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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"
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");
STATISTIC(NumZeroStoresPromoted, "Number of narrow zero stores promoted");
STATISTIC(NumLoadsFromStoresPromoted, "Number of loads from stores promoted");
// The LdStLimit limits how far we search for load/store pairs.
static cl::opt<unsigned> LdStLimit("aarch64-load-store-scan-limit",
cl::init(20), cl::Hidden);
// The UpdateLimit limits how far we search for update instructions when we form
// pre-/post-index instructions.
static cl::opt<unsigned> UpdateLimit("aarch64-update-scan-limit", cl::init(100),
cl::Hidden);
#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;
const AArch64Subtarget *Subtarget;
// Track which registers have been modified and used.
BitVector ModifiedRegs, UsedRegs;
// 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,
bool FindNarrowMerge);
// Scan the instructions looking for a store that writes to the address from
// which the current load instruction reads. Return true if one is found.
bool findMatchingStore(MachineBasicBlock::iterator I, unsigned Limit,
MachineBasicBlock::iterator &StoreI);
// Merge the two instructions indicated into a wider narrow store instruction.
MachineBasicBlock::iterator
mergeNarrowZeroStores(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator MergeMI,
const LdStPairFlags &Flags);
// Merge the two instructions indicated into a single pair-wise instruction.
MachineBasicBlock::iterator
mergePairedInsns(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Paired,
const LdStPairFlags &Flags);
// Promote the load that reads directly from the address stored to.
MachineBasicBlock::iterator
promoteLoadFromStore(MachineBasicBlock::iterator LoadI,
MachineBasicBlock::iterator StoreI);
// 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,
int UnscaledOffset, unsigned Limit);
// 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);
// Find an instruction that updates the base register of the ld/st
// instruction.
bool isMatchingUpdateInsn(MachineInstr &MemMI, MachineInstr &MI,
unsigned BaseReg, int Offset);
// Merge a pre- or post-index base register update into a ld/st instruction.
MachineBasicBlock::iterator
mergeUpdateInsn(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Update, bool IsPreIdx);
// Find and merge zero store instructions.
bool tryToMergeZeroStInst(MachineBasicBlock::iterator &MBBI);
// Find and pair ldr/str instructions.
bool tryToPairLdStInst(MachineBasicBlock::iterator &MBBI);
// Find and promote load instructions which read directly from store.
bool tryToPromoteLoadFromStore(MachineBasicBlock::iterator &MBBI);
bool optimizeBlock(MachineBasicBlock &MBB, bool EnableNarrowZeroStOpt);
bool runOnMachineFunction(MachineFunction &Fn) override;
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
MachineFunctionProperties::Property::NoVRegs);
}
StringRef 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 isNarrowStore(unsigned Opc) {
switch (Opc) {
default:
return false;
case AArch64::STRBBui:
case AArch64::STURBBi:
case AArch64::STRHHui:
case AArch64::STURHHi:
return true;
}
}
// Scaling factor for unscaled load or store.
static int getMemScale(MachineInstr &MI) {
switch (MI.getOpcode()) {
default:
llvm_unreachable("Opcode has unknown scale!");
case AArch64::LDRBBui:
case AArch64::LDURBBi:
case AArch64::LDRSBWui:
case AArch64::LDURSBWi:
case AArch64::STRBBui:
case AArch64::STURBBi:
return 1;
case AArch64::LDRHHui:
case AArch64::LDURHHi:
case AArch64::LDRSHWui:
case AArch64::LDURSHWi:
case AArch64::STRHHui:
case AArch64::STURHHi:
return 2;
case AArch64::LDRSui:
case AArch64::LDURSi:
case AArch64::LDRSWui:
case AArch64::LDURSWi:
case AArch64::LDRWui:
case AArch64::LDURWi:
case AArch64::STRSui:
case AArch64::STURSi:
case AArch64::STRWui:
case AArch64::STURWi:
case AArch64::LDPSi:
case AArch64::LDPSWi:
case AArch64::LDPWi:
case AArch64::STPSi:
case AArch64::STPWi:
return 4;
case AArch64::LDRDui:
case AArch64::LDURDi:
case AArch64::LDRXui:
case AArch64::LDURXi:
case AArch64::STRDui:
case AArch64::STURDi:
case AArch64::STRXui:
case AArch64::STURXi:
case AArch64::LDPDi:
case AArch64::LDPXi:
case AArch64::STPDi:
case AArch64::STPXi:
return 8;
case AArch64::LDRQui:
case AArch64::LDURQi:
case AArch64::STRQui:
case AArch64::STURQi:
case AArch64::LDPQi:
case AArch64::STPQi:
return 16;
}
}
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::STRBBui:
case AArch64::STURBBi:
case AArch64::STRHHui:
case AArch64::STURHHi:
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 getMatchingWideOpcode(unsigned Opc) {
switch (Opc) {
default:
llvm_unreachable("Opcode has no wide equivalent!");
case AArch64::STRBBui:
return AArch64::STRHHui;
case AArch64::STRHHui:
return AArch64::STRWui;
case AArch64::STURBBi:
return AArch64::STURHHi;
case AArch64::STURHHi:
return AArch64::STURWi;
case AArch64::STURWi:
return AArch64::STURXi;
case AArch64::STRWui:
return AArch64::STRXui;
}
}
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 isMatchingStore(MachineInstr &LoadInst,
MachineInstr &StoreInst) {
unsigned LdOpc = LoadInst.getOpcode();
unsigned StOpc = StoreInst.getOpcode();
switch (LdOpc) {
default:
llvm_unreachable("Unsupported load instruction!");
case AArch64::LDRBBui:
return StOpc == AArch64::STRBBui || StOpc == AArch64::STRHHui ||
StOpc == AArch64::STRWui || StOpc == AArch64::STRXui;
case AArch64::LDURBBi:
return StOpc == AArch64::STURBBi || StOpc == AArch64::STURHHi ||
StOpc == AArch64::STURWi || StOpc == AArch64::STURXi;
case AArch64::LDRHHui:
return StOpc == AArch64::STRHHui || StOpc == AArch64::STRWui ||
StOpc == AArch64::STRXui;
case AArch64::LDURHHi:
return StOpc == AArch64::STURHHi || StOpc == AArch64::STURWi ||
StOpc == AArch64::STURXi;
case AArch64::LDRWui:
return StOpc == AArch64::STRWui || StOpc == AArch64::STRXui;
case AArch64::LDURWi:
return StOpc == AArch64::STURWi || StOpc == AArch64::STURXi;
case AArch64::LDRXui:
return StOpc == AArch64::STRXui;
case AArch64::LDURXi:
return StOpc == AArch64::STURXi;
}
}
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::STRBBui:
return AArch64::STRBBpre;
case AArch64::STRHHui:
return AArch64::STRHHpre;
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::LDRBBui:
return AArch64::LDRBBpre;
case AArch64::LDRHHui:
return AArch64::LDRHHpre;
case AArch64::LDRWui:
return AArch64::LDRWpre;
case AArch64::LDRXui:
return AArch64::LDRXpre;
case AArch64::LDRSWui:
return AArch64::LDRSWpre;
case AArch64::LDPSi:
return AArch64::LDPSpre;
case AArch64::LDPSWi:
return AArch64::LDPSWpre;
case AArch64::LDPDi:
return AArch64::LDPDpre;
case AArch64::LDPQi:
return AArch64::LDPQpre;
case AArch64::LDPWi:
return AArch64::LDPWpre;
case AArch64::LDPXi:
return AArch64::LDPXpre;
case AArch64::STPSi:
return AArch64::STPSpre;
case AArch64::STPDi:
return AArch64::STPDpre;
case AArch64::STPQi:
return AArch64::STPQpre;
case AArch64::STPWi:
return AArch64::STPWpre;
case AArch64::STPXi:
return AArch64::STPXpre;
}
}
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::STRBBui:
return AArch64::STRBBpost;
case AArch64::STRHHui:
return AArch64::STRHHpost;
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::LDRBBui:
return AArch64::LDRBBpost;
case AArch64::LDRHHui:
return AArch64::LDRHHpost;
case AArch64::LDRWui:
return AArch64::LDRWpost;
case AArch64::LDRXui:
return AArch64::LDRXpost;
case AArch64::LDRSWui:
return AArch64::LDRSWpost;
case AArch64::LDPSi:
return AArch64::LDPSpost;
case AArch64::LDPSWi:
return AArch64::LDPSWpost;
case AArch64::LDPDi:
return AArch64::LDPDpost;
case AArch64::LDPQi:
return AArch64::LDPQpost;
case AArch64::LDPWi:
return AArch64::LDPWpost;
case AArch64::LDPXi:
return AArch64::LDPXpost;
case AArch64::STPSi:
return AArch64::STPSpost;
case AArch64::STPDi:
return AArch64::STPDpost;
case AArch64::STPQi:
return AArch64::STPQpost;
case AArch64::STPWi:
return AArch64::STPWpost;
case AArch64::STPXi:
return AArch64::STPXpost;
}
}
static bool isPairedLdSt(const MachineInstr &MI) {
switch (MI.getOpcode()) {
default:
return false;
case AArch64::LDPSi:
case AArch64::LDPSWi:
case AArch64::LDPDi:
case AArch64::LDPQi:
case AArch64::LDPWi:
case AArch64::LDPXi:
case AArch64::STPSi:
case AArch64::STPDi:
case AArch64::STPQi:
case AArch64::STPWi:
case AArch64::STPXi:
return true;
}
}
static const MachineOperand &getLdStRegOp(const MachineInstr &MI,
unsigned PairedRegOp = 0) {
assert(PairedRegOp < 2 && "Unexpected register operand idx.");
unsigned Idx = isPairedLdSt(MI) ? PairedRegOp : 0;
return MI.getOperand(Idx);
}
static const MachineOperand &getLdStBaseOp(const MachineInstr &MI) {
unsigned Idx = isPairedLdSt(MI) ? 2 : 1;
return MI.getOperand(Idx);
}
static const MachineOperand &getLdStOffsetOp(const MachineInstr &MI) {
unsigned Idx = isPairedLdSt(MI) ? 3 : 2;
return MI.getOperand(Idx);
}
static bool isLdOffsetInRangeOfSt(MachineInstr &LoadInst,
MachineInstr &StoreInst,
const AArch64InstrInfo *TII) {
assert(isMatchingStore(LoadInst, StoreInst) && "Expect only matched ld/st.");
int LoadSize = getMemScale(LoadInst);
int StoreSize = getMemScale(StoreInst);
int UnscaledStOffset = TII->isUnscaledLdSt(StoreInst)
? getLdStOffsetOp(StoreInst).getImm()
: getLdStOffsetOp(StoreInst).getImm() * StoreSize;
int UnscaledLdOffset = TII->isUnscaledLdSt(LoadInst)
? getLdStOffsetOp(LoadInst).getImm()
: getLdStOffsetOp(LoadInst).getImm() * LoadSize;
return (UnscaledStOffset <= UnscaledLdOffset) &&
(UnscaledLdOffset + LoadSize <= (UnscaledStOffset + StoreSize));
}
static bool isPromotableZeroStoreInst(MachineInstr &MI) {
unsigned Opc = MI.getOpcode();
return (Opc == AArch64::STRWui || Opc == AArch64::STURWi ||
isNarrowStore(Opc)) &&
getLdStRegOp(MI).getReg() == AArch64::WZR;
}
MachineBasicBlock::iterator
AArch64LoadStoreOpt::mergeNarrowZeroStores(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator MergeMI,
const LdStPairFlags &Flags) {
assert(isPromotableZeroStoreInst(*I) && isPromotableZeroStoreInst(*MergeMI) &&
"Expected promotable zero stores.");
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 == MergeMI)
++NextI;
unsigned Opc = I->getOpcode();
bool IsScaled = !TII->isUnscaledLdSt(Opc);
int OffsetStride = IsScaled ? 1 : getMemScale(*I);
bool MergeForward = Flags.getMergeForward();
// Insert our new paired instruction after whichever of the paired
// instructions MergeForward indicates.
MachineBasicBlock::iterator InsertionPoint = MergeForward ? MergeMI : 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(*MergeMI) : getLdStBaseOp(*I);
// Which register is Rt and which is Rt2 depends on the offset order.
MachineInstr *RtMI;
if (getLdStOffsetOp(*I).getImm() ==
getLdStOffsetOp(*MergeMI).getImm() + OffsetStride)
RtMI = &*MergeMI;
else
RtMI = &*I;
int OffsetImm = getLdStOffsetOp(*RtMI).getImm();
// Change the scaled offset from small to large type.
if (IsScaled) {
assert(((OffsetImm & 1) == 0) && "Unexpected offset to merge");
OffsetImm /= 2;
}
// Construct the new instruction.
DebugLoc DL = I->getDebugLoc();
MachineBasicBlock *MBB = I->getParent();
MachineInstrBuilder MIB;
MIB = BuildMI(*MBB, InsertionPoint, DL, TII->get(getMatchingWideOpcode(Opc)))
.addReg(isNarrowStore(Opc) ? AArch64::WZR : AArch64::XZR)
.add(BaseRegOp)
.addImm(OffsetImm)
.setMemRefs(I->mergeMemRefsWith(*MergeMI));
(void)MIB;
DEBUG(dbgs() << "Creating wider store. Replacing instructions:\n ");
DEBUG(I->print(dbgs()));
DEBUG(dbgs() << " ");
DEBUG(MergeMI->print(dbgs()));
DEBUG(dbgs() << " with instruction:\n ");
DEBUG(((MachineInstr *)MIB)->print(dbgs()));
DEBUG(dbgs() << "\n");
// Erase the old instructions.
I->eraseFromParent();
MergeMI->eraseFromParent();
return NextI;
}
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 = TII->isUnscaledLdSt(Opc);
int OffsetStride = IsUnscaled ? getMemScale(*I) : 1;
bool MergeForward = Flags.getMergeForward();
// 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 = TII->isUnscaledLdSt(Paired->getOpcode());
if (IsUnscaled != PairedIsUnscaled) {
// 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).
int MemSize = getMemScale(*Paired);
if (PairedIsUnscaled) {
// If the unscaled offset isn't a multiple of the MemSize, we can't
// pair the operations together.
assert(!(PairedOffset % getMemScale(*Paired)) &&
"Offset should be a multiple of the stride!");
PairedOffset /= MemSize;
} else {
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;
}
int OffsetImm = getLdStOffsetOp(*RtMI).getImm();
// Scale the immediate offset, if necessary.
if (TII->isUnscaledLdSt(RtMI->getOpcode())) {
assert(!(OffsetImm % getMemScale(*RtMI)) &&
"Unscaled offset cannot be scaled.");
OffsetImm /= getMemScale(*RtMI);
}
// Construct the new instruction.
MachineInstrBuilder MIB;
DebugLoc DL = I->getDebugLoc();
MachineBasicBlock *MBB = I->getParent();
MachineOperand RegOp0 = getLdStRegOp(*RtMI);
MachineOperand RegOp1 = getLdStRegOp(*Rt2MI);
// Kill flags may become invalid when moving stores for pairing.
if (RegOp0.isUse()) {
if (!MergeForward) {
// Clear kill flags on store if moving upwards. Example:
// STRWui %w0, ...
// USE %w1
// STRWui kill %w1 ; need to clear kill flag when moving STRWui upwards
RegOp0.setIsKill(false);
RegOp1.setIsKill(false);
} else {
// Clear kill flags of the first stores register. Example:
// STRWui %w1, ...
// USE kill %w1 ; need to clear kill flag when moving STRWui downwards
// STRW %w0
unsigned Reg = getLdStRegOp(*I).getReg();
for (MachineInstr &MI : make_range(std::next(I), Paired))
MI.clearRegisterKills(Reg, TRI);
}
}
MIB = BuildMI(*MBB, InsertionPoint, DL, TII->get(getMatchingPairOpcode(Opc)))
.add(RegOp0)
.add(RegOp1)
.add(BaseRegOp)
.addImm(OffsetImm)
.setMemRefs(I->mergeMemRefsWith(*Paired));
(void)MIB;
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(*MBB, InsertionPoint, DL, TII->get(TargetOpcode::KILL), DstRegW)
.addReg(DstRegW)
.addReg(DstRegX, RegState::Define);
MIBKill->getOperand(2).setImplicit();
// Create the sign extension.
MachineInstrBuilder MIBSXTW =
BuildMI(*MBB, InsertionPoint, DL, TII->get(AArch64::SBFMXri), DstRegX)
.addReg(DstRegX)
.addImm(0)
.addImm(31);
(void)MIBSXTW;
DEBUG(dbgs() << " Extend operand:\n ");
DEBUG(((MachineInstr *)MIBSXTW)->print(dbgs()));
} else {
DEBUG(((MachineInstr *)MIB)->print(dbgs()));
}
DEBUG(dbgs() << "\n");
// Erase the old instructions.
I->eraseFromParent();
Paired->eraseFromParent();
return NextI;
}
MachineBasicBlock::iterator
AArch64LoadStoreOpt::promoteLoadFromStore(MachineBasicBlock::iterator LoadI,
MachineBasicBlock::iterator StoreI) {
MachineBasicBlock::iterator NextI = LoadI;
++NextI;
int LoadSize = getMemScale(*LoadI);
int StoreSize = getMemScale(*StoreI);
unsigned LdRt = getLdStRegOp(*LoadI).getReg();
unsigned StRt = getLdStRegOp(*StoreI).getReg();
bool IsStoreXReg = TRI->getRegClass(AArch64::GPR64RegClassID)->contains(StRt);
assert((IsStoreXReg ||
TRI->getRegClass(AArch64::GPR32RegClassID)->contains(StRt)) &&
"Unexpected RegClass");
MachineInstr *BitExtMI;
if (LoadSize == StoreSize && (LoadSize == 4 || LoadSize == 8)) {
// Remove the load, if the destination register of the loads is the same
// register for stored value.
if (StRt == LdRt && LoadSize == 8) {
StoreI->clearRegisterKills(StRt, TRI);
DEBUG(dbgs() << "Remove load instruction:\n ");
DEBUG(LoadI->print(dbgs()));
DEBUG(dbgs() << "\n");
LoadI->eraseFromParent();
return NextI;
}
// Replace the load with a mov if the load and store are in the same size.
BitExtMI =
BuildMI(*LoadI->getParent(), LoadI, LoadI->getDebugLoc(),
TII->get(IsStoreXReg ? AArch64::ORRXrs : AArch64::ORRWrs), LdRt)
.addReg(IsStoreXReg ? AArch64::XZR : AArch64::WZR)
.addReg(StRt)
.addImm(AArch64_AM::getShifterImm(AArch64_AM::LSL, 0));
} else {
// FIXME: Currently we disable this transformation in big-endian targets as
// performance and correctness are verified only in little-endian.
if (!Subtarget->isLittleEndian())
return NextI;
bool IsUnscaled = TII->isUnscaledLdSt(*LoadI);
assert(IsUnscaled == TII->isUnscaledLdSt(*StoreI) &&
"Unsupported ld/st match");
assert(LoadSize <= StoreSize && "Invalid load size");
int UnscaledLdOffset = IsUnscaled
? getLdStOffsetOp(*LoadI).getImm()
: getLdStOffsetOp(*LoadI).getImm() * LoadSize;
int UnscaledStOffset = IsUnscaled
? getLdStOffsetOp(*StoreI).getImm()
: getLdStOffsetOp(*StoreI).getImm() * StoreSize;
int Width = LoadSize * 8;
int Immr = 8 * (UnscaledLdOffset - UnscaledStOffset);
int Imms = Immr + Width - 1;
unsigned DestReg = IsStoreXReg
? TRI->getMatchingSuperReg(LdRt, AArch64::sub_32,
&AArch64::GPR64RegClass)
: LdRt;
assert((UnscaledLdOffset >= UnscaledStOffset &&
(UnscaledLdOffset + LoadSize) <= UnscaledStOffset + StoreSize) &&
"Invalid offset");
Immr = 8 * (UnscaledLdOffset - UnscaledStOffset);
Imms = Immr + Width - 1;
if (UnscaledLdOffset == UnscaledStOffset) {
uint32_t AndMaskEncoded = ((IsStoreXReg ? 1 : 0) << 12) // N
| ((Immr) << 6) // immr
| ((Imms) << 0) // imms
;
BitExtMI =
BuildMI(*LoadI->getParent(), LoadI, LoadI->getDebugLoc(),
TII->get(IsStoreXReg ? AArch64::ANDXri : AArch64::ANDWri),
DestReg)
.addReg(StRt)
.addImm(AndMaskEncoded);
} else {
BitExtMI =
BuildMI(*LoadI->getParent(), LoadI, LoadI->getDebugLoc(),
TII->get(IsStoreXReg ? AArch64::UBFMXri : AArch64::UBFMWri),
DestReg)
.addReg(StRt)
.addImm(Immr)
.addImm(Imms);
}
}
StoreI->clearRegisterKills(StRt, TRI);
(void)BitExtMI;
DEBUG(dbgs() << "Promoting load by replacing :\n ");
DEBUG(StoreI->print(dbgs()));
DEBUG(dbgs() << " ");
DEBUG(LoadI->print(dbgs()));
DEBUG(dbgs() << " with instructions:\n ");
DEBUG(StoreI->print(dbgs()));
DEBUG(dbgs() << " ");
DEBUG((BitExtMI)->print(dbgs()));
DEBUG(dbgs() << "\n");
// Erase the old instructions.
LoadI->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 (!Reg)
continue;
if (MO.isDef()) {
// WZR/XZR are not modified even when used as a destination register.
if (Reg != AArch64::WZR && Reg != AArch64::XZR)
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 alignTo 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 (MachineInstr *MIb : MemInsns)
if (mayAlias(MIa, *MIb, TII))
return true;
return false;
}
bool AArch64LoadStoreOpt::findMatchingStore(
MachineBasicBlock::iterator I, unsigned Limit,
MachineBasicBlock::iterator &StoreI) {
MachineBasicBlock::iterator B = I->getParent()->begin();
MachineBasicBlock::iterator MBBI = I;
MachineInstr &LoadMI = *I;
unsigned BaseReg = getLdStBaseOp(LoadMI).getReg();
// If the load is the first instruction in the block, there's obviously
// not any matching store.
if (MBBI == B)
return false;
// Track which registers have been modified and used between the first insn
// and the second insn.
ModifiedRegs.reset();
UsedRegs.reset();
unsigned Count = 0;
do {
--MBBI;
MachineInstr &MI = *MBBI;
// Don't count transient instructions towards the search limit since there
// may be different numbers of them if e.g. debug information is present.
if (!MI.isTransient())
++Count;
// If the load instruction reads directly from the address to which the
// store instruction writes and the stored value is not modified, we can
// promote the load. Since we do not handle stores with pre-/post-index,
// it's unnecessary to check if BaseReg is modified by the store itself.
if (MI.mayStore() && isMatchingStore(LoadMI, MI) &&
BaseReg == getLdStBaseOp(MI).getReg() &&
isLdOffsetInRangeOfSt(LoadMI, MI, TII) &&
!ModifiedRegs[getLdStRegOp(MI).getReg()]) {
StoreI = MBBI;
return true;
}
if (MI.isCall())
return false;
// 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 false;
// If we encounter a store aliased with the load, return early.
if (MI.mayStore() && mayAlias(LoadMI, MI, TII))
return false;
} while (MBBI != B && Count < Limit);
return false;
}
// Returns true if FirstMI and MI are candidates for merging or pairing.
// Otherwise, returns false.
static bool areCandidatesToMergeOrPair(MachineInstr &FirstMI, MachineInstr &MI,
LdStPairFlags &Flags,
const AArch64InstrInfo *TII) {
// If this is volatile or if pairing is suppressed, not a candidate.
if (MI.hasOrderedMemoryRef() || TII->isLdStPairSuppressed(MI))
return false;
// We should have already checked FirstMI for pair suppression and volatility.
assert(!FirstMI.hasOrderedMemoryRef() &&
!TII->isLdStPairSuppressed(FirstMI) &&
"FirstMI shouldn't get here if either of these checks are true.");
unsigned OpcA = FirstMI.getOpcode();
unsigned OpcB = MI.getOpcode();
// Opcodes match: nothing more to check.
if (OpcA == OpcB)
return true;
// Try to match a sign-extended load/store with a zero-extended load/store.
bool IsValidLdStrOpc, PairIsValidLdStrOpc;
unsigned NonSExtOpc = getMatchingNonSExtOpcode(OpcA, &IsValidLdStrOpc);
assert(IsValidLdStrOpc &&
"Given Opc should be a Load or Store with an immediate");
// OpcA will be the first instruction in the pair.
if (NonSExtOpc == getMatchingNonSExtOpcode(OpcB, &PairIsValidLdStrOpc)) {
Flags.setSExtIdx(NonSExtOpc == (unsigned)OpcA ? 1 : 0);
return true;
}
// If the second instruction isn't even a mergable/pairable load/store, bail
// out.
if (!PairIsValidLdStrOpc)
return false;
// FIXME: We don't support merging narrow stores with mixed scaled/unscaled
// offsets.
if (isNarrowStore(OpcA) || isNarrowStore(OpcB))
return false;
// Try to match an unscaled load/store with a scaled load/store.
return TII->isUnscaledLdSt(OpcA) != TII->isUnscaledLdSt(OpcB) &&
getMatchingPairOpcode(OpcA) == getMatchingPairOpcode(OpcB);
// FIXME: Can we also match a mixed sext/zext unscaled/scaled pair?
}
/// Scan the instructions looking for a load/store that can be combined with the
/// current instruction into a wider equivalent or a load/store pair.
MachineBasicBlock::iterator
AArch64LoadStoreOpt::findMatchingInsn(MachineBasicBlock::iterator I,
LdStPairFlags &Flags, unsigned Limit,
bool FindNarrowMerge) {
MachineBasicBlock::iterator E = I->getParent()->end();
MachineBasicBlock::iterator MBBI = I;
MachineInstr &FirstMI = *I;
++MBBI;
bool MayLoad = FirstMI.mayLoad();
bool IsUnscaled = TII->isUnscaledLdSt(FirstMI);
unsigned Reg = getLdStRegOp(FirstMI).getReg();
unsigned BaseReg = getLdStBaseOp(FirstMI).getReg();
int Offset = getLdStOffsetOp(FirstMI).getImm();
int OffsetStride = IsUnscaled ? getMemScale(FirstMI) : 1;
bool IsPromotableZeroStore = isPromotableZeroStoreInst(FirstMI);
// Track which registers have been modified and used between the first insn
// (inclusive) and the second insn.
ModifiedRegs.reset();
UsedRegs.reset();
// 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;
// Don't count transient instructions towards the search limit since there
// may be different numbers of them if e.g. debug information is present.
if (!MI.isTransient())
++Count;
Flags.setSExtIdx(-1);
if (areCandidatesToMergeOrPair(FirstMI, MI, Flags, TII) &&
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.
unsigned MIBaseReg = getLdStBaseOp(MI).getReg();
int MIOffset = getLdStOffsetOp(MI).getImm();
bool MIIsUnscaled = TII->isUnscaledLdSt(MI);
if (IsUnscaled != MIIsUnscaled) {
// 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).
int MemSize = getMemScale(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) {
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
MemInsns.push_back(&MI);
continue;
}
MIOffset /= MemSize;
} else {
MIOffset *= MemSize;
}
}
if (BaseReg == MIBaseReg && ((Offset == MIOffset + OffsetStride) ||
(Offset + OffsetStride == MIOffset))) {
int MinOffset = Offset < MIOffset ? Offset : MIOffset;
if (FindNarrowMerge) {
// If the alignment requirements of the scaled wide load/store
// instruction can't express the offset of the scaled narrow input,
// bail and keep looking. For promotable zero stores, allow only when
// the stored value is the same (i.e., WZR).
if ((!IsUnscaled && alignTo(MinOffset, 2) != MinOffset) ||
(IsPromotableZeroStore && Reg != getLdStRegOp(MI).getReg())) {
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
MemInsns.push_back(&MI);
continue;
}
} else {
// Pairwise instructions have a 7-bit signed offset field. Single
// insns have a 12-bit unsigned offset field. 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 && (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::mergeUpdateInsn(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Update,
bool IsPreIdx) {
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-/post-indexed load / store");
if (Update->getOpcode() == AArch64::SUBXri)
Value = -Value;
unsigned NewOpc = IsPreIdx ? getPreIndexedOpcode(I->getOpcode())
: getPostIndexedOpcode(I->getOpcode());
MachineInstrBuilder MIB;
if (!isPairedLdSt(*I)) {
// Non-paired instruction.
MIB = BuildMI(*I->getParent(), I, I->getDebugLoc(), TII->get(NewOpc))
.add(getLdStRegOp(*Update))
.add(getLdStRegOp(*I))
.add(getLdStBaseOp(*I))
.addImm(Value)
.setMemRefs(I->memoperands_begin(), I->memoperands_end());
} else {
// Paired instruction.
int Scale = getMemScale(*I);
MIB = BuildMI(*I->getParent(), I, I->getDebugLoc(), TII->get(NewOpc))
.add(getLdStRegOp(*Update))
.add(getLdStRegOp(*I, 0))
.add(getLdStRegOp(*I, 1))
.add(getLdStBaseOp(*I))
.addImm(Value / Scale)
.setMemRefs(I->memoperands_begin(), I->memoperands_end());
}
(void)MIB;
if (IsPreIdx)
DEBUG(dbgs() << "Creating pre-indexed load/store.");
else
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;
}
bool AArch64LoadStoreOpt::isMatchingUpdateInsn(MachineInstr &MemMI,
MachineInstr &MI,
unsigned BaseReg, int Offset) {
switch (MI.getOpcode()) {
default:
break;
case AArch64::SUBXri:
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;
// The update instruction source and destination register must be the
// same as the load/store base register.
if (MI.getOperand(0).getReg() != BaseReg ||
MI.getOperand(1).getReg() != BaseReg)
break;
bool IsPairedInsn = isPairedLdSt(MemMI);
int UpdateOffset = MI.getOperand(2).getImm();
if (MI.getOpcode() == AArch64::SUBXri)
UpdateOffset = -UpdateOffset;
// For non-paired load/store instructions, the immediate must fit in a
// signed 9-bit integer.
if (!IsPairedInsn && (UpdateOffset > 255 || UpdateOffset < -256))
break;
// For paired load/store instructions, the immediate must be a multiple of
// the scaling factor. The scaled offset must also fit into a signed 7-bit
// integer.
if (IsPairedInsn) {
int Scale = getMemScale(MemMI);
if (UpdateOffset % Scale != 0)
break;
int ScaledOffset = UpdateOffset / Scale;
if (ScaledOffset > 63 || ScaledOffset < -64)
break;
}
// If we have a non-zero Offset, we check that it matches the amount
// we're adding to the register.
if (!Offset || Offset == UpdateOffset)
return true;
break;
}
return false;
}
MachineBasicBlock::iterator AArch64LoadStoreOpt::findMatchingUpdateInsnForward(
MachineBasicBlock::iterator I, int UnscaledOffset, unsigned Limit) {
MachineBasicBlock::iterator E = I->getParent()->end();
MachineInstr &MemMI = *I;
MachineBasicBlock::iterator MBBI = I;
unsigned BaseReg = getLdStBaseOp(MemMI).getReg();
int MIUnscaledOffset = getLdStOffsetOp(MemMI).getImm() * getMemScale(MemMI);
// Scan forward looking for post-index opportunities. Updating instructions
// can't be formed if the memory instruction doesn't have the offset we're
// looking for.
if (MIUnscaledOffset != UnscaledOffset)
return E;
// If the base register overlaps a destination register, we can't
// merge the update.
bool IsPairedInsn = isPairedLdSt(MemMI);
for (unsigned i = 0, e = IsPairedInsn ? 2 : 1; i != e; ++i) {
unsigned DestReg = getLdStRegOp(MemMI, i).getReg();
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.
ModifiedRegs.reset();
UsedRegs.reset();
++MBBI;
for (unsigned Count = 0; MBBI != E && Count < Limit; ++MBBI) {
MachineInstr &MI = *MBBI;
// Don't count transient instructions towards the search limit since there
// may be different numbers of them if e.g. debug information is present.
if (!MI.isTransient())
++Count;
// If we found a match, return it.
if (isMatchingUpdateInsn(*I, MI, BaseReg, UnscaledOffset))
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;
unsigned BaseReg = getLdStBaseOp(MemMI).getReg();
int Offset = getLdStOffsetOp(MemMI).getImm();
// 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 a destination register, we can't
// merge the update.
bool IsPairedInsn = isPairedLdSt(MemMI);
for (unsigned i = 0, e = IsPairedInsn ? 2 : 1; i != e; ++i) {
unsigned DestReg = getLdStRegOp(MemMI, i).getReg();
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.
ModifiedRegs.reset();
UsedRegs.reset();
unsigned Count = 0;
do {
--MBBI;
MachineInstr &MI = *MBBI;
// Don't count transient instructions towards the search limit since there
// may be different numbers of them if e.g. debug information is present.
if (!MI.isTransient())
++Count;
// If we found a match, return it.
if (isMatchingUpdateInsn(*I, MI, BaseReg, Offset))
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;
} while (MBBI != B && Count < Limit);
return E;
}
bool AArch64LoadStoreOpt::tryToPromoteLoadFromStore(
MachineBasicBlock::iterator &MBBI) {
MachineInstr &MI = *MBBI;
// If this is a volatile load, don't mess with it.
if (MI.hasOrderedMemoryRef())
return false;
// Make sure this is a reg+imm.
// FIXME: It is possible to extend it to handle reg+reg cases.
if (!getLdStOffsetOp(MI).isImm())
return false;
// Look backward up to LdStLimit instructions.
MachineBasicBlock::iterator StoreI;
if (findMatchingStore(MBBI, LdStLimit, StoreI)) {
++NumLoadsFromStoresPromoted;
// Promote the load. 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 = promoteLoadFromStore(MBBI, StoreI);
return true;
}
return false;
}
// Merge adjacent zero stores into a wider store.
bool AArch64LoadStoreOpt::tryToMergeZeroStInst(
MachineBasicBlock::iterator &MBBI) {
assert(isPromotableZeroStoreInst(*MBBI) && "Expected narrow store.");
MachineInstr &MI = *MBBI;
MachineBasicBlock::iterator E = MI.getParent()->end();
if (!TII->isCandidateToMergeOrPair(MI))
return false;
// Look ahead up to LdStLimit instructions for a mergable instruction.
LdStPairFlags Flags;
MachineBasicBlock::iterator MergeMI =
findMatchingInsn(MBBI, Flags, LdStLimit, /* FindNarrowMerge = */ true);
if (MergeMI != E) {
++NumZeroStoresPromoted;
// 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 = mergeNarrowZeroStores(MBBI, MergeMI, Flags);
return true;
}
return false;
}
// Find loads and stores that can be merged into a single load or store pair
// instruction.
bool AArch64LoadStoreOpt::tryToPairLdStInst(MachineBasicBlock::iterator &MBBI) {
MachineInstr &MI = *MBBI;
MachineBasicBlock::iterator E = MI.getParent()->end();
if (!TII->isCandidateToMergeOrPair(MI))
return false;
// Early exit if the offset is 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)
bool IsUnscaled = TII->isUnscaledLdSt(MI);
int Offset = getLdStOffsetOp(MI).getImm();
int OffsetStride = IsUnscaled ? getMemScale(MI) : 1;
// Allow one more for offset.
if (Offset > 0)
Offset -= OffsetStride;
if (!inBoundsForPair(IsUnscaled, Offset, OffsetStride))
return false;
// Look ahead up to LdStLimit instructions for a pairable instruction.
LdStPairFlags Flags;
MachineBasicBlock::iterator Paired =
findMatchingInsn(MBBI, Flags, LdStLimit, /* FindNarrowMerge = */ false);
if (Paired != E) {
++NumPairCreated;
if (TII->isUnscaledLdSt(MI))
++NumUnscaledPairCreated;
// 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);
return true;
}
return false;
}
bool AArch64LoadStoreOpt::optimizeBlock(MachineBasicBlock &MBB,
bool EnableNarrowZeroStOpt) {
bool Modified = false;
// Four tranformations to do here:
// 1) Find loads that directly read from stores and promote them by
// replacing with mov instructions. If the store is wider than the load,
// the load will be replaced with a bitfield extract.
// e.g.,
// str w1, [x0, #4]
// ldrh w2, [x0, #6]
// ; becomes
// str w1, [x0, #4]
// lsr w2, w1, #16
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;
// Scaled instructions.
case AArch64::LDRBBui:
case AArch64::LDRHHui:
case AArch64::LDRWui:
case AArch64::LDRXui:
// Unscaled instructions.
case AArch64::LDURBBi:
case AArch64::LDURHHi:
case AArch64::LDURWi:
case AArch64::LDURXi: {
if (tryToPromoteLoadFromStore(MBBI)) {
Modified = true;
break;
}
++MBBI;
break;
}
}
}
// 2) Merge adjacent zero stores into a wider store.
// e.g.,
// strh wzr, [x0]
// strh wzr, [x0, #2]
// ; becomes
// str wzr, [x0]
// e.g.,
// str wzr, [x0]
// str wzr, [x0, #4]
// ; becomes
// str xzr, [x0]
for (MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end();
EnableNarrowZeroStOpt && MBBI != E;) {
if (isPromotableZeroStoreInst(*MBBI)) {
if (tryToMergeZeroStInst(MBBI)) {
Modified = true;
} else
++MBBI;
} else
++MBBI;
}
// 3) 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]
for (MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end();
MBBI != E;) {
if (TII->isPairableLdStInst(*MBBI) && tryToPairLdStInst(MBBI))
Modified = true;
else
++MBBI;
}
// 4) 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;
// Do update merging. It's simpler to keep this separate from the above
// switchs, though not strictly necessary.
unsigned Opc = MI.getOpcode();
switch (Opc) {
default:
// Just move on to the next instruction.
++MBBI;
break;
// Scaled instructions.
case AArch64::STRSui:
case AArch64::STRDui:
case AArch64::STRQui:
case AArch64::STRXui:
case AArch64::STRWui:
case AArch64::STRHHui:
case AArch64::STRBBui:
case AArch64::LDRSui:
case AArch64::LDRDui:
case AArch64::LDRQui:
case AArch64::LDRXui:
case AArch64::LDRWui:
case AArch64::LDRHHui:
case AArch64::LDRBBui:
// Unscaled instructions.
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:
// Paired instructions.
case AArch64::LDPSi:
case AArch64::LDPSWi:
case AArch64::LDPDi:
case AArch64::LDPQi:
case AArch64::LDPWi:
case AArch64::LDPXi:
case AArch64::STPSi:
case AArch64::STPDi:
case AArch64::STPQi:
case AArch64::STPWi:
case AArch64::STPXi: {
// Make sure this is a reg+imm (as opposed to an address reloc).
if (!getLdStOffsetOp(MI).isImm()) {
++MBBI;
break;
}
// Look forward to try to form a post-index instruction. For example,
// ldr x0, [x20]
// add x20, x20, #32
// merged into:
// ldr x0, [x20], #32
MachineBasicBlock::iterator Update =
findMatchingUpdateInsnForward(MBBI, 0, UpdateLimit);
if (Update != E) {
// Merge the update into the ld/st.
MBBI = mergeUpdateInsn(MBBI, Update, /*IsPreIdx=*/false);
Modified = true;
++NumPostFolded;
break;
}
// Don't know how to handle pre/post-index versions, so move to the next
// instruction.
if (TII->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, UpdateLimit);
if (Update != E) {
// Merge the update into the ld/st.
MBBI = mergeUpdateInsn(MBBI, Update, /*IsPreIdx=*/true);
Modified = true;
++NumPreFolded;
break;
}
// The immediate in the load/store is scaled by the size of the memory
// operation. The immediate in the add we're looking for,
// however, is not, so adjust here.
int UnscaledOffset = getLdStOffsetOp(MI).getImm() * getMemScale(MI);
// 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]!
Update = findMatchingUpdateInsnForward(MBBI, UnscaledOffset, UpdateLimit);
if (Update != E) {
// Merge the update into the ld/st.
MBBI = mergeUpdateInsn(MBBI, Update, /*IsPreIdx=*/true);
Modified = true;
++NumPreFolded;
break;
}
// Nothing found. Just move to the next instruction.
++MBBI;
break;
}
}
}
return Modified;
}
bool AArch64LoadStoreOpt::runOnMachineFunction(MachineFunction &Fn) {
if (skipFunction(*Fn.getFunction()))
return false;
Subtarget = &static_cast<const AArch64Subtarget &>(Fn.getSubtarget());
TII = static_cast<const AArch64InstrInfo *>(Subtarget->getInstrInfo());
TRI = Subtarget->getRegisterInfo();
// Resize the modified and used register bitfield trackers. We do this once
// per function and then clear the bitfield each time we optimize a load or
// store.
ModifiedRegs.resize(TRI->getNumRegs());
UsedRegs.resize(TRI->getNumRegs());
bool Modified = false;
bool enableNarrowZeroStOpt = !Subtarget->requiresStrictAlign();
for (auto &MBB : Fn)
Modified |= optimizeBlock(MBB, enableNarrowZeroStOpt);
return Modified;
}
// FIXME: Do we need/want a pre-alloc pass like ARM has to try to keep loads and
// stores near one another? Note: The pre-RA instruction scheduler already has
// hooks to try and schedule pairable loads/stores together to improve pairing
// opportunities. Thus, pre-RA pairing pass may not be worth the effort.
// FIXME: When pairing store instructions it's very possible for this pass to
// hoist a store with a KILL marker above another use (without a KILL marker).
// The resulting IR is invalid, but nothing uses the KILL markers after this
// pass, so it's never caused a problem in practice.
/// createAArch64LoadStoreOptimizationPass - returns an instance of the
/// load / store optimization pass.
FunctionPass *llvm::createAArch64LoadStoreOptimizationPass() {
return new AArch64LoadStoreOpt();
}
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