1 //=== A15SDOptimizerPass.cpp - Optimize DPR and SPR register accesses on A15==//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // The Cortex-A15 processor employs a tracking scheme in its register renaming
10 // in order to process each instruction's micro-ops speculatively and
11 // out-of-order with appropriate forwarding. The ARM architecture allows VFP
12 // instructions to read and write 32-bit S-registers. Each S-register
13 // corresponds to one half (upper or lower) of an overlaid 64-bit D-register.
15 // There are several instruction patterns which can be used to provide this
16 // capability which can provide higher performance than other, potentially more
17 // direct patterns, specifically around when one micro-op reads a D-register
18 // operand that has recently been written as one or more S-register results.
20 // This file defines a pre-regalloc pass which looks for SPR producers which
21 // are going to be used by a DPR (or QPR) consumers and creates the more
22 // optimized access pattern.
24 //===----------------------------------------------------------------------===//
27 #include "ARMBaseInstrInfo.h"
28 #include "ARMBaseRegisterInfo.h"
29 #include "ARMSubtarget.h"
30 #include "llvm/ADT/Statistic.h"
31 #include "llvm/CodeGen/MachineFunction.h"
32 #include "llvm/CodeGen/MachineFunctionPass.h"
33 #include "llvm/CodeGen/MachineInstr.h"
34 #include "llvm/CodeGen/MachineInstrBuilder.h"
35 #include "llvm/CodeGen/MachineRegisterInfo.h"
36 #include "llvm/CodeGen/TargetRegisterInfo.h"
37 #include "llvm/CodeGen/TargetSubtargetInfo.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Support/raw_ostream.h"
45 #define DEBUG_TYPE "a15-sd-optimizer"
48 struct A15SDOptimizer : public MachineFunctionPass {
50 A15SDOptimizer() : MachineFunctionPass(ID) {}
52 bool runOnMachineFunction(MachineFunction &Fn) override;
54 StringRef getPassName() const override { return "ARM A15 S->D optimizer"; }
57 const ARMBaseInstrInfo *TII;
58 const TargetRegisterInfo *TRI;
59 MachineRegisterInfo *MRI;
61 bool runOnInstruction(MachineInstr *MI);
64 // Instruction builder helpers
66 unsigned createDupLane(MachineBasicBlock &MBB,
67 MachineBasicBlock::iterator InsertBefore,
68 const DebugLoc &DL, unsigned Reg, unsigned Lane,
71 unsigned createExtractSubreg(MachineBasicBlock &MBB,
72 MachineBasicBlock::iterator InsertBefore,
73 const DebugLoc &DL, unsigned DReg,
74 unsigned Lane, const TargetRegisterClass *TRC);
76 unsigned createVExt(MachineBasicBlock &MBB,
77 MachineBasicBlock::iterator InsertBefore,
78 const DebugLoc &DL, unsigned Ssub0, unsigned Ssub1);
80 unsigned createRegSequence(MachineBasicBlock &MBB,
81 MachineBasicBlock::iterator InsertBefore,
82 const DebugLoc &DL, unsigned Reg1,
85 unsigned createInsertSubreg(MachineBasicBlock &MBB,
86 MachineBasicBlock::iterator InsertBefore,
87 const DebugLoc &DL, unsigned DReg,
88 unsigned Lane, unsigned ToInsert);
90 unsigned createImplicitDef(MachineBasicBlock &MBB,
91 MachineBasicBlock::iterator InsertBefore,
95 // Various property checkers
97 bool usesRegClass(MachineOperand &MO, const TargetRegisterClass *TRC);
98 bool hasPartialWrite(MachineInstr *MI);
99 SmallVector<unsigned, 8> getReadDPRs(MachineInstr *MI);
100 unsigned getDPRLaneFromSPR(unsigned SReg);
103 // Methods used for getting the definitions of partial registers
106 MachineInstr *elideCopies(MachineInstr *MI);
107 void elideCopiesAndPHIs(MachineInstr *MI,
108 SmallVectorImpl<MachineInstr*> &Outs);
111 // Pattern optimization methods
113 unsigned optimizeAllLanesPattern(MachineInstr *MI, unsigned Reg);
114 unsigned optimizeSDPattern(MachineInstr *MI);
115 unsigned getPrefSPRLane(unsigned SReg);
118 // Sanitizing method - used to make sure if don't leave dead code around.
120 void eraseInstrWithNoUses(MachineInstr *MI);
123 // A map used to track the changes done by this pass.
125 std::map<MachineInstr*, unsigned> Replacements;
126 std::set<MachineInstr *> DeadInstr;
128 char A15SDOptimizer::ID = 0;
129 } // end anonymous namespace
131 // Returns true if this is a use of a SPR register.
132 bool A15SDOptimizer::usesRegClass(MachineOperand &MO,
133 const TargetRegisterClass *TRC) {
136 Register Reg = MO.getReg();
139 return MRI->getRegClass(Reg)->hasSuperClassEq(TRC);
141 return TRC->contains(Reg);
144 unsigned A15SDOptimizer::getDPRLaneFromSPR(unsigned SReg) {
145 unsigned DReg = TRI->getMatchingSuperReg(SReg, ARM::ssub_1,
147 if (DReg != ARM::NoRegister) return ARM::ssub_1;
151 // Get the subreg type that is most likely to be coalesced
152 // for an SPR register that will be used in VDUP32d pseudo.
153 unsigned A15SDOptimizer::getPrefSPRLane(unsigned SReg) {
154 if (!Register::isVirtualRegister(SReg))
155 return getDPRLaneFromSPR(SReg);
157 MachineInstr *MI = MRI->getVRegDef(SReg);
158 if (!MI) return ARM::ssub_0;
159 MachineOperand *MO = MI->findRegisterDefOperand(SReg);
160 if (!MO) return ARM::ssub_0;
161 assert(MO->isReg() && "Non-register operand found!");
163 if (MI->isCopy() && usesRegClass(MI->getOperand(1),
164 &ARM::SPRRegClass)) {
165 SReg = MI->getOperand(1).getReg();
168 if (Register::isVirtualRegister(SReg)) {
169 if (MO->getSubReg() == ARM::ssub_1) return ARM::ssub_1;
172 return getDPRLaneFromSPR(SReg);
175 // MI is known to be dead. Figure out what instructions
176 // are also made dead by this and mark them for removal.
177 void A15SDOptimizer::eraseInstrWithNoUses(MachineInstr *MI) {
178 SmallVector<MachineInstr *, 8> Front;
179 DeadInstr.insert(MI);
181 LLVM_DEBUG(dbgs() << "Deleting base instruction " << *MI << "\n");
184 while (Front.size() != 0) {
185 MI = Front.pop_back_val();
187 // MI is already known to be dead. We need to see
188 // if other instructions can also be removed.
189 for (MachineOperand &MO : MI->operands()) {
190 if ((!MO.isReg()) || (!MO.isUse()))
192 Register Reg = MO.getReg();
193 if (!Reg.isVirtual())
195 MachineOperand *Op = MI->findRegisterDefOperand(Reg);
200 MachineInstr *Def = Op->getParent();
202 // We don't need to do anything if we have already marked
203 // this instruction as being dead.
204 if (DeadInstr.find(Def) != DeadInstr.end())
207 // Check if all the uses of this instruction are marked as
208 // dead. If so, we can also mark this instruction as being
211 for (MachineOperand &MODef : Def->operands()) {
212 if ((!MODef.isReg()) || (!MODef.isDef()))
214 Register DefReg = MODef.getReg();
215 if (!DefReg.isVirtual()) {
219 for (MachineInstr &Use : MRI->use_instructions(Reg)) {
220 // We don't care about self references.
223 if (DeadInstr.find(&Use) == DeadInstr.end()) {
230 if (!IsDead) continue;
232 LLVM_DEBUG(dbgs() << "Deleting instruction " << *Def << "\n");
233 DeadInstr.insert(Def);
238 // Creates the more optimized patterns and generally does all the code
239 // transformations in this pass.
240 unsigned A15SDOptimizer::optimizeSDPattern(MachineInstr *MI) {
242 return optimizeAllLanesPattern(MI, MI->getOperand(1).getReg());
245 if (MI->isInsertSubreg()) {
246 Register DPRReg = MI->getOperand(1).getReg();
247 Register SPRReg = MI->getOperand(2).getReg();
249 if (DPRReg.isVirtual() && SPRReg.isVirtual()) {
250 MachineInstr *DPRMI = MRI->getVRegDef(MI->getOperand(1).getReg());
251 MachineInstr *SPRMI = MRI->getVRegDef(MI->getOperand(2).getReg());
253 if (DPRMI && SPRMI) {
254 // See if the first operand of this insert_subreg is IMPLICIT_DEF
255 MachineInstr *ECDef = elideCopies(DPRMI);
256 if (ECDef && ECDef->isImplicitDef()) {
257 // Another corner case - if we're inserting something that is purely
258 // a subreg copy of a DPR, just use that DPR.
260 MachineInstr *EC = elideCopies(SPRMI);
261 // Is it a subreg copy of ssub_0?
262 if (EC && EC->isCopy() &&
263 EC->getOperand(1).getSubReg() == ARM::ssub_0) {
264 LLVM_DEBUG(dbgs() << "Found a subreg copy: " << *SPRMI);
266 // Find the thing we're subreg copying out of - is it of the same
267 // regclass as DPRMI? (i.e. a DPR or QPR).
268 Register FullReg = SPRMI->getOperand(1).getReg();
269 const TargetRegisterClass *TRC =
270 MRI->getRegClass(MI->getOperand(1).getReg());
271 if (TRC->hasSuperClassEq(MRI->getRegClass(FullReg))) {
272 LLVM_DEBUG(dbgs() << "Subreg copy is compatible - returning ");
273 LLVM_DEBUG(dbgs() << printReg(FullReg) << "\n");
274 eraseInstrWithNoUses(MI);
279 return optimizeAllLanesPattern(MI, MI->getOperand(2).getReg());
283 return optimizeAllLanesPattern(MI, MI->getOperand(0).getReg());
286 if (MI->isRegSequence() && usesRegClass(MI->getOperand(1),
287 &ARM::SPRRegClass)) {
288 // See if all bar one of the operands are IMPLICIT_DEF and insert the
289 // optimizer pattern accordingly.
290 unsigned NumImplicit = 0, NumTotal = 0;
291 unsigned NonImplicitReg = ~0U;
293 for (MachineOperand &MO : llvm::drop_begin(MI->explicit_operands())) {
297 Register OpReg = MO.getReg();
299 if (!OpReg.isVirtual())
302 MachineInstr *Def = MRI->getVRegDef(OpReg);
305 if (Def->isImplicitDef())
308 NonImplicitReg = MO.getReg();
311 if (NumImplicit == NumTotal - 1)
312 return optimizeAllLanesPattern(MI, NonImplicitReg);
314 return optimizeAllLanesPattern(MI, MI->getOperand(0).getReg());
317 llvm_unreachable("Unhandled update pattern!");
320 // Return true if this MachineInstr inserts a scalar (SPR) value into
321 // a D or Q register.
322 bool A15SDOptimizer::hasPartialWrite(MachineInstr *MI) {
323 // The only way we can do a partial register update is through a COPY,
324 // INSERT_SUBREG or REG_SEQUENCE.
325 if (MI->isCopy() && usesRegClass(MI->getOperand(1), &ARM::SPRRegClass))
328 if (MI->isInsertSubreg() && usesRegClass(MI->getOperand(2),
332 if (MI->isRegSequence() && usesRegClass(MI->getOperand(1), &ARM::SPRRegClass))
338 // Looks through full copies to get the instruction that defines the input
340 MachineInstr *A15SDOptimizer::elideCopies(MachineInstr *MI) {
341 if (!MI->isFullCopy())
343 if (!MI->getOperand(1).getReg().isVirtual())
345 MachineInstr *Def = MRI->getVRegDef(MI->getOperand(1).getReg());
348 return elideCopies(Def);
351 // Look through full copies and PHIs to get the set of non-copy MachineInstrs
352 // that can produce MI.
353 void A15SDOptimizer::elideCopiesAndPHIs(MachineInstr *MI,
354 SmallVectorImpl<MachineInstr*> &Outs) {
355 // Looking through PHIs may create loops so we need to track what
356 // instructions we have visited before.
357 std::set<MachineInstr *> Reached;
358 SmallVector<MachineInstr *, 8> Front;
360 while (Front.size() != 0) {
361 MI = Front.pop_back_val();
363 // If we have already explored this MachineInstr, ignore it.
364 if (!Reached.insert(MI).second)
367 for (unsigned I = 1, E = MI->getNumOperands(); I != E; I += 2) {
368 Register Reg = MI->getOperand(I).getReg();
369 if (!Reg.isVirtual()) {
372 MachineInstr *NewMI = MRI->getVRegDef(Reg);
375 Front.push_back(NewMI);
377 } else if (MI->isFullCopy()) {
378 if (!MI->getOperand(1).getReg().isVirtual())
380 MachineInstr *NewMI = MRI->getVRegDef(MI->getOperand(1).getReg());
383 Front.push_back(NewMI);
385 LLVM_DEBUG(dbgs() << "Found partial copy" << *MI << "\n");
391 // Return the DPR virtual registers that are read by this machine instruction
393 SmallVector<unsigned, 8> A15SDOptimizer::getReadDPRs(MachineInstr *MI) {
394 if (MI->isCopyLike() || MI->isInsertSubreg() || MI->isRegSequence() ||
396 return SmallVector<unsigned, 8>();
398 SmallVector<unsigned, 8> Defs;
399 for (MachineOperand &MO : MI->operands()) {
400 if (!MO.isReg() || !MO.isUse())
402 if (!usesRegClass(MO, &ARM::DPRRegClass) &&
403 !usesRegClass(MO, &ARM::QPRRegClass) &&
404 !usesRegClass(MO, &ARM::DPairRegClass)) // Treat DPair as QPR
407 Defs.push_back(MO.getReg());
412 // Creates a DPR register from an SPR one by using a VDUP.
413 unsigned A15SDOptimizer::createDupLane(MachineBasicBlock &MBB,
414 MachineBasicBlock::iterator InsertBefore,
415 const DebugLoc &DL, unsigned Reg,
416 unsigned Lane, bool QPR) {
418 MRI->createVirtualRegister(QPR ? &ARM::QPRRegClass : &ARM::DPRRegClass);
419 BuildMI(MBB, InsertBefore, DL,
420 TII->get(QPR ? ARM::VDUPLN32q : ARM::VDUPLN32d), Out)
423 .add(predOps(ARMCC::AL));
428 // Creates a SPR register from a DPR by copying the value in lane 0.
429 unsigned A15SDOptimizer::createExtractSubreg(
430 MachineBasicBlock &MBB, MachineBasicBlock::iterator InsertBefore,
431 const DebugLoc &DL, unsigned DReg, unsigned Lane,
432 const TargetRegisterClass *TRC) {
433 Register Out = MRI->createVirtualRegister(TRC);
437 TII->get(TargetOpcode::COPY), Out)
438 .addReg(DReg, 0, Lane);
443 // Takes two SPR registers and creates a DPR by using a REG_SEQUENCE.
444 unsigned A15SDOptimizer::createRegSequence(
445 MachineBasicBlock &MBB, MachineBasicBlock::iterator InsertBefore,
446 const DebugLoc &DL, unsigned Reg1, unsigned Reg2) {
447 Register Out = MRI->createVirtualRegister(&ARM::QPRRegClass);
451 TII->get(TargetOpcode::REG_SEQUENCE), Out)
455 .addImm(ARM::dsub_1);
459 // Takes two DPR registers that have previously been VDUPed (Ssub0 and Ssub1)
460 // and merges them into one DPR register.
461 unsigned A15SDOptimizer::createVExt(MachineBasicBlock &MBB,
462 MachineBasicBlock::iterator InsertBefore,
463 const DebugLoc &DL, unsigned Ssub0,
465 Register Out = MRI->createVirtualRegister(&ARM::DPRRegClass);
466 BuildMI(MBB, InsertBefore, DL, TII->get(ARM::VEXTd32), Out)
470 .add(predOps(ARMCC::AL));
474 unsigned A15SDOptimizer::createInsertSubreg(
475 MachineBasicBlock &MBB, MachineBasicBlock::iterator InsertBefore,
476 const DebugLoc &DL, unsigned DReg, unsigned Lane, unsigned ToInsert) {
477 Register Out = MRI->createVirtualRegister(&ARM::DPR_VFP2RegClass);
481 TII->get(TargetOpcode::INSERT_SUBREG), Out)
490 A15SDOptimizer::createImplicitDef(MachineBasicBlock &MBB,
491 MachineBasicBlock::iterator InsertBefore,
492 const DebugLoc &DL) {
493 Register Out = MRI->createVirtualRegister(&ARM::DPRRegClass);
497 TII->get(TargetOpcode::IMPLICIT_DEF), Out);
501 // This function inserts instructions in order to optimize interactions between
502 // SPR registers and DPR/QPR registers. It does so by performing VDUPs on all
503 // lanes, and the using VEXT instructions to recompose the result.
505 A15SDOptimizer::optimizeAllLanesPattern(MachineInstr *MI, unsigned Reg) {
506 MachineBasicBlock::iterator InsertPt(MI);
507 DebugLoc DL = MI->getDebugLoc();
508 MachineBasicBlock &MBB = *MI->getParent();
512 // DPair has the same length as QPR and also has two DPRs as subreg.
513 // Treat DPair as QPR.
514 if (MRI->getRegClass(Reg)->hasSuperClassEq(&ARM::QPRRegClass) ||
515 MRI->getRegClass(Reg)->hasSuperClassEq(&ARM::DPairRegClass)) {
516 unsigned DSub0 = createExtractSubreg(MBB, InsertPt, DL, Reg,
517 ARM::dsub_0, &ARM::DPRRegClass);
518 unsigned DSub1 = createExtractSubreg(MBB, InsertPt, DL, Reg,
519 ARM::dsub_1, &ARM::DPRRegClass);
521 unsigned Out1 = createDupLane(MBB, InsertPt, DL, DSub0, 0);
522 unsigned Out2 = createDupLane(MBB, InsertPt, DL, DSub0, 1);
523 Out = createVExt(MBB, InsertPt, DL, Out1, Out2);
525 unsigned Out3 = createDupLane(MBB, InsertPt, DL, DSub1, 0);
526 unsigned Out4 = createDupLane(MBB, InsertPt, DL, DSub1, 1);
527 Out2 = createVExt(MBB, InsertPt, DL, Out3, Out4);
529 Out = createRegSequence(MBB, InsertPt, DL, Out, Out2);
531 } else if (MRI->getRegClass(Reg)->hasSuperClassEq(&ARM::DPRRegClass)) {
532 unsigned Out1 = createDupLane(MBB, InsertPt, DL, Reg, 0);
533 unsigned Out2 = createDupLane(MBB, InsertPt, DL, Reg, 1);
534 Out = createVExt(MBB, InsertPt, DL, Out1, Out2);
537 assert(MRI->getRegClass(Reg)->hasSuperClassEq(&ARM::SPRRegClass) &&
538 "Found unexpected regclass!");
540 unsigned PrefLane = getPrefSPRLane(Reg);
543 case ARM::ssub_0: Lane = 0; break;
544 case ARM::ssub_1: Lane = 1; break;
545 default: llvm_unreachable("Unknown preferred lane!");
548 // Treat DPair as QPR
549 bool UsesQPR = usesRegClass(MI->getOperand(0), &ARM::QPRRegClass) ||
550 usesRegClass(MI->getOperand(0), &ARM::DPairRegClass);
552 Out = createImplicitDef(MBB, InsertPt, DL);
553 Out = createInsertSubreg(MBB, InsertPt, DL, Out, PrefLane, Reg);
554 Out = createDupLane(MBB, InsertPt, DL, Out, Lane, UsesQPR);
555 eraseInstrWithNoUses(MI);
560 bool A15SDOptimizer::runOnInstruction(MachineInstr *MI) {
561 // We look for instructions that write S registers that are then read as
562 // D/Q registers. These can only be caused by COPY, INSERT_SUBREG and
563 // REG_SEQUENCE pseudos that insert an SPR value into a DPR register or
564 // merge two SPR values to form a DPR register. In order avoid false
565 // positives we make sure that there is an SPR producer so we look past
566 // COPY and PHI nodes to find it.
568 // The best code pattern for when an SPR producer is going to be used by a
569 // DPR or QPR consumer depends on whether the other lanes of the
570 // corresponding DPR/QPR are currently defined.
572 // We can handle these efficiently, depending on the type of
573 // pseudo-instruction that is producing the pattern
575 // * COPY: * VDUP all lanes and merge the results together
578 // * INSERT_SUBREG: * If the SPR value was originally in another DPR/QPR
579 // lane, and the other lane(s) of the DPR/QPR register
580 // that we are inserting in are undefined, use the
581 // original DPR/QPR value.
582 // * Otherwise, fall back on the same stategy as COPY.
584 // * REG_SEQUENCE: * If all except one of the input operands are
585 // IMPLICIT_DEFs, insert the VDUP pattern for just the
586 // defined input operand
587 // * Otherwise, fall back on the same stategy as COPY.
590 // First, get all the reads of D-registers done by this instruction.
591 SmallVector<unsigned, 8> Defs = getReadDPRs(MI);
592 bool Modified = false;
594 for (unsigned I : Defs) {
595 // Follow the def-use chain for this DPR through COPYs, and also through
596 // PHIs (which are essentially multi-way COPYs). It is because of PHIs that
597 // we can end up with multiple defs of this DPR.
599 SmallVector<MachineInstr *, 8> DefSrcs;
600 if (!Register::isVirtualRegister(I))
602 MachineInstr *Def = MRI->getVRegDef(I);
606 elideCopiesAndPHIs(Def, DefSrcs);
608 for (MachineInstr *MI : DefSrcs) {
609 // If we've already analyzed and replaced this operand, don't do
611 if (Replacements.find(MI) != Replacements.end())
614 // Now, work out if the instruction causes a SPR->DPR dependency.
615 if (!hasPartialWrite(MI))
618 // Collect all the uses of this MI's DPR def for updating later.
619 SmallVector<MachineOperand*, 8> Uses;
620 Register DPRDefReg = MI->getOperand(0).getReg();
621 for (MachineOperand &MO : MRI->use_operands(DPRDefReg))
624 // We can optimize this.
625 unsigned NewReg = optimizeSDPattern(MI);
629 for (MachineOperand *Use : Uses) {
630 // Make sure to constrain the register class of the new register to
631 // match what we're replacing. Otherwise we can optimize a DPR_VFP2
632 // reference into a plain DPR, and that will end poorly. NewReg is
633 // always virtual here, so there will always be a matching subclass
635 MRI->constrainRegClass(NewReg, MRI->getRegClass(Use->getReg()));
637 LLVM_DEBUG(dbgs() << "Replacing operand " << *Use << " with "
638 << printReg(NewReg) << "\n");
639 Use->substVirtReg(NewReg, 0, *TRI);
642 Replacements[MI] = NewReg;
648 bool A15SDOptimizer::runOnMachineFunction(MachineFunction &Fn) {
649 if (skipFunction(Fn.getFunction()))
652 const ARMSubtarget &STI = Fn.getSubtarget<ARMSubtarget>();
653 // Since the A15SDOptimizer pass can insert VDUP instructions, it can only be
654 // enabled when NEON is available.
655 if (!(STI.useSplatVFPToNeon() && STI.hasNEON()))
658 TII = STI.getInstrInfo();
659 TRI = STI.getRegisterInfo();
660 MRI = &Fn.getRegInfo();
661 bool Modified = false;
663 LLVM_DEBUG(dbgs() << "Running on function " << Fn.getName() << "\n");
666 Replacements.clear();
668 for (MachineBasicBlock &MBB : Fn) {
669 for (MachineInstr &MI : MBB) {
670 Modified |= runOnInstruction(&MI);
674 for (MachineInstr *MI : DeadInstr) {
675 MI->eraseFromParent();
681 FunctionPass *llvm::createA15SDOptimizerPass() {
682 return new A15SDOptimizer();