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llvm-project/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp

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//=- AArch64LoadStoreOptimizer.cpp - AArch64 load/store opt. pass -*- C++ -*-=//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains a pass that performs load / store related peephole
// optimizations. This pass should be run after register allocation.
//
//===----------------------------------------------------------------------===//
#include "AArch64InstrInfo.h"
#include "AArch64Subtarget.h"
#include "MCTargetDesc/AArch64AddressingModes.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
using namespace llvm;
#define DEBUG_TYPE "aarch64-ldst-opt"
/// AArch64AllocLoadStoreOpt - Post-register allocation pass to combine
/// load / store instructions to form ldp / stp instructions.
STATISTIC(NumPairCreated, "Number of load/store pair instructions generated");
STATISTIC(NumPostFolded, "Number of post-index updates folded");
STATISTIC(NumPreFolded, "Number of pre-index updates folded");
STATISTIC(NumUnscaledPairCreated,
"Number of load/store from unscaled generated");
static cl::opt<unsigned> ScanLimit("aarch64-load-store-scan-limit",
cl::init(20), cl::Hidden);
// Place holder while testing unscaled load/store combining
static cl::opt<bool> EnableAArch64UnscaledMemOp(
"aarch64-unscaled-mem-op", cl::Hidden,
cl::desc("Allow AArch64 unscaled load/store combining"), cl::init(true));
namespace llvm {
void initializeAArch64LoadStoreOptPass(PassRegistry &);
}
#define AARCH64_LOAD_STORE_OPT_NAME "AArch64 load / store optimization pass"
namespace {
typedef struct LdStPairFlags {
// If a matching instruction is found, MergeForward is set to true if the
// merge is to remove the first instruction and replace the second with
// a pair-wise insn, and false if the reverse is true.
bool MergeForward;
// SExtIdx gives the index of the result of the load pair that must be
// extended. The value of SExtIdx assumes that the paired load produces the
// value in this order: (I, returned iterator), i.e., -1 means no value has
// to be extended, 0 means I, and 1 means the returned iterator.
int SExtIdx;
LdStPairFlags() : MergeForward(false), SExtIdx(-1) {}
void setMergeForward(bool V = true) { MergeForward = V; }
bool getMergeForward() const { return MergeForward; }
void setSExtIdx(int V) { SExtIdx = V; }
int getSExtIdx() const { return SExtIdx; }
} LdStPairFlags;
struct AArch64LoadStoreOpt : public MachineFunctionPass {
static char ID;
AArch64LoadStoreOpt() : MachineFunctionPass(ID) {
initializeAArch64LoadStoreOptPass(*PassRegistry::getPassRegistry());
}
const AArch64InstrInfo *TII;
const TargetRegisterInfo *TRI;
// Scan the instructions looking for a load/store that can be combined
// with the current instruction into a load/store pair.
// Return the matching instruction if one is found, else MBB->end().
MachineBasicBlock::iterator findMatchingInsn(MachineBasicBlock::iterator I,
LdStPairFlags &Flags,
unsigned Limit);
// Merge the two instructions indicated into a single pair-wise instruction.
// If MergeForward is true, erase the first instruction and fold its
// operation into the second. If false, the reverse. Return the instruction
// following the first instruction (which may change during processing).
MachineBasicBlock::iterator
mergePairedInsns(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Paired,
const LdStPairFlags &Flags);
// Scan the instruction list to find a base register update that can
// be combined with the current instruction (a load or store) using
// pre or post indexed addressing with writeback. Scan forwards.
MachineBasicBlock::iterator
findMatchingUpdateInsnForward(MachineBasicBlock::iterator I, unsigned Limit,
int Value);
// Scan the instruction list to find a base register update that can
// be combined with the current instruction (a load or store) using
// pre or post indexed addressing with writeback. Scan backwards.
MachineBasicBlock::iterator
findMatchingUpdateInsnBackward(MachineBasicBlock::iterator I, unsigned Limit);
// Merge a pre-index base register update into a ld/st instruction.
MachineBasicBlock::iterator
mergePreIdxUpdateInsn(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Update);
// Merge a post-index base register update into a ld/st instruction.
MachineBasicBlock::iterator
mergePostIdxUpdateInsn(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Update);
bool optimizeBlock(MachineBasicBlock &MBB);
bool runOnMachineFunction(MachineFunction &Fn) override;
const char *getPassName() const override {
return AARCH64_LOAD_STORE_OPT_NAME;
}
};
char AArch64LoadStoreOpt::ID = 0;
} // namespace
INITIALIZE_PASS(AArch64LoadStoreOpt, "aarch64-ldst-opt",
AARCH64_LOAD_STORE_OPT_NAME, false, false)
static bool isUnscaledLdSt(unsigned Opc) {
switch (Opc) {
default:
return false;
case AArch64::STURSi:
case AArch64::STURDi:
case AArch64::STURQi:
case AArch64::STURWi:
case AArch64::STURXi:
case AArch64::LDURSi:
case AArch64::LDURDi:
case AArch64::LDURQi:
case AArch64::LDURWi:
case AArch64::LDURXi:
case AArch64::LDURSWi:
return true;
}
}
static bool isUnscaledLdSt(MachineInstr *MI) {
return isUnscaledLdSt(MI->getOpcode());
}
// Size in bytes of the data moved by an unscaled load or store
static int getMemSize(MachineInstr *MI) {
switch (MI->getOpcode()) {
default:
llvm_unreachable("Opcode has unknown size!");
case AArch64::STRSui:
case AArch64::STURSi:
return 4;
case AArch64::STRDui:
case AArch64::STURDi:
return 8;
case AArch64::STRQui:
case AArch64::STURQi:
return 16;
case AArch64::STRWui:
case AArch64::STURWi:
return 4;
case AArch64::STRXui:
case AArch64::STURXi:
return 8;
case AArch64::LDRSui:
case AArch64::LDURSi:
return 4;
case AArch64::LDRDui:
case AArch64::LDURDi:
return 8;
case AArch64::LDRQui:
case AArch64::LDURQi:
return 16;
case AArch64::LDRWui:
case AArch64::LDURWi:
return 4;
case AArch64::LDRXui:
case AArch64::LDURXi:
return 8;
case AArch64::LDRSWui:
case AArch64::LDURSWi:
return 4;
}
}
static unsigned getMatchingNonSExtOpcode(unsigned Opc,
bool *IsValidLdStrOpc = nullptr) {
if (IsValidLdStrOpc)
*IsValidLdStrOpc = true;
switch (Opc) {
default:
if (IsValidLdStrOpc)
*IsValidLdStrOpc = false;
return UINT_MAX;
case AArch64::STRDui:
case AArch64::STURDi:
case AArch64::STRQui:
case AArch64::STURQi:
case AArch64::STRWui:
case AArch64::STURWi:
case AArch64::STRXui:
case AArch64::STURXi:
case AArch64::LDRDui:
case AArch64::LDURDi:
case AArch64::LDRQui:
case AArch64::LDURQi:
case AArch64::LDRWui:
case AArch64::LDURWi:
case AArch64::LDRXui:
case AArch64::LDURXi:
case AArch64::STRSui:
case AArch64::STURSi:
case AArch64::LDRSui:
case AArch64::LDURSi:
return Opc;
case AArch64::LDRSWui:
return AArch64::LDRWui;
case AArch64::LDURSWi:
return AArch64::LDURWi;
}
}
static unsigned getMatchingPairOpcode(unsigned Opc) {
switch (Opc) {
default:
llvm_unreachable("Opcode has no pairwise equivalent!");
case AArch64::STRSui:
case AArch64::STURSi:
return AArch64::STPSi;
case AArch64::STRDui:
case AArch64::STURDi:
return AArch64::STPDi;
case AArch64::STRQui:
case AArch64::STURQi:
return AArch64::STPQi;
case AArch64::STRWui:
case AArch64::STURWi:
return AArch64::STPWi;
case AArch64::STRXui:
case AArch64::STURXi:
return AArch64::STPXi;
case AArch64::LDRSui:
case AArch64::LDURSi:
return AArch64::LDPSi;
case AArch64::LDRDui:
case AArch64::LDURDi:
return AArch64::LDPDi;
case AArch64::LDRQui:
case AArch64::LDURQi:
return AArch64::LDPQi;
case AArch64::LDRWui:
case AArch64::LDURWi:
return AArch64::LDPWi;
case AArch64::LDRXui:
case AArch64::LDURXi:
return AArch64::LDPXi;
case AArch64::LDRSWui:
case AArch64::LDURSWi:
return AArch64::LDPSWi;
}
}
static unsigned getPreIndexedOpcode(unsigned Opc) {
switch (Opc) {
default:
llvm_unreachable("Opcode has no pre-indexed equivalent!");
case AArch64::STRSui:
return AArch64::STRSpre;
case AArch64::STRDui:
return AArch64::STRDpre;
case AArch64::STRQui:
return AArch64::STRQpre;
case AArch64::STRWui:
return AArch64::STRWpre;
case AArch64::STRXui:
return AArch64::STRXpre;
case AArch64::LDRSui:
return AArch64::LDRSpre;
case AArch64::LDRDui:
return AArch64::LDRDpre;
case AArch64::LDRQui:
return AArch64::LDRQpre;
case AArch64::LDRWui:
return AArch64::LDRWpre;
case AArch64::LDRXui:
return AArch64::LDRXpre;
case AArch64::LDRSWui:
return AArch64::LDRSWpre;
}
}
static unsigned getPostIndexedOpcode(unsigned Opc) {
switch (Opc) {
default:
llvm_unreachable("Opcode has no post-indexed wise equivalent!");
case AArch64::STRSui:
return AArch64::STRSpost;
case AArch64::STRDui:
return AArch64::STRDpost;
case AArch64::STRQui:
return AArch64::STRQpost;
case AArch64::STRWui:
return AArch64::STRWpost;
case AArch64::STRXui:
return AArch64::STRXpost;
case AArch64::LDRSui:
return AArch64::LDRSpost;
case AArch64::LDRDui:
return AArch64::LDRDpost;
case AArch64::LDRQui:
return AArch64::LDRQpost;
case AArch64::LDRWui:
return AArch64::LDRWpost;
case AArch64::LDRXui:
return AArch64::LDRXpost;
case AArch64::LDRSWui:
return AArch64::LDRSWpost;
}
}
static const MachineOperand &getLdStRegOp(const MachineInstr *MI) {
return MI->getOperand(0);
}
static const MachineOperand &getLdStBaseOp(const MachineInstr *MI) {
return MI->getOperand(1);
}
static const MachineOperand &getLdStOffsetOp(const MachineInstr *MI) {
return MI->getOperand(2);
}
MachineBasicBlock::iterator
AArch64LoadStoreOpt::mergePairedInsns(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Paired,
const LdStPairFlags &Flags) {
MachineBasicBlock::iterator NextI = I;
++NextI;
// If NextI is the second of the two instructions to be merged, we need
// to skip one further. Either way we merge will invalidate the iterator,
// and we don't need to scan the new instruction, as it's a pairwise
// instruction, which we're not considering for further action anyway.
if (NextI == Paired)
++NextI;
int SExtIdx = Flags.getSExtIdx();
unsigned Opc =
SExtIdx == -1 ? I->getOpcode() : getMatchingNonSExtOpcode(I->getOpcode());
bool IsUnscaled = isUnscaledLdSt(Opc);
int OffsetStride =
IsUnscaled && EnableAArch64UnscaledMemOp ? getMemSize(I) : 1;
bool MergeForward = Flags.getMergeForward();
unsigned NewOpc = getMatchingPairOpcode(Opc);
// Insert our new paired instruction after whichever of the paired
// instructions MergeForward indicates.
MachineBasicBlock::iterator InsertionPoint = MergeForward ? Paired : I;
// Also based on MergeForward is from where we copy the base register operand
// so we get the flags compatible with the input code.
const MachineOperand &BaseRegOp =
MergeForward ? getLdStBaseOp(Paired) : getLdStBaseOp(I);
int Offset = getLdStOffsetOp(I).getImm();
int PairedOffset = getLdStOffsetOp(Paired).getImm();
bool PairedIsUnscaled = isUnscaledLdSt(Paired->getOpcode());
// We're trying to pair instructions that differ in how they are scaled.
// If I is scaled then scale the offset of Paired accordingly.
// Otherwise, do the opposite (i.e., make Paired's offset unscaled).
if (IsUnscaled != PairedIsUnscaled) {
int MemSize = getMemSize(Paired);
assert(!(PairedOffset % getMemSize(Paired)) &&
"Offset should be a multiple of the stride!");
PairedOffset =
PairedIsUnscaled ? PairedOffset / MemSize : PairedOffset * MemSize;
}
// Which register is Rt and which is Rt2 depends on the offset order.
MachineInstr *RtMI, *Rt2MI;
if (Offset == PairedOffset + OffsetStride) {
RtMI = Paired;
Rt2MI = I;
// Here we swapped the assumption made for SExtIdx.
// I.e., we turn ldp I, Paired into ldp Paired, I.
// Update the index accordingly.
if (SExtIdx != -1)
SExtIdx = (SExtIdx + 1) % 2;
} else {
RtMI = I;
Rt2MI = Paired;
}
// Scale the immediate offset, if necessary.
int OffsetImm = getLdStOffsetOp(RtMI).getImm();
if (isUnscaledLdSt(RtMI->getOpcode()) && EnableAArch64UnscaledMemOp) {
assert(!(OffsetImm % getMemSize(RtMI)) &&
"Offset should be a multiple of the stride!");
OffsetImm /= getMemSize(RtMI);
}
// Construct the new instruction.
MachineInstrBuilder MIB = BuildMI(*I->getParent(), InsertionPoint,
I->getDebugLoc(), TII->get(NewOpc))
.addOperand(getLdStRegOp(RtMI))
.addOperand(getLdStRegOp(Rt2MI))
.addOperand(BaseRegOp)
.addImm(OffsetImm);
(void)MIB;
// FIXME: Do we need/want to copy the mem operands from the source
// instructions? Probably. What uses them after this?
DEBUG(dbgs() << "Creating pair load/store. Replacing instructions:\n ");
DEBUG(I->print(dbgs()));
DEBUG(dbgs() << " ");
DEBUG(Paired->print(dbgs()));
DEBUG(dbgs() << " with instruction:\n ");
if (SExtIdx != -1) {
// Generate the sign extension for the proper result of the ldp.
// I.e., with X1, that would be:
// %W1<def> = KILL %W1, %X1<imp-def>
// %X1<def> = SBFMXri %X1<kill>, 0, 31
MachineOperand &DstMO = MIB->getOperand(SExtIdx);
// Right now, DstMO has the extended register, since it comes from an
// extended opcode.
unsigned DstRegX = DstMO.getReg();
// Get the W variant of that register.
unsigned DstRegW = TRI->getSubReg(DstRegX, AArch64::sub_32);
// Update the result of LDP to use the W instead of the X variant.
DstMO.setReg(DstRegW);
DEBUG(((MachineInstr *)MIB)->print(dbgs()));
DEBUG(dbgs() << "\n");
// Make the machine verifier happy by providing a definition for
// the X register.
// Insert this definition right after the generated LDP, i.e., before
// InsertionPoint.
MachineInstrBuilder MIBKill =
BuildMI(*I->getParent(), InsertionPoint, I->getDebugLoc(),
TII->get(TargetOpcode::KILL), DstRegW)
.addReg(DstRegW)
.addReg(DstRegX, RegState::Define);
MIBKill->getOperand(2).setImplicit();
// Create the sign extension.
MachineInstrBuilder MIBSXTW =
BuildMI(*I->getParent(), InsertionPoint, I->getDebugLoc(),
TII->get(AArch64::SBFMXri), DstRegX)
.addReg(DstRegX)
.addImm(0)
.addImm(31);
(void)MIBSXTW;
DEBUG(dbgs() << " Extend operand:\n ");
DEBUG(((MachineInstr *)MIBSXTW)->print(dbgs()));
DEBUG(dbgs() << "\n");
} else {
DEBUG(((MachineInstr *)MIB)->print(dbgs()));
DEBUG(dbgs() << "\n");
}
// Erase the old instructions.
I->eraseFromParent();
Paired->eraseFromParent();
return NextI;
}
/// trackRegDefsUses - Remember what registers the specified instruction uses
/// and modifies.
static void trackRegDefsUses(const MachineInstr *MI, BitVector &ModifiedRegs,
BitVector &UsedRegs,
const TargetRegisterInfo *TRI) {
for (const MachineOperand &MO : MI->operands()) {
if (MO.isRegMask())
ModifiedRegs.setBitsNotInMask(MO.getRegMask());
if (!MO.isReg())
continue;
unsigned Reg = MO.getReg();
if (MO.isDef()) {
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
ModifiedRegs.set(*AI);
} else {
assert(MO.isUse() && "Reg operand not a def and not a use?!?");
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
UsedRegs.set(*AI);
}
}
}
static bool inBoundsForPair(bool IsUnscaled, int Offset, int OffsetStride) {
// Convert the byte-offset used by unscaled into an "element" offset used
// by the scaled pair load/store instructions.
if (IsUnscaled) {
// If the byte-offset isn't a multiple of the stride, there's no point
// trying to match it.
if (Offset % OffsetStride)
return false;
Offset /= OffsetStride;
}
return Offset <= 63 && Offset >= -64;
}
// Do alignment, specialized to power of 2 and for signed ints,
// avoiding having to do a C-style cast from uint_64t to int when
// using RoundUpToAlignment from include/llvm/Support/MathExtras.h.
// FIXME: Move this function to include/MathExtras.h?
static int alignTo(int Num, int PowOf2) {
return (Num + PowOf2 - 1) & ~(PowOf2 - 1);
}
static bool mayAlias(MachineInstr *MIa, MachineInstr *MIb,
const AArch64InstrInfo *TII) {
// One of the instructions must modify memory.
if (!MIa->mayStore() && !MIb->mayStore())
return false;
// Both instructions must be memory operations.
if (!MIa->mayLoadOrStore() && !MIb->mayLoadOrStore())
return false;
return !TII->areMemAccessesTriviallyDisjoint(MIa, MIb);
}
static bool mayAlias(MachineInstr *MIa,
SmallVectorImpl<MachineInstr *> &MemInsns,
const AArch64InstrInfo *TII) {
for (auto &MIb : MemInsns)
if (mayAlias(MIa, MIb, TII))
return true;
return false;
}
static bool canMergeOpc(unsigned Opc, unsigned PairOpc, LdStPairFlags &Flags) {
// Opcodes match: nothing more to check.
if (Opc == PairOpc)
return true;
// Try to match a sign-extended load/store with a zero-extended load/store.
Flags.setSExtIdx(-1);
bool IsValidLdStrOpc, PairIsValidLdStrOpc;
unsigned NonSExtOpc = getMatchingNonSExtOpcode(Opc, &IsValidLdStrOpc);
assert(IsValidLdStrOpc &&
"Given Opc should be a Load or Store with an immediate");
// Opc will be the first instruction in the pair.
if (NonSExtOpc == getMatchingNonSExtOpcode(PairOpc, &PairIsValidLdStrOpc)) {
Flags.setSExtIdx(NonSExtOpc == (unsigned)Opc ? 1 : 0);
return true;
}
// FIXME: Can we also match a mixed sext/zext unscaled/scaled pair?
// If the second instruction isn't even a load/store, bail out.
if (!PairIsValidLdStrOpc)
return false;
// Try to match an unscaled load/store with a scaled load/store.
return isUnscaledLdSt(Opc) != isUnscaledLdSt(PairOpc) &&
getMatchingPairOpcode(Opc) == getMatchingPairOpcode(PairOpc);
}
/// findMatchingInsn - Scan the instructions looking for a load/store that can
/// be combined with the current instruction into a load/store pair.
MachineBasicBlock::iterator
AArch64LoadStoreOpt::findMatchingInsn(MachineBasicBlock::iterator I,
LdStPairFlags &Flags,
unsigned Limit) {
MachineBasicBlock::iterator E = I->getParent()->end();
MachineBasicBlock::iterator MBBI = I;
MachineInstr *FirstMI = I;
++MBBI;
unsigned Opc = FirstMI->getOpcode();
bool MayLoad = FirstMI->mayLoad();
bool IsUnscaled = isUnscaledLdSt(FirstMI);
unsigned Reg = getLdStRegOp(FirstMI).getReg();
unsigned BaseReg = getLdStBaseOp(FirstMI).getReg();
int Offset = getLdStOffsetOp(FirstMI).getImm();
// Early exit if the first instruction modifies the base register.
// e.g., ldr x0, [x0]
if (FirstMI->modifiesRegister(BaseReg, TRI))
return E;
// Early exit if the offset if not possible to match. (6 bits of positive
// range, plus allow an extra one in case we find a later insn that matches
// with Offset-1)
int OffsetStride =
IsUnscaled && EnableAArch64UnscaledMemOp ? getMemSize(FirstMI) : 1;
if (!inBoundsForPair(IsUnscaled, Offset, OffsetStride))
return E;
// Track which registers have been modified and used between the first insn
// (inclusive) and the second insn.
BitVector ModifiedRegs, UsedRegs;
ModifiedRegs.resize(TRI->getNumRegs());
UsedRegs.resize(TRI->getNumRegs());
// Remember any instructions that read/write memory between FirstMI and MI.
SmallVector<MachineInstr *, 4> MemInsns;
for (unsigned Count = 0; MBBI != E && Count < Limit; ++MBBI) {
MachineInstr *MI = MBBI;
// Skip DBG_VALUE instructions. Otherwise debug info can affect the
// optimization by changing how far we scan.
if (MI->isDebugValue())
continue;
// Now that we know this is a real instruction, count it.
++Count;
if (canMergeOpc(Opc, MI->getOpcode(), Flags) &&
getLdStOffsetOp(MI).isImm()) {
assert(MI->mayLoadOrStore() && "Expected memory operation.");
// If we've found another instruction with the same opcode, check to see
// if the base and offset are compatible with our starting instruction.
// These instructions all have scaled immediate operands, so we just
// check for +1/-1. Make sure to check the new instruction offset is
// actually an immediate and not a symbolic reference destined for
// a relocation.
//
// Pairwise instructions have a 7-bit signed offset field. Single insns
// have a 12-bit unsigned offset field. To be a valid combine, the
// final offset must be in range.
unsigned MIBaseReg = getLdStBaseOp(MI).getReg();
int MIOffset = getLdStOffsetOp(MI).getImm();
// We're trying to pair instructions that differ in how they are scaled.
// If FirstMI is scaled then scale the offset of MI accordingly.
// Otherwise, do the opposite (i.e., make MI's offset unscaled).
bool MIIsUnscaled = isUnscaledLdSt(MI);
if (IsUnscaled != MIIsUnscaled) {
int MemSize = getMemSize(MI);
if (MIIsUnscaled) {
// If the unscaled offset isn't a multiple of the MemSize, we can't
// pair the operations together: bail and keep looking.
if (MIOffset % MemSize)
continue;
MIOffset /= MemSize;
} else {
MIOffset *= MemSize;
}
}
if (BaseReg == MIBaseReg && ((Offset == MIOffset + OffsetStride) ||
(Offset + OffsetStride == MIOffset))) {
int MinOffset = Offset < MIOffset ? Offset : MIOffset;
// If this is a volatile load/store that otherwise matched, stop looking
// as something is going on that we don't have enough information to
// safely transform. Similarly, stop if we see a hint to avoid pairs.
if (MI->hasOrderedMemoryRef() || TII->isLdStPairSuppressed(MI))
return E;
// If the resultant immediate offset of merging these instructions
// is out of range for a pairwise instruction, bail and keep looking.
if (!inBoundsForPair(IsUnscaled, MinOffset, OffsetStride)) {
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
MemInsns.push_back(MI);
continue;
}
// If the alignment requirements of the paired (scaled) instruction
// can't express the offset of the unscaled input, bail and keep
// looking.
if (IsUnscaled && EnableAArch64UnscaledMemOp &&
(alignTo(MinOffset, OffsetStride) != MinOffset)) {
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
MemInsns.push_back(MI);
continue;
}
// If the destination register of the loads is the same register, bail
// and keep looking. A load-pair instruction with both destination
// registers the same is UNPREDICTABLE and will result in an exception.
if (MayLoad && Reg == getLdStRegOp(MI).getReg()) {
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
MemInsns.push_back(MI);
continue;
}
// If the Rt of the second instruction was not modified or used between
// the two instructions and none of the instructions between the second
// and first alias with the second, we can combine the second into the
// first.
if (!ModifiedRegs[getLdStRegOp(MI).getReg()] &&
!(MI->mayLoad() && UsedRegs[getLdStRegOp(MI).getReg()]) &&
!mayAlias(MI, MemInsns, TII)) {
Flags.setMergeForward(false);
return MBBI;
}
// Likewise, if the Rt of the first instruction is not modified or used
// between the two instructions and none of the instructions between the
// first and the second alias with the first, we can combine the first
// into the second.
if (!ModifiedRegs[getLdStRegOp(FirstMI).getReg()] &&
!(MayLoad && UsedRegs[getLdStRegOp(FirstMI).getReg()]) &&
!mayAlias(FirstMI, MemInsns, TII)) {
Flags.setMergeForward(true);
return MBBI;
}
// Unable to combine these instructions due to interference in between.
// Keep looking.
}
}
// If the instruction wasn't a matching load or store. Stop searching if we
// encounter a call instruction that might modify memory.
if (MI->isCall())
return E;
// Update modified / uses register lists.
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
// Otherwise, if the base register is modified, we have no match, so
// return early.
if (ModifiedRegs[BaseReg])
return E;
// Update list of instructions that read/write memory.
if (MI->mayLoadOrStore())
MemInsns.push_back(MI);
}
return E;
}
MachineBasicBlock::iterator
AArch64LoadStoreOpt::mergePreIdxUpdateInsn(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Update) {
assert((Update->getOpcode() == AArch64::ADDXri ||
Update->getOpcode() == AArch64::SUBXri) &&
"Unexpected base register update instruction to merge!");
MachineBasicBlock::iterator NextI = I;
// Return the instruction following the merged instruction, which is
// the instruction following our unmerged load. Unless that's the add/sub
// instruction we're merging, in which case it's the one after that.
if (++NextI == Update)
++NextI;
int Value = Update->getOperand(2).getImm();
assert(AArch64_AM::getShiftValue(Update->getOperand(3).getImm()) == 0 &&
"Can't merge 1 << 12 offset into pre-indexed load / store");
if (Update->getOpcode() == AArch64::SUBXri)
Value = -Value;
unsigned NewOpc = getPreIndexedOpcode(I->getOpcode());
MachineInstrBuilder MIB =
BuildMI(*I->getParent(), I, I->getDebugLoc(), TII->get(NewOpc))
.addOperand(getLdStRegOp(Update))
.addOperand(getLdStRegOp(I))
.addOperand(getLdStBaseOp(I))
.addImm(Value);
(void)MIB;
DEBUG(dbgs() << "Creating pre-indexed load/store.");
DEBUG(dbgs() << " Replacing instructions:\n ");
DEBUG(I->print(dbgs()));
DEBUG(dbgs() << " ");
DEBUG(Update->print(dbgs()));
DEBUG(dbgs() << " with instruction:\n ");
DEBUG(((MachineInstr *)MIB)->print(dbgs()));
DEBUG(dbgs() << "\n");
// Erase the old instructions for the block.
I->eraseFromParent();
Update->eraseFromParent();
return NextI;
}
MachineBasicBlock::iterator AArch64LoadStoreOpt::mergePostIdxUpdateInsn(
MachineBasicBlock::iterator I, MachineBasicBlock::iterator Update) {
assert((Update->getOpcode() == AArch64::ADDXri ||
Update->getOpcode() == AArch64::SUBXri) &&
"Unexpected base register update instruction to merge!");
MachineBasicBlock::iterator NextI = I;
// Return the instruction following the merged instruction, which is
// the instruction following our unmerged load. Unless that's the add/sub
// instruction we're merging, in which case it's the one after that.
if (++NextI == Update)
++NextI;
int Value = Update->getOperand(2).getImm();
assert(AArch64_AM::getShiftValue(Update->getOperand(3).getImm()) == 0 &&
"Can't merge 1 << 12 offset into post-indexed load / store");
if (Update->getOpcode() == AArch64::SUBXri)
Value = -Value;
unsigned NewOpc = getPostIndexedOpcode(I->getOpcode());
MachineInstrBuilder MIB =
BuildMI(*I->getParent(), I, I->getDebugLoc(), TII->get(NewOpc))
.addOperand(getLdStRegOp(Update))
.addOperand(getLdStRegOp(I))
.addOperand(getLdStBaseOp(I))
.addImm(Value);
(void)MIB;
DEBUG(dbgs() << "Creating post-indexed load/store.");
DEBUG(dbgs() << " Replacing instructions:\n ");
DEBUG(I->print(dbgs()));
DEBUG(dbgs() << " ");
DEBUG(Update->print(dbgs()));
DEBUG(dbgs() << " with instruction:\n ");
DEBUG(((MachineInstr *)MIB)->print(dbgs()));
DEBUG(dbgs() << "\n");
// Erase the old instructions for the block.
I->eraseFromParent();
Update->eraseFromParent();
return NextI;
}
static bool isMatchingUpdateInsn(MachineInstr *MI, unsigned BaseReg,
int Offset) {
switch (MI->getOpcode()) {
default:
break;
case AArch64::SUBXri:
// Negate the offset for a SUB instruction.
Offset *= -1;
// FALLTHROUGH
case AArch64::ADDXri:
// Make sure it's a vanilla immediate operand, not a relocation or
// anything else we can't handle.
if (!MI->getOperand(2).isImm())
break;
// Watch out for 1 << 12 shifted value.
if (AArch64_AM::getShiftValue(MI->getOperand(3).getImm()))
break;
// If the instruction has the base register as source and dest and the
// immediate will fit in a signed 9-bit integer, then we have a match.
if (getLdStRegOp(MI).getReg() == BaseReg &&
getLdStBaseOp(MI).getReg() == BaseReg &&
getLdStOffsetOp(MI).getImm() <= 255 &&
getLdStOffsetOp(MI).getImm() >= -256) {
// If we have a non-zero Offset, we check that it matches the amount
// we're adding to the register.
if (!Offset || Offset == MI->getOperand(2).getImm())
return true;
}
break;
}
return false;
}
MachineBasicBlock::iterator AArch64LoadStoreOpt::findMatchingUpdateInsnForward(
MachineBasicBlock::iterator I, unsigned Limit, int Value) {
MachineBasicBlock::iterator E = I->getParent()->end();
MachineInstr *MemMI = I;
MachineBasicBlock::iterator MBBI = I;
const MachineFunction &MF = *MemMI->getParent()->getParent();
unsigned DestReg = getLdStRegOp(MemMI).getReg();
unsigned BaseReg = getLdStBaseOp(MemMI).getReg();
int Offset = getLdStOffsetOp(MemMI).getImm() *
TII->getRegClass(MemMI->getDesc(), 0, TRI, MF)->getSize();
// If the base register overlaps the destination register, we can't
// merge the update.
if (DestReg == BaseReg || TRI->isSubRegister(BaseReg, DestReg))
return E;
// Scan forward looking for post-index opportunities.
// Updating instructions can't be formed if the memory insn already
// has an offset other than the value we're looking for.
if (Offset != Value)
return E;
// Track which registers have been modified and used between the first insn
// (inclusive) and the second insn.
BitVector ModifiedRegs, UsedRegs;
ModifiedRegs.resize(TRI->getNumRegs());
UsedRegs.resize(TRI->getNumRegs());
++MBBI;
for (unsigned Count = 0; MBBI != E; ++MBBI) {
MachineInstr *MI = MBBI;
// Skip DBG_VALUE instructions. Otherwise debug info can affect the
// optimization by changing how far we scan.
if (MI->isDebugValue())
continue;
// Now that we know this is a real instruction, count it.
++Count;
// If we found a match, return it.
if (isMatchingUpdateInsn(MI, BaseReg, Value))
return MBBI;
// Update the status of what the instruction clobbered and used.
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
// Otherwise, if the base register is used or modified, we have no match, so
// return early.
if (ModifiedRegs[BaseReg] || UsedRegs[BaseReg])
return E;
}
return E;
}
MachineBasicBlock::iterator AArch64LoadStoreOpt::findMatchingUpdateInsnBackward(
MachineBasicBlock::iterator I, unsigned Limit) {
MachineBasicBlock::iterator B = I->getParent()->begin();
MachineBasicBlock::iterator E = I->getParent()->end();
MachineInstr *MemMI = I;
MachineBasicBlock::iterator MBBI = I;
const MachineFunction &MF = *MemMI->getParent()->getParent();
unsigned DestReg = getLdStRegOp(MemMI).getReg();
unsigned BaseReg = getLdStBaseOp(MemMI).getReg();
int Offset = getLdStOffsetOp(MemMI).getImm();
unsigned RegSize = TII->getRegClass(MemMI->getDesc(), 0, TRI, MF)->getSize();
// If the load/store is the first instruction in the block, there's obviously
// not any matching update. Ditto if the memory offset isn't zero.
if (MBBI == B || Offset != 0)
return E;
// If the base register overlaps the destination register, we can't
// merge the update.
if (DestReg == BaseReg || TRI->isSubRegister(BaseReg, DestReg))
return E;
// Track which registers have been modified and used between the first insn
// (inclusive) and the second insn.
BitVector ModifiedRegs, UsedRegs;
ModifiedRegs.resize(TRI->getNumRegs());
UsedRegs.resize(TRI->getNumRegs());
--MBBI;
for (unsigned Count = 0; MBBI != B; --MBBI) {
MachineInstr *MI = MBBI;
// Skip DBG_VALUE instructions. Otherwise debug info can affect the
// optimization by changing how far we scan.
if (MI->isDebugValue())
continue;
// Now that we know this is a real instruction, count it.
++Count;
// If we found a match, return it.
if (isMatchingUpdateInsn(MI, BaseReg, RegSize))
return MBBI;
// Update the status of what the instruction clobbered and used.
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
// Otherwise, if the base register is used or modified, we have no match, so
// return early.
if (ModifiedRegs[BaseReg] || UsedRegs[BaseReg])
return E;
}
return E;
}
bool AArch64LoadStoreOpt::optimizeBlock(MachineBasicBlock &MBB) {
bool Modified = false;
// Two tranformations to do here:
// 1) Find loads and stores that can be merged into a single load or store
// pair instruction.
// e.g.,
// ldr x0, [x2]
// ldr x1, [x2, #8]
// ; becomes
// ldp x0, x1, [x2]
// 2) Find base register updates that can be merged into the load or store
// as a base-reg writeback.
// e.g.,
// ldr x0, [x2]
// add x2, x2, #4
// ; becomes
// ldr x0, [x2], #4
for (MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end();
MBBI != E;) {
MachineInstr *MI = MBBI;
switch (MI->getOpcode()) {
default:
// Just move on to the next instruction.
++MBBI;
break;
case AArch64::STRSui:
case AArch64::STRDui:
case AArch64::STRQui:
case AArch64::STRXui:
case AArch64::STRWui:
case AArch64::LDRSui:
case AArch64::LDRDui:
case AArch64::LDRQui:
case AArch64::LDRXui:
case AArch64::LDRWui:
case AArch64::LDRSWui:
// do the unscaled versions as well
case AArch64::STURSi:
case AArch64::STURDi:
case AArch64::STURQi:
case AArch64::STURWi:
case AArch64::STURXi:
case AArch64::LDURSi:
case AArch64::LDURDi:
case AArch64::LDURQi:
case AArch64::LDURWi:
case AArch64::LDURXi:
case AArch64::LDURSWi: {
// If this is a volatile load/store, don't mess with it.
if (MI->hasOrderedMemoryRef()) {
++MBBI;
break;
}
// Make sure this is a reg+imm (as opposed to an address reloc).
if (!getLdStOffsetOp(MI).isImm()) {
++MBBI;
break;
}
// Check if this load/store has a hint to avoid pair formation.
// MachineMemOperands hints are set by the AArch64StorePairSuppress pass.
if (TII->isLdStPairSuppressed(MI)) {
++MBBI;
break;
}
// Look ahead up to ScanLimit instructions for a pairable instruction.
LdStPairFlags Flags;
MachineBasicBlock::iterator Paired =
findMatchingInsn(MBBI, Flags, ScanLimit);
if (Paired != E) {
++NumPairCreated;
if (isUnscaledLdSt(MI))
++NumUnscaledPairCreated;
// Merge the loads into a pair. Keeping the iterator straight is a
// pain, so we let the merge routine tell us what the next instruction
// is after it's done mucking about.
MBBI = mergePairedInsns(MBBI, Paired, Flags);
Modified = true;
break;
}
++MBBI;
break;
}
// FIXME: Do the other instructions.
}
}
for (MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end();
MBBI != E;) {
MachineInstr *MI = MBBI;
// Do update merging. It's simpler to keep this separate from the above
// switch, though not strictly necessary.
unsigned Opc = MI->getOpcode();
switch (Opc) {
default:
// Just move on to the next instruction.
++MBBI;
break;
case AArch64::STRSui:
case AArch64::STRDui:
case AArch64::STRQui:
case AArch64::STRXui:
case AArch64::STRWui:
case AArch64::LDRSui:
case AArch64::LDRDui:
case AArch64::LDRQui:
case AArch64::LDRXui:
case AArch64::LDRWui:
// do the unscaled versions as well
case AArch64::STURSi:
case AArch64::STURDi:
case AArch64::STURQi:
case AArch64::STURWi:
case AArch64::STURXi:
case AArch64::LDURSi:
case AArch64::LDURDi:
case AArch64::LDURQi:
case AArch64::LDURWi:
case AArch64::LDURXi: {
// Make sure this is a reg+imm (as opposed to an address reloc).
if (!getLdStOffsetOp(MI).isImm()) {
++MBBI;
break;
}
// Look ahead up to ScanLimit instructions for a mergable instruction.
MachineBasicBlock::iterator Update =
findMatchingUpdateInsnForward(MBBI, ScanLimit, 0);
if (Update != E) {
// Merge the update into the ld/st.
MBBI = mergePostIdxUpdateInsn(MBBI, Update);
Modified = true;
++NumPostFolded;
break;
}
// Don't know how to handle pre/post-index versions, so move to the next
// instruction.
if (isUnscaledLdSt(Opc)) {
++MBBI;
break;
}
// Look back to try to find a pre-index instruction. For example,
// add x0, x0, #8
// ldr x1, [x0]
// merged into:
// ldr x1, [x0, #8]!
Update = findMatchingUpdateInsnBackward(MBBI, ScanLimit);
if (Update != E) {
// Merge the update into the ld/st.
MBBI = mergePreIdxUpdateInsn(MBBI, Update);
Modified = true;
++NumPreFolded;
break;
}
// Look forward to try to find a post-index instruction. For example,
// ldr x1, [x0, #64]
// add x0, x0, #64
// merged into:
// ldr x1, [x0, #64]!
// The immediate in the load/store is scaled by the size of the register
// being loaded. The immediate in the add we're looking for,
// however, is not, so adjust here.
int Value = MI->getOperand(2).getImm() *
TII->getRegClass(MI->getDesc(), 0, TRI, *(MBB.getParent()))
->getSize();
Update = findMatchingUpdateInsnForward(MBBI, ScanLimit, Value);
if (Update != E) {
// Merge the update into the ld/st.
MBBI = mergePreIdxUpdateInsn(MBBI, Update);
Modified = true;
++NumPreFolded;
break;
}
// Nothing found. Just move to the next instruction.
++MBBI;
break;
}
// FIXME: Do the other instructions.
}
}
return Modified;
}
bool AArch64LoadStoreOpt::runOnMachineFunction(MachineFunction &Fn) {
TII = static_cast<const AArch64InstrInfo *>(Fn.getSubtarget().getInstrInfo());
TRI = Fn.getSubtarget().getRegisterInfo();
bool Modified = false;
for (auto &MBB : Fn)
Modified |= optimizeBlock(MBB);
return Modified;
}
// FIXME: Do we need/want a pre-alloc pass like ARM has to try to keep
// loads and stores near one another?
/// createAArch64LoadStoreOptimizationPass - returns an instance of the
/// load / store optimization pass.
FunctionPass *llvm::createAArch64LoadStoreOptimizationPass() {
return new AArch64LoadStoreOpt();
}
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