Skip to content
This repository has been archived by the owner on Aug 31, 2019. It is now read-only.

Commit

Permalink
[AArch64]Merge halfword loads into a 32-bit load
Browse files Browse the repository at this point in the history 
This recommits r250719, which caused a failure in SPEC2000.gcc
because of the incorrect insert point for the new wider load.

Convert two halfword loads into a single 32-bit word load with bitfield extract
instructions. For example :
  ldrh w0, [x2]
  ldrh w1, [x2, llvm-mirror#2]
becomes
  ldr w0, [x2]
  ubfx w1, w0, llvm-mirror#16, llvm-mirror#16
  and  w0, w0, #ffff

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251438 91177308-0d34-0410-b5e6-96231b3b80d8
  • Loading branch information
Jun Bum Lim committed Oct 27, 2015
1 parent c287d4c commit b0bca8e
Show file tree
Hide file tree
Showing 2 changed files with 265 additions and 45 deletions.
261 changes: 216 additions & 45 deletions lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,7 @@ 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(NumSmallTypeMerged, "Number of small type loads merged");

static cl::opt<unsigned> ScanLimit("aarch64-load-store-scan-limit",
cl::init(20), cl::Hidden);
Expand Down Expand Up @@ -77,12 +78,13 @@ typedef struct LdStPairFlags {

struct AArch64LoadStoreOpt : public MachineFunctionPass {
static char ID;
AArch64LoadStoreOpt() : MachineFunctionPass(ID) {
AArch64LoadStoreOpt() : MachineFunctionPass(ID), IsStrictAlign(false) {
initializeAArch64LoadStoreOptPass(*PassRegistry::getPassRegistry());
}

const AArch64InstrInfo *TII;
const TargetRegisterInfo *TRI;
bool IsStrictAlign;

// Scan the instructions looking for a load/store that can be combined
// with the current instruction into a load/store pair.
Expand Down Expand Up @@ -122,6 +124,9 @@ struct AArch64LoadStoreOpt : public MachineFunctionPass {
mergeUpdateInsn(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Update, bool IsPreIdx);

// Find and merge foldable ldr/str instructions.
bool tryToMergeLdStInst(MachineBasicBlock::iterator &MBBI);

bool optimizeBlock(MachineBasicBlock &MBB);

bool runOnMachineFunction(MachineFunction &Fn) override;
Expand Down Expand Up @@ -151,6 +156,7 @@ static bool isUnscaledLdSt(unsigned Opc) {
case AArch64::LDURWi:
case AArch64::LDURXi:
case AArch64::LDURSWi:
case AArch64::LDURHHi:
return true;
}
}
Expand All @@ -159,6 +165,20 @@ static bool isUnscaledLdSt(MachineInstr *MI) {
return isUnscaledLdSt(MI->getOpcode());
}

static bool isSmallTypeLdMerge(unsigned Opc) {
switch (Opc) {
default:
return false;
case AArch64::LDRHHui:
case AArch64::LDURHHi:
return true;
// FIXME: Add other instructions (e.g, LDRBBui, LDURSHWi, LDRSHWui, etc.).
}
}
static bool isSmallTypeLdMerge(MachineInstr *MI) {
return isSmallTypeLdMerge(MI->getOpcode());
}

// Scaling factor for unscaled load or store.
static int getMemScale(MachineInstr *MI) {
switch (MI->getOpcode()) {
Expand All @@ -168,6 +188,7 @@ static int getMemScale(MachineInstr *MI) {
case AArch64::STRBBui:
return 1;
case AArch64::LDRHHui:
case AArch64::LDURHHi:
case AArch64::STRHHui:
return 2;
case AArch64::LDRSui:
Expand Down Expand Up @@ -238,6 +259,8 @@ static unsigned getMatchingNonSExtOpcode(unsigned Opc,
case AArch64::STURSi:
case AArch64::LDRSui:
case AArch64::LDURSi:
case AArch64::LDRHHui:
case AArch64::LDURHHi:
return Opc;
case AArch64::LDRSWui:
return AArch64::LDRWui;
Expand Down Expand Up @@ -283,6 +306,10 @@ static unsigned getMatchingPairOpcode(unsigned Opc) {
case AArch64::LDRSWui:
case AArch64::LDURSWi:
return AArch64::LDPSWi;
case AArch64::LDRHHui:
return AArch64::LDRWui;
case AArch64::LDURHHi:
return AArch64::LDURWi;
}
}

Expand Down Expand Up @@ -440,6 +467,21 @@ static const MachineOperand &getLdStOffsetOp(const MachineInstr *MI) {
return MI->getOperand(Idx);
}

// Copy MachineMemOperands from Op0 and Op1 to a new array assigned to MI.
static void concatenateMemOperands(MachineInstr *MI, MachineInstr *Op0,
MachineInstr *Op1) {
assert(MI->memoperands_empty() && "expected a new machineinstr");
size_t numMemRefs = (Op0->memoperands_end() - Op0->memoperands_begin()) +
(Op1->memoperands_end() - Op1->memoperands_begin());

MachineFunction *MF = MI->getParent()->getParent();
MachineSDNode::mmo_iterator MemBegin = MF->allocateMemRefsArray(numMemRefs);
MachineSDNode::mmo_iterator MemEnd =
std::copy(Op0->memoperands_begin(), Op0->memoperands_end(), MemBegin);
MemEnd = std::copy(Op1->memoperands_begin(), Op1->memoperands_end(), MemEnd);
MI->setMemRefs(MemBegin, MemEnd);
}

MachineBasicBlock::iterator
AArch64LoadStoreOpt::mergePairedInsns(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Paired,
Expand Down Expand Up @@ -484,8 +526,79 @@ AArch64LoadStoreOpt::mergePairedInsns(MachineBasicBlock::iterator I,
RtMI = I;
Rt2MI = Paired;
}
// Handle Unscaled

int OffsetImm = getLdStOffsetOp(RtMI).getImm();

if (isSmallTypeLdMerge(Opc)) {
// Change the scaled offset from small to large type.
if (!IsUnscaled)
OffsetImm /= 2;
MachineInstr *RtNewDest = MergeForward ? I : Paired;
// Construct the new load instruction.
// FIXME: currently we support only halfword unsigned load. We need to
// handle byte type, signed, and store instructions as well.
MachineInstr *NewMemMI, *BitExtMI1, *BitExtMI2;
NewMemMI = BuildMI(*I->getParent(), InsertionPoint, I->getDebugLoc(),
TII->get(NewOpc))
.addOperand(getLdStRegOp(RtNewDest))
.addOperand(BaseRegOp)
.addImm(OffsetImm);

// Copy MachineMemOperands from the original loads.
concatenateMemOperands(NewMemMI, I, Paired);

DEBUG(
dbgs()
<< "Creating the new load and extract. Replacing instructions:\n ");
DEBUG(I->print(dbgs()));
DEBUG(dbgs() << " ");
DEBUG(Paired->print(dbgs()));
DEBUG(dbgs() << " with instructions:\n ");
DEBUG((NewMemMI)->print(dbgs()));

MachineInstr *ExtDestMI = MergeForward ? Paired : I;
if (ExtDestMI == Rt2MI) {
// Create the bitfield extract for high half.
BitExtMI1 = BuildMI(*I->getParent(), InsertionPoint, I->getDebugLoc(),
TII->get(AArch64::UBFMWri))
.addOperand(getLdStRegOp(Rt2MI))
.addReg(getLdStRegOp(RtNewDest).getReg())
.addImm(16)
.addImm(31);
// Create the bitfield extract for low half.
BitExtMI2 = BuildMI(*I->getParent(), InsertionPoint, I->getDebugLoc(),
TII->get(AArch64::ANDWri))
.addOperand(getLdStRegOp(RtMI))
.addReg(getLdStRegOp(RtNewDest).getReg())
.addImm(15);
} else {
// Create the bitfield extract for low half.
BitExtMI1 = BuildMI(*I->getParent(), InsertionPoint, I->getDebugLoc(),
TII->get(AArch64::ANDWri))
.addOperand(getLdStRegOp(RtMI))
.addReg(getLdStRegOp(RtNewDest).getReg())
.addImm(15);
// Create the bitfield extract for high half.
BitExtMI2 = BuildMI(*I->getParent(), InsertionPoint, I->getDebugLoc(),
TII->get(AArch64::UBFMWri))
.addOperand(getLdStRegOp(Rt2MI))
.addReg(getLdStRegOp(RtNewDest).getReg())
.addImm(16)
.addImm(31);
}
DEBUG(dbgs() << " ");
DEBUG((BitExtMI1)->print(dbgs()));
DEBUG(dbgs() << " ");
DEBUG((BitExtMI2)->print(dbgs()));
DEBUG(dbgs() << "\n");

// Erase the old instructions.
I->eraseFromParent();
Paired->eraseFromParent();
return NextI;
}

// Handle Unscaled
if (IsUnscaled)
OffsetImm /= OffsetStride;

Expand Down Expand Up @@ -622,8 +735,7 @@ static bool mayAlias(MachineInstr *MIa,
/// be combined with the current instruction into a load/store pair.
MachineBasicBlock::iterator
AArch64LoadStoreOpt::findMatchingInsn(MachineBasicBlock::iterator I,
LdStPairFlags &Flags,
unsigned Limit) {
LdStPairFlags &Flags, unsigned Limit) {
MachineBasicBlock::iterator E = I->getParent()->end();
MachineBasicBlock::iterator MBBI = I;
MachineInstr *FirstMI = I;
Expand All @@ -645,7 +757,8 @@ AArch64LoadStoreOpt::findMatchingInsn(MachineBasicBlock::iterator I,
// range, plus allow an extra one in case we find a later insn that matches
// with Offset-1)
int OffsetStride = IsUnscaled ? getMemScale(FirstMI) : 1;
if (!inBoundsForPair(IsUnscaled, Offset, OffsetStride))
if (!isSmallTypeLdMerge(Opc) &&
!inBoundsForPair(IsUnscaled, Offset, OffsetStride))
return E;

// Track which registers have been modified and used between the first insn
Expand Down Expand Up @@ -704,18 +817,32 @@ AArch64LoadStoreOpt::findMatchingInsn(MachineBasicBlock::iterator I,
// If the resultant immediate offset of merging these instructions
// is out of range for a pairwise instruction, bail and keep looking.
bool MIIsUnscaled = isUnscaledLdSt(MI);
if (!inBoundsForPair(MIIsUnscaled, MinOffset, OffsetStride)) {
bool IsSmallTypeLd = isSmallTypeLdMerge(MI->getOpcode());
if (!IsSmallTypeLd &&
!inBoundsForPair(MIIsUnscaled, 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 (IsSmallTypeLd) {
// If the alignment requirements of the larger type scaled load
// instruction can't express the scaled offset of the smaller type
// input, bail and keep looking.
if (!IsUnscaled && alignTo(MinOffset, 2) != MinOffset) {
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
MemInsns.push_back(MI);
continue;
}
} else {
// 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
Expand Down Expand Up @@ -996,24 +1123,94 @@ MachineBasicBlock::iterator AArch64LoadStoreOpt::findMatchingUpdateInsnBackward(
return E;
}

bool AArch64LoadStoreOpt::tryToMergeLdStInst(
MachineBasicBlock::iterator &MBBI) {
MachineInstr *MI = MBBI;
MachineBasicBlock::iterator E = MI->getParent()->end();
// If this is a volatile load/store, don't mess with it.
if (MI->hasOrderedMemoryRef())
return false;

// Make sure this is a reg+imm (as opposed to an address reloc).
if (!getLdStOffsetOp(MI).isImm())
return false;

// Check if this load/store has a hint to avoid pair formation.
// MachineMemOperands hints are set by the AArch64StorePairSuppress pass.
if (TII->isLdStPairSuppressed(MI))
return false;

// Look ahead up to ScanLimit instructions for a pairable instruction.
LdStPairFlags Flags;
MachineBasicBlock::iterator Paired = findMatchingInsn(MBBI, Flags, ScanLimit);
if (Paired != E) {
if (isSmallTypeLdMerge(MI)) {
++NumSmallTypeMerged;
} else {
++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);
return true;
}
return false;
}

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
// Three tranformations to do here:
// 1) Find halfword loads that can be merged into a single 32-bit word load
// with bitfield extract instructions.
// e.g.,
// ldrh w0, [x2]
// ldrh w1, [x2, #2]
// ; becomes
// ldr w0, [x2]
// ubfx w1, w0, #16, #16
// and w0, w0, #ffff
// 2) 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
// 3) 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();
!IsStrictAlign && MBBI != E;) {
MachineInstr *MI = MBBI;
switch (MI->getOpcode()) {
default:
// Just move on to the next instruction.
++MBBI;
break;
// Scaled instructions.
case AArch64::LDRHHui:
// Unscaled instructions.
case AArch64::LDURHHi: {
if (tryToMergeLdStInst(MBBI)) {
Modified = true;
break;
}
++MBBI;
break;
}
// FIXME: Do the other instructions.
}
}

for (MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end();
MBBI != E;) {
MachineInstr *MI = MBBI;
Expand Down Expand Up @@ -1046,35 +1243,7 @@ bool AArch64LoadStoreOpt::optimizeBlock(MachineBasicBlock &MBB) {
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);
if (tryToMergeLdStInst(MBBI)) {
Modified = true;
break;
}
Expand Down Expand Up @@ -1206,6 +1375,8 @@ bool AArch64LoadStoreOpt::optimizeBlock(MachineBasicBlock &MBB) {
bool AArch64LoadStoreOpt::runOnMachineFunction(MachineFunction &Fn) {
TII = static_cast<const AArch64InstrInfo *>(Fn.getSubtarget().getInstrInfo());
TRI = Fn.getSubtarget().getRegisterInfo();
IsStrictAlign = (static_cast<const AArch64Subtarget &>(Fn.getSubtarget()))
.requiresStrictAlign();

bool Modified = false;
for (auto &MBB : Fn)
Expand Down
Loading

0 comments on commit b0bca8e

Please sign in to comment.