1 //===-- ARMConstantIslandPass.cpp - ARM constant islands ------------------===//
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 // This file contains a pass that splits the constant pool up into 'islands'
11 // which are scattered through-out the function. This is required due to the
12 // limited pc-relative displacements that ARM has.
14 //===----------------------------------------------------------------------===//
16 #define DEBUG_TYPE "arm-cp-islands"
18 #include "ARMMachineFunctionInfo.h"
19 #include "ARMInstrInfo.h"
20 #include "Thumb2InstrInfo.h"
21 #include "MCTargetDesc/ARMAddressingModes.h"
22 #include "llvm/CodeGen/MachineConstantPool.h"
23 #include "llvm/CodeGen/MachineFunctionPass.h"
24 #include "llvm/CodeGen/MachineJumpTableInfo.h"
25 #include "llvm/Target/TargetData.h"
26 #include "llvm/Target/TargetMachine.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/ErrorHandling.h"
29 #include "llvm/Support/Format.h"
30 #include "llvm/Support/raw_ostream.h"
31 #include "llvm/ADT/SmallSet.h"
32 #include "llvm/ADT/SmallVector.h"
33 #include "llvm/ADT/STLExtras.h"
34 #include "llvm/ADT/Statistic.h"
35 #include "llvm/Support/CommandLine.h"
39 STATISTIC(NumCPEs, "Number of constpool entries");
40 STATISTIC(NumSplit, "Number of uncond branches inserted");
41 STATISTIC(NumCBrFixed, "Number of cond branches fixed");
42 STATISTIC(NumUBrFixed, "Number of uncond branches fixed");
43 STATISTIC(NumTBs, "Number of table branches generated");
44 STATISTIC(NumT2CPShrunk, "Number of Thumb2 constantpool instructions shrunk");
45 STATISTIC(NumT2BrShrunk, "Number of Thumb2 immediate branches shrunk");
46 STATISTIC(NumCBZ, "Number of CBZ / CBNZ formed");
47 STATISTIC(NumJTMoved, "Number of jump table destination blocks moved");
48 STATISTIC(NumJTInserted, "Number of jump table intermediate blocks inserted");
52 AdjustJumpTableBlocks("arm-adjust-jump-tables", cl::Hidden, cl::init(true),
53 cl::desc("Adjust basic block layout to better use TB[BH]"));
56 AlignConstantIslands("arm-align-constant-island", cl::Hidden,
57 cl::desc("Align constant islands in code"));
59 /// UnknownPadding - Return the worst case padding that could result from
60 /// unknown offset bits. This does not include alignment padding caused by
61 /// known offset bits.
63 /// @param LogAlign log2(alignment)
64 /// @param KnownBits Number of known low offset bits.
65 static inline unsigned UnknownPadding(unsigned LogAlign, unsigned KnownBits) {
66 if (KnownBits < LogAlign)
67 return (1u << LogAlign) - (1u << KnownBits);
71 /// WorstCaseAlign - Assuming only the low KnownBits bits in Offset are exact,
72 /// add padding such that:
74 /// 1. The result is aligned to 1 << LogAlign.
76 /// 2. No other value of the unknown bits would require more padding.
78 /// This may add more padding than is required to satisfy just one of the
79 /// constraints. It is necessary to compute alignment this way to guarantee
80 /// that we don't underestimate the padding before an aligned block. If the
81 /// real padding before a block is larger than we think, constant pool entries
82 /// may go out of range.
83 static inline unsigned WorstCaseAlign(unsigned Offset, unsigned LogAlign,
85 // Add the worst possible padding that the unknown bits could cause.
86 Offset += UnknownPadding(LogAlign, KnownBits);
88 // Then align the result.
89 return RoundUpToAlignment(Offset, 1u << LogAlign);
93 /// ARMConstantIslands - Due to limited PC-relative displacements, ARM
94 /// requires constant pool entries to be scattered among the instructions
95 /// inside a function. To do this, it completely ignores the normal LLVM
96 /// constant pool; instead, it places constants wherever it feels like with
97 /// special instructions.
99 /// The terminology used in this pass includes:
100 /// Islands - Clumps of constants placed in the function.
101 /// Water - Potential places where an island could be formed.
102 /// CPE - A constant pool entry that has been placed somewhere, which
103 /// tracks a list of users.
104 class ARMConstantIslands : public MachineFunctionPass {
105 /// BasicBlockInfo - Information about the offset and size of a single
107 struct BasicBlockInfo {
108 /// Offset - Distance from the beginning of the function to the beginning
109 /// of this basic block.
111 /// The offset is always aligned as required by the basic block.
114 /// Size - Size of the basic block in bytes. If the block contains
115 /// inline assembly, this is a worst case estimate.
117 /// The size does not include any alignment padding whether from the
118 /// beginning of the block, or from an aligned jump table at the end.
121 /// KnownBits - The number of low bits in Offset that are known to be
122 /// exact. The remaining bits of Offset are an upper bound.
125 /// Unalign - When non-zero, the block contains instructions (inline asm)
126 /// of unknown size. The real size may be smaller than Size bytes by a
127 /// multiple of 1 << Unalign.
130 /// PostAlign - When non-zero, the block terminator contains a .align
131 /// directive, so the end of the block is aligned to 1 << PostAlign
135 BasicBlockInfo() : Offset(0), Size(0), KnownBits(0), Unalign(0),
138 /// Compute the number of known offset bits internally to this block.
139 /// This number should be used to predict worst case padding when
140 /// splitting the block.
141 unsigned internalKnownBits() const {
142 return Unalign ? Unalign : KnownBits;
145 /// Compute the offset immediately following this block. If LogAlign is
146 /// specified, return the offset the successor block will get if it has
148 unsigned postOffset(unsigned LogAlign = 0) const {
149 unsigned PO = Offset + Size;
150 unsigned LA = std::max(unsigned(PostAlign), LogAlign);
153 // Add alignment padding from the terminator.
154 return WorstCaseAlign(PO, LA, internalKnownBits());
157 /// Compute the number of known low bits of postOffset. If this block
158 /// contains inline asm, the number of known bits drops to the
159 /// instruction alignment. An aligned terminator may increase the number
161 /// If LogAlign is given, also consider the alignment of the next block.
162 unsigned postKnownBits(unsigned LogAlign = 0) const {
163 return std::max(std::max(unsigned(PostAlign), LogAlign),
164 internalKnownBits());
168 std::vector<BasicBlockInfo> BBInfo;
170 /// WaterList - A sorted list of basic blocks where islands could be placed
171 /// (i.e. blocks that don't fall through to the following block, due
172 /// to a return, unreachable, or unconditional branch).
173 std::vector<MachineBasicBlock*> WaterList;
175 /// NewWaterList - The subset of WaterList that was created since the
176 /// previous iteration by inserting unconditional branches.
177 SmallSet<MachineBasicBlock*, 4> NewWaterList;
179 typedef std::vector<MachineBasicBlock*>::iterator water_iterator;
181 /// CPUser - One user of a constant pool, keeping the machine instruction
182 /// pointer, the constant pool being referenced, and the max displacement
183 /// allowed from the instruction to the CP. The HighWaterMark records the
184 /// highest basic block where a new CPEntry can be placed. To ensure this
185 /// pass terminates, the CP entries are initially placed at the end of the
186 /// function and then move monotonically to lower addresses. The
187 /// exception to this rule is when the current CP entry for a particular
188 /// CPUser is out of range, but there is another CP entry for the same
189 /// constant value in range. We want to use the existing in-range CP
190 /// entry, but if it later moves out of range, the search for new water
191 /// should resume where it left off. The HighWaterMark is used to record
196 MachineBasicBlock *HighWaterMark;
200 CPUser(MachineInstr *mi, MachineInstr *cpemi, unsigned maxdisp,
201 bool neg, bool soimm)
202 : MI(mi), CPEMI(cpemi), MaxDisp(maxdisp), NegOk(neg), IsSoImm(soimm) {
203 HighWaterMark = CPEMI->getParent();
207 /// CPUsers - Keep track of all of the machine instructions that use various
208 /// constant pools and their max displacement.
209 std::vector<CPUser> CPUsers;
211 /// CPEntry - One per constant pool entry, keeping the machine instruction
212 /// pointer, the constpool index, and the number of CPUser's which
213 /// reference this entry.
218 CPEntry(MachineInstr *cpemi, unsigned cpi, unsigned rc = 0)
219 : CPEMI(cpemi), CPI(cpi), RefCount(rc) {}
222 /// CPEntries - Keep track of all of the constant pool entry machine
223 /// instructions. For each original constpool index (i.e. those that
224 /// existed upon entry to this pass), it keeps a vector of entries.
225 /// Original elements are cloned as we go along; the clones are
226 /// put in the vector of the original element, but have distinct CPIs.
227 std::vector<std::vector<CPEntry> > CPEntries;
229 /// ImmBranch - One per immediate branch, keeping the machine instruction
230 /// pointer, conditional or unconditional, the max displacement,
231 /// and (if isCond is true) the corresponding unconditional branch
235 unsigned MaxDisp : 31;
238 ImmBranch(MachineInstr *mi, unsigned maxdisp, bool cond, int ubr)
239 : MI(mi), MaxDisp(maxdisp), isCond(cond), UncondBr(ubr) {}
242 /// ImmBranches - Keep track of all the immediate branch instructions.
244 std::vector<ImmBranch> ImmBranches;
246 /// PushPopMIs - Keep track of all the Thumb push / pop instructions.
248 SmallVector<MachineInstr*, 4> PushPopMIs;
250 /// T2JumpTables - Keep track of all the Thumb2 jumptable instructions.
251 SmallVector<MachineInstr*, 4> T2JumpTables;
253 /// HasFarJump - True if any far jump instruction has been emitted during
254 /// the branch fix up pass.
258 MachineConstantPool *MCP;
259 const ARMInstrInfo *TII;
260 const ARMSubtarget *STI;
261 ARMFunctionInfo *AFI;
267 ARMConstantIslands() : MachineFunctionPass(ID) {}
269 virtual bool runOnMachineFunction(MachineFunction &MF);
271 virtual const char *getPassName() const {
272 return "ARM constant island placement and branch shortening pass";
276 void DoInitialPlacement(std::vector<MachineInstr*> &CPEMIs);
277 CPEntry *findConstPoolEntry(unsigned CPI, const MachineInstr *CPEMI);
278 unsigned getCPELogAlign(const MachineInstr *CPEMI);
279 void JumpTableFunctionScan();
280 void InitialFunctionScan(const std::vector<MachineInstr*> &CPEMIs);
281 MachineBasicBlock *SplitBlockBeforeInstr(MachineInstr *MI);
282 void UpdateForInsertedWaterBlock(MachineBasicBlock *NewBB);
283 void AdjustBBOffsetsAfter(MachineBasicBlock *BB);
284 bool DecrementOldEntry(unsigned CPI, MachineInstr* CPEMI);
285 int LookForExistingCPEntry(CPUser& U, unsigned UserOffset);
286 bool LookForWater(CPUser&U, unsigned UserOffset, water_iterator &WaterIter);
287 void CreateNewWater(unsigned CPUserIndex, unsigned UserOffset,
288 MachineBasicBlock *&NewMBB);
289 bool HandleConstantPoolUser(unsigned CPUserIndex);
290 void RemoveDeadCPEMI(MachineInstr *CPEMI);
291 bool RemoveUnusedCPEntries();
292 bool CPEIsInRange(MachineInstr *MI, unsigned UserOffset,
293 MachineInstr *CPEMI, unsigned Disp, bool NegOk,
294 bool DoDump = false);
295 bool WaterIsInRange(unsigned UserOffset, MachineBasicBlock *Water,
297 bool BBIsInRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned Disp);
298 bool FixUpImmediateBr(ImmBranch &Br);
299 bool FixUpConditionalBr(ImmBranch &Br);
300 bool FixUpUnconditionalBr(ImmBranch &Br);
301 bool UndoLRSpillRestore();
302 bool OptimizeThumb2Instructions();
303 bool OptimizeThumb2Branches();
304 bool ReorderThumb2JumpTables();
305 bool OptimizeThumb2JumpTables();
306 MachineBasicBlock *AdjustJTTargetBlockForward(MachineBasicBlock *BB,
307 MachineBasicBlock *JTBB);
309 void ComputeBlockSize(MachineBasicBlock *MBB);
310 unsigned GetOffsetOf(MachineInstr *MI) const;
314 bool OffsetIsInRange(unsigned UserOffset, unsigned TrialOffset,
315 unsigned Disp, bool NegativeOK, bool IsSoImm = false);
316 bool OffsetIsInRange(unsigned UserOffset, unsigned TrialOffset,
318 return OffsetIsInRange(UserOffset, TrialOffset,
319 U.MaxDisp, U.NegOk, U.IsSoImm);
322 char ARMConstantIslands::ID = 0;
325 /// verify - check BBOffsets, BBSizes, alignment of islands
326 void ARMConstantIslands::verify() {
328 for (MachineFunction::iterator MBBI = MF->begin(), E = MF->end();
330 MachineBasicBlock *MBB = MBBI;
331 unsigned Align = MBB->getAlignment();
332 unsigned MBBId = MBB->getNumber();
333 assert(BBInfo[MBBId].Offset % (1u << Align) == 0);
334 assert(!MBBId || BBInfo[MBBId - 1].postOffset() <= BBInfo[MBBId].Offset);
336 for (unsigned i = 0, e = CPUsers.size(); i != e; ++i) {
337 CPUser &U = CPUsers[i];
338 unsigned UserOffset = GetOffsetOf(U.MI) + (isThumb ? 4 : 8);
339 unsigned CPEOffset = GetOffsetOf(U.CPEMI);
340 unsigned Disp = UserOffset < CPEOffset ? CPEOffset - UserOffset :
341 UserOffset - CPEOffset;
342 assert(Disp <= U.MaxDisp || "Constant pool entry out of range!");
347 /// print block size and offset information - debugging
348 void ARMConstantIslands::dumpBBs() {
350 for (unsigned J = 0, E = BBInfo.size(); J !=E; ++J) {
351 const BasicBlockInfo &BBI = BBInfo[J];
352 dbgs() << format("%08x BB#%u\t", BBI.Offset, J)
353 << " kb=" << unsigned(BBI.KnownBits)
354 << " ua=" << unsigned(BBI.Unalign)
355 << " pa=" << unsigned(BBI.PostAlign)
356 << format(" size=%#x\n", BBInfo[J].Size);
361 /// createARMConstantIslandPass - returns an instance of the constpool
363 FunctionPass *llvm::createARMConstantIslandPass() {
364 return new ARMConstantIslands();
367 bool ARMConstantIslands::runOnMachineFunction(MachineFunction &mf) {
369 MCP = mf.getConstantPool();
371 DEBUG(dbgs() << "***** ARMConstantIslands: "
372 << MCP->getConstants().size() << " CP entries, aligned to "
373 << MCP->getConstantPoolAlignment() << " bytes *****\n");
375 TII = (const ARMInstrInfo*)MF->getTarget().getInstrInfo();
376 AFI = MF->getInfo<ARMFunctionInfo>();
377 STI = &MF->getTarget().getSubtarget<ARMSubtarget>();
379 isThumb = AFI->isThumbFunction();
380 isThumb1 = AFI->isThumb1OnlyFunction();
381 isThumb2 = AFI->isThumb2Function();
385 // Renumber all of the machine basic blocks in the function, guaranteeing that
386 // the numbers agree with the position of the block in the function.
387 MF->RenumberBlocks();
389 // Try to reorder and otherwise adjust the block layout to make good use
390 // of the TB[BH] instructions.
391 bool MadeChange = false;
392 if (isThumb2 && AdjustJumpTableBlocks) {
393 JumpTableFunctionScan();
394 MadeChange |= ReorderThumb2JumpTables();
395 // Data is out of date, so clear it. It'll be re-computed later.
396 T2JumpTables.clear();
397 // Blocks may have shifted around. Keep the numbering up to date.
398 MF->RenumberBlocks();
401 // Thumb1 functions containing constant pools get 4-byte alignment.
402 // This is so we can keep exact track of where the alignment padding goes.
404 // ARM and Thumb2 functions need to be 4-byte aligned.
406 MF->EnsureAlignment(2); // 2 = log2(4)
408 // Perform the initial placement of the constant pool entries. To start with,
409 // we put them all at the end of the function.
410 std::vector<MachineInstr*> CPEMIs;
412 DoInitialPlacement(CPEMIs);
414 /// The next UID to take is the first unused one.
415 AFI->initPICLabelUId(CPEMIs.size());
417 // Do the initial scan of the function, building up information about the
418 // sizes of each block, the location of all the water, and finding all of the
419 // constant pool users.
420 InitialFunctionScan(CPEMIs);
425 /// Remove dead constant pool entries.
426 MadeChange |= RemoveUnusedCPEntries();
428 // Iteratively place constant pool entries and fix up branches until there
430 unsigned NoCPIters = 0, NoBRIters = 0;
432 DEBUG(dbgs() << "Beginning CP iteration #" << NoCPIters << '\n');
433 bool CPChange = false;
434 for (unsigned i = 0, e = CPUsers.size(); i != e; ++i)
435 CPChange |= HandleConstantPoolUser(i);
436 if (CPChange && ++NoCPIters > 30)
437 llvm_unreachable("Constant Island pass failed to converge!");
440 // Clear NewWaterList now. If we split a block for branches, it should
441 // appear as "new water" for the next iteration of constant pool placement.
442 NewWaterList.clear();
444 DEBUG(dbgs() << "Beginning BR iteration #" << NoBRIters << '\n');
445 bool BRChange = false;
446 for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i)
447 BRChange |= FixUpImmediateBr(ImmBranches[i]);
448 if (BRChange && ++NoBRIters > 30)
449 llvm_unreachable("Branch Fix Up pass failed to converge!");
452 if (!CPChange && !BRChange)
457 // Shrink 32-bit Thumb2 branch, load, and store instructions.
458 if (isThumb2 && !STI->prefers32BitThumb())
459 MadeChange |= OptimizeThumb2Instructions();
461 // After a while, this might be made debug-only, but it is not expensive.
464 // If LR has been forced spilled and no far jump (i.e. BL) has been issued,
465 // undo the spill / restore of LR if possible.
466 if (isThumb && !HasFarJump && AFI->isLRSpilledForFarJump())
467 MadeChange |= UndoLRSpillRestore();
469 // Save the mapping between original and cloned constpool entries.
470 for (unsigned i = 0, e = CPEntries.size(); i != e; ++i) {
471 for (unsigned j = 0, je = CPEntries[i].size(); j != je; ++j) {
472 const CPEntry & CPE = CPEntries[i][j];
473 AFI->recordCPEClone(i, CPE.CPI);
477 DEBUG(dbgs() << '\n'; dumpBBs());
485 T2JumpTables.clear();
490 /// DoInitialPlacement - Perform the initial placement of the constant pool
491 /// entries. To start with, we put them all at the end of the function.
493 ARMConstantIslands::DoInitialPlacement(std::vector<MachineInstr*> &CPEMIs) {
494 // Create the basic block to hold the CPE's.
495 MachineBasicBlock *BB = MF->CreateMachineBasicBlock();
498 // MachineConstantPool measures alignment in bytes. We measure in log2(bytes).
499 unsigned MaxAlign = Log2_32(MF->getConstantPool()->getConstantPoolAlignment());
501 // Mark the basic block as required by the const-pool.
502 // If AlignConstantIslands isn't set, use 4-byte alignment for everything.
503 BB->setAlignment(AlignConstantIslands ? MaxAlign : 2);
505 // The function needs to be as aligned as the basic blocks. The linker may
506 // move functions around based on their alignment.
507 MF->EnsureAlignment(BB->getAlignment());
509 // Order the entries in BB by descending alignment. That ensures correct
510 // alignment of all entries as long as BB is sufficiently aligned. Keep
511 // track of the insertion point for each alignment. We are going to bucket
512 // sort the entries as they are created.
513 SmallVector<MachineBasicBlock::iterator, 8> InsPoint(MaxAlign + 1, BB->end());
515 // Add all of the constants from the constant pool to the end block, use an
516 // identity mapping of CPI's to CPE's.
517 const std::vector<MachineConstantPoolEntry> &CPs =
518 MF->getConstantPool()->getConstants();
520 const TargetData &TD = *MF->getTarget().getTargetData();
521 for (unsigned i = 0, e = CPs.size(); i != e; ++i) {
522 unsigned Size = TD.getTypeAllocSize(CPs[i].getType());
523 assert(Size >= 4 && "Too small constant pool entry");
524 unsigned Align = CPs[i].getAlignment();
525 assert(isPowerOf2_32(Align) && "Invalid alignment");
526 // Verify that all constant pool entries are a multiple of their alignment.
527 // If not, we would have to pad them out so that instructions stay aligned.
528 assert((Size % Align) == 0 && "CP Entry not multiple of 4 bytes!");
530 // Insert CONSTPOOL_ENTRY before entries with a smaller alignment.
531 unsigned LogAlign = Log2_32(Align);
532 MachineBasicBlock::iterator InsAt = InsPoint[LogAlign];
533 MachineInstr *CPEMI =
534 BuildMI(*BB, InsAt, DebugLoc(), TII->get(ARM::CONSTPOOL_ENTRY))
535 .addImm(i).addConstantPoolIndex(i).addImm(Size);
536 CPEMIs.push_back(CPEMI);
538 // Ensure that future entries with higher alignment get inserted before
539 // CPEMI. This is bucket sort with iterators.
540 for (unsigned a = LogAlign + 1; a < MaxAlign; ++a)
541 if (InsPoint[a] == InsAt)
544 // Add a new CPEntry, but no corresponding CPUser yet.
545 std::vector<CPEntry> CPEs;
546 CPEs.push_back(CPEntry(CPEMI, i));
547 CPEntries.push_back(CPEs);
549 DEBUG(dbgs() << "Moved CPI#" << i << " to end of function\n");
554 /// BBHasFallthrough - Return true if the specified basic block can fallthrough
555 /// into the block immediately after it.
556 static bool BBHasFallthrough(MachineBasicBlock *MBB) {
557 // Get the next machine basic block in the function.
558 MachineFunction::iterator MBBI = MBB;
559 // Can't fall off end of function.
560 if (llvm::next(MBBI) == MBB->getParent()->end())
563 MachineBasicBlock *NextBB = llvm::next(MBBI);
564 for (MachineBasicBlock::succ_iterator I = MBB->succ_begin(),
565 E = MBB->succ_end(); I != E; ++I)
572 /// findConstPoolEntry - Given the constpool index and CONSTPOOL_ENTRY MI,
573 /// look up the corresponding CPEntry.
574 ARMConstantIslands::CPEntry
575 *ARMConstantIslands::findConstPoolEntry(unsigned CPI,
576 const MachineInstr *CPEMI) {
577 std::vector<CPEntry> &CPEs = CPEntries[CPI];
578 // Number of entries per constpool index should be small, just do a
580 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) {
581 if (CPEs[i].CPEMI == CPEMI)
587 /// getCPELogAlign - Returns the required alignment of the constant pool entry
588 /// represented by CPEMI. Alignment is measured in log2(bytes) units.
589 unsigned ARMConstantIslands::getCPELogAlign(const MachineInstr *CPEMI) {
590 assert(CPEMI && CPEMI->getOpcode() == ARM::CONSTPOOL_ENTRY);
592 // Everything is 4-byte aligned unless AlignConstantIslands is set.
593 if (!AlignConstantIslands)
596 unsigned CPI = CPEMI->getOperand(1).getIndex();
597 assert(CPI < MCP->getConstants().size() && "Invalid constant pool index.");
598 unsigned Align = MCP->getConstants()[CPI].getAlignment();
599 assert(isPowerOf2_32(Align) && "Invalid CPE alignment");
600 return Log2_32(Align);
603 /// JumpTableFunctionScan - Do a scan of the function, building up
604 /// information about the sizes of each block and the locations of all
606 void ARMConstantIslands::JumpTableFunctionScan() {
607 for (MachineFunction::iterator MBBI = MF->begin(), E = MF->end();
609 MachineBasicBlock &MBB = *MBBI;
611 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
613 if (I->isBranch() && I->getOpcode() == ARM::t2BR_JT)
614 T2JumpTables.push_back(I);
618 /// InitialFunctionScan - Do the initial scan of the function, building up
619 /// information about the sizes of each block, the location of all the water,
620 /// and finding all of the constant pool users.
621 void ARMConstantIslands::
622 InitialFunctionScan(const std::vector<MachineInstr*> &CPEMIs) {
624 BBInfo.resize(MF->getNumBlockIDs());
626 // First thing, compute the size of all basic blocks, and see if the function
627 // has any inline assembly in it. If so, we have to be conservative about
628 // alignment assumptions, as we don't know for sure the size of any
629 // instructions in the inline assembly.
630 for (MachineFunction::iterator I = MF->begin(), E = MF->end(); I != E; ++I)
633 // The known bits of the entry block offset are determined by the function
635 BBInfo.front().KnownBits = MF->getAlignment();
637 // Compute block offsets and known bits.
638 AdjustBBOffsetsAfter(MF->begin());
640 // Now go back through the instructions and build up our data structures.
641 for (MachineFunction::iterator MBBI = MF->begin(), E = MF->end();
643 MachineBasicBlock &MBB = *MBBI;
645 // If this block doesn't fall through into the next MBB, then this is
646 // 'water' that a constant pool island could be placed.
647 if (!BBHasFallthrough(&MBB))
648 WaterList.push_back(&MBB);
650 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
652 if (I->isDebugValue())
655 int Opc = I->getOpcode();
663 continue; // Ignore other JT branches
665 T2JumpTables.push_back(I);
666 continue; // Does not get an entry in ImmBranches
697 // Record this immediate branch.
698 unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale;
699 ImmBranches.push_back(ImmBranch(I, MaxOffs, isCond, UOpc));
702 if (Opc == ARM::tPUSH || Opc == ARM::tPOP_RET)
703 PushPopMIs.push_back(I);
705 if (Opc == ARM::CONSTPOOL_ENTRY)
708 // Scan the instructions for constant pool operands.
709 for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op)
710 if (I->getOperand(op).isCPI()) {
711 // We found one. The addressing mode tells us the max displacement
712 // from the PC that this instruction permits.
714 // Basic size info comes from the TSFlags field.
718 bool IsSoImm = false;
722 llvm_unreachable("Unknown addressing mode for CP reference!");
725 // Taking the address of a CP entry.
727 // This takes a SoImm, which is 8 bit immediate rotated. We'll
728 // pretend the maximum offset is 255 * 4. Since each instruction
729 // 4 byte wide, this is always correct. We'll check for other
730 // displacements that fits in a SoImm as well.
736 case ARM::t2LEApcrel:
748 Bits = 12; // +-offset_12
754 Scale = 4; // +(offset_8*4)
760 Scale = 4; // +-(offset_8*4)
765 // Remember that this is a user of a CP entry.
766 unsigned CPI = I->getOperand(op).getIndex();
767 MachineInstr *CPEMI = CPEMIs[CPI];
768 unsigned MaxOffs = ((1 << Bits)-1) * Scale;
769 CPUsers.push_back(CPUser(I, CPEMI, MaxOffs, NegOk, IsSoImm));
771 // Increment corresponding CPEntry reference count.
772 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI);
773 assert(CPE && "Cannot find a corresponding CPEntry!");
776 // Instructions can only use one CP entry, don't bother scanning the
777 // rest of the operands.
784 /// ComputeBlockSize - Compute the size and some alignment information for MBB.
785 /// This function updates BBInfo directly.
786 void ARMConstantIslands::ComputeBlockSize(MachineBasicBlock *MBB) {
787 BasicBlockInfo &BBI = BBInfo[MBB->getNumber()];
792 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
794 BBI.Size += TII->GetInstSizeInBytes(I);
795 // For inline asm, GetInstSizeInBytes returns a conservative estimate.
796 // The actual size may be smaller, but still a multiple of the instr size.
797 if (I->isInlineAsm())
798 BBI.Unalign = isThumb ? 1 : 2;
801 // tBR_JTr contains a .align 2 directive.
802 if (!MBB->empty() && MBB->back().getOpcode() == ARM::tBR_JTr) {
804 MBB->getParent()->EnsureAlignment(2);
808 /// GetOffsetOf - Return the current offset of the specified machine instruction
809 /// from the start of the function. This offset changes as stuff is moved
810 /// around inside the function.
811 unsigned ARMConstantIslands::GetOffsetOf(MachineInstr *MI) const {
812 MachineBasicBlock *MBB = MI->getParent();
814 // The offset is composed of two things: the sum of the sizes of all MBB's
815 // before this instruction's block, and the offset from the start of the block
817 unsigned Offset = BBInfo[MBB->getNumber()].Offset;
819 // Sum instructions before MI in MBB.
820 for (MachineBasicBlock::iterator I = MBB->begin(); ; ++I) {
821 assert(I != MBB->end() && "Didn't find MI in its own basic block?");
822 if (&*I == MI) return Offset;
823 Offset += TII->GetInstSizeInBytes(I);
827 /// CompareMBBNumbers - Little predicate function to sort the WaterList by MBB
829 static bool CompareMBBNumbers(const MachineBasicBlock *LHS,
830 const MachineBasicBlock *RHS) {
831 return LHS->getNumber() < RHS->getNumber();
834 /// UpdateForInsertedWaterBlock - When a block is newly inserted into the
835 /// machine function, it upsets all of the block numbers. Renumber the blocks
836 /// and update the arrays that parallel this numbering.
837 void ARMConstantIslands::UpdateForInsertedWaterBlock(MachineBasicBlock *NewBB) {
838 // Renumber the MBB's to keep them consecutive.
839 NewBB->getParent()->RenumberBlocks(NewBB);
841 // Insert an entry into BBInfo to align it properly with the (newly
842 // renumbered) block numbers.
843 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo());
845 // Next, update WaterList. Specifically, we need to add NewMBB as having
846 // available water after it.
848 std::lower_bound(WaterList.begin(), WaterList.end(), NewBB,
850 WaterList.insert(IP, NewBB);
854 /// Split the basic block containing MI into two blocks, which are joined by
855 /// an unconditional branch. Update data structures and renumber blocks to
856 /// account for this change and returns the newly created block.
857 MachineBasicBlock *ARMConstantIslands::SplitBlockBeforeInstr(MachineInstr *MI) {
858 MachineBasicBlock *OrigBB = MI->getParent();
860 // Create a new MBB for the code after the OrigBB.
861 MachineBasicBlock *NewBB =
862 MF->CreateMachineBasicBlock(OrigBB->getBasicBlock());
863 MachineFunction::iterator MBBI = OrigBB; ++MBBI;
864 MF->insert(MBBI, NewBB);
866 // Splice the instructions starting with MI over to NewBB.
867 NewBB->splice(NewBB->end(), OrigBB, MI, OrigBB->end());
869 // Add an unconditional branch from OrigBB to NewBB.
870 // Note the new unconditional branch is not being recorded.
871 // There doesn't seem to be meaningful DebugInfo available; this doesn't
872 // correspond to anything in the source.
873 unsigned Opc = isThumb ? (isThumb2 ? ARM::t2B : ARM::tB) : ARM::B;
875 BuildMI(OrigBB, DebugLoc(), TII->get(Opc)).addMBB(NewBB);
877 BuildMI(OrigBB, DebugLoc(), TII->get(Opc)).addMBB(NewBB)
878 .addImm(ARMCC::AL).addReg(0);
881 // Update the CFG. All succs of OrigBB are now succs of NewBB.
882 NewBB->transferSuccessors(OrigBB);
884 // OrigBB branches to NewBB.
885 OrigBB->addSuccessor(NewBB);
887 // Update internal data structures to account for the newly inserted MBB.
888 // This is almost the same as UpdateForInsertedWaterBlock, except that
889 // the Water goes after OrigBB, not NewBB.
890 MF->RenumberBlocks(NewBB);
892 // Insert an entry into BBInfo to align it properly with the (newly
893 // renumbered) block numbers.
894 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo());
896 // Next, update WaterList. Specifically, we need to add OrigMBB as having
897 // available water after it (but not if it's already there, which happens
898 // when splitting before a conditional branch that is followed by an
899 // unconditional branch - in that case we want to insert NewBB).
901 std::lower_bound(WaterList.begin(), WaterList.end(), OrigBB,
903 MachineBasicBlock* WaterBB = *IP;
904 if (WaterBB == OrigBB)
905 WaterList.insert(llvm::next(IP), NewBB);
907 WaterList.insert(IP, OrigBB);
908 NewWaterList.insert(OrigBB);
910 // Figure out how large the OrigBB is. As the first half of the original
911 // block, it cannot contain a tablejump. The size includes
912 // the new jump we added. (It should be possible to do this without
913 // recounting everything, but it's very confusing, and this is rarely
915 ComputeBlockSize(OrigBB);
917 // Figure out how large the NewMBB is. As the second half of the original
918 // block, it may contain a tablejump.
919 ComputeBlockSize(NewBB);
921 // All BBOffsets following these blocks must be modified.
922 AdjustBBOffsetsAfter(OrigBB);
927 /// OffsetIsInRange - Checks whether UserOffset (the location of a constant pool
928 /// reference) is within MaxDisp of TrialOffset (a proposed location of a
929 /// constant pool entry).
930 bool ARMConstantIslands::OffsetIsInRange(unsigned UserOffset,
931 unsigned TrialOffset, unsigned MaxDisp,
932 bool NegativeOK, bool IsSoImm) {
933 // On Thumb offsets==2 mod 4 are rounded down by the hardware for
934 // purposes of the displacement computation; compensate for that here.
935 // Effectively, the valid range of displacements is 2 bytes smaller for such
937 unsigned TotalAdj = 0;
938 if (isThumb && UserOffset%4 !=0) {
942 // CPEs will be rounded up to a multiple of 4.
943 if (isThumb && TrialOffset%4 != 0) {
948 // In Thumb2 mode, later branch adjustments can shift instructions up and
949 // cause alignment change. In the worst case scenario this can cause the
950 // user's effective address to be subtracted by 2 and the CPE's address to
952 if (isThumb2 && TotalAdj != 4)
953 MaxDisp -= (4 - TotalAdj);
955 if (UserOffset <= TrialOffset) {
956 // User before the Trial.
957 if (TrialOffset - UserOffset <= MaxDisp)
959 // FIXME: Make use full range of soimm values.
960 } else if (NegativeOK) {
961 if (UserOffset - TrialOffset <= MaxDisp)
963 // FIXME: Make use full range of soimm values.
968 /// WaterIsInRange - Returns true if a CPE placed after the specified
969 /// Water (a basic block) will be in range for the specific MI.
971 bool ARMConstantIslands::WaterIsInRange(unsigned UserOffset,
972 MachineBasicBlock* Water, CPUser &U) {
973 unsigned CPEOffset = BBInfo[Water->getNumber()].postOffset();
975 // If the CPE is to be inserted before the instruction, that will raise
976 // the offset of the instruction.
977 if (CPEOffset < UserOffset)
978 UserOffset += U.CPEMI->getOperand(2).getImm();
980 return OffsetIsInRange(UserOffset, CPEOffset, U);
983 /// CPEIsInRange - Returns true if the distance between specific MI and
984 /// specific ConstPool entry instruction can fit in MI's displacement field.
985 bool ARMConstantIslands::CPEIsInRange(MachineInstr *MI, unsigned UserOffset,
986 MachineInstr *CPEMI, unsigned MaxDisp,
987 bool NegOk, bool DoDump) {
988 unsigned CPEOffset = GetOffsetOf(CPEMI);
989 assert(CPEOffset % 4 == 0 && "Misaligned CPE");
993 unsigned Block = MI->getParent()->getNumber();
994 const BasicBlockInfo &BBI = BBInfo[Block];
995 dbgs() << "User of CPE#" << CPEMI->getOperand(0).getImm()
996 << " max delta=" << MaxDisp
997 << format(" insn address=%#x", UserOffset)
998 << " in BB#" << Block << ": "
999 << format("%#x-%x\t", BBI.Offset, BBI.postOffset()) << *MI
1000 << format("CPE address=%#x offset=%+d: ", CPEOffset,
1001 int(CPEOffset-UserOffset));
1005 return OffsetIsInRange(UserOffset, CPEOffset, MaxDisp, NegOk);
1009 /// BBIsJumpedOver - Return true of the specified basic block's only predecessor
1010 /// unconditionally branches to its only successor.
1011 static bool BBIsJumpedOver(MachineBasicBlock *MBB) {
1012 if (MBB->pred_size() != 1 || MBB->succ_size() != 1)
1015 MachineBasicBlock *Succ = *MBB->succ_begin();
1016 MachineBasicBlock *Pred = *MBB->pred_begin();
1017 MachineInstr *PredMI = &Pred->back();
1018 if (PredMI->getOpcode() == ARM::B || PredMI->getOpcode() == ARM::tB
1019 || PredMI->getOpcode() == ARM::t2B)
1020 return PredMI->getOperand(0).getMBB() == Succ;
1025 void ARMConstantIslands::AdjustBBOffsetsAfter(MachineBasicBlock *BB) {
1026 for(unsigned i = BB->getNumber() + 1, e = MF->getNumBlockIDs(); i < e; ++i) {
1027 // Get the offset and known bits at the end of the layout predecessor.
1028 // Include the alignment of the current block.
1029 unsigned LogAlign = MF->getBlockNumbered(i)->getAlignment();
1030 unsigned Offset = BBInfo[i - 1].postOffset(LogAlign);
1031 unsigned KnownBits = BBInfo[i - 1].postKnownBits(LogAlign);
1033 // This is where block i begins.
1034 BBInfo[i].Offset = Offset;
1035 BBInfo[i].KnownBits = KnownBits;
1039 /// DecrementOldEntry - find the constant pool entry with index CPI
1040 /// and instruction CPEMI, and decrement its refcount. If the refcount
1041 /// becomes 0 remove the entry and instruction. Returns true if we removed
1042 /// the entry, false if we didn't.
1044 bool ARMConstantIslands::DecrementOldEntry(unsigned CPI, MachineInstr *CPEMI) {
1045 // Find the old entry. Eliminate it if it is no longer used.
1046 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI);
1047 assert(CPE && "Unexpected!");
1048 if (--CPE->RefCount == 0) {
1049 RemoveDeadCPEMI(CPEMI);
1057 /// LookForCPEntryInRange - see if the currently referenced CPE is in range;
1058 /// if not, see if an in-range clone of the CPE is in range, and if so,
1059 /// change the data structures so the user references the clone. Returns:
1060 /// 0 = no existing entry found
1061 /// 1 = entry found, and there were no code insertions or deletions
1062 /// 2 = entry found, and there were code insertions or deletions
1063 int ARMConstantIslands::LookForExistingCPEntry(CPUser& U, unsigned UserOffset)
1065 MachineInstr *UserMI = U.MI;
1066 MachineInstr *CPEMI = U.CPEMI;
1068 // Check to see if the CPE is already in-range.
1069 if (CPEIsInRange(UserMI, UserOffset, CPEMI, U.MaxDisp, U.NegOk, true)) {
1070 DEBUG(dbgs() << "In range\n");
1074 // No. Look for previously created clones of the CPE that are in range.
1075 unsigned CPI = CPEMI->getOperand(1).getIndex();
1076 std::vector<CPEntry> &CPEs = CPEntries[CPI];
1077 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) {
1078 // We already tried this one
1079 if (CPEs[i].CPEMI == CPEMI)
1081 // Removing CPEs can leave empty entries, skip
1082 if (CPEs[i].CPEMI == NULL)
1084 if (CPEIsInRange(UserMI, UserOffset, CPEs[i].CPEMI, U.MaxDisp, U.NegOk)) {
1085 DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#"
1086 << CPEs[i].CPI << "\n");
1087 // Point the CPUser node to the replacement
1088 U.CPEMI = CPEs[i].CPEMI;
1089 // Change the CPI in the instruction operand to refer to the clone.
1090 for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j)
1091 if (UserMI->getOperand(j).isCPI()) {
1092 UserMI->getOperand(j).setIndex(CPEs[i].CPI);
1095 // Adjust the refcount of the clone...
1097 // ...and the original. If we didn't remove the old entry, none of the
1098 // addresses changed, so we don't need another pass.
1099 return DecrementOldEntry(CPI, CPEMI) ? 2 : 1;
1105 /// getUnconditionalBrDisp - Returns the maximum displacement that can fit in
1106 /// the specific unconditional branch instruction.
1107 static inline unsigned getUnconditionalBrDisp(int Opc) {
1110 return ((1<<10)-1)*2;
1112 return ((1<<23)-1)*2;
1117 return ((1<<23)-1)*4;
1120 /// LookForWater - Look for an existing entry in the WaterList in which
1121 /// we can place the CPE referenced from U so it's within range of U's MI.
1122 /// Returns true if found, false if not. If it returns true, WaterIter
1123 /// is set to the WaterList entry. For Thumb, prefer water that will not
1124 /// introduce padding to water that will. To ensure that this pass
1125 /// terminates, the CPE location for a particular CPUser is only allowed to
1126 /// move to a lower address, so search backward from the end of the list and
1127 /// prefer the first water that is in range.
1128 bool ARMConstantIslands::LookForWater(CPUser &U, unsigned UserOffset,
1129 water_iterator &WaterIter) {
1130 if (WaterList.empty())
1133 bool FoundWaterThatWouldPad = false;
1134 water_iterator IPThatWouldPad;
1135 for (water_iterator IP = prior(WaterList.end()),
1136 B = WaterList.begin();; --IP) {
1137 MachineBasicBlock* WaterBB = *IP;
1138 // Check if water is in range and is either at a lower address than the
1139 // current "high water mark" or a new water block that was created since
1140 // the previous iteration by inserting an unconditional branch. In the
1141 // latter case, we want to allow resetting the high water mark back to
1142 // this new water since we haven't seen it before. Inserting branches
1143 // should be relatively uncommon and when it does happen, we want to be
1144 // sure to take advantage of it for all the CPEs near that block, so that
1145 // we don't insert more branches than necessary.
1146 if (WaterIsInRange(UserOffset, WaterBB, U) &&
1147 (WaterBB->getNumber() < U.HighWaterMark->getNumber() ||
1148 NewWaterList.count(WaterBB))) {
1149 unsigned WBBId = WaterBB->getNumber();
1150 if (isThumb && BBInfo[WBBId].postOffset()%4 != 0) {
1151 // This is valid Water, but would introduce padding. Remember
1152 // it in case we don't find any Water that doesn't do this.
1153 if (!FoundWaterThatWouldPad) {
1154 FoundWaterThatWouldPad = true;
1155 IPThatWouldPad = IP;
1165 if (FoundWaterThatWouldPad) {
1166 WaterIter = IPThatWouldPad;
1172 /// CreateNewWater - No existing WaterList entry will work for
1173 /// CPUsers[CPUserIndex], so create a place to put the CPE. The end of the
1174 /// block is used if in range, and the conditional branch munged so control
1175 /// flow is correct. Otherwise the block is split to create a hole with an
1176 /// unconditional branch around it. In either case NewMBB is set to a
1177 /// block following which the new island can be inserted (the WaterList
1178 /// is not adjusted).
1179 void ARMConstantIslands::CreateNewWater(unsigned CPUserIndex,
1180 unsigned UserOffset,
1181 MachineBasicBlock *&NewMBB) {
1182 CPUser &U = CPUsers[CPUserIndex];
1183 MachineInstr *UserMI = U.MI;
1184 MachineInstr *CPEMI = U.CPEMI;
1185 MachineBasicBlock *UserMBB = UserMI->getParent();
1186 const BasicBlockInfo &UserBBI = BBInfo[UserMBB->getNumber()];
1187 unsigned OffsetOfNextBlock = UserBBI.postOffset();
1189 // If the block does not end in an unconditional branch already, and if the
1190 // end of the block is within range, make new water there. (The addition
1191 // below is for the unconditional branch we will be adding: 4 bytes on ARM +
1192 // Thumb2, 2 on Thumb1. Possible Thumb1 alignment padding is allowed for
1193 // inside OffsetIsInRange.
1194 if (BBHasFallthrough(UserMBB) &&
1195 OffsetIsInRange(UserOffset, OffsetOfNextBlock + (isThumb1 ? 2: 4), U)) {
1196 DEBUG(dbgs() << "Split at end of block\n");
1197 if (&UserMBB->back() == UserMI)
1198 assert(BBHasFallthrough(UserMBB) && "Expected a fallthrough BB!");
1199 NewMBB = llvm::next(MachineFunction::iterator(UserMBB));
1200 // Add an unconditional branch from UserMBB to fallthrough block.
1201 // Record it for branch lengthening; this new branch will not get out of
1202 // range, but if the preceding conditional branch is out of range, the
1203 // targets will be exchanged, and the altered branch may be out of
1204 // range, so the machinery has to know about it.
1205 int UncondBr = isThumb ? ((isThumb2) ? ARM::t2B : ARM::tB) : ARM::B;
1207 BuildMI(UserMBB, DebugLoc(), TII->get(UncondBr)).addMBB(NewMBB);
1209 BuildMI(UserMBB, DebugLoc(), TII->get(UncondBr)).addMBB(NewMBB)
1210 .addImm(ARMCC::AL).addReg(0);
1211 unsigned MaxDisp = getUnconditionalBrDisp(UncondBr);
1212 ImmBranches.push_back(ImmBranch(&UserMBB->back(),
1213 MaxDisp, false, UncondBr));
1214 int delta = isThumb1 ? 2 : 4;
1215 BBInfo[UserMBB->getNumber()].Size += delta;
1216 AdjustBBOffsetsAfter(UserMBB);
1218 // What a big block. Find a place within the block to split it.
1219 // This is a little tricky on Thumb1 since instructions are 2 bytes
1220 // and constant pool entries are 4 bytes: if instruction I references
1221 // island CPE, and instruction I+1 references CPE', it will
1222 // not work well to put CPE as far forward as possible, since then
1223 // CPE' cannot immediately follow it (that location is 2 bytes
1224 // farther away from I+1 than CPE was from I) and we'd need to create
1225 // a new island. So, we make a first guess, then walk through the
1226 // instructions between the one currently being looked at and the
1227 // possible insertion point, and make sure any other instructions
1228 // that reference CPEs will be able to use the same island area;
1229 // if not, we back up the insertion point.
1231 // Try to split the block so it's fully aligned. Compute the latest split
1232 // point where we can add a 4-byte branch instruction, and then
1233 // WorstCaseAlign to LogAlign.
1234 unsigned LogAlign = UserMBB->getParent()->getAlignment();
1235 unsigned KnownBits = UserBBI.internalKnownBits();
1236 unsigned UPad = UnknownPadding(LogAlign, KnownBits);
1237 unsigned BaseInsertOffset = UserOffset + U.MaxDisp;
1238 DEBUG(dbgs() << format("Split in middle of big block before %#x",
1241 // Account for alignment and unknown padding.
1242 BaseInsertOffset &= ~((1u << LogAlign) - 1);
1243 BaseInsertOffset -= UPad;
1245 // The 4 in the following is for the unconditional branch we'll be
1246 // inserting (allows for long branch on Thumb1). Alignment of the
1247 // island is handled inside OffsetIsInRange.
1248 BaseInsertOffset -= 4;
1250 DEBUG(dbgs() << format(", adjusted to %#x", BaseInsertOffset)
1251 << " la=" << LogAlign
1252 << " kb=" << KnownBits
1253 << " up=" << UPad << '\n');
1255 // This could point off the end of the block if we've already got
1256 // constant pool entries following this block; only the last one is
1257 // in the water list. Back past any possible branches (allow for a
1258 // conditional and a maximally long unconditional).
1259 if (BaseInsertOffset >= BBInfo[UserMBB->getNumber()+1].Offset)
1260 BaseInsertOffset = BBInfo[UserMBB->getNumber()+1].Offset -
1262 unsigned EndInsertOffset =
1263 WorstCaseAlign(BaseInsertOffset + 4, LogAlign, KnownBits) +
1264 CPEMI->getOperand(2).getImm();
1265 MachineBasicBlock::iterator MI = UserMI;
1267 unsigned CPUIndex = CPUserIndex+1;
1268 unsigned NumCPUsers = CPUsers.size();
1269 MachineInstr *LastIT = 0;
1270 for (unsigned Offset = UserOffset+TII->GetInstSizeInBytes(UserMI);
1271 Offset < BaseInsertOffset;
1272 Offset += TII->GetInstSizeInBytes(MI),
1273 MI = llvm::next(MI)) {
1274 if (CPUIndex < NumCPUsers && CPUsers[CPUIndex].MI == MI) {
1275 CPUser &U = CPUsers[CPUIndex];
1276 if (!OffsetIsInRange(Offset, EndInsertOffset, U)) {
1277 BaseInsertOffset -= 1u << LogAlign;
1278 EndInsertOffset -= 1u << LogAlign;
1280 // This is overly conservative, as we don't account for CPEMIs
1281 // being reused within the block, but it doesn't matter much.
1282 EndInsertOffset += CPUsers[CPUIndex].CPEMI->getOperand(2).getImm();
1286 // Remember the last IT instruction.
1287 if (MI->getOpcode() == ARM::t2IT)
1293 // Avoid splitting an IT block.
1295 unsigned PredReg = 0;
1296 ARMCC::CondCodes CC = llvm::getITInstrPredicate(MI, PredReg);
1297 if (CC != ARMCC::AL)
1300 NewMBB = SplitBlockBeforeInstr(MI);
1304 /// HandleConstantPoolUser - Analyze the specified user, checking to see if it
1305 /// is out-of-range. If so, pick up the constant pool value and move it some
1306 /// place in-range. Return true if we changed any addresses (thus must run
1307 /// another pass of branch lengthening), false otherwise.
1308 bool ARMConstantIslands::HandleConstantPoolUser(unsigned CPUserIndex) {
1309 CPUser &U = CPUsers[CPUserIndex];
1310 MachineInstr *UserMI = U.MI;
1311 MachineInstr *CPEMI = U.CPEMI;
1312 unsigned CPI = CPEMI->getOperand(1).getIndex();
1313 unsigned Size = CPEMI->getOperand(2).getImm();
1314 // Compute this only once, it's expensive. The 4 or 8 is the value the
1315 // hardware keeps in the PC.
1316 unsigned UserOffset = GetOffsetOf(UserMI) + (isThumb ? 4 : 8);
1318 // See if the current entry is within range, or there is a clone of it
1320 int result = LookForExistingCPEntry(U, UserOffset);
1321 if (result==1) return false;
1322 else if (result==2) return true;
1324 // No existing clone of this CPE is within range.
1325 // We will be generating a new clone. Get a UID for it.
1326 unsigned ID = AFI->createPICLabelUId();
1328 // Look for water where we can place this CPE.
1329 MachineBasicBlock *NewIsland = MF->CreateMachineBasicBlock();
1330 MachineBasicBlock *NewMBB;
1332 if (LookForWater(U, UserOffset, IP)) {
1333 DEBUG(dbgs() << "Found water in range\n");
1334 MachineBasicBlock *WaterBB = *IP;
1336 // If the original WaterList entry was "new water" on this iteration,
1337 // propagate that to the new island. This is just keeping NewWaterList
1338 // updated to match the WaterList, which will be updated below.
1339 if (NewWaterList.count(WaterBB)) {
1340 NewWaterList.erase(WaterBB);
1341 NewWaterList.insert(NewIsland);
1343 // The new CPE goes before the following block (NewMBB).
1344 NewMBB = llvm::next(MachineFunction::iterator(WaterBB));
1348 DEBUG(dbgs() << "No water found\n");
1349 CreateNewWater(CPUserIndex, UserOffset, NewMBB);
1351 // SplitBlockBeforeInstr adds to WaterList, which is important when it is
1352 // called while handling branches so that the water will be seen on the
1353 // next iteration for constant pools, but in this context, we don't want
1354 // it. Check for this so it will be removed from the WaterList.
1355 // Also remove any entry from NewWaterList.
1356 MachineBasicBlock *WaterBB = prior(MachineFunction::iterator(NewMBB));
1357 IP = std::find(WaterList.begin(), WaterList.end(), WaterBB);
1358 if (IP != WaterList.end())
1359 NewWaterList.erase(WaterBB);
1361 // We are adding new water. Update NewWaterList.
1362 NewWaterList.insert(NewIsland);
1365 // Remove the original WaterList entry; we want subsequent insertions in
1366 // this vicinity to go after the one we're about to insert. This
1367 // considerably reduces the number of times we have to move the same CPE
1368 // more than once and is also important to ensure the algorithm terminates.
1369 if (IP != WaterList.end())
1370 WaterList.erase(IP);
1372 // Okay, we know we can put an island before NewMBB now, do it!
1373 MF->insert(NewMBB, NewIsland);
1375 // Update internal data structures to account for the newly inserted MBB.
1376 UpdateForInsertedWaterBlock(NewIsland);
1378 // Decrement the old entry, and remove it if refcount becomes 0.
1379 DecrementOldEntry(CPI, CPEMI);
1381 // Now that we have an island to add the CPE to, clone the original CPE and
1382 // add it to the island.
1383 U.HighWaterMark = NewIsland;
1384 U.CPEMI = BuildMI(NewIsland, DebugLoc(), TII->get(ARM::CONSTPOOL_ENTRY))
1385 .addImm(ID).addConstantPoolIndex(CPI).addImm(Size);
1386 CPEntries[CPI].push_back(CPEntry(U.CPEMI, ID, 1));
1389 // Mark the basic block as aligned as required by the const-pool entry.
1390 NewIsland->setAlignment(getCPELogAlign(U.CPEMI));
1392 // Increase the size of the island block to account for the new entry.
1393 BBInfo[NewIsland->getNumber()].Size += Size;
1394 AdjustBBOffsetsAfter(llvm::prior(MachineFunction::iterator(NewIsland)));
1396 // Finally, change the CPI in the instruction operand to be ID.
1397 for (unsigned i = 0, e = UserMI->getNumOperands(); i != e; ++i)
1398 if (UserMI->getOperand(i).isCPI()) {
1399 UserMI->getOperand(i).setIndex(ID);
1403 DEBUG(dbgs() << " Moved CPE to #" << ID << " CPI=" << CPI
1404 << format(" offset=%#x\n", BBInfo[NewIsland->getNumber()].Offset));
1409 /// RemoveDeadCPEMI - Remove a dead constant pool entry instruction. Update
1410 /// sizes and offsets of impacted basic blocks.
1411 void ARMConstantIslands::RemoveDeadCPEMI(MachineInstr *CPEMI) {
1412 MachineBasicBlock *CPEBB = CPEMI->getParent();
1413 unsigned Size = CPEMI->getOperand(2).getImm();
1414 CPEMI->eraseFromParent();
1415 BBInfo[CPEBB->getNumber()].Size -= Size;
1416 // All succeeding offsets have the current size value added in, fix this.
1417 if (CPEBB->empty()) {
1418 BBInfo[CPEBB->getNumber()].Size = 0;
1420 // This block no longer needs to be aligned. <rdar://problem/10534709>.
1421 CPEBB->setAlignment(0);
1423 // Entries are sorted by descending alignment, so realign from the front.
1424 CPEBB->setAlignment(getCPELogAlign(CPEBB->begin()));
1426 AdjustBBOffsetsAfter(CPEBB);
1427 // An island has only one predecessor BB and one successor BB. Check if
1428 // this BB's predecessor jumps directly to this BB's successor. This
1429 // shouldn't happen currently.
1430 assert(!BBIsJumpedOver(CPEBB) && "How did this happen?");
1431 // FIXME: remove the empty blocks after all the work is done?
1434 /// RemoveUnusedCPEntries - Remove constant pool entries whose refcounts
1436 bool ARMConstantIslands::RemoveUnusedCPEntries() {
1437 unsigned MadeChange = false;
1438 for (unsigned i = 0, e = CPEntries.size(); i != e; ++i) {
1439 std::vector<CPEntry> &CPEs = CPEntries[i];
1440 for (unsigned j = 0, ee = CPEs.size(); j != ee; ++j) {
1441 if (CPEs[j].RefCount == 0 && CPEs[j].CPEMI) {
1442 RemoveDeadCPEMI(CPEs[j].CPEMI);
1443 CPEs[j].CPEMI = NULL;
1451 /// BBIsInRange - Returns true if the distance between specific MI and
1452 /// specific BB can fit in MI's displacement field.
1453 bool ARMConstantIslands::BBIsInRange(MachineInstr *MI,MachineBasicBlock *DestBB,
1455 unsigned PCAdj = isThumb ? 4 : 8;
1456 unsigned BrOffset = GetOffsetOf(MI) + PCAdj;
1457 unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset;
1459 DEBUG(dbgs() << "Branch of destination BB#" << DestBB->getNumber()
1460 << " from BB#" << MI->getParent()->getNumber()
1461 << " max delta=" << MaxDisp
1462 << " from " << GetOffsetOf(MI) << " to " << DestOffset
1463 << " offset " << int(DestOffset-BrOffset) << "\t" << *MI);
1465 if (BrOffset <= DestOffset) {
1466 // Branch before the Dest.
1467 if (DestOffset-BrOffset <= MaxDisp)
1470 if (BrOffset-DestOffset <= MaxDisp)
1476 /// FixUpImmediateBr - Fix up an immediate branch whose destination is too far
1477 /// away to fit in its displacement field.
1478 bool ARMConstantIslands::FixUpImmediateBr(ImmBranch &Br) {
1479 MachineInstr *MI = Br.MI;
1480 MachineBasicBlock *DestBB = MI->getOperand(0).getMBB();
1482 // Check to see if the DestBB is already in-range.
1483 if (BBIsInRange(MI, DestBB, Br.MaxDisp))
1487 return FixUpUnconditionalBr(Br);
1488 return FixUpConditionalBr(Br);
1491 /// FixUpUnconditionalBr - Fix up an unconditional branch whose destination is
1492 /// too far away to fit in its displacement field. If the LR register has been
1493 /// spilled in the epilogue, then we can use BL to implement a far jump.
1494 /// Otherwise, add an intermediate branch instruction to a branch.
1496 ARMConstantIslands::FixUpUnconditionalBr(ImmBranch &Br) {
1497 MachineInstr *MI = Br.MI;
1498 MachineBasicBlock *MBB = MI->getParent();
1500 llvm_unreachable("FixUpUnconditionalBr is Thumb1 only!");
1502 // Use BL to implement far jump.
1503 Br.MaxDisp = (1 << 21) * 2;
1504 MI->setDesc(TII->get(ARM::tBfar));
1505 BBInfo[MBB->getNumber()].Size += 2;
1506 AdjustBBOffsetsAfter(MBB);
1510 DEBUG(dbgs() << " Changed B to long jump " << *MI);
1515 /// FixUpConditionalBr - Fix up a conditional branch whose destination is too
1516 /// far away to fit in its displacement field. It is converted to an inverse
1517 /// conditional branch + an unconditional branch to the destination.
1519 ARMConstantIslands::FixUpConditionalBr(ImmBranch &Br) {
1520 MachineInstr *MI = Br.MI;
1521 MachineBasicBlock *DestBB = MI->getOperand(0).getMBB();
1523 // Add an unconditional branch to the destination and invert the branch
1524 // condition to jump over it:
1530 ARMCC::CondCodes CC = (ARMCC::CondCodes)MI->getOperand(1).getImm();
1531 CC = ARMCC::getOppositeCondition(CC);
1532 unsigned CCReg = MI->getOperand(2).getReg();
1534 // If the branch is at the end of its MBB and that has a fall-through block,
1535 // direct the updated conditional branch to the fall-through block. Otherwise,
1536 // split the MBB before the next instruction.
1537 MachineBasicBlock *MBB = MI->getParent();
1538 MachineInstr *BMI = &MBB->back();
1539 bool NeedSplit = (BMI != MI) || !BBHasFallthrough(MBB);
1543 if (llvm::next(MachineBasicBlock::iterator(MI)) == prior(MBB->end()) &&
1544 BMI->getOpcode() == Br.UncondBr) {
1545 // Last MI in the BB is an unconditional branch. Can we simply invert the
1546 // condition and swap destinations:
1552 MachineBasicBlock *NewDest = BMI->getOperand(0).getMBB();
1553 if (BBIsInRange(MI, NewDest, Br.MaxDisp)) {
1554 DEBUG(dbgs() << " Invert Bcc condition and swap its destination with "
1556 BMI->getOperand(0).setMBB(DestBB);
1557 MI->getOperand(0).setMBB(NewDest);
1558 MI->getOperand(1).setImm(CC);
1565 SplitBlockBeforeInstr(MI);
1566 // No need for the branch to the next block. We're adding an unconditional
1567 // branch to the destination.
1568 int delta = TII->GetInstSizeInBytes(&MBB->back());
1569 BBInfo[MBB->getNumber()].Size -= delta;
1570 MBB->back().eraseFromParent();
1571 // BBInfo[SplitBB].Offset is wrong temporarily, fixed below
1573 MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(MBB));
1575 DEBUG(dbgs() << " Insert B to BB#" << DestBB->getNumber()
1576 << " also invert condition and change dest. to BB#"
1577 << NextBB->getNumber() << "\n");
1579 // Insert a new conditional branch and a new unconditional branch.
1580 // Also update the ImmBranch as well as adding a new entry for the new branch.
1581 BuildMI(MBB, DebugLoc(), TII->get(MI->getOpcode()))
1582 .addMBB(NextBB).addImm(CC).addReg(CCReg);
1583 Br.MI = &MBB->back();
1584 BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back());
1586 BuildMI(MBB, DebugLoc(), TII->get(Br.UncondBr)).addMBB(DestBB)
1587 .addImm(ARMCC::AL).addReg(0);
1589 BuildMI(MBB, DebugLoc(), TII->get(Br.UncondBr)).addMBB(DestBB);
1590 BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back());
1591 unsigned MaxDisp = getUnconditionalBrDisp(Br.UncondBr);
1592 ImmBranches.push_back(ImmBranch(&MBB->back(), MaxDisp, false, Br.UncondBr));
1594 // Remove the old conditional branch. It may or may not still be in MBB.
1595 BBInfo[MI->getParent()->getNumber()].Size -= TII->GetInstSizeInBytes(MI);
1596 MI->eraseFromParent();
1597 AdjustBBOffsetsAfter(MBB);
1601 /// UndoLRSpillRestore - Remove Thumb push / pop instructions that only spills
1602 /// LR / restores LR to pc. FIXME: This is done here because it's only possible
1603 /// to do this if tBfar is not used.
1604 bool ARMConstantIslands::UndoLRSpillRestore() {
1605 bool MadeChange = false;
1606 for (unsigned i = 0, e = PushPopMIs.size(); i != e; ++i) {
1607 MachineInstr *MI = PushPopMIs[i];
1608 // First two operands are predicates.
1609 if (MI->getOpcode() == ARM::tPOP_RET &&
1610 MI->getOperand(2).getReg() == ARM::PC &&
1611 MI->getNumExplicitOperands() == 3) {
1612 // Create the new insn and copy the predicate from the old.
1613 BuildMI(MI->getParent(), MI->getDebugLoc(), TII->get(ARM::tBX_RET))
1614 .addOperand(MI->getOperand(0))
1615 .addOperand(MI->getOperand(1));
1616 MI->eraseFromParent();
1623 bool ARMConstantIslands::OptimizeThumb2Instructions() {
1624 bool MadeChange = false;
1626 // Shrink ADR and LDR from constantpool.
1627 for (unsigned i = 0, e = CPUsers.size(); i != e; ++i) {
1628 CPUser &U = CPUsers[i];
1629 unsigned Opcode = U.MI->getOpcode();
1630 unsigned NewOpc = 0;
1635 case ARM::t2LEApcrel:
1636 if (isARMLowRegister(U.MI->getOperand(0).getReg())) {
1637 NewOpc = ARM::tLEApcrel;
1643 if (isARMLowRegister(U.MI->getOperand(0).getReg())) {
1644 NewOpc = ARM::tLDRpci;
1654 unsigned UserOffset = GetOffsetOf(U.MI) + 4;
1655 unsigned MaxOffs = ((1 << Bits) - 1) * Scale;
1656 // FIXME: Check if offset is multiple of scale if scale is not 4.
1657 if (CPEIsInRange(U.MI, UserOffset, U.CPEMI, MaxOffs, false, true)) {
1658 U.MI->setDesc(TII->get(NewOpc));
1659 MachineBasicBlock *MBB = U.MI->getParent();
1660 BBInfo[MBB->getNumber()].Size -= 2;
1661 AdjustBBOffsetsAfter(MBB);
1667 MadeChange |= OptimizeThumb2Branches();
1668 MadeChange |= OptimizeThumb2JumpTables();
1672 bool ARMConstantIslands::OptimizeThumb2Branches() {
1673 bool MadeChange = false;
1675 for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i) {
1676 ImmBranch &Br = ImmBranches[i];
1677 unsigned Opcode = Br.MI->getOpcode();
1678 unsigned NewOpc = 0;
1696 unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale;
1697 MachineBasicBlock *DestBB = Br.MI->getOperand(0).getMBB();
1698 if (BBIsInRange(Br.MI, DestBB, MaxOffs)) {
1699 Br.MI->setDesc(TII->get(NewOpc));
1700 MachineBasicBlock *MBB = Br.MI->getParent();
1701 BBInfo[MBB->getNumber()].Size -= 2;
1702 AdjustBBOffsetsAfter(MBB);
1708 Opcode = Br.MI->getOpcode();
1709 if (Opcode != ARM::tBcc)
1713 unsigned PredReg = 0;
1714 ARMCC::CondCodes Pred = llvm::getInstrPredicate(Br.MI, PredReg);
1715 if (Pred == ARMCC::EQ)
1717 else if (Pred == ARMCC::NE)
1718 NewOpc = ARM::tCBNZ;
1721 MachineBasicBlock *DestBB = Br.MI->getOperand(0).getMBB();
1722 // Check if the distance is within 126. Subtract starting offset by 2
1723 // because the cmp will be eliminated.
1724 unsigned BrOffset = GetOffsetOf(Br.MI) + 4 - 2;
1725 unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset;
1726 if (BrOffset < DestOffset && (DestOffset - BrOffset) <= 126) {
1727 MachineBasicBlock::iterator CmpMI = Br.MI;
1728 if (CmpMI != Br.MI->getParent()->begin()) {
1730 if (CmpMI->getOpcode() == ARM::tCMPi8) {
1731 unsigned Reg = CmpMI->getOperand(0).getReg();
1732 Pred = llvm::getInstrPredicate(CmpMI, PredReg);
1733 if (Pred == ARMCC::AL &&
1734 CmpMI->getOperand(1).getImm() == 0 &&
1735 isARMLowRegister(Reg)) {
1736 MachineBasicBlock *MBB = Br.MI->getParent();
1737 MachineInstr *NewBR =
1738 BuildMI(*MBB, CmpMI, Br.MI->getDebugLoc(), TII->get(NewOpc))
1739 .addReg(Reg).addMBB(DestBB,Br.MI->getOperand(0).getTargetFlags());
1740 CmpMI->eraseFromParent();
1741 Br.MI->eraseFromParent();
1743 BBInfo[MBB->getNumber()].Size -= 2;
1744 AdjustBBOffsetsAfter(MBB);
1756 /// OptimizeThumb2JumpTables - Use tbb / tbh instructions to generate smaller
1757 /// jumptables when it's possible.
1758 bool ARMConstantIslands::OptimizeThumb2JumpTables() {
1759 bool MadeChange = false;
1761 // FIXME: After the tables are shrunk, can we get rid some of the
1762 // constantpool tables?
1763 MachineJumpTableInfo *MJTI = MF->getJumpTableInfo();
1764 if (MJTI == 0) return false;
1766 const std::vector<MachineJumpTableEntry> &JT = MJTI->getJumpTables();
1767 for (unsigned i = 0, e = T2JumpTables.size(); i != e; ++i) {
1768 MachineInstr *MI = T2JumpTables[i];
1769 const MCInstrDesc &MCID = MI->getDesc();
1770 unsigned NumOps = MCID.getNumOperands();
1771 unsigned JTOpIdx = NumOps - (MI->isPredicable() ? 3 : 2);
1772 MachineOperand JTOP = MI->getOperand(JTOpIdx);
1773 unsigned JTI = JTOP.getIndex();
1774 assert(JTI < JT.size());
1777 bool HalfWordOk = true;
1778 unsigned JTOffset = GetOffsetOf(MI) + 4;
1779 const std::vector<MachineBasicBlock*> &JTBBs = JT[JTI].MBBs;
1780 for (unsigned j = 0, ee = JTBBs.size(); j != ee; ++j) {
1781 MachineBasicBlock *MBB = JTBBs[j];
1782 unsigned DstOffset = BBInfo[MBB->getNumber()].Offset;
1783 // Negative offset is not ok. FIXME: We should change BB layout to make
1784 // sure all the branches are forward.
1785 if (ByteOk && (DstOffset - JTOffset) > ((1<<8)-1)*2)
1787 unsigned TBHLimit = ((1<<16)-1)*2;
1788 if (HalfWordOk && (DstOffset - JTOffset) > TBHLimit)
1790 if (!ByteOk && !HalfWordOk)
1794 if (ByteOk || HalfWordOk) {
1795 MachineBasicBlock *MBB = MI->getParent();
1796 unsigned BaseReg = MI->getOperand(0).getReg();
1797 bool BaseRegKill = MI->getOperand(0).isKill();
1800 unsigned IdxReg = MI->getOperand(1).getReg();
1801 bool IdxRegKill = MI->getOperand(1).isKill();
1803 // Scan backwards to find the instruction that defines the base
1804 // register. Due to post-RA scheduling, we can't count on it
1805 // immediately preceding the branch instruction.
1806 MachineBasicBlock::iterator PrevI = MI;
1807 MachineBasicBlock::iterator B = MBB->begin();
1808 while (PrevI != B && !PrevI->definesRegister(BaseReg))
1811 // If for some reason we didn't find it, we can't do anything, so
1812 // just skip this one.
1813 if (!PrevI->definesRegister(BaseReg))
1816 MachineInstr *AddrMI = PrevI;
1818 // Examine the instruction that calculates the jumptable entry address.
1819 // Make sure it only defines the base register and kills any uses
1820 // other than the index register.
1821 for (unsigned k = 0, eee = AddrMI->getNumOperands(); k != eee; ++k) {
1822 const MachineOperand &MO = AddrMI->getOperand(k);
1823 if (!MO.isReg() || !MO.getReg())
1825 if (MO.isDef() && MO.getReg() != BaseReg) {
1829 if (MO.isUse() && !MO.isKill() && MO.getReg() != IdxReg) {
1837 // Now scan back again to find the tLEApcrel or t2LEApcrelJT instruction
1838 // that gave us the initial base register definition.
1839 for (--PrevI; PrevI != B && !PrevI->definesRegister(BaseReg); --PrevI)
1842 // The instruction should be a tLEApcrel or t2LEApcrelJT; we want
1843 // to delete it as well.
1844 MachineInstr *LeaMI = PrevI;
1845 if ((LeaMI->getOpcode() != ARM::tLEApcrelJT &&
1846 LeaMI->getOpcode() != ARM::t2LEApcrelJT) ||
1847 LeaMI->getOperand(0).getReg() != BaseReg)
1853 unsigned Opc = ByteOk ? ARM::t2TBB_JT : ARM::t2TBH_JT;
1854 MachineInstr *NewJTMI = BuildMI(MBB, MI->getDebugLoc(), TII->get(Opc))
1855 .addReg(IdxReg, getKillRegState(IdxRegKill))
1856 .addJumpTableIndex(JTI, JTOP.getTargetFlags())
1857 .addImm(MI->getOperand(JTOpIdx+1).getImm());
1858 // FIXME: Insert an "ALIGN" instruction to ensure the next instruction
1859 // is 2-byte aligned. For now, asm printer will fix it up.
1860 unsigned NewSize = TII->GetInstSizeInBytes(NewJTMI);
1861 unsigned OrigSize = TII->GetInstSizeInBytes(AddrMI);
1862 OrigSize += TII->GetInstSizeInBytes(LeaMI);
1863 OrigSize += TII->GetInstSizeInBytes(MI);
1865 AddrMI->eraseFromParent();
1866 LeaMI->eraseFromParent();
1867 MI->eraseFromParent();
1869 int delta = OrigSize - NewSize;
1870 BBInfo[MBB->getNumber()].Size -= delta;
1871 AdjustBBOffsetsAfter(MBB);
1881 /// ReorderThumb2JumpTables - Adjust the function's block layout to ensure that
1882 /// jump tables always branch forwards, since that's what tbb and tbh need.
1883 bool ARMConstantIslands::ReorderThumb2JumpTables() {
1884 bool MadeChange = false;
1886 MachineJumpTableInfo *MJTI = MF->getJumpTableInfo();
1887 if (MJTI == 0) return false;
1889 const std::vector<MachineJumpTableEntry> &JT = MJTI->getJumpTables();
1890 for (unsigned i = 0, e = T2JumpTables.size(); i != e; ++i) {
1891 MachineInstr *MI = T2JumpTables[i];
1892 const MCInstrDesc &MCID = MI->getDesc();
1893 unsigned NumOps = MCID.getNumOperands();
1894 unsigned JTOpIdx = NumOps - (MI->isPredicable() ? 3 : 2);
1895 MachineOperand JTOP = MI->getOperand(JTOpIdx);
1896 unsigned JTI = JTOP.getIndex();
1897 assert(JTI < JT.size());
1899 // We prefer if target blocks for the jump table come after the jump
1900 // instruction so we can use TB[BH]. Loop through the target blocks
1901 // and try to adjust them such that that's true.
1902 int JTNumber = MI->getParent()->getNumber();
1903 const std::vector<MachineBasicBlock*> &JTBBs = JT[JTI].MBBs;
1904 for (unsigned j = 0, ee = JTBBs.size(); j != ee; ++j) {
1905 MachineBasicBlock *MBB = JTBBs[j];
1906 int DTNumber = MBB->getNumber();
1908 if (DTNumber < JTNumber) {
1909 // The destination precedes the switch. Try to move the block forward
1910 // so we have a positive offset.
1911 MachineBasicBlock *NewBB =
1912 AdjustJTTargetBlockForward(MBB, MI->getParent());
1914 MJTI->ReplaceMBBInJumpTable(JTI, JTBBs[j], NewBB);
1923 MachineBasicBlock *ARMConstantIslands::
1924 AdjustJTTargetBlockForward(MachineBasicBlock *BB, MachineBasicBlock *JTBB)
1926 // If the destination block is terminated by an unconditional branch,
1927 // try to move it; otherwise, create a new block following the jump
1928 // table that branches back to the actual target. This is a very simple
1929 // heuristic. FIXME: We can definitely improve it.
1930 MachineBasicBlock *TBB = 0, *FBB = 0;
1931 SmallVector<MachineOperand, 4> Cond;
1932 SmallVector<MachineOperand, 4> CondPrior;
1933 MachineFunction::iterator BBi = BB;
1934 MachineFunction::iterator OldPrior = prior(BBi);
1936 // If the block terminator isn't analyzable, don't try to move the block
1937 bool B = TII->AnalyzeBranch(*BB, TBB, FBB, Cond);
1939 // If the block ends in an unconditional branch, move it. The prior block
1940 // has to have an analyzable terminator for us to move this one. Be paranoid
1941 // and make sure we're not trying to move the entry block of the function.
1942 if (!B && Cond.empty() && BB != MF->begin() &&
1943 !TII->AnalyzeBranch(*OldPrior, TBB, FBB, CondPrior)) {
1944 BB->moveAfter(JTBB);
1945 OldPrior->updateTerminator();
1946 BB->updateTerminator();
1947 // Update numbering to account for the block being moved.
1948 MF->RenumberBlocks();
1953 // Create a new MBB for the code after the jump BB.
1954 MachineBasicBlock *NewBB =
1955 MF->CreateMachineBasicBlock(JTBB->getBasicBlock());
1956 MachineFunction::iterator MBBI = JTBB; ++MBBI;
1957 MF->insert(MBBI, NewBB);
1959 // Add an unconditional branch from NewBB to BB.
1960 // There doesn't seem to be meaningful DebugInfo available; this doesn't
1961 // correspond directly to anything in the source.
1962 assert (isThumb2 && "Adjusting for TB[BH] but not in Thumb2?");
1963 BuildMI(NewBB, DebugLoc(), TII->get(ARM::t2B)).addMBB(BB)
1964 .addImm(ARMCC::AL).addReg(0);
1966 // Update internal data structures to account for the newly inserted MBB.
1967 MF->RenumberBlocks(NewBB);
1970 NewBB->addSuccessor(BB);
1971 JTBB->removeSuccessor(BB);
1972 JTBB->addSuccessor(NewBB);