1 //===-- PeepholeOptimizer.cpp - Peephole Optimizations --------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Perform peephole optimizations on the machine code:
12 // - Optimize Extensions
14 // Optimization of sign / zero extension instructions. It may be extended to
15 // handle other instructions with similar properties.
17 // On some targets, some instructions, e.g. X86 sign / zero extension, may
18 // leave the source value in the lower part of the result. This optimization
19 // will replace some uses of the pre-extension value with uses of the
20 // sub-register of the results.
22 // - Optimize Comparisons
24 // Optimization of comparison instructions. For instance, in this code:
30 // If the "sub" instruction all ready sets (or could be modified to set) the
31 // same flag that the "cmp" instruction sets and that "bz" uses, then we can
32 // eliminate the "cmp" instruction.
34 // Another instance, in this code:
36 // sub r1, r3 | sub r1, imm
37 // cmp r3, r1 or cmp r1, r3 | cmp r1, imm
40 // If the branch instruction can use flag from "sub", then we can replace
41 // "sub" with "subs" and eliminate the "cmp" instruction.
45 // Loads that can be folded into a later instruction. A load is foldable
46 // if it loads to virtual registers and the virtual register defined has
49 // - Optimize Copies and Bitcast (more generally, target specific copies):
51 // Rewrite copies and bitcasts to avoid cross register bank copies
53 // E.g., Consider the following example, where capital and lower
54 // letters denote different register file:
55 // b = copy A <-- cross-bank copy
56 // C = copy b <-- cross-bank copy
58 // b = copy A <-- cross-bank copy
59 // C = copy A <-- same-bank copy
62 // b = bitcast A <-- cross-bank copy
63 // C = bitcast b <-- cross-bank copy
65 // b = bitcast A <-- cross-bank copy
66 // C = copy A <-- same-bank copy
67 //===----------------------------------------------------------------------===//
69 #include "llvm/CodeGen/Passes.h"
70 #include "llvm/ADT/DenseMap.h"
71 #include "llvm/ADT/SmallPtrSet.h"
72 #include "llvm/ADT/SmallSet.h"
73 #include "llvm/ADT/Statistic.h"
74 #include "llvm/CodeGen/MachineDominators.h"
75 #include "llvm/CodeGen/MachineInstrBuilder.h"
76 #include "llvm/CodeGen/MachineRegisterInfo.h"
77 #include "llvm/Support/CommandLine.h"
78 #include "llvm/Support/Debug.h"
79 #include "llvm/Target/TargetInstrInfo.h"
80 #include "llvm/Target/TargetRegisterInfo.h"
81 #include "llvm/Target/TargetSubtargetInfo.h"
85 #define DEBUG_TYPE "peephole-opt"
87 // Optimize Extensions
89 Aggressive("aggressive-ext-opt", cl::Hidden,
90 cl::desc("Aggressive extension optimization"));
93 DisablePeephole("disable-peephole", cl::Hidden, cl::init(false),
94 cl::desc("Disable the peephole optimizer"));
97 DisableAdvCopyOpt("disable-adv-copy-opt", cl::Hidden, cl::init(false),
98 cl::desc("Disable advanced copy optimization"));
100 STATISTIC(NumReuse, "Number of extension results reused");
101 STATISTIC(NumCmps, "Number of compares eliminated");
102 STATISTIC(NumImmFold, "Number of move immediate folded");
103 STATISTIC(NumLoadFold, "Number of loads folded");
104 STATISTIC(NumSelects, "Number of selects optimized");
105 STATISTIC(NumUncoalescableCopies, "Number of uncoalescable copies optimized");
106 STATISTIC(NumRewrittenCopies, "Number of copies rewritten");
109 class PeepholeOptimizer : public MachineFunctionPass {
111 const TargetInstrInfo *TII;
112 const TargetRegisterInfo *TRI;
113 MachineRegisterInfo *MRI;
114 MachineDominatorTree *DT; // Machine dominator tree
117 static char ID; // Pass identification
118 PeepholeOptimizer() : MachineFunctionPass(ID) {
119 initializePeepholeOptimizerPass(*PassRegistry::getPassRegistry());
122 bool runOnMachineFunction(MachineFunction &MF) override;
124 void getAnalysisUsage(AnalysisUsage &AU) const override {
125 AU.setPreservesCFG();
126 MachineFunctionPass::getAnalysisUsage(AU);
128 AU.addRequired<MachineDominatorTree>();
129 AU.addPreserved<MachineDominatorTree>();
134 bool optimizeCmpInstr(MachineInstr *MI, MachineBasicBlock *MBB);
135 bool optimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
136 SmallPtrSetImpl<MachineInstr*> &LocalMIs);
137 bool optimizeSelect(MachineInstr *MI);
138 bool optimizeCopyOrBitcast(MachineInstr *MI);
139 bool optimizeCoalescableCopy(MachineInstr *MI);
140 bool optimizeUncoalescableCopy(MachineInstr *MI,
141 SmallPtrSetImpl<MachineInstr *> &LocalMIs);
142 bool findNextSource(unsigned &Reg, unsigned &SubReg);
143 bool isMoveImmediate(MachineInstr *MI,
144 SmallSet<unsigned, 4> &ImmDefRegs,
145 DenseMap<unsigned, MachineInstr*> &ImmDefMIs);
146 bool foldImmediate(MachineInstr *MI, MachineBasicBlock *MBB,
147 SmallSet<unsigned, 4> &ImmDefRegs,
148 DenseMap<unsigned, MachineInstr*> &ImmDefMIs);
149 bool isLoadFoldable(MachineInstr *MI,
150 SmallSet<unsigned, 16> &FoldAsLoadDefCandidates);
152 /// \brief Check whether \p MI is understood by the register coalescer
153 /// but may require some rewriting.
154 bool isCoalescableCopy(const MachineInstr &MI) {
155 // SubregToRegs are not interesting, because they are already register
156 // coalescer friendly.
157 return MI.isCopy() || (!DisableAdvCopyOpt &&
158 (MI.isRegSequence() || MI.isInsertSubreg() ||
159 MI.isExtractSubreg()));
162 /// \brief Check whether \p MI is a copy like instruction that is
163 /// not recognized by the register coalescer.
164 bool isUncoalescableCopy(const MachineInstr &MI) {
165 return MI.isBitcast() ||
166 (!DisableAdvCopyOpt &&
167 (MI.isRegSequenceLike() || MI.isInsertSubregLike() ||
168 MI.isExtractSubregLike()));
172 /// \brief Helper class to track the possible sources of a value defined by
173 /// a (chain of) copy related instructions.
174 /// Given a definition (instruction and definition index), this class
175 /// follows the use-def chain to find successive suitable sources.
176 /// The given source can be used to rewrite the definition into
179 /// For instance, let us consider the following snippet:
181 /// v2 = INSERT_SUBREG v1, v0, sub0
182 /// def = COPY v2.sub0
184 /// Using a ValueTracker for def = COPY v2.sub0 will give the following
185 /// suitable sources:
187 /// Then, def can be rewritten into def = COPY v0.
190 /// The current point into the use-def chain.
191 const MachineInstr *Def;
192 /// The index of the definition in Def.
194 /// The sub register index of the definition.
196 /// The register where the value can be found.
198 /// Specifiy whether or not the value tracking looks through
199 /// complex instructions. When this is false, the value tracker
200 /// bails on everything that is not a copy or a bitcast.
202 /// Note: This could have been implemented as a specialized version of
203 /// the ValueTracker class but that would have complicated the code of
204 /// the users of this class.
205 bool UseAdvancedTracking;
206 /// MachineRegisterInfo used to perform tracking.
207 const MachineRegisterInfo &MRI;
208 /// Optional TargetInstrInfo used to perform some complex
210 const TargetInstrInfo *TII;
212 /// \brief Dispatcher to the right underlying implementation of
214 bool getNextSourceImpl(unsigned &SrcReg, unsigned &SrcSubReg);
215 /// \brief Specialized version of getNextSource for Copy instructions.
216 bool getNextSourceFromCopy(unsigned &SrcReg, unsigned &SrcSubReg);
217 /// \brief Specialized version of getNextSource for Bitcast instructions.
218 bool getNextSourceFromBitcast(unsigned &SrcReg, unsigned &SrcSubReg);
219 /// \brief Specialized version of getNextSource for RegSequence
221 bool getNextSourceFromRegSequence(unsigned &SrcReg, unsigned &SrcSubReg);
222 /// \brief Specialized version of getNextSource for InsertSubreg
224 bool getNextSourceFromInsertSubreg(unsigned &SrcReg, unsigned &SrcSubReg);
225 /// \brief Specialized version of getNextSource for ExtractSubreg
227 bool getNextSourceFromExtractSubreg(unsigned &SrcReg, unsigned &SrcSubReg);
228 /// \brief Specialized version of getNextSource for SubregToReg
230 bool getNextSourceFromSubregToReg(unsigned &SrcReg, unsigned &SrcSubReg);
233 /// \brief Create a ValueTracker instance for the value defined by \p Reg.
234 /// \p DefSubReg represents the sub register index the value tracker will
235 /// track. It does not need to match the sub register index used in the
236 /// definition of \p Reg.
237 /// \p UseAdvancedTracking specifies whether or not the value tracker looks
238 /// through complex instructions. By default (false), it handles only copy
239 /// and bitcast instructions.
240 /// If \p Reg is a physical register, a value tracker constructed with
241 /// this constructor will not find any alternative source.
242 /// Indeed, when \p Reg is a physical register that constructor does not
243 /// know which definition of \p Reg it should track.
244 /// Use the next constructor to track a physical register.
245 ValueTracker(unsigned Reg, unsigned DefSubReg,
246 const MachineRegisterInfo &MRI,
247 bool UseAdvancedTracking = false,
248 const TargetInstrInfo *TII = nullptr)
249 : Def(nullptr), DefIdx(0), DefSubReg(DefSubReg), Reg(Reg),
250 UseAdvancedTracking(UseAdvancedTracking), MRI(MRI), TII(TII) {
251 if (!TargetRegisterInfo::isPhysicalRegister(Reg)) {
252 Def = MRI.getVRegDef(Reg);
253 DefIdx = MRI.def_begin(Reg).getOperandNo();
257 /// \brief Create a ValueTracker instance for the value defined by
258 /// the pair \p MI, \p DefIdx.
259 /// Unlike the other constructor, the value tracker produced by this one
260 /// may be able to find a new source when the definition is a physical
262 /// This could be useful to rewrite target specific instructions into
263 /// generic copy instructions.
264 ValueTracker(const MachineInstr &MI, unsigned DefIdx, unsigned DefSubReg,
265 const MachineRegisterInfo &MRI,
266 bool UseAdvancedTracking = false,
267 const TargetInstrInfo *TII = nullptr)
268 : Def(&MI), DefIdx(DefIdx), DefSubReg(DefSubReg),
269 UseAdvancedTracking(UseAdvancedTracking), MRI(MRI), TII(TII) {
270 assert(DefIdx < Def->getDesc().getNumDefs() &&
271 Def->getOperand(DefIdx).isReg() && "Invalid definition");
272 Reg = Def->getOperand(DefIdx).getReg();
275 /// \brief Following the use-def chain, get the next available source
276 /// for the tracked value.
277 /// When the returned value is not nullptr, \p SrcReg gives the register
278 /// that contain the tracked value.
279 /// \note The sub register index returned in \p SrcSubReg must be used
280 /// on \p SrcReg to access the actual value.
281 /// \return Unless the returned value is nullptr (i.e., no source found),
282 /// \p SrcReg gives the register of the next source used in the returned
283 /// instruction and \p SrcSubReg the sub-register index to be used on that
284 /// source to get the tracked value. When nullptr is returned, no
285 /// alternative source has been found.
286 const MachineInstr *getNextSource(unsigned &SrcReg, unsigned &SrcSubReg);
288 /// \brief Get the last register where the initial value can be found.
289 /// Initially this is the register of the definition.
290 /// Then, after each successful call to getNextSource, this is the
291 /// register of the last source.
292 unsigned getReg() const { return Reg; }
296 char PeepholeOptimizer::ID = 0;
297 char &llvm::PeepholeOptimizerID = PeepholeOptimizer::ID;
298 INITIALIZE_PASS_BEGIN(PeepholeOptimizer, "peephole-opts",
299 "Peephole Optimizations", false, false)
300 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
301 INITIALIZE_PASS_END(PeepholeOptimizer, "peephole-opts",
302 "Peephole Optimizations", false, false)
304 /// optimizeExtInstr - If instruction is a copy-like instruction, i.e. it reads
305 /// a single register and writes a single register and it does not modify the
306 /// source, and if the source value is preserved as a sub-register of the
307 /// result, then replace all reachable uses of the source with the subreg of the
310 /// Do not generate an EXTRACT that is used only in a debug use, as this changes
311 /// the code. Since this code does not currently share EXTRACTs, just ignore all
313 bool PeepholeOptimizer::
314 optimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
315 SmallPtrSetImpl<MachineInstr*> &LocalMIs) {
316 unsigned SrcReg, DstReg, SubIdx;
317 if (!TII->isCoalescableExtInstr(*MI, SrcReg, DstReg, SubIdx))
320 if (TargetRegisterInfo::isPhysicalRegister(DstReg) ||
321 TargetRegisterInfo::isPhysicalRegister(SrcReg))
324 if (MRI->hasOneNonDBGUse(SrcReg))
328 // Ensure DstReg can get a register class that actually supports
329 // sub-registers. Don't change the class until we commit.
330 const TargetRegisterClass *DstRC = MRI->getRegClass(DstReg);
331 DstRC = TRI->getSubClassWithSubReg(DstRC, SubIdx);
335 // The ext instr may be operating on a sub-register of SrcReg as well.
336 // PPC::EXTSW is a 32 -> 64-bit sign extension, but it reads a 64-bit
338 // If UseSrcSubIdx is Set, SubIdx also applies to SrcReg, and only uses of
339 // SrcReg:SubIdx should be replaced.
341 TRI->getSubClassWithSubReg(MRI->getRegClass(SrcReg), SubIdx) != nullptr;
343 // The source has other uses. See if we can replace the other uses with use of
344 // the result of the extension.
345 SmallPtrSet<MachineBasicBlock*, 4> ReachedBBs;
346 for (MachineInstr &UI : MRI->use_nodbg_instructions(DstReg))
347 ReachedBBs.insert(UI.getParent());
349 // Uses that are in the same BB of uses of the result of the instruction.
350 SmallVector<MachineOperand*, 8> Uses;
352 // Uses that the result of the instruction can reach.
353 SmallVector<MachineOperand*, 8> ExtendedUses;
355 bool ExtendLife = true;
356 for (MachineOperand &UseMO : MRI->use_nodbg_operands(SrcReg)) {
357 MachineInstr *UseMI = UseMO.getParent();
361 if (UseMI->isPHI()) {
366 // Only accept uses of SrcReg:SubIdx.
367 if (UseSrcSubIdx && UseMO.getSubReg() != SubIdx)
370 // It's an error to translate this:
372 // %reg1025 = <sext> %reg1024
374 // %reg1026 = SUBREG_TO_REG 0, %reg1024, 4
378 // %reg1025 = <sext> %reg1024
380 // %reg1027 = COPY %reg1025:4
381 // %reg1026 = SUBREG_TO_REG 0, %reg1027, 4
383 // The problem here is that SUBREG_TO_REG is there to assert that an
384 // implicit zext occurs. It doesn't insert a zext instruction. If we allow
385 // the COPY here, it will give us the value after the <sext>, not the
386 // original value of %reg1024 before <sext>.
387 if (UseMI->getOpcode() == TargetOpcode::SUBREG_TO_REG)
390 MachineBasicBlock *UseMBB = UseMI->getParent();
392 // Local uses that come after the extension.
393 if (!LocalMIs.count(UseMI))
394 Uses.push_back(&UseMO);
395 } else if (ReachedBBs.count(UseMBB)) {
396 // Non-local uses where the result of the extension is used. Always
397 // replace these unless it's a PHI.
398 Uses.push_back(&UseMO);
399 } else if (Aggressive && DT->dominates(MBB, UseMBB)) {
400 // We may want to extend the live range of the extension result in order
401 // to replace these uses.
402 ExtendedUses.push_back(&UseMO);
404 // Both will be live out of the def MBB anyway. Don't extend live range of
405 // the extension result.
411 if (ExtendLife && !ExtendedUses.empty())
412 // Extend the liveness of the extension result.
413 std::copy(ExtendedUses.begin(), ExtendedUses.end(),
414 std::back_inserter(Uses));
416 // Now replace all uses.
417 bool Changed = false;
419 SmallPtrSet<MachineBasicBlock*, 4> PHIBBs;
421 // Look for PHI uses of the extended result, we don't want to extend the
422 // liveness of a PHI input. It breaks all kinds of assumptions down
423 // stream. A PHI use is expected to be the kill of its source values.
424 for (MachineInstr &UI : MRI->use_nodbg_instructions(DstReg))
426 PHIBBs.insert(UI.getParent());
428 const TargetRegisterClass *RC = MRI->getRegClass(SrcReg);
429 for (unsigned i = 0, e = Uses.size(); i != e; ++i) {
430 MachineOperand *UseMO = Uses[i];
431 MachineInstr *UseMI = UseMO->getParent();
432 MachineBasicBlock *UseMBB = UseMI->getParent();
433 if (PHIBBs.count(UseMBB))
436 // About to add uses of DstReg, clear DstReg's kill flags.
438 MRI->clearKillFlags(DstReg);
439 MRI->constrainRegClass(DstReg, DstRC);
442 unsigned NewVR = MRI->createVirtualRegister(RC);
443 MachineInstr *Copy = BuildMI(*UseMBB, UseMI, UseMI->getDebugLoc(),
444 TII->get(TargetOpcode::COPY), NewVR)
445 .addReg(DstReg, 0, SubIdx);
446 // SubIdx applies to both SrcReg and DstReg when UseSrcSubIdx is set.
448 Copy->getOperand(0).setSubReg(SubIdx);
449 Copy->getOperand(0).setIsUndef();
451 UseMO->setReg(NewVR);
460 /// optimizeCmpInstr - If the instruction is a compare and the previous
461 /// instruction it's comparing against all ready sets (or could be modified to
462 /// set) the same flag as the compare, then we can remove the comparison and use
463 /// the flag from the previous instruction.
464 bool PeepholeOptimizer::optimizeCmpInstr(MachineInstr *MI,
465 MachineBasicBlock *MBB) {
466 // If this instruction is a comparison against zero and isn't comparing a
467 // physical register, we can try to optimize it.
468 unsigned SrcReg, SrcReg2;
469 int CmpMask, CmpValue;
470 if (!TII->analyzeCompare(MI, SrcReg, SrcReg2, CmpMask, CmpValue) ||
471 TargetRegisterInfo::isPhysicalRegister(SrcReg) ||
472 (SrcReg2 != 0 && TargetRegisterInfo::isPhysicalRegister(SrcReg2)))
475 // Attempt to optimize the comparison instruction.
476 if (TII->optimizeCompareInstr(MI, SrcReg, SrcReg2, CmpMask, CmpValue, MRI)) {
484 /// Optimize a select instruction.
485 bool PeepholeOptimizer::optimizeSelect(MachineInstr *MI) {
487 unsigned FalseOp = 0;
488 bool Optimizable = false;
489 SmallVector<MachineOperand, 4> Cond;
490 if (TII->analyzeSelect(MI, Cond, TrueOp, FalseOp, Optimizable))
494 if (!TII->optimizeSelect(MI))
496 MI->eraseFromParent();
501 /// \brief Check if the registers defined by the pair (RegisterClass, SubReg)
502 /// share the same register file.
503 static bool shareSameRegisterFile(const TargetRegisterInfo &TRI,
504 const TargetRegisterClass *DefRC,
506 const TargetRegisterClass *SrcRC,
507 unsigned SrcSubReg) {
508 // Same register class.
512 // Both operands are sub registers. Check if they share a register class.
513 unsigned SrcIdx, DefIdx;
514 if (SrcSubReg && DefSubReg)
515 return TRI.getCommonSuperRegClass(SrcRC, SrcSubReg, DefRC, DefSubReg,
516 SrcIdx, DefIdx) != nullptr;
517 // At most one of the register is a sub register, make it Src to avoid
518 // duplicating the test.
520 std::swap(DefSubReg, SrcSubReg);
521 std::swap(DefRC, SrcRC);
524 // One of the register is a sub register, check if we can get a superclass.
526 return TRI.getMatchingSuperRegClass(SrcRC, DefRC, SrcSubReg) != nullptr;
528 return TRI.getCommonSubClass(DefRC, SrcRC) != nullptr;
531 /// \brief Try to find the next source that share the same register file
532 /// for the value defined by \p Reg and \p SubReg.
533 /// When true is returned, \p Reg and \p SubReg are updated with the
534 /// register number and sub-register index of the new source.
535 /// \return False if no alternative sources are available. True otherwise.
536 bool PeepholeOptimizer::findNextSource(unsigned &Reg, unsigned &SubReg) {
537 // Do not try to find a new source for a physical register.
538 // So far we do not have any motivating example for doing that.
539 // Thus, instead of maintaining untested code, we will revisit that if
540 // that changes at some point.
541 if (TargetRegisterInfo::isPhysicalRegister(Reg))
544 const TargetRegisterClass *DefRC = MRI->getRegClass(Reg);
545 unsigned DefSubReg = SubReg;
549 bool ShouldRewrite = false;
551 // Follow the chain of copies until we reach the top of the use-def chain
552 // or find a more suitable source.
553 ValueTracker ValTracker(Reg, DefSubReg, *MRI, !DisableAdvCopyOpt, TII);
555 unsigned CopySrcReg, CopySrcSubReg;
556 if (!ValTracker.getNextSource(CopySrcReg, CopySrcSubReg))
559 SrcSubReg = CopySrcSubReg;
561 // Do not extend the live-ranges of physical registers as they add
562 // constraints to the register allocator.
563 // Moreover, if we want to extend the live-range of a physical register,
564 // unlike SSA virtual register, we will have to check that they are not
565 // redefine before the related use.
566 if (TargetRegisterInfo::isPhysicalRegister(Src))
569 const TargetRegisterClass *SrcRC = MRI->getRegClass(Src);
571 // If this source does not incur a cross register bank copy, use it.
572 ShouldRewrite = shareSameRegisterFile(*TRI, DefRC, DefSubReg, SrcRC,
574 } while (!ShouldRewrite);
576 // If we did not find a more suitable source, there is nothing to optimize.
577 if (!ShouldRewrite || Src == Reg)
586 /// \brief Helper class to rewrite the arguments of a copy-like instruction.
589 /// The copy-like instruction.
590 MachineInstr &CopyLike;
591 /// The index of the source being rewritten.
592 unsigned CurrentSrcIdx;
595 CopyRewriter(MachineInstr &MI) : CopyLike(MI), CurrentSrcIdx(0) {}
597 virtual ~CopyRewriter() {}
599 /// \brief Get the next rewritable source (SrcReg, SrcSubReg) and
600 /// the related value that it affects (TrackReg, TrackSubReg).
601 /// A source is considered rewritable if its register class and the
602 /// register class of the related TrackReg may not be register
603 /// coalescer friendly. In other words, given a copy-like instruction
604 /// not all the arguments may be returned at rewritable source, since
605 /// some arguments are none to be register coalescer friendly.
607 /// Each call of this method moves the current source to the next
608 /// rewritable source.
609 /// For instance, let CopyLike be the instruction to rewrite.
610 /// CopyLike has one definition and one source:
611 /// dst.dstSubIdx = CopyLike src.srcSubIdx.
613 /// The first call will give the first rewritable source, i.e.,
614 /// the only source this instruction has:
615 /// (SrcReg, SrcSubReg) = (src, srcSubIdx).
616 /// This source defines the whole definition, i.e.,
617 /// (TrackReg, TrackSubReg) = (dst, dstSubIdx).
619 /// The second and subsequent calls will return false, has there is only one
620 /// rewritable source.
622 /// \return True if a rewritable source has been found, false otherwise.
623 /// The output arguments are valid if and only if true is returned.
624 virtual bool getNextRewritableSource(unsigned &SrcReg, unsigned &SrcSubReg,
626 unsigned &TrackSubReg) {
627 // If CurrentSrcIdx == 1, this means this function has already been
628 // called once. CopyLike has one defintiion and one argument, thus,
629 // there is nothing else to rewrite.
630 if (!CopyLike.isCopy() || CurrentSrcIdx == 1)
632 // This is the first call to getNextRewritableSource.
633 // Move the CurrentSrcIdx to remember that we made that call.
635 // The rewritable source is the argument.
636 const MachineOperand &MOSrc = CopyLike.getOperand(1);
637 SrcReg = MOSrc.getReg();
638 SrcSubReg = MOSrc.getSubReg();
639 // What we track are the alternative sources of the definition.
640 const MachineOperand &MODef = CopyLike.getOperand(0);
641 TrackReg = MODef.getReg();
642 TrackSubReg = MODef.getSubReg();
646 /// \brief Rewrite the current source with \p NewReg and \p NewSubReg
648 /// \return True if the rewritting was possible, false otherwise.
649 virtual bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) {
650 if (!CopyLike.isCopy() || CurrentSrcIdx != 1)
652 MachineOperand &MOSrc = CopyLike.getOperand(CurrentSrcIdx);
653 MOSrc.setReg(NewReg);
654 MOSrc.setSubReg(NewSubReg);
659 /// \brief Specialized rewriter for INSERT_SUBREG instruction.
660 class InsertSubregRewriter : public CopyRewriter {
662 InsertSubregRewriter(MachineInstr &MI) : CopyRewriter(MI) {
663 assert(MI.isInsertSubreg() && "Invalid instruction");
666 /// \brief See CopyRewriter::getNextRewritableSource.
667 /// Here CopyLike has the following form:
668 /// dst = INSERT_SUBREG Src1, Src2.src2SubIdx, subIdx.
669 /// Src1 has the same register class has dst, hence, there is
670 /// nothing to rewrite.
671 /// Src2.src2SubIdx, may not be register coalescer friendly.
672 /// Therefore, the first call to this method returns:
673 /// (SrcReg, SrcSubReg) = (Src2, src2SubIdx).
674 /// (TrackReg, TrackSubReg) = (dst, subIdx).
676 /// Subsequence calls will return false.
677 bool getNextRewritableSource(unsigned &SrcReg, unsigned &SrcSubReg,
679 unsigned &TrackSubReg) override {
680 // If we already get the only source we can rewrite, return false.
681 if (CurrentSrcIdx == 2)
683 // We are looking at v2 = INSERT_SUBREG v0, v1, sub0.
685 const MachineOperand &MOInsertedReg = CopyLike.getOperand(2);
686 SrcReg = MOInsertedReg.getReg();
687 SrcSubReg = MOInsertedReg.getSubReg();
688 const MachineOperand &MODef = CopyLike.getOperand(0);
690 // We want to track something that is compatible with the
691 // partial definition.
692 TrackReg = MODef.getReg();
693 if (MODef.getSubReg())
694 // Bails if we have to compose sub-register indices.
696 TrackSubReg = (unsigned)CopyLike.getOperand(3).getImm();
699 bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override {
700 if (CurrentSrcIdx != 2)
702 // We are rewriting the inserted reg.
703 MachineOperand &MO = CopyLike.getOperand(CurrentSrcIdx);
705 MO.setSubReg(NewSubReg);
710 /// \brief Specialized rewriter for EXTRACT_SUBREG instruction.
711 class ExtractSubregRewriter : public CopyRewriter {
712 const TargetInstrInfo &TII;
715 ExtractSubregRewriter(MachineInstr &MI, const TargetInstrInfo &TII)
716 : CopyRewriter(MI), TII(TII) {
717 assert(MI.isExtractSubreg() && "Invalid instruction");
720 /// \brief See CopyRewriter::getNextRewritableSource.
721 /// Here CopyLike has the following form:
722 /// dst.dstSubIdx = EXTRACT_SUBREG Src, subIdx.
723 /// There is only one rewritable source: Src.subIdx,
724 /// which defines dst.dstSubIdx.
725 bool getNextRewritableSource(unsigned &SrcReg, unsigned &SrcSubReg,
727 unsigned &TrackSubReg) override {
728 // If we already get the only source we can rewrite, return false.
729 if (CurrentSrcIdx == 1)
731 // We are looking at v1 = EXTRACT_SUBREG v0, sub0.
733 const MachineOperand &MOExtractedReg = CopyLike.getOperand(1);
734 SrcReg = MOExtractedReg.getReg();
735 // If we have to compose sub-register indices, bails out.
736 if (MOExtractedReg.getSubReg())
739 SrcSubReg = CopyLike.getOperand(2).getImm();
741 // We want to track something that is compatible with the definition.
742 const MachineOperand &MODef = CopyLike.getOperand(0);
743 TrackReg = MODef.getReg();
744 TrackSubReg = MODef.getSubReg();
748 bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override {
749 // The only source we can rewrite is the input register.
750 if (CurrentSrcIdx != 1)
753 CopyLike.getOperand(CurrentSrcIdx).setReg(NewReg);
755 // If we find a source that does not require to extract something,
756 // rewrite the operation with a copy.
758 // Move the current index to an invalid position.
759 // We do not want another call to this method to be able
762 // Rewrite the operation as a COPY.
763 // Get rid of the sub-register index.
764 CopyLike.RemoveOperand(2);
765 // Morph the operation into a COPY.
766 CopyLike.setDesc(TII.get(TargetOpcode::COPY));
769 CopyLike.getOperand(CurrentSrcIdx + 1).setImm(NewSubReg);
774 /// \brief Specialized rewriter for REG_SEQUENCE instruction.
775 class RegSequenceRewriter : public CopyRewriter {
777 RegSequenceRewriter(MachineInstr &MI) : CopyRewriter(MI) {
778 assert(MI.isRegSequence() && "Invalid instruction");
781 /// \brief See CopyRewriter::getNextRewritableSource.
782 /// Here CopyLike has the following form:
783 /// dst = REG_SEQUENCE Src1.src1SubIdx, subIdx1, Src2.src2SubIdx, subIdx2.
784 /// Each call will return a different source, walking all the available
787 /// The first call returns:
788 /// (SrcReg, SrcSubReg) = (Src1, src1SubIdx).
789 /// (TrackReg, TrackSubReg) = (dst, subIdx1).
791 /// The second call returns:
792 /// (SrcReg, SrcSubReg) = (Src2, src2SubIdx).
793 /// (TrackReg, TrackSubReg) = (dst, subIdx2).
795 /// And so on, until all the sources have been traversed, then
796 /// it returns false.
797 bool getNextRewritableSource(unsigned &SrcReg, unsigned &SrcSubReg,
799 unsigned &TrackSubReg) override {
800 // We are looking at v0 = REG_SEQUENCE v1, sub1, v2, sub2, etc.
802 // If this is the first call, move to the first argument.
803 if (CurrentSrcIdx == 0) {
806 // Otherwise, move to the next argument and check that it is valid.
808 if (CurrentSrcIdx >= CopyLike.getNumOperands())
811 const MachineOperand &MOInsertedReg = CopyLike.getOperand(CurrentSrcIdx);
812 SrcReg = MOInsertedReg.getReg();
813 // If we have to compose sub-register indices, bails out.
814 if ((SrcSubReg = MOInsertedReg.getSubReg()))
817 // We want to track something that is compatible with the related
818 // partial definition.
819 TrackSubReg = CopyLike.getOperand(CurrentSrcIdx + 1).getImm();
821 const MachineOperand &MODef = CopyLike.getOperand(0);
822 TrackReg = MODef.getReg();
823 // If we have to compose sub-registers, bails.
824 return MODef.getSubReg() == 0;
827 bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override {
828 // We cannot rewrite out of bound operands.
829 // Moreover, rewritable sources are at odd positions.
830 if ((CurrentSrcIdx & 1) != 1 || CurrentSrcIdx > CopyLike.getNumOperands())
833 MachineOperand &MO = CopyLike.getOperand(CurrentSrcIdx);
835 MO.setSubReg(NewSubReg);
841 /// \brief Get the appropriated CopyRewriter for \p MI.
842 /// \return A pointer to a dynamically allocated CopyRewriter or nullptr
843 /// if no rewriter works for \p MI.
844 static CopyRewriter *getCopyRewriter(MachineInstr &MI,
845 const TargetInstrInfo &TII) {
846 switch (MI.getOpcode()) {
849 case TargetOpcode::COPY:
850 return new CopyRewriter(MI);
851 case TargetOpcode::INSERT_SUBREG:
852 return new InsertSubregRewriter(MI);
853 case TargetOpcode::EXTRACT_SUBREG:
854 return new ExtractSubregRewriter(MI, TII);
855 case TargetOpcode::REG_SEQUENCE:
856 return new RegSequenceRewriter(MI);
858 llvm_unreachable(nullptr);
861 /// \brief Optimize generic copy instructions to avoid cross
862 /// register bank copy. The optimization looks through a chain of
863 /// copies and tries to find a source that has a compatible register
865 /// Two register classes are considered to be compatible if they share
866 /// the same register bank.
867 /// New copies issued by this optimization are register allocator
868 /// friendly. This optimization does not remove any copy as it may
869 /// overconstraint the register allocator, but replaces some operands
871 /// \pre isCoalescableCopy(*MI) is true.
872 /// \return True, when \p MI has been rewritten. False otherwise.
873 bool PeepholeOptimizer::optimizeCoalescableCopy(MachineInstr *MI) {
874 assert(MI && isCoalescableCopy(*MI) && "Invalid argument");
875 assert(MI->getDesc().getNumDefs() == 1 &&
876 "Coalescer can understand multiple defs?!");
877 const MachineOperand &MODef = MI->getOperand(0);
878 // Do not rewrite physical definitions.
879 if (TargetRegisterInfo::isPhysicalRegister(MODef.getReg()))
882 bool Changed = false;
883 // Get the right rewriter for the current copy.
884 std::unique_ptr<CopyRewriter> CpyRewriter(getCopyRewriter(*MI, *TII));
885 // If none exists, bails out.
888 // Rewrite each rewritable source.
889 unsigned SrcReg, SrcSubReg, TrackReg, TrackSubReg;
890 while (CpyRewriter->getNextRewritableSource(SrcReg, SrcSubReg, TrackReg,
892 unsigned NewSrc = TrackReg;
893 unsigned NewSubReg = TrackSubReg;
894 // Try to find a more suitable source.
895 // If we failed to do so, or get the actual source,
896 // move to the next source.
897 if (!findNextSource(NewSrc, NewSubReg) || SrcReg == NewSrc)
900 if (CpyRewriter->RewriteCurrentSource(NewSrc, NewSubReg)) {
901 // We may have extended the live-range of NewSrc, account for that.
902 MRI->clearKillFlags(NewSrc);
906 // TODO: We could have a clean-up method to tidy the instruction.
907 // E.g., v0 = INSERT_SUBREG v1, v1.sub0, sub0
909 // Currently we haven't seen motivating example for that and we
910 // want to avoid untested code.
911 NumRewrittenCopies += Changed == true;
915 /// \brief Optimize copy-like instructions to create
916 /// register coalescer friendly instruction.
917 /// The optimization tries to kill-off the \p MI by looking
918 /// through a chain of copies to find a source that has a compatible
920 /// If such a source is found, it replace \p MI by a generic COPY
922 /// \pre isUncoalescableCopy(*MI) is true.
923 /// \return True, when \p MI has been optimized. In that case, \p MI has
924 /// been removed from its parent.
925 /// All COPY instructions created, are inserted in \p LocalMIs.
926 bool PeepholeOptimizer::optimizeUncoalescableCopy(
927 MachineInstr *MI, SmallPtrSetImpl<MachineInstr *> &LocalMIs) {
928 assert(MI && isUncoalescableCopy(*MI) && "Invalid argument");
930 // Check if we can rewrite all the values defined by this instruction.
932 std::pair<TargetInstrInfo::RegSubRegPair, TargetInstrInfo::RegSubRegPair>,
934 for (const MachineOperand &MODef : MI->defs()) {
936 // We can ignore those.
939 // If a physical register is here, this is probably for a good reason.
940 // Do not rewrite that.
941 if (TargetRegisterInfo::isPhysicalRegister(MODef.getReg()))
944 // If we do not know how to rewrite this definition, there is no point
945 // in trying to kill this instruction.
946 TargetInstrInfo::RegSubRegPair Def(MODef.getReg(), MODef.getSubReg());
947 TargetInstrInfo::RegSubRegPair Src = Def;
948 if (!findNextSource(Src.Reg, Src.SubReg))
950 RewritePairs.push_back(std::make_pair(Def, Src));
952 // The change is possible for all defs, do it.
953 for (const auto &PairDefSrc : RewritePairs) {
954 const auto &Def = PairDefSrc.first;
955 const auto &Src = PairDefSrc.second;
956 // Rewrite the "copy" in a way the register coalescer understands.
957 assert(!TargetRegisterInfo::isPhysicalRegister(Def.Reg) &&
958 "We do not rewrite physical registers");
959 const TargetRegisterClass *DefRC = MRI->getRegClass(Def.Reg);
960 unsigned NewVR = MRI->createVirtualRegister(DefRC);
961 MachineInstr *NewCopy = BuildMI(*MI->getParent(), MI, MI->getDebugLoc(),
962 TII->get(TargetOpcode::COPY),
963 NewVR).addReg(Src.Reg, 0, Src.SubReg);
964 NewCopy->getOperand(0).setSubReg(Def.SubReg);
966 NewCopy->getOperand(0).setIsUndef();
967 LocalMIs.insert(NewCopy);
968 MRI->replaceRegWith(Def.Reg, NewVR);
969 MRI->clearKillFlags(NewVR);
970 // We extended the lifetime of Src.
971 // Clear the kill flags to account for that.
972 MRI->clearKillFlags(Src.Reg);
975 MI->eraseFromParent();
976 ++NumUncoalescableCopies;
980 /// isLoadFoldable - Check whether MI is a candidate for folding into a later
981 /// instruction. We only fold loads to virtual registers and the virtual
982 /// register defined has a single use.
983 bool PeepholeOptimizer::isLoadFoldable(
985 SmallSet<unsigned, 16> &FoldAsLoadDefCandidates) {
986 if (!MI->canFoldAsLoad() || !MI->mayLoad())
988 const MCInstrDesc &MCID = MI->getDesc();
989 if (MCID.getNumDefs() != 1)
992 unsigned Reg = MI->getOperand(0).getReg();
993 // To reduce compilation time, we check MRI->hasOneNonDBGUse when inserting
994 // loads. It should be checked when processing uses of the load, since
995 // uses can be removed during peephole.
996 if (!MI->getOperand(0).getSubReg() &&
997 TargetRegisterInfo::isVirtualRegister(Reg) &&
998 MRI->hasOneNonDBGUse(Reg)) {
999 FoldAsLoadDefCandidates.insert(Reg);
1005 bool PeepholeOptimizer::isMoveImmediate(MachineInstr *MI,
1006 SmallSet<unsigned, 4> &ImmDefRegs,
1007 DenseMap<unsigned, MachineInstr*> &ImmDefMIs) {
1008 const MCInstrDesc &MCID = MI->getDesc();
1009 if (!MI->isMoveImmediate())
1011 if (MCID.getNumDefs() != 1)
1013 unsigned Reg = MI->getOperand(0).getReg();
1014 if (TargetRegisterInfo::isVirtualRegister(Reg)) {
1015 ImmDefMIs.insert(std::make_pair(Reg, MI));
1016 ImmDefRegs.insert(Reg);
1023 /// foldImmediate - Try folding register operands that are defined by move
1024 /// immediate instructions, i.e. a trivial constant folding optimization, if
1025 /// and only if the def and use are in the same BB.
1026 bool PeepholeOptimizer::foldImmediate(MachineInstr *MI, MachineBasicBlock *MBB,
1027 SmallSet<unsigned, 4> &ImmDefRegs,
1028 DenseMap<unsigned, MachineInstr*> &ImmDefMIs) {
1029 for (unsigned i = 0, e = MI->getDesc().getNumOperands(); i != e; ++i) {
1030 MachineOperand &MO = MI->getOperand(i);
1031 if (!MO.isReg() || MO.isDef())
1033 unsigned Reg = MO.getReg();
1034 if (!TargetRegisterInfo::isVirtualRegister(Reg))
1036 if (ImmDefRegs.count(Reg) == 0)
1038 DenseMap<unsigned, MachineInstr*>::iterator II = ImmDefMIs.find(Reg);
1039 assert(II != ImmDefMIs.end());
1040 if (TII->FoldImmediate(MI, II->second, Reg, MRI)) {
1048 bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &mf) {
1049 if (skipOptnoneFunction(*mf.getFunction()))
1052 DEBUG(dbgs() << "********** PEEPHOLE OPTIMIZER **********\n");
1053 DEBUG(dbgs() << "********** Function: " << mf.getName() << '\n');
1055 if (DisablePeephole)
1059 TII = MF->getSubtarget().getInstrInfo();
1060 TRI = MF->getSubtarget().getRegisterInfo();
1061 MRI = &MF->getRegInfo();
1062 DT = Aggressive ? &getAnalysis<MachineDominatorTree>() : nullptr;
1064 bool Changed = false;
1066 for (MachineFunction::iterator I = MF->begin(), E = MF->end(); I != E; ++I) {
1067 MachineBasicBlock *MBB = &*I;
1069 bool SeenMoveImm = false;
1070 SmallPtrSet<MachineInstr*, 16> LocalMIs;
1071 SmallSet<unsigned, 4> ImmDefRegs;
1072 DenseMap<unsigned, MachineInstr*> ImmDefMIs;
1073 SmallSet<unsigned, 16> FoldAsLoadDefCandidates;
1075 for (MachineBasicBlock::iterator
1076 MII = I->begin(), MIE = I->end(); MII != MIE; ) {
1077 MachineInstr *MI = &*MII;
1078 // We may be erasing MI below, increment MII now.
1080 LocalMIs.insert(MI);
1082 // Skip debug values. They should not affect this peephole optimization.
1083 if (MI->isDebugValue())
1086 // If there exists an instruction which belongs to the following
1087 // categories, we will discard the load candidates.
1088 if (MI->isPosition() || MI->isPHI() || MI->isImplicitDef() ||
1089 MI->isKill() || MI->isInlineAsm() ||
1090 MI->hasUnmodeledSideEffects()) {
1091 FoldAsLoadDefCandidates.clear();
1094 if (MI->mayStore() || MI->isCall())
1095 FoldAsLoadDefCandidates.clear();
1097 if ((isUncoalescableCopy(*MI) &&
1098 optimizeUncoalescableCopy(MI, LocalMIs)) ||
1099 (MI->isCompare() && optimizeCmpInstr(MI, MBB)) ||
1100 (MI->isSelect() && optimizeSelect(MI))) {
1107 if (isCoalescableCopy(*MI) && optimizeCoalescableCopy(MI)) {
1108 // MI is just rewritten.
1113 if (isMoveImmediate(MI, ImmDefRegs, ImmDefMIs)) {
1116 Changed |= optimizeExtInstr(MI, MBB, LocalMIs);
1117 // optimizeExtInstr might have created new instructions after MI
1118 // and before the already incremented MII. Adjust MII so that the
1119 // next iteration sees the new instructions.
1123 Changed |= foldImmediate(MI, MBB, ImmDefRegs, ImmDefMIs);
1126 // Check whether MI is a load candidate for folding into a later
1127 // instruction. If MI is not a candidate, check whether we can fold an
1128 // earlier load into MI.
1129 if (!isLoadFoldable(MI, FoldAsLoadDefCandidates) &&
1130 !FoldAsLoadDefCandidates.empty()) {
1131 const MCInstrDesc &MIDesc = MI->getDesc();
1132 for (unsigned i = MIDesc.getNumDefs(); i != MIDesc.getNumOperands();
1134 const MachineOperand &MOp = MI->getOperand(i);
1137 unsigned FoldAsLoadDefReg = MOp.getReg();
1138 if (FoldAsLoadDefCandidates.count(FoldAsLoadDefReg)) {
1139 // We need to fold load after optimizeCmpInstr, since
1140 // optimizeCmpInstr can enable folding by converting SUB to CMP.
1141 // Save FoldAsLoadDefReg because optimizeLoadInstr() resets it and
1142 // we need it for markUsesInDebugValueAsUndef().
1143 unsigned FoldedReg = FoldAsLoadDefReg;
1144 MachineInstr *DefMI = nullptr;
1145 MachineInstr *FoldMI = TII->optimizeLoadInstr(MI, MRI,
1149 // Update LocalMIs since we replaced MI with FoldMI and deleted
1151 DEBUG(dbgs() << "Replacing: " << *MI);
1152 DEBUG(dbgs() << " With: " << *FoldMI);
1154 LocalMIs.erase(DefMI);
1155 LocalMIs.insert(FoldMI);
1156 MI->eraseFromParent();
1157 DefMI->eraseFromParent();
1158 MRI->markUsesInDebugValueAsUndef(FoldedReg);
1159 FoldAsLoadDefCandidates.erase(FoldedReg);
1161 // MI is replaced with FoldMI.
1174 bool ValueTracker::getNextSourceFromCopy(unsigned &SrcReg,
1175 unsigned &SrcSubReg) {
1176 assert(Def->isCopy() && "Invalid definition");
1177 // Copy instruction are supposed to be: Def = Src.
1178 // If someone breaks this assumption, bad things will happen everywhere.
1179 assert(Def->getNumOperands() == 2 && "Invalid number of operands");
1181 if (Def->getOperand(DefIdx).getSubReg() != DefSubReg)
1182 // If we look for a different subreg, it means we want a subreg of src.
1183 // Bails as we do not support composing subreg yet.
1185 // Otherwise, we want the whole source.
1186 const MachineOperand &Src = Def->getOperand(1);
1187 SrcReg = Src.getReg();
1188 SrcSubReg = Src.getSubReg();
1192 bool ValueTracker::getNextSourceFromBitcast(unsigned &SrcReg,
1193 unsigned &SrcSubReg) {
1194 assert(Def->isBitcast() && "Invalid definition");
1196 // Bail if there are effects that a plain copy will not expose.
1197 if (Def->hasUnmodeledSideEffects())
1200 // Bitcasts with more than one def are not supported.
1201 if (Def->getDesc().getNumDefs() != 1)
1203 if (Def->getOperand(DefIdx).getSubReg() != DefSubReg)
1204 // If we look for a different subreg, it means we want a subreg of the src.
1205 // Bails as we do not support composing subreg yet.
1208 unsigned SrcIdx = Def->getNumOperands();
1209 for (unsigned OpIdx = DefIdx + 1, EndOpIdx = SrcIdx; OpIdx != EndOpIdx;
1211 const MachineOperand &MO = Def->getOperand(OpIdx);
1212 if (!MO.isReg() || !MO.getReg())
1214 assert(!MO.isDef() && "We should have skipped all the definitions by now");
1215 if (SrcIdx != EndOpIdx)
1216 // Multiple sources?
1220 const MachineOperand &Src = Def->getOperand(SrcIdx);
1221 SrcReg = Src.getReg();
1222 SrcSubReg = Src.getSubReg();
1226 bool ValueTracker::getNextSourceFromRegSequence(unsigned &SrcReg,
1227 unsigned &SrcSubReg) {
1228 assert((Def->isRegSequence() || Def->isRegSequenceLike()) &&
1229 "Invalid definition");
1231 if (Def->getOperand(DefIdx).getSubReg())
1232 // If we are composing subreg, bails out.
1233 // The case we are checking is Def.<subreg> = REG_SEQUENCE.
1234 // This should almost never happen as the SSA property is tracked at
1235 // the register level (as opposed to the subreg level).
1239 // is a valid SSA representation for Def.sub0 and Def.sub1, but not for
1240 // Def. Thus, it must not be generated.
1241 // However, some code could theoretically generates a single
1242 // Def.sub0 (i.e, not defining the other subregs) and we would
1244 // If we can ascertain (or force) that this never happens, we could
1245 // turn that into an assertion.
1249 // We could handle the REG_SEQUENCE here, but we do not want to
1250 // duplicate the code from the generic TII.
1253 SmallVector<TargetInstrInfo::RegSubRegPairAndIdx, 8> RegSeqInputRegs;
1254 if (!TII->getRegSequenceInputs(*Def, DefIdx, RegSeqInputRegs))
1257 // We are looking at:
1258 // Def = REG_SEQUENCE v0, sub0, v1, sub1, ...
1259 // Check if one of the operand defines the subreg we are interested in.
1260 for (auto &RegSeqInput : RegSeqInputRegs) {
1261 if (RegSeqInput.SubIdx == DefSubReg) {
1262 if (RegSeqInput.SubReg)
1263 // Bails if we have to compose sub registers.
1266 SrcReg = RegSeqInput.Reg;
1267 SrcSubReg = RegSeqInput.SubReg;
1272 // If the subreg we are tracking is super-defined by another subreg,
1273 // we could follow this value. However, this would require to compose
1274 // the subreg and we do not do that for now.
1278 bool ValueTracker::getNextSourceFromInsertSubreg(unsigned &SrcReg,
1279 unsigned &SrcSubReg) {
1280 assert((Def->isInsertSubreg() || Def->isInsertSubregLike()) &&
1281 "Invalid definition");
1283 if (Def->getOperand(DefIdx).getSubReg())
1284 // If we are composing subreg, bails out.
1285 // Same remark as getNextSourceFromRegSequence.
1286 // I.e., this may be turned into an assert.
1290 // We could handle the REG_SEQUENCE here, but we do not want to
1291 // duplicate the code from the generic TII.
1294 TargetInstrInfo::RegSubRegPair BaseReg;
1295 TargetInstrInfo::RegSubRegPairAndIdx InsertedReg;
1296 if (!TII->getInsertSubregInputs(*Def, DefIdx, BaseReg, InsertedReg))
1299 // We are looking at:
1300 // Def = INSERT_SUBREG v0, v1, sub1
1301 // There are two cases:
1302 // 1. DefSubReg == sub1, get v1.
1303 // 2. DefSubReg != sub1, the value may be available through v0.
1305 // #1 Check if the inserted register matches the required sub index.
1306 if (InsertedReg.SubIdx == DefSubReg) {
1307 SrcReg = InsertedReg.Reg;
1308 SrcSubReg = InsertedReg.SubReg;
1311 // #2 Otherwise, if the sub register we are looking for is not partial
1312 // defined by the inserted element, we can look through the main
1314 const MachineOperand &MODef = Def->getOperand(DefIdx);
1315 // If the result register (Def) and the base register (v0) do not
1316 // have the same register class or if we have to compose
1317 // subregisters, bails out.
1318 if (MRI.getRegClass(MODef.getReg()) != MRI.getRegClass(BaseReg.Reg) ||
1322 // Get the TRI and check if the inserted sub-register overlaps with the
1323 // sub-register we are tracking.
1324 const TargetRegisterInfo *TRI = MRI.getTargetRegisterInfo();
1326 (TRI->getSubRegIndexLaneMask(DefSubReg) &
1327 TRI->getSubRegIndexLaneMask(InsertedReg.SubIdx)) != 0)
1329 // At this point, the value is available in v0 via the same subreg
1331 SrcReg = BaseReg.Reg;
1332 SrcSubReg = DefSubReg;
1336 bool ValueTracker::getNextSourceFromExtractSubreg(unsigned &SrcReg,
1337 unsigned &SrcSubReg) {
1338 assert((Def->isExtractSubreg() ||
1339 Def->isExtractSubregLike()) && "Invalid definition");
1340 // We are looking at:
1341 // Def = EXTRACT_SUBREG v0, sub0
1343 // Bails if we have to compose sub registers.
1344 // Indeed, if DefSubReg != 0, we would have to compose it with sub0.
1349 // We could handle the EXTRACT_SUBREG here, but we do not want to
1350 // duplicate the code from the generic TII.
1353 TargetInstrInfo::RegSubRegPairAndIdx ExtractSubregInputReg;
1354 if (!TII->getExtractSubregInputs(*Def, DefIdx, ExtractSubregInputReg))
1357 // Bails if we have to compose sub registers.
1358 // Likewise, if v0.subreg != 0, we would have to compose v0.subreg with sub0.
1359 if (ExtractSubregInputReg.SubReg)
1361 // Otherwise, the value is available in the v0.sub0.
1362 SrcReg = ExtractSubregInputReg.Reg;
1363 SrcSubReg = ExtractSubregInputReg.SubIdx;
1367 bool ValueTracker::getNextSourceFromSubregToReg(unsigned &SrcReg,
1368 unsigned &SrcSubReg) {
1369 assert(Def->isSubregToReg() && "Invalid definition");
1370 // We are looking at:
1371 // Def = SUBREG_TO_REG Imm, v0, sub0
1373 // Bails if we have to compose sub registers.
1374 // If DefSubReg != sub0, we would have to check that all the bits
1375 // we track are included in sub0 and if yes, we would have to
1376 // determine the right subreg in v0.
1377 if (DefSubReg != Def->getOperand(3).getImm())
1379 // Bails if we have to compose sub registers.
1380 // Likewise, if v0.subreg != 0, we would have to compose it with sub0.
1381 if (Def->getOperand(2).getSubReg())
1384 SrcReg = Def->getOperand(2).getReg();
1385 SrcSubReg = Def->getOperand(3).getImm();
1389 bool ValueTracker::getNextSourceImpl(unsigned &SrcReg, unsigned &SrcSubReg) {
1390 assert(Def && "This method needs a valid definition");
1393 (DefIdx < Def->getDesc().getNumDefs() || Def->getDesc().isVariadic()) &&
1394 Def->getOperand(DefIdx).isDef() && "Invalid DefIdx");
1396 return getNextSourceFromCopy(SrcReg, SrcSubReg);
1397 if (Def->isBitcast())
1398 return getNextSourceFromBitcast(SrcReg, SrcSubReg);
1399 // All the remaining cases involve "complex" instructions.
1400 // Bails if we did not ask for the advanced tracking.
1401 if (!UseAdvancedTracking)
1403 if (Def->isRegSequence() || Def->isRegSequenceLike())
1404 return getNextSourceFromRegSequence(SrcReg, SrcSubReg);
1405 if (Def->isInsertSubreg() || Def->isInsertSubregLike())
1406 return getNextSourceFromInsertSubreg(SrcReg, SrcSubReg);
1407 if (Def->isExtractSubreg() || Def->isExtractSubregLike())
1408 return getNextSourceFromExtractSubreg(SrcReg, SrcSubReg);
1409 if (Def->isSubregToReg())
1410 return getNextSourceFromSubregToReg(SrcReg, SrcSubReg);
1414 const MachineInstr *ValueTracker::getNextSource(unsigned &SrcReg,
1415 unsigned &SrcSubReg) {
1416 // If we reach a point where we cannot move up in the use-def chain,
1417 // there is nothing we can get.
1421 const MachineInstr *PrevDef = nullptr;
1422 // Try to find the next source.
1423 if (getNextSourceImpl(SrcReg, SrcSubReg)) {
1424 // Update definition, definition index, and subregister for the
1425 // next call of getNextSource.
1426 // Update the current register.
1428 // Update the return value before moving up in the use-def chain.
1430 // If we can still move up in the use-def chain, move to the next
1432 if (!TargetRegisterInfo::isPhysicalRegister(Reg)) {
1433 Def = MRI.getVRegDef(Reg);
1434 DefIdx = MRI.def_begin(Reg).getOperandNo();
1435 DefSubReg = SrcSubReg;
1439 // If we end up here, this means we will not be able to find another source
1440 // for the next iteration.
1441 // Make sure any new call to getNextSource bails out early by cutting the