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Revert "[AArch64] merge index address with large offset into base add…
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…ress"

This reverts commit 32878c2 due to #79756 and #76202.

(cherry picked from commit 915c3d9)
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@davemgreen @tstellar
davemgreen authored and tstellar committed Jan 29, 2024
1 parent 0680e84 commit bab01ae
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Showing 5 changed files with 12 additions and 250 deletions.
10 changes: 0 additions & 10 deletions llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
View file
Expand Up @@ -4098,16 +4098,6 @@ AArch64InstrInfo::getLdStOffsetOp(const MachineInstr &MI) {
return MI.getOperand(Idx);
}

const MachineOperand &
AArch64InstrInfo::getLdStAmountOp(const MachineInstr &MI) {
switch (MI.getOpcode()) {
default:
llvm_unreachable("Unexpected opcode");
case AArch64::LDRBBroX:
return MI.getOperand(4);
}
}

static const TargetRegisterClass *getRegClass(const MachineInstr &MI,
Register Reg) {
if (MI.getParent() == nullptr)
Expand Down
3 changes: 0 additions & 3 deletions llvm/lib/Target/AArch64/AArch64InstrInfo.h
View file
Expand Up @@ -111,9 +111,6 @@ class AArch64InstrInfo final : public AArch64GenInstrInfo {
/// Returns the immediate offset operator of a load/store.
static const MachineOperand &getLdStOffsetOp(const MachineInstr &MI);

/// Returns the shift amount operator of a load/store.
static const MachineOperand &getLdStAmountOp(const MachineInstr &MI);

/// Returns whether the instruction is FP or NEON.
static bool isFpOrNEON(const MachineInstr &MI);

Expand Down
229 changes: 0 additions & 229 deletions llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
View file
Expand Up @@ -62,8 +62,6 @@ 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");
STATISTIC(NumConstOffsetFolded,
"Number of const offset of index address folded");

DEBUG_COUNTER(RegRenamingCounter, DEBUG_TYPE "-reg-renaming",
"Controls which pairs are considered for renaming");
Expand All @@ -77,11 +75,6 @@ static cl::opt<unsigned> LdStLimit("aarch64-load-store-scan-limit",
static cl::opt<unsigned> UpdateLimit("aarch64-update-scan-limit", cl::init(100),
cl::Hidden);

// The LdStConstLimit limits how far we search for const offset instructions
// when we form index address load/store instructions.
static cl::opt<unsigned> LdStConstLimit("aarch64-load-store-const-scan-limit",
cl::init(10), cl::Hidden);

// Enable register renaming to find additional store pairing opportunities.
static cl::opt<bool> EnableRenaming("aarch64-load-store-renaming",
cl::init(true), cl::Hidden);
Expand Down Expand Up @@ -178,13 +171,6 @@ struct AArch64LoadStoreOpt : public MachineFunctionPass {
findMatchingUpdateInsnForward(MachineBasicBlock::iterator I,
int UnscaledOffset, unsigned Limit);

// Scan the instruction list to find a register assigned with a const
// value that can be combined with the current instruction (a load or store)
// using base addressing with writeback. Scan forwards.
MachineBasicBlock::iterator
findMatchingConstOffsetBackward(MachineBasicBlock::iterator I, unsigned Limit,
unsigned &Offset);

// 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.
Expand All @@ -196,19 +182,11 @@ struct AArch64LoadStoreOpt : public MachineFunctionPass {
bool isMatchingUpdateInsn(MachineInstr &MemMI, MachineInstr &MI,
unsigned BaseReg, int Offset);

bool isMatchingMovConstInsn(MachineInstr &MemMI, MachineInstr &MI,
unsigned IndexReg, unsigned &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);

MachineBasicBlock::iterator
mergeConstOffsetInsn(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Update, unsigned Offset,
int Scale);

// Find and merge zero store instructions.
bool tryToMergeZeroStInst(MachineBasicBlock::iterator &MBBI);

Expand All @@ -221,9 +199,6 @@ struct AArch64LoadStoreOpt : public MachineFunctionPass {
// Find and merge a base register updates before or after a ld/st instruction.
bool tryToMergeLdStUpdate(MachineBasicBlock::iterator &MBBI);

// Find and merge a index ldr/st instructions into a base ld/st instruction.
bool tryToMergeIndexLdSt(MachineBasicBlock::iterator &MBBI, int Scale);

bool optimizeBlock(MachineBasicBlock &MBB, bool EnableNarrowZeroStOpt);

bool runOnMachineFunction(MachineFunction &Fn) override;
Expand Down Expand Up @@ -506,16 +481,6 @@ static unsigned getPreIndexedOpcode(unsigned Opc) {
}
}

static unsigned getBaseAddressOpcode(unsigned Opc) {
// TODO: Add more index address loads/stores.
switch (Opc) {
default:
llvm_unreachable("Opcode has no base address equivalent!");
case AArch64::LDRBBroX:
return AArch64::LDRBBui;
}
}

static unsigned getPostIndexedOpcode(unsigned Opc) {
switch (Opc) {
default:
Expand Down Expand Up @@ -757,20 +722,6 @@ static bool isMergeableLdStUpdate(MachineInstr &MI) {
}
}

// Make sure this is a reg+reg Ld/St
static bool isMergeableIndexLdSt(MachineInstr &MI, int &Scale) {
unsigned Opc = MI.getOpcode();
switch (Opc) {
default:
return false;
// Scaled instructions.
// TODO: Add more index address loads/stores.
case AArch64::LDRBBroX:
Scale = 1;
return true;
}
}

static bool isRewritableImplicitDef(unsigned Opc) {
switch (Opc) {
default:
Expand Down Expand Up @@ -2097,63 +2048,6 @@ AArch64LoadStoreOpt::mergeUpdateInsn(MachineBasicBlock::iterator I,
return NextI;
}

MachineBasicBlock::iterator
AArch64LoadStoreOpt::mergeConstOffsetInsn(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Update,
unsigned Offset, int Scale) {
assert((Update->getOpcode() == AArch64::MOVKWi) &&
"Unexpected const mov instruction to merge!");
MachineBasicBlock::iterator E = I->getParent()->end();
MachineBasicBlock::iterator NextI = next_nodbg(I, E);
MachineBasicBlock::iterator PrevI = prev_nodbg(Update, E);
MachineInstr &MemMI = *I;
unsigned Mask = (1 << 12) * Scale - 1;
unsigned Low = Offset & Mask;
unsigned High = Offset - Low;
Register BaseReg = AArch64InstrInfo::getLdStBaseOp(MemMI).getReg();
Register IndexReg = AArch64InstrInfo::getLdStOffsetOp(MemMI).getReg();
MachineInstrBuilder AddMIB, MemMIB;

// Add IndexReg, BaseReg, High (the BaseReg may be SP)
AddMIB =
BuildMI(*I->getParent(), I, I->getDebugLoc(), TII->get(AArch64::ADDXri))
.addDef(IndexReg)
.addUse(BaseReg)
.addImm(High >> 12) // shifted value
.addImm(12); // shift 12
(void)AddMIB;
// Ld/St DestReg, IndexReg, Imm12
unsigned NewOpc = getBaseAddressOpcode(I->getOpcode());
MemMIB = BuildMI(*I->getParent(), I, I->getDebugLoc(), TII->get(NewOpc))
.add(getLdStRegOp(MemMI))
.add(AArch64InstrInfo::getLdStOffsetOp(MemMI))
.addImm(Low / Scale)
.setMemRefs(I->memoperands())
.setMIFlags(I->mergeFlagsWith(*Update));
(void)MemMIB;

++NumConstOffsetFolded;
LLVM_DEBUG(dbgs() << "Creating base address load/store.\n");
LLVM_DEBUG(dbgs() << " Replacing instructions:\n ");
LLVM_DEBUG(PrevI->print(dbgs()));
LLVM_DEBUG(dbgs() << " ");
LLVM_DEBUG(Update->print(dbgs()));
LLVM_DEBUG(dbgs() << " ");
LLVM_DEBUG(I->print(dbgs()));
LLVM_DEBUG(dbgs() << " with instruction:\n ");
LLVM_DEBUG(((MachineInstr *)AddMIB)->print(dbgs()));
LLVM_DEBUG(dbgs() << " ");
LLVM_DEBUG(((MachineInstr *)MemMIB)->print(dbgs()));
LLVM_DEBUG(dbgs() << "\n");

// Erase the old instructions for the block.
I->eraseFromParent();
PrevI->eraseFromParent();
Update->eraseFromParent();

return NextI;
}

bool AArch64LoadStoreOpt::isMatchingUpdateInsn(MachineInstr &MemMI,
MachineInstr &MI,
unsigned BaseReg, int Offset) {
Expand Down Expand Up @@ -2201,31 +2095,6 @@ bool AArch64LoadStoreOpt::isMatchingUpdateInsn(MachineInstr &MemMI,
return false;
}

bool AArch64LoadStoreOpt::isMatchingMovConstInsn(MachineInstr &MemMI,
MachineInstr &MI,
unsigned IndexReg,
unsigned &Offset) {
// The update instruction source and destination register must be the
// same as the load/store index register.
if (MI.getOpcode() == AArch64::MOVKWi &&
TRI->isSuperOrSubRegisterEq(IndexReg, MI.getOperand(1).getReg())) {

// movz + movk hold a large offset of a Ld/St instruction.
MachineBasicBlock::iterator B = MI.getParent()->begin();
MachineBasicBlock::iterator MBBI = &MI;
MBBI = prev_nodbg(MBBI, B);
MachineInstr &MovzMI = *MBBI;
if (MovzMI.getOpcode() == AArch64::MOVZWi) {
unsigned Low = MovzMI.getOperand(1).getImm();
unsigned High = MI.getOperand(2).getImm() << MI.getOperand(3).getImm();
Offset = High + Low;
// 12-bit optionally shifted immediates are legal for adds.
return Offset >> 24 == 0;
}
}
return false;
}

MachineBasicBlock::iterator AArch64LoadStoreOpt::findMatchingUpdateInsnForward(
MachineBasicBlock::iterator I, int UnscaledOffset, unsigned Limit) {
MachineBasicBlock::iterator E = I->getParent()->end();
Expand Down Expand Up @@ -2381,60 +2250,6 @@ MachineBasicBlock::iterator AArch64LoadStoreOpt::findMatchingUpdateInsnBackward(
return E;
}

MachineBasicBlock::iterator
AArch64LoadStoreOpt::findMatchingConstOffsetBackward(
MachineBasicBlock::iterator I, unsigned Limit, unsigned &Offset) {
MachineBasicBlock::iterator B = I->getParent()->begin();
MachineBasicBlock::iterator E = I->getParent()->end();
MachineInstr &MemMI = *I;
MachineBasicBlock::iterator MBBI = I;

// If the load is the first instruction in the block, there's obviously
// not any matching load or store.
if (MBBI == B)
return E;

// Make sure the IndexReg is killed and the shift amount is zero.
// TODO: Relex this restriction to extend, simplify processing now.
if (!AArch64InstrInfo::getLdStOffsetOp(MemMI).isKill() ||
!AArch64InstrInfo::getLdStAmountOp(MemMI).isImm() ||
(AArch64InstrInfo::getLdStAmountOp(MemMI).getImm() != 0))
return E;

Register IndexReg = AArch64InstrInfo::getLdStOffsetOp(MemMI).getReg();

// Track which register units have been modified and used between the first
// insn (inclusive) and the second insn.
ModifiedRegUnits.clear();
UsedRegUnits.clear();
unsigned Count = 0;
do {
MBBI = prev_nodbg(MBBI, B);
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 (isMatchingMovConstInsn(*I, MI, IndexReg, Offset)) {
return MBBI;
}

// Update the status of what the instruction clobbered and used.
LiveRegUnits::accumulateUsedDefed(MI, ModifiedRegUnits, UsedRegUnits, TRI);

// Otherwise, if the index register is used or modified, we have no match,
// so return early.
if (!ModifiedRegUnits.available(IndexReg) ||
!UsedRegUnits.available(IndexReg))
return E;

} while (MBBI != B && Count < Limit);
return E;
}

bool AArch64LoadStoreOpt::tryToPromoteLoadFromStore(
MachineBasicBlock::iterator &MBBI) {
MachineInstr &MI = *MBBI;
Expand Down Expand Up @@ -2619,34 +2434,6 @@ bool AArch64LoadStoreOpt::tryToMergeLdStUpdate
return false;
}

bool AArch64LoadStoreOpt::tryToMergeIndexLdSt(MachineBasicBlock::iterator &MBBI,
int Scale) {
MachineInstr &MI = *MBBI;
MachineBasicBlock::iterator E = MI.getParent()->end();
MachineBasicBlock::iterator Update;

// Don't know how to handle unscaled pre/post-index versions below, so bail.
if (TII->hasUnscaledLdStOffset(MI.getOpcode()))
return false;

// Look back to try to find a const offset for index LdSt instruction. For
// example,
// mov x8, #LargeImm ; = a * (1<<12) + imm12
// ldr x1, [x0, x8]
// merged into:
// add x8, x0, a * (1<<12)
// ldr x1, [x8, imm12]
unsigned Offset;
Update = findMatchingConstOffsetBackward(MBBI, LdStConstLimit, Offset);
if (Update != E && (Offset & (Scale - 1)) == 0) {
// Merge the imm12 into the ld/st.
MBBI = mergeConstOffsetInsn(MBBI, Update, Offset, Scale);
return true;
}

return false;
}

bool AArch64LoadStoreOpt::optimizeBlock(MachineBasicBlock &MBB,
bool EnableNarrowZeroStOpt) {

Expand Down Expand Up @@ -2725,22 +2512,6 @@ bool AArch64LoadStoreOpt::optimizeBlock(MachineBasicBlock &MBB,
++MBBI;
}

// 5) Find a register assigned with a const value that can be combined with
// into the load or store. e.g.,
// mov x8, #LargeImm ; = a * (1<<12) + imm12
// ldr x1, [x0, x8]
// ; becomes
// add x8, x0, a * (1<<12)
// ldr x1, [x8, imm12]
for (MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end();
MBBI != E;) {
int Scale;
if (isMergeableIndexLdSt(*MBBI, Scale) && tryToMergeIndexLdSt(MBBI, Scale))
Modified = true;
else
++MBBI;
}

return Modified;
}

Expand Down
15 changes: 9 additions & 6 deletions llvm/test/CodeGen/AArch64/arm64-addrmode.ll
View file
Expand Up @@ -214,8 +214,9 @@ define void @t17(i64 %a) {
define i8 @LdOffset_i8(ptr %a) {
; CHECK-LABEL: LdOffset_i8:
; CHECK: // %bb.0:
; CHECK-NEXT: add x8, x0, #253, lsl #12 // =1036288
; CHECK-NEXT: ldrb w0, [x8, #3704]
; CHECK-NEXT: mov w8, #56952 // =0xde78
; CHECK-NEXT: movk w8, #15, lsl #16
; CHECK-NEXT: ldrb w0, [x0, x8]
; CHECK-NEXT: ret
%arrayidx = getelementptr inbounds i8, ptr %a, i64 1039992
%val = load i8, ptr %arrayidx, align 1
Expand All @@ -226,8 +227,9 @@ define i8 @LdOffset_i8(ptr %a) {
define i32 @LdOffset_i8_zext32(ptr %a) {
; CHECK-LABEL: LdOffset_i8_zext32:
; CHECK: // %bb.0:
; CHECK-NEXT: add x8, x0, #253, lsl #12 // =1036288
; CHECK-NEXT: ldrb w0, [x8, #3704]
; CHECK-NEXT: mov w8, #56952 // =0xde78
; CHECK-NEXT: movk w8, #15, lsl #16
; CHECK-NEXT: ldrb w0, [x0, x8]
; CHECK-NEXT: ret
%arrayidx = getelementptr inbounds i8, ptr %a, i64 1039992
%val = load i8, ptr %arrayidx, align 1
Expand All @@ -253,8 +255,9 @@ define i32 @LdOffset_i8_sext32(ptr %a) {
define i64 @LdOffset_i8_zext64(ptr %a) {
; CHECK-LABEL: LdOffset_i8_zext64:
; CHECK: // %bb.0:
; CHECK-NEXT: add x8, x0, #253, lsl #12 // =1036288
; CHECK-NEXT: ldrb w0, [x8, #3704]
; CHECK-NEXT: mov w8, #56952 // =0xde78
; CHECK-NEXT: movk w8, #15, lsl #16
; CHECK-NEXT: ldrb w0, [x0, x8]
; CHECK-NEXT: ret
%arrayidx = getelementptr inbounds i8, ptr %a, i64 1039992
%val = load i8, ptr %arrayidx, align 1
Expand Down
5 changes: 3 additions & 2 deletions llvm/test/CodeGen/AArch64/large-offset-ldr-merge.mir
View file
Expand Up @@ -14,8 +14,9 @@ body: |
; CHECK-LABEL: name: LdOffset
; CHECK: liveins: $x0
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: $x8 = ADDXri $x0, 253, 12
; CHECK-NEXT: renamable $w0 = LDRBBui killed renamable $x8, 3704
; CHECK-NEXT: renamable $w8 = MOVZWi 56952, 0
; CHECK-NEXT: renamable $w8 = MOVKWi $w8, 15, 16, implicit-def $x8
; CHECK-NEXT: renamable $w0 = LDRBBroX killed renamable $x0, killed renamable $x8, 0, 0
; CHECK-NEXT: RET undef $lr, implicit $w0
renamable $w8 = MOVZWi 56952, 0
renamable $w8 = MOVKWi $w8, 15, 16, implicit-def $x8
Expand Down

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