand1 != Cmp2Operand1)
continue;
NewImm1 = Imm1 = (int16_t)CMPI1->getOperand(2).getImm();
NewImm2 = Imm2 = (int16_t)CMPI2->getOperand(2).getImm();
// If immediate are not same, we try to adjust by changing predicate;
// e.g. GT imm means GE (imm+1).
if (Imm1 != Imm2 && (!isEqOrNe(BI2) || !isEqOrNe(BI1))) {
int Diff = Imm1 - Imm2;
if (Diff < -2 || Diff > 2)
continue;
unsigned PredToInc1 = getPredicateToIncImm(BI1, CMPI1);
unsigned PredToDec1 = getPredicateToDecImm(BI1, CMPI1);
unsigned PredToInc2 = getPredicateToIncImm(BI2, CMPI2);
unsigned PredToDec2 = getPredicateToDecImm(BI2, CMPI2);
if (Diff == 2) {
if (PredToInc2 && PredToDec1) {
NewPredicate2 = PredToInc2;
NewPredicate1 = PredToDec1;
NewImm2++;
NewImm1--;
}
}
else if (Diff == 1) {
if (PredToInc2) {
NewImm2++;
NewPredicate2 = PredToInc2;
}
else if (PredToDec1) {
NewImm1--;
NewPredicate1 = PredToDec1;
}
}
else if (Diff == -1) {
if (PredToDec2) {
NewImm2--;
NewPredicate2 = PredToDec2;
}
else if (PredToInc1) {
NewImm1++;
NewPredicate1 = PredToInc1;
}
}
else if (Diff == -2) {
if (PredToDec2 && PredToInc1) {
NewPredicate2 = PredToDec2;
NewPredicate1 = PredToInc1;
NewImm2--;
NewImm1++;
}
}
}
// We cannot merge two compares if the immediates are not same.
if (NewImm2 != NewImm1)
continue;
}
LLVM_DEBUG(dbgs() << "Optimize two pairs of compare and branch:\n");
LLVM_DEBUG(CMPI1->dump());
LLVM_DEBUG(BI1->dump());
LLVM_DEBUG(CMPI2->dump());
LLVM_DEBUG(BI2->dump());
// We adjust opcode, predicates and immediate as we determined above.
if (NewOpCode != 0 && NewOpCode != CMPI1->getOpcode()) {
CMPI1->setDesc(TII->get(NewOpCode));
}
if (NewPredicate1) {
BI1->getOperand(0).setImm(NewPredicate1);
}
if (NewPredicate2) {
BI2->getOperand(0).setImm(NewPredicate2);
}
if (NewImm1 != Imm1) {
CMPI1->getOperand(2).setImm(NewImm1);
}
if (IsPartiallyRedundant) {
// We touch up the compare instruction in MBB2 and move it to
// a previous BB to handle partially redundant case.
if (SwapOperands) {
Register Op1 = CMPI2->getOperand(1).getReg();
Register Op2 = CMPI2->getOperand(2).getReg();
CMPI2->getOperand(1).setReg(Op2);
CMPI2->getOperand(2).setReg(Op1);
}
if (NewImm2 != Imm2)
CMPI2->getOperand(2).setImm(NewImm2);
for (int I = 1; I <= 2; I++) {
if (CMPI2->getOperand(I).isReg()) {
MachineInstr *Inst = MRI->getVRegDef(CMPI2->getOperand(I).getReg());
if (Inst->getParent() != &MBB2)
continue;
assert(Inst->getOpcode() == PPC::PHI &&
"We cannot support if an operand comes from this BB.");
unsigned SrcReg = getIncomingRegForBlock(Inst, MBBtoMoveCmp);
CMPI2->getOperand(I).setReg(SrcReg);
}
}
auto I = MachineBasicBlock::iterator(MBBtoMoveCmp->getFirstTerminator());
MBBtoMoveCmp->splice(I, &MBB2, MachineBasicBlock::iterator(CMPI2));
DebugLoc DL = CMPI2->getDebugLoc();
Register NewVReg = MRI->createVirtualRegister(&PPC::CRRCRegClass);
BuildMI(MBB2, MBB2.begin(), DL,
TII->get(PPC::PHI), NewVReg)
.addReg(BI1->getOperand(1).getReg()).addMBB(MBB1)
.addReg(BI2->getOperand(1).getReg()).addMBB(MBBtoMoveCmp);
BI2->getOperand(1).setReg(NewVReg);
}
else {
// We finally eliminate compare instruction in MBB2.
BI2->getOperand(1).setReg(BI1->getOperand(1).getReg());
CMPI2->eraseFromParent();
}
BI2->getOperand(1).setIsKill(true);
BI1->getOperand(1).setIsKill(false);
LLVM_DEBUG(dbgs() << "into a compare and two branches:\n");
LLVM_DEBUG(CMPI1->dump());
LLVM_DEBUG(BI1->dump());
LLVM_DEBUG(BI2->dump());
if (IsPartiallyRedundant) {
LLVM_DEBUG(dbgs() << "The following compare is moved into "
<< printMBBReference(*MBBtoMoveCmp)
<< " to handle partial redundancy.\n");
LLVM_DEBUG(CMPI2->dump());
}
Simplified = true;
}
return Simplified;
}
// We miss the opportunity to emit an RLDIC when lowering jump tables
// since ISEL sees only a single basic block. When selecting, the clear
// and shift left will be in different blocks.
bool PPCMIPeephole::emitRLDICWhenLoweringJumpTables(MachineInstr &MI) {
if (MI.getOpcode() != PPC::RLDICR)
return false;
Register SrcReg = MI.getOperand(1).getReg();
if (!Register::isVirtualRegister(SrcReg))
return false;
MachineInstr *SrcMI = MRI->getVRegDef(SrcReg);
if (SrcMI->getOpcode() != PPC::RLDICL)
return false;
MachineOperand MOpSHSrc = SrcMI->getOperand(2);
MachineOperand MOpMBSrc = SrcMI->getOperand(3);
MachineOperand MOpSHMI = MI.getOperand(2);
MachineOperand MOpMEMI = MI.getOperand(3);
if (!(MOpSHSrc.isImm() && MOpMBSrc.isImm() && MOpSHMI.isImm() &&
MOpMEMI.isImm()))
return false;
uint64_t SHSrc = MOpSHSrc.getImm();
uint64_t MBSrc = MOpMBSrc.getImm();
uint64_t SHMI = MOpSHMI.getImm();
uint64_t MEMI = MOpMEMI.getImm();
uint64_t NewSH = SHSrc + SHMI;
uint64_t NewMB = MBSrc - SHMI;
if (NewMB > 63 || NewSH > 63)
return false;
// The bits cleared with RLDICL are [0, MBSrc).
// The bits cleared with RLDICR are (MEMI, 63].
// After the sequence, the bits cleared are:
// [0, MBSrc-SHMI) and (MEMI, 63).
//
// The bits cleared with RLDIC are [0, NewMB) and (63-NewSH, 63].
if ((63 - NewSH) != MEMI)
return false;
LLVM_DEBUG(dbgs() << "Converting pair: ");
LLVM_DEBUG(SrcMI->dump());
LLVM_DEBUG(MI.dump());
MI.setDesc(TII->get(PPC::RLDIC));
MI.getOperand(1).setReg(SrcMI->getOperand(1).getReg());
MI.getOperand(2).setImm(NewSH);
MI.getOperand(3).setImm(NewMB);
MI.getOperand(1).setIsKill(SrcMI->getOperand(1).isKill());
SrcMI->getOperand(1).setIsKill(false);
LLVM_DEBUG(dbgs() << "To: ");
LLVM_DEBUG(MI.dump());
NumRotatesCollapsed++;
// If SrcReg has no non-debug use it's safe to delete its def SrcMI.
if (MRI->use_nodbg_empty(SrcReg)) {
assert(!SrcMI->hasImplicitDef() &&
"Not expecting an implicit def with this instr.");
SrcMI->eraseFromParent();
}
return true;
}
// For case in LLVM IR
// entry:
// %iconv = sext i32 %index to i64
// br i1 undef label %true, label %false
// true:
// %ptr = getelementptr inbounds i32, i32* null, i64 %iconv
// ...
// PPCISelLowering::combineSHL fails to combine, because sext and shl are in
// different BBs when conducting instruction selection. We can do a peephole
// optimization to combine these two instructions into extswsli after
// instruction selection.
bool PPCMIPeephole::combineSEXTAndSHL(MachineInstr &MI,
MachineInstr *&ToErase) {
if (MI.getOpcode() != PPC::RLDICR)
return false;
if (!MF->getSubtarget<PPCSubtarget>().isISA3_0())
return false;
assert(MI.getNumOperands() == 4 && "RLDICR should have 4 operands");
MachineOperand MOpSHMI = MI.getOperand(2);
MachineOperand MOpMEMI = MI.getOperand(3);
if (!(MOpSHMI.isImm() && MOpMEMI.isImm()))
return false;
uint64_t SHMI = MOpSHMI.getImm();
uint64_t MEMI = MOpMEMI.getImm();
if (SHMI + MEMI != 63)
return false;
Register SrcReg = MI.getOperand(1).getReg();
if (!Register::isVirtualRegister(SrcReg))
return false;
MachineInstr *SrcMI = MRI->getVRegDef(SrcReg);
if (SrcMI->getOpcode() != PPC::EXTSW &&
SrcMI->getOpcode() != PPC::EXTSW_32_64)
return false;
// If the register defined by extsw has more than one use, combination is not
// needed.
if (!MRI->hasOneNonDBGUse(SrcReg))
return false;
assert(SrcMI->getNumOperands() == 2 && "EXTSW should have 2 operands");
assert(SrcMI->getOperand(1).isReg() &&
"EXTSW's second operand should be a register");
if (!Register::isVirtualRegister(SrcMI->getOperand(1).getReg()))
return false;
LLVM_DEBUG(dbgs() << "Combining pair: ");
LLVM_DEBUG(SrcMI->dump());
LLVM_DEBUG(MI.dump());
MachineInstr *NewInstr =
BuildMI(*MI.getParent(), &MI, MI.getDebugLoc(),
SrcMI->getOpcode() == PPC::EXTSW ? TII->get(PPC::EXTSWSLI)
: TII->get(PPC::EXTSWSLI_32_64),
MI.getOperand(0).getReg())
.add(SrcMI->getOperand(1))
.add(MOpSHMI);
(void)NewInstr;
LLVM_DEBUG(dbgs() << "TO: ");
LLVM_DEBUG(NewInstr->dump());
++NumEXTSWAndSLDICombined;
ToErase = &MI;
// SrcMI, which is extsw, is of no use now, erase it.
SrcMI->eraseFromParent();
return true;
}
} // end default namespace
INITIALIZE_PASS_BEGIN(PPCMIPeephole, DEBUG_TYPE,
"PowerPC MI Peephole Optimization", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineBlockFrequencyInfo)
INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_PASS_DEPENDENCY(MachinePostDominatorTree)
INITIALIZE_PASS_END(PPCMIPeephole, DEBUG_TYPE,
"PowerPC MI Peephole Optimization", false, false)
char PPCMIPeephole::ID = 0;
FunctionPass*
llvm::createPPCMIPeepholePass() { return new PPCMIPeephole(); }
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