1//===- MipsConstantIslandPass.cpp - Emit Pc Relative loads ----------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This pass is used to make Pc relative loads of constants.
10// For now, only Mips16 will use this.
11//
12// Loading constants inline is expensive on Mips16 and it's in general better
13// to place the constant nearby in code space and then it can be loaded with a
14// simple 16 bit load instruction.
15//
16// The constants can be not just numbers but addresses of functions and labels.
17// This can be particularly helpful in static relocation mode for embedded
18// non-linux targets.
19//
20//===----------------------------------------------------------------------===//
21
22#include "Mips.h"
23#include "Mips16InstrInfo.h"
24#include "MipsMachineFunction.h"
25#include "MipsSubtarget.h"
26#include "llvm/ADT/STLExtras.h"
27#include "llvm/ADT/SmallSet.h"
28#include "llvm/ADT/SmallVector.h"
29#include "llvm/ADT/Statistic.h"
30#include "llvm/ADT/StringRef.h"
31#include "llvm/CodeGen/MachineBasicBlock.h"
32#include "llvm/CodeGen/MachineConstantPool.h"
33#include "llvm/CodeGen/MachineFunction.h"
34#include "llvm/CodeGen/MachineFunctionPass.h"
35#include "llvm/CodeGen/MachineInstr.h"
36#include "llvm/CodeGen/MachineInstrBuilder.h"
37#include "llvm/CodeGen/MachineOperand.h"
38#include "llvm/CodeGen/MachineRegisterInfo.h"
39#include "llvm/Config/llvm-config.h"
40#include "llvm/IR/Constants.h"
41#include "llvm/IR/DataLayout.h"
42#include "llvm/IR/DebugLoc.h"
43#include "llvm/IR/Function.h"
44#include "llvm/IR/Type.h"
45#include "llvm/Support/CommandLine.h"
46#include "llvm/Support/Compiler.h"
47#include "llvm/Support/Debug.h"
48#include "llvm/Support/ErrorHandling.h"
49#include "llvm/Support/Format.h"
50#include "llvm/Support/MathExtras.h"
51#include "llvm/Support/raw_ostream.h"
52#include <algorithm>
53#include <cassert>
54#include <cstdint>
55#include <iterator>
56#include <vector>
57
58using namespace llvm;
59
60#define DEBUG_TYPE "mips-constant-islands"
61
62STATISTIC(NumCPEs, "Number of constpool entries");
63STATISTIC(NumSplit, "Number of uncond branches inserted");
64STATISTIC(NumCBrFixed, "Number of cond branches fixed");
65STATISTIC(NumUBrFixed, "Number of uncond branches fixed");
66
67// FIXME: This option should be removed once it has received sufficient testing.
68static cl::opt<bool>
69AlignConstantIslands("mips-align-constant-islands", cl::Hidden, cl::init(Val: true),
70 cl::desc("Align constant islands in code"));
71
72// Rather than do make check tests with huge amounts of code, we force
73// the test to use this amount.
74static cl::opt<int> ConstantIslandsSmallOffset(
75 "mips-constant-islands-small-offset",
76 cl::init(Val: 0),
77 cl::desc("Make small offsets be this amount for testing purposes"),
78 cl::Hidden);
79
80// For testing purposes we tell it to not use relaxed load forms so that it
81// will split blocks.
82static cl::opt<bool> NoLoadRelaxation(
83 "mips-constant-islands-no-load-relaxation",
84 cl::init(Val: false),
85 cl::desc("Don't relax loads to long loads - for testing purposes"),
86 cl::Hidden);
87
88static unsigned int branchTargetOperand(MachineInstr *MI) {
89 switch (MI->getOpcode()) {
90 case Mips::Bimm16:
91 case Mips::BimmX16:
92 case Mips::Bteqz16:
93 case Mips::BteqzX16:
94 case Mips::Btnez16:
95 case Mips::BtnezX16:
96 case Mips::JalB16:
97 return 0;
98 case Mips::BeqzRxImm16:
99 case Mips::BeqzRxImmX16:
100 case Mips::BnezRxImm16:
101 case Mips::BnezRxImmX16:
102 return 1;
103 }
104 llvm_unreachable("Unknown branch type");
105}
106
107static unsigned int longformBranchOpcode(unsigned int Opcode) {
108 switch (Opcode) {
109 case Mips::Bimm16:
110 case Mips::BimmX16:
111 return Mips::BimmX16;
112 case Mips::Bteqz16:
113 case Mips::BteqzX16:
114 return Mips::BteqzX16;
115 case Mips::Btnez16:
116 case Mips::BtnezX16:
117 return Mips::BtnezX16;
118 case Mips::JalB16:
119 return Mips::JalB16;
120 case Mips::BeqzRxImm16:
121 case Mips::BeqzRxImmX16:
122 return Mips::BeqzRxImmX16;
123 case Mips::BnezRxImm16:
124 case Mips::BnezRxImmX16:
125 return Mips::BnezRxImmX16;
126 }
127 llvm_unreachable("Unknown branch type");
128}
129
130// FIXME: need to go through this whole constant islands port and check
131// the math for branch ranges and clean this up and make some functions
132// to calculate things that are done many times identically.
133// Need to refactor some of the code to call this routine.
134static unsigned int branchMaxOffsets(unsigned int Opcode) {
135 unsigned Bits, Scale;
136 switch (Opcode) {
137 case Mips::Bimm16:
138 Bits = 11;
139 Scale = 2;
140 break;
141 case Mips::BimmX16:
142 Bits = 16;
143 Scale = 2;
144 break;
145 case Mips::BeqzRxImm16:
146 Bits = 8;
147 Scale = 2;
148 break;
149 case Mips::BeqzRxImmX16:
150 Bits = 16;
151 Scale = 2;
152 break;
153 case Mips::BnezRxImm16:
154 Bits = 8;
155 Scale = 2;
156 break;
157 case Mips::BnezRxImmX16:
158 Bits = 16;
159 Scale = 2;
160 break;
161 case Mips::Bteqz16:
162 Bits = 8;
163 Scale = 2;
164 break;
165 case Mips::BteqzX16:
166 Bits = 16;
167 Scale = 2;
168 break;
169 case Mips::Btnez16:
170 Bits = 8;
171 Scale = 2;
172 break;
173 case Mips::BtnezX16:
174 Bits = 16;
175 Scale = 2;
176 break;
177 default:
178 llvm_unreachable("Unknown branch type");
179 }
180 unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale;
181 return MaxOffs;
182}
183
184namespace {
185
186 using Iter = MachineBasicBlock::iterator;
187 using ReverseIter = MachineBasicBlock::reverse_iterator;
188
189 /// MipsConstantIslands - Due to limited PC-relative displacements, Mips
190 /// requires constant pool entries to be scattered among the instructions
191 /// inside a function. To do this, it completely ignores the normal LLVM
192 /// constant pool; instead, it places constants wherever it feels like with
193 /// special instructions.
194 ///
195 /// The terminology used in this pass includes:
196 /// Islands - Clumps of constants placed in the function.
197 /// Water - Potential places where an island could be formed.
198 /// CPE - A constant pool entry that has been placed somewhere, which
199 /// tracks a list of users.
200
201 class MipsConstantIslands : public MachineFunctionPass {
202 /// BasicBlockInfo - Information about the offset and size of a single
203 /// basic block.
204 struct BasicBlockInfo {
205 /// Offset - Distance from the beginning of the function to the beginning
206 /// of this basic block.
207 ///
208 /// Offsets are computed assuming worst case padding before an aligned
209 /// block. This means that subtracting basic block offsets always gives a
210 /// conservative estimate of the real distance which may be smaller.
211 ///
212 /// Because worst case padding is used, the computed offset of an aligned
213 /// block may not actually be aligned.
214 unsigned Offset = 0;
215
216 /// Size - Size of the basic block in bytes. If the block contains
217 /// inline assembly, this is a worst case estimate.
218 ///
219 /// The size does not include any alignment padding whether from the
220 /// beginning of the block, or from an aligned jump table at the end.
221 unsigned Size = 0;
222
223 BasicBlockInfo() = default;
224
225 unsigned postOffset() const { return Offset + Size; }
226 };
227
228 std::vector<BasicBlockInfo> BBInfo;
229
230 /// WaterList - A sorted list of basic blocks where islands could be placed
231 /// (i.e. blocks that don't fall through to the following block, due
232 /// to a return, unreachable, or unconditional branch).
233 std::vector<MachineBasicBlock*> WaterList;
234
235 /// NewWaterList - The subset of WaterList that was created since the
236 /// previous iteration by inserting unconditional branches.
237 SmallSet<MachineBasicBlock*, 4> NewWaterList;
238
239 using water_iterator = std::vector<MachineBasicBlock *>::iterator;
240
241 /// CPUser - One user of a constant pool, keeping the machine instruction
242 /// pointer, the constant pool being referenced, and the max displacement
243 /// allowed from the instruction to the CP. The HighWaterMark records the
244 /// highest basic block where a new CPEntry can be placed. To ensure this
245 /// pass terminates, the CP entries are initially placed at the end of the
246 /// function and then move monotonically to lower addresses. The
247 /// exception to this rule is when the current CP entry for a particular
248 /// CPUser is out of range, but there is another CP entry for the same
249 /// constant value in range. We want to use the existing in-range CP
250 /// entry, but if it later moves out of range, the search for new water
251 /// should resume where it left off. The HighWaterMark is used to record
252 /// that point.
253 struct CPUser {
254 MachineInstr *MI;
255 MachineInstr *CPEMI;
256 MachineBasicBlock *HighWaterMark;
257
258 private:
259 unsigned MaxDisp;
260 unsigned LongFormMaxDisp; // mips16 has 16/32 bit instructions
261 // with different displacements
262 unsigned LongFormOpcode;
263
264 public:
265 bool NegOk;
266
267 CPUser(MachineInstr *mi, MachineInstr *cpemi, unsigned maxdisp,
268 bool neg,
269 unsigned longformmaxdisp, unsigned longformopcode)
270 : MI(mi), CPEMI(cpemi), MaxDisp(maxdisp),
271 LongFormMaxDisp(longformmaxdisp), LongFormOpcode(longformopcode),
272 NegOk(neg){
273 HighWaterMark = CPEMI->getParent();
274 }
275
276 /// getMaxDisp - Returns the maximum displacement supported by MI.
277 unsigned getMaxDisp() const {
278 unsigned xMaxDisp = ConstantIslandsSmallOffset?
279 ConstantIslandsSmallOffset: MaxDisp;
280 return xMaxDisp;
281 }
282
283 void setMaxDisp(unsigned val) {
284 MaxDisp = val;
285 }
286
287 unsigned getLongFormMaxDisp() const {
288 return LongFormMaxDisp;
289 }
290
291 unsigned getLongFormOpcode() const {
292 return LongFormOpcode;
293 }
294 };
295
296 /// CPUsers - Keep track of all of the machine instructions that use various
297 /// constant pools and their max displacement.
298 std::vector<CPUser> CPUsers;
299
300 /// CPEntry - One per constant pool entry, keeping the machine instruction
301 /// pointer, the constpool index, and the number of CPUser's which
302 /// reference this entry.
303 struct CPEntry {
304 MachineInstr *CPEMI;
305 unsigned CPI;
306 unsigned RefCount;
307
308 CPEntry(MachineInstr *cpemi, unsigned cpi, unsigned rc = 0)
309 : CPEMI(cpemi), CPI(cpi), RefCount(rc) {}
310 };
311
312 /// CPEntries - Keep track of all of the constant pool entry machine
313 /// instructions. For each original constpool index (i.e. those that
314 /// existed upon entry to this pass), it keeps a vector of entries.
315 /// Original elements are cloned as we go along; the clones are
316 /// put in the vector of the original element, but have distinct CPIs.
317 std::vector<std::vector<CPEntry>> CPEntries;
318
319 /// ImmBranch - One per immediate branch, keeping the machine instruction
320 /// pointer, conditional or unconditional, the max displacement,
321 /// and (if isCond is true) the corresponding unconditional branch
322 /// opcode.
323 struct ImmBranch {
324 MachineInstr *MI;
325 unsigned MaxDisp : 31;
326 bool isCond : 1;
327 int UncondBr;
328
329 ImmBranch(MachineInstr *mi, unsigned maxdisp, bool cond, int ubr)
330 : MI(mi), MaxDisp(maxdisp), isCond(cond), UncondBr(ubr) {}
331 };
332
333 /// ImmBranches - Keep track of all the immediate branch instructions.
334 ///
335 std::vector<ImmBranch> ImmBranches;
336
337 /// HasFarJump - True if any far jump instruction has been emitted during
338 /// the branch fix up pass.
339 bool HasFarJump;
340
341 const MipsSubtarget *STI = nullptr;
342 const Mips16InstrInfo *TII;
343 MipsFunctionInfo *MFI;
344 MachineFunction *MF = nullptr;
345 MachineConstantPool *MCP = nullptr;
346
347 unsigned PICLabelUId;
348 bool PrescannedForConstants = false;
349
350 void initPICLabelUId(unsigned UId) {
351 PICLabelUId = UId;
352 }
353
354 unsigned createPICLabelUId() {
355 return PICLabelUId++;
356 }
357
358 public:
359 static char ID;
360
361 MipsConstantIslands() : MachineFunctionPass(ID) {}
362
363 StringRef getPassName() const override { return "Mips Constant Islands"; }
364
365 bool runOnMachineFunction(MachineFunction &F) override;
366
367 MachineFunctionProperties getRequiredProperties() const override {
368 return MachineFunctionProperties().set(
369 MachineFunctionProperties::Property::NoVRegs);
370 }
371
372 void doInitialPlacement(std::vector<MachineInstr*> &CPEMIs);
373 CPEntry *findConstPoolEntry(unsigned CPI, const MachineInstr *CPEMI);
374 Align getCPEAlign(const MachineInstr &CPEMI);
375 void initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs);
376 unsigned getOffsetOf(MachineInstr *MI) const;
377 unsigned getUserOffset(CPUser&) const;
378 void dumpBBs();
379
380 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset,
381 unsigned Disp, bool NegativeOK);
382 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset,
383 const CPUser &U);
384
385 void computeBlockSize(MachineBasicBlock *MBB);
386 MachineBasicBlock *splitBlockBeforeInstr(MachineInstr &MI);
387 void updateForInsertedWaterBlock(MachineBasicBlock *NewBB);
388 void adjustBBOffsetsAfter(MachineBasicBlock *BB);
389 bool decrementCPEReferenceCount(unsigned CPI, MachineInstr* CPEMI);
390 int findInRangeCPEntry(CPUser& U, unsigned UserOffset);
391 int findLongFormInRangeCPEntry(CPUser& U, unsigned UserOffset);
392 bool findAvailableWater(CPUser&U, unsigned UserOffset,
393 water_iterator &WaterIter);
394 void createNewWater(unsigned CPUserIndex, unsigned UserOffset,
395 MachineBasicBlock *&NewMBB);
396 bool handleConstantPoolUser(unsigned CPUserIndex);
397 void removeDeadCPEMI(MachineInstr *CPEMI);
398 bool removeUnusedCPEntries();
399 bool isCPEntryInRange(MachineInstr *MI, unsigned UserOffset,
400 MachineInstr *CPEMI, unsigned Disp, bool NegOk,
401 bool DoDump = false);
402 bool isWaterInRange(unsigned UserOffset, MachineBasicBlock *Water,
403 CPUser &U, unsigned &Growth);
404 bool isBBInRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned Disp);
405 bool fixupImmediateBr(ImmBranch &Br);
406 bool fixupConditionalBr(ImmBranch &Br);
407 bool fixupUnconditionalBr(ImmBranch &Br);
408
409 void prescanForConstants();
410 };
411
412} // end anonymous namespace
413
414char MipsConstantIslands::ID = 0;
415
416bool MipsConstantIslands::isOffsetInRange
417 (unsigned UserOffset, unsigned TrialOffset,
418 const CPUser &U) {
419 return isOffsetInRange(UserOffset, TrialOffset,
420 Disp: U.getMaxDisp(), NegativeOK: U.NegOk);
421}
422
423#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
424/// print block size and offset information - debugging
425LLVM_DUMP_METHOD void MipsConstantIslands::dumpBBs() {
426 for (unsigned J = 0, E = BBInfo.size(); J !=E; ++J) {
427 const BasicBlockInfo &BBI = BBInfo[J];
428 dbgs() << format("%08x %bb.%u\t", BBI.Offset, J)
429 << format(" size=%#x\n", BBInfo[J].Size);
430 }
431}
432#endif
433
434bool MipsConstantIslands::runOnMachineFunction(MachineFunction &mf) {
435 // The intention is for this to be a mips16 only pass for now
436 // FIXME:
437 MF = &mf;
438 MCP = mf.getConstantPool();
439 STI = &mf.getSubtarget<MipsSubtarget>();
440 LLVM_DEBUG(dbgs() << "constant island machine function "
441 << "\n");
442 if (!STI->inMips16Mode() || !MipsSubtarget::useConstantIslands()) {
443 return false;
444 }
445 TII = (const Mips16InstrInfo *)STI->getInstrInfo();
446 MFI = MF->getInfo<MipsFunctionInfo>();
447 LLVM_DEBUG(dbgs() << "constant island processing "
448 << "\n");
449 //
450 // will need to make predermination if there is any constants we need to
451 // put in constant islands. TBD.
452 //
453 if (!PrescannedForConstants) prescanForConstants();
454
455 HasFarJump = false;
456 // This pass invalidates liveness information when it splits basic blocks.
457 MF->getRegInfo().invalidateLiveness();
458
459 // Renumber all of the machine basic blocks in the function, guaranteeing that
460 // the numbers agree with the position of the block in the function.
461 MF->RenumberBlocks();
462
463 bool MadeChange = false;
464
465 // Perform the initial placement of the constant pool entries. To start with,
466 // we put them all at the end of the function.
467 std::vector<MachineInstr*> CPEMIs;
468 if (!MCP->isEmpty())
469 doInitialPlacement(CPEMIs);
470
471 /// The next UID to take is the first unused one.
472 initPICLabelUId(UId: CPEMIs.size());
473
474 // Do the initial scan of the function, building up information about the
475 // sizes of each block, the location of all the water, and finding all of the
476 // constant pool users.
477 initializeFunctionInfo(CPEMIs);
478 CPEMIs.clear();
479 LLVM_DEBUG(dumpBBs());
480
481 /// Remove dead constant pool entries.
482 MadeChange |= removeUnusedCPEntries();
483
484 // Iteratively place constant pool entries and fix up branches until there
485 // is no change.
486 unsigned NoCPIters = 0, NoBRIters = 0;
487 (void)NoBRIters;
488 while (true) {
489 LLVM_DEBUG(dbgs() << "Beginning CP iteration #" << NoCPIters << '\n');
490 bool CPChange = false;
491 for (unsigned i = 0, e = CPUsers.size(); i != e; ++i)
492 CPChange |= handleConstantPoolUser(CPUserIndex: i);
493 if (CPChange && ++NoCPIters > 30)
494 report_fatal_error(reason: "Constant Island pass failed to converge!");
495 LLVM_DEBUG(dumpBBs());
496
497 // Clear NewWaterList now. If we split a block for branches, it should
498 // appear as "new water" for the next iteration of constant pool placement.
499 NewWaterList.clear();
500
501 LLVM_DEBUG(dbgs() << "Beginning BR iteration #" << NoBRIters << '\n');
502 bool BRChange = false;
503 for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i)
504 BRChange |= fixupImmediateBr(Br&: ImmBranches[i]);
505 if (BRChange && ++NoBRIters > 30)
506 report_fatal_error(reason: "Branch Fix Up pass failed to converge!");
507 LLVM_DEBUG(dumpBBs());
508 if (!CPChange && !BRChange)
509 break;
510 MadeChange = true;
511 }
512
513 LLVM_DEBUG(dbgs() << '\n'; dumpBBs());
514
515 BBInfo.clear();
516 WaterList.clear();
517 CPUsers.clear();
518 CPEntries.clear();
519 ImmBranches.clear();
520 return MadeChange;
521}
522
523/// doInitialPlacement - Perform the initial placement of the constant pool
524/// entries. To start with, we put them all at the end of the function.
525void
526MipsConstantIslands::doInitialPlacement(std::vector<MachineInstr*> &CPEMIs) {
527 // Create the basic block to hold the CPE's.
528 MachineBasicBlock *BB = MF->CreateMachineBasicBlock();
529 MF->push_back(MBB: BB);
530
531 // MachineConstantPool measures alignment in bytes. We measure in log2(bytes).
532 const Align MaxAlign = MCP->getConstantPoolAlign();
533
534 // Mark the basic block as required by the const-pool.
535 // If AlignConstantIslands isn't set, use 4-byte alignment for everything.
536 BB->setAlignment(AlignConstantIslands ? MaxAlign : Align(4));
537
538 // The function needs to be as aligned as the basic blocks. The linker may
539 // move functions around based on their alignment.
540 MF->ensureAlignment(A: BB->getAlignment());
541
542 // Order the entries in BB by descending alignment. That ensures correct
543 // alignment of all entries as long as BB is sufficiently aligned. Keep
544 // track of the insertion point for each alignment. We are going to bucket
545 // sort the entries as they are created.
546 SmallVector<MachineBasicBlock::iterator, 8> InsPoint(Log2(A: MaxAlign) + 1,
547 BB->end());
548
549 // Add all of the constants from the constant pool to the end block, use an
550 // identity mapping of CPI's to CPE's.
551 const std::vector<MachineConstantPoolEntry> &CPs = MCP->getConstants();
552
553 const DataLayout &TD = MF->getDataLayout();
554 for (unsigned i = 0, e = CPs.size(); i != e; ++i) {
555 unsigned Size = CPs[i].getSizeInBytes(DL: TD);
556 assert(Size >= 4 && "Too small constant pool entry");
557 Align Alignment = CPs[i].getAlign();
558 // Verify that all constant pool entries are a multiple of their alignment.
559 // If not, we would have to pad them out so that instructions stay aligned.
560 assert(isAligned(Alignment, Size) && "CP Entry not multiple of 4 bytes!");
561
562 // Insert CONSTPOOL_ENTRY before entries with a smaller alignment.
563 unsigned LogAlign = Log2(A: Alignment);
564 MachineBasicBlock::iterator InsAt = InsPoint[LogAlign];
565
566 MachineInstr *CPEMI =
567 BuildMI(BB&: *BB, I: InsAt, MIMD: DebugLoc(), MCID: TII->get(Opcode: Mips::CONSTPOOL_ENTRY))
568 .addImm(Val: i).addConstantPoolIndex(Idx: i).addImm(Val: Size);
569
570 CPEMIs.push_back(x: CPEMI);
571
572 // Ensure that future entries with higher alignment get inserted before
573 // CPEMI. This is bucket sort with iterators.
574 for (unsigned a = LogAlign + 1; a <= Log2(A: MaxAlign); ++a)
575 if (InsPoint[a] == InsAt)
576 InsPoint[a] = CPEMI;
577 // Add a new CPEntry, but no corresponding CPUser yet.
578 CPEntries.emplace_back(args: 1, args: CPEntry(CPEMI, i));
579 ++NumCPEs;
580 LLVM_DEBUG(dbgs() << "Moved CPI#" << i << " to end of function, size = "
581 << Size << ", align = " << Alignment.value() << '\n');
582 }
583 LLVM_DEBUG(BB->dump());
584}
585
586/// BBHasFallthrough - Return true if the specified basic block can fallthrough
587/// into the block immediately after it.
588static bool BBHasFallthrough(MachineBasicBlock *MBB) {
589 // Get the next machine basic block in the function.
590 MachineFunction::iterator MBBI = MBB->getIterator();
591 // Can't fall off end of function.
592 if (std::next(x: MBBI) == MBB->getParent()->end())
593 return false;
594
595 MachineBasicBlock *NextBB = &*std::next(x: MBBI);
596 return llvm::is_contained(Range: MBB->successors(), Element: NextBB);
597}
598
599/// findConstPoolEntry - Given the constpool index and CONSTPOOL_ENTRY MI,
600/// look up the corresponding CPEntry.
601MipsConstantIslands::CPEntry
602*MipsConstantIslands::findConstPoolEntry(unsigned CPI,
603 const MachineInstr *CPEMI) {
604 std::vector<CPEntry> &CPEs = CPEntries[CPI];
605 // Number of entries per constpool index should be small, just do a
606 // linear search.
607 for (CPEntry &CPE : CPEs) {
608 if (CPE.CPEMI == CPEMI)
609 return &CPE;
610 }
611 return nullptr;
612}
613
614/// getCPEAlign - Returns the required alignment of the constant pool entry
615/// represented by CPEMI. Alignment is measured in log2(bytes) units.
616Align MipsConstantIslands::getCPEAlign(const MachineInstr &CPEMI) {
617 assert(CPEMI.getOpcode() == Mips::CONSTPOOL_ENTRY);
618
619 // Everything is 4-byte aligned unless AlignConstantIslands is set.
620 if (!AlignConstantIslands)
621 return Align(4);
622
623 unsigned CPI = CPEMI.getOperand(i: 1).getIndex();
624 assert(CPI < MCP->getConstants().size() && "Invalid constant pool index.");
625 return MCP->getConstants()[CPI].getAlign();
626}
627
628/// initializeFunctionInfo - Do the initial scan of the function, building up
629/// information about the sizes of each block, the location of all the water,
630/// and finding all of the constant pool users.
631void MipsConstantIslands::
632initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs) {
633 BBInfo.clear();
634 BBInfo.resize(new_size: MF->getNumBlockIDs());
635
636 // First thing, compute the size of all basic blocks, and see if the function
637 // has any inline assembly in it. If so, we have to be conservative about
638 // alignment assumptions, as we don't know for sure the size of any
639 // instructions in the inline assembly.
640 for (MachineBasicBlock &MBB : *MF)
641 computeBlockSize(MBB: &MBB);
642
643 // Compute block offsets.
644 adjustBBOffsetsAfter(BB: &MF->front());
645
646 // Now go back through the instructions and build up our data structures.
647 for (MachineBasicBlock &MBB : *MF) {
648 // If this block doesn't fall through into the next MBB, then this is
649 // 'water' that a constant pool island could be placed.
650 if (!BBHasFallthrough(MBB: &MBB))
651 WaterList.push_back(x: &MBB);
652 for (MachineInstr &MI : MBB) {
653 if (MI.isDebugInstr())
654 continue;
655
656 int Opc = MI.getOpcode();
657 if (MI.isBranch()) {
658 bool isCond = false;
659 unsigned Bits = 0;
660 unsigned Scale = 1;
661 int UOpc = Opc;
662 switch (Opc) {
663 default:
664 continue; // Ignore other branches for now
665 case Mips::Bimm16:
666 Bits = 11;
667 Scale = 2;
668 isCond = false;
669 break;
670 case Mips::BimmX16:
671 Bits = 16;
672 Scale = 2;
673 isCond = false;
674 break;
675 case Mips::BeqzRxImm16:
676 UOpc=Mips::Bimm16;
677 Bits = 8;
678 Scale = 2;
679 isCond = true;
680 break;
681 case Mips::BeqzRxImmX16:
682 UOpc=Mips::Bimm16;
683 Bits = 16;
684 Scale = 2;
685 isCond = true;
686 break;
687 case Mips::BnezRxImm16:
688 UOpc=Mips::Bimm16;
689 Bits = 8;
690 Scale = 2;
691 isCond = true;
692 break;
693 case Mips::BnezRxImmX16:
694 UOpc=Mips::Bimm16;
695 Bits = 16;
696 Scale = 2;
697 isCond = true;
698 break;
699 case Mips::Bteqz16:
700 UOpc=Mips::Bimm16;
701 Bits = 8;
702 Scale = 2;
703 isCond = true;
704 break;
705 case Mips::BteqzX16:
706 UOpc=Mips::Bimm16;
707 Bits = 16;
708 Scale = 2;
709 isCond = true;
710 break;
711 case Mips::Btnez16:
712 UOpc=Mips::Bimm16;
713 Bits = 8;
714 Scale = 2;
715 isCond = true;
716 break;
717 case Mips::BtnezX16:
718 UOpc=Mips::Bimm16;
719 Bits = 16;
720 Scale = 2;
721 isCond = true;
722 break;
723 }
724 // Record this immediate branch.
725 unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale;
726 ImmBranches.push_back(x: ImmBranch(&MI, MaxOffs, isCond, UOpc));
727 }
728
729 if (Opc == Mips::CONSTPOOL_ENTRY)
730 continue;
731
732 // Scan the instructions for constant pool operands.
733 for (const MachineOperand &MO : MI.operands())
734 if (MO.isCPI()) {
735 // We found one. The addressing mode tells us the max displacement
736 // from the PC that this instruction permits.
737
738 // Basic size info comes from the TSFlags field.
739 unsigned Bits = 0;
740 unsigned Scale = 1;
741 bool NegOk = false;
742 unsigned LongFormBits = 0;
743 unsigned LongFormScale = 0;
744 unsigned LongFormOpcode = 0;
745 switch (Opc) {
746 default:
747 llvm_unreachable("Unknown addressing mode for CP reference!");
748 case Mips::LwRxPcTcp16:
749 Bits = 8;
750 Scale = 4;
751 LongFormOpcode = Mips::LwRxPcTcpX16;
752 LongFormBits = 14;
753 LongFormScale = 1;
754 break;
755 case Mips::LwRxPcTcpX16:
756 Bits = 14;
757 Scale = 1;
758 NegOk = true;
759 break;
760 }
761 // Remember that this is a user of a CP entry.
762 unsigned CPI = MO.getIndex();
763 MachineInstr *CPEMI = CPEMIs[CPI];
764 unsigned MaxOffs = ((1 << Bits)-1) * Scale;
765 unsigned LongFormMaxOffs = ((1 << LongFormBits)-1) * LongFormScale;
766 CPUsers.push_back(x: CPUser(&MI, CPEMI, MaxOffs, NegOk, LongFormMaxOffs,
767 LongFormOpcode));
768
769 // Increment corresponding CPEntry reference count.
770 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI);
771 assert(CPE && "Cannot find a corresponding CPEntry!");
772 CPE->RefCount++;
773
774 // Instructions can only use one CP entry, don't bother scanning the
775 // rest of the operands.
776 break;
777 }
778 }
779 }
780}
781
782/// computeBlockSize - Compute the size and some alignment information for MBB.
783/// This function updates BBInfo directly.
784void MipsConstantIslands::computeBlockSize(MachineBasicBlock *MBB) {
785 BasicBlockInfo &BBI = BBInfo[MBB->getNumber()];
786 BBI.Size = 0;
787
788 for (const MachineInstr &MI : *MBB)
789 BBI.Size += TII->getInstSizeInBytes(MI);
790}
791
792/// getOffsetOf - Return the current offset of the specified machine instruction
793/// from the start of the function. This offset changes as stuff is moved
794/// around inside the function.
795unsigned MipsConstantIslands::getOffsetOf(MachineInstr *MI) const {
796 MachineBasicBlock *MBB = MI->getParent();
797
798 // The offset is composed of two things: the sum of the sizes of all MBB's
799 // before this instruction's block, and the offset from the start of the block
800 // it is in.
801 unsigned Offset = BBInfo[MBB->getNumber()].Offset;
802
803 // Sum instructions before MI in MBB.
804 for (MachineBasicBlock::iterator I = MBB->begin(); &*I != MI; ++I) {
805 assert(I != MBB->end() && "Didn't find MI in its own basic block?");
806 Offset += TII->getInstSizeInBytes(MI: *I);
807 }
808 return Offset;
809}
810
811/// CompareMBBNumbers - Little predicate function to sort the WaterList by MBB
812/// ID.
813static bool CompareMBBNumbers(const MachineBasicBlock *LHS,
814 const MachineBasicBlock *RHS) {
815 return LHS->getNumber() < RHS->getNumber();
816}
817
818/// updateForInsertedWaterBlock - When a block is newly inserted into the
819/// machine function, it upsets all of the block numbers. Renumber the blocks
820/// and update the arrays that parallel this numbering.
821void MipsConstantIslands::updateForInsertedWaterBlock
822 (MachineBasicBlock *NewBB) {
823 // Renumber the MBB's to keep them consecutive.
824 NewBB->getParent()->RenumberBlocks(MBBFrom: NewBB);
825
826 // Insert an entry into BBInfo to align it properly with the (newly
827 // renumbered) block numbers.
828 BBInfo.insert(position: BBInfo.begin() + NewBB->getNumber(), x: BasicBlockInfo());
829
830 // Next, update WaterList. Specifically, we need to add NewMBB as having
831 // available water after it.
832 water_iterator IP = llvm::lower_bound(Range&: WaterList, Value&: NewBB, C: CompareMBBNumbers);
833 WaterList.insert(position: IP, x: NewBB);
834}
835
836unsigned MipsConstantIslands::getUserOffset(CPUser &U) const {
837 return getOffsetOf(MI: U.MI);
838}
839
840/// Split the basic block containing MI into two blocks, which are joined by
841/// an unconditional branch. Update data structures and renumber blocks to
842/// account for this change and returns the newly created block.
843MachineBasicBlock *
844MipsConstantIslands::splitBlockBeforeInstr(MachineInstr &MI) {
845 MachineBasicBlock *OrigBB = MI.getParent();
846
847 // Create a new MBB for the code after the OrigBB.
848 MachineBasicBlock *NewBB =
849 MF->CreateMachineBasicBlock(BB: OrigBB->getBasicBlock());
850 MachineFunction::iterator MBBI = ++OrigBB->getIterator();
851 MF->insert(MBBI, MBB: NewBB);
852
853 // Splice the instructions starting with MI over to NewBB.
854 NewBB->splice(Where: NewBB->end(), Other: OrigBB, From: MI, To: OrigBB->end());
855
856 // Add an unconditional branch from OrigBB to NewBB.
857 // Note the new unconditional branch is not being recorded.
858 // There doesn't seem to be meaningful DebugInfo available; this doesn't
859 // correspond to anything in the source.
860 BuildMI(BB: OrigBB, MIMD: DebugLoc(), MCID: TII->get(Opcode: Mips::Bimm16)).addMBB(MBB: NewBB);
861 ++NumSplit;
862
863 // Update the CFG. All succs of OrigBB are now succs of NewBB.
864 NewBB->transferSuccessors(FromMBB: OrigBB);
865
866 // OrigBB branches to NewBB.
867 OrigBB->addSuccessor(Succ: NewBB);
868
869 // Update internal data structures to account for the newly inserted MBB.
870 // This is almost the same as updateForInsertedWaterBlock, except that
871 // the Water goes after OrigBB, not NewBB.
872 MF->RenumberBlocks(MBBFrom: NewBB);
873
874 // Insert an entry into BBInfo to align it properly with the (newly
875 // renumbered) block numbers.
876 BBInfo.insert(position: BBInfo.begin() + NewBB->getNumber(), x: BasicBlockInfo());
877
878 // Next, update WaterList. Specifically, we need to add OrigMBB as having
879 // available water after it (but not if it's already there, which happens
880 // when splitting before a conditional branch that is followed by an
881 // unconditional branch - in that case we want to insert NewBB).
882 water_iterator IP = llvm::lower_bound(Range&: WaterList, Value&: OrigBB, C: CompareMBBNumbers);
883 MachineBasicBlock* WaterBB = *IP;
884 if (WaterBB == OrigBB)
885 WaterList.insert(position: std::next(x: IP), x: NewBB);
886 else
887 WaterList.insert(position: IP, x: OrigBB);
888 NewWaterList.insert(Ptr: OrigBB);
889
890 // Figure out how large the OrigBB is. As the first half of the original
891 // block, it cannot contain a tablejump. The size includes
892 // the new jump we added. (It should be possible to do this without
893 // recounting everything, but it's very confusing, and this is rarely
894 // executed.)
895 computeBlockSize(MBB: OrigBB);
896
897 // Figure out how large the NewMBB is. As the second half of the original
898 // block, it may contain a tablejump.
899 computeBlockSize(MBB: NewBB);
900
901 // All BBOffsets following these blocks must be modified.
902 adjustBBOffsetsAfter(BB: OrigBB);
903
904 return NewBB;
905}
906
907/// isOffsetInRange - Checks whether UserOffset (the location of a constant pool
908/// reference) is within MaxDisp of TrialOffset (a proposed location of a
909/// constant pool entry).
910bool MipsConstantIslands::isOffsetInRange(unsigned UserOffset,
911 unsigned TrialOffset, unsigned MaxDisp,
912 bool NegativeOK) {
913 if (UserOffset <= TrialOffset) {
914 // User before the Trial.
915 if (TrialOffset - UserOffset <= MaxDisp)
916 return true;
917 } else if (NegativeOK) {
918 if (UserOffset - TrialOffset <= MaxDisp)
919 return true;
920 }
921 return false;
922}
923
924/// isWaterInRange - Returns true if a CPE placed after the specified
925/// Water (a basic block) will be in range for the specific MI.
926///
927/// Compute how much the function will grow by inserting a CPE after Water.
928bool MipsConstantIslands::isWaterInRange(unsigned UserOffset,
929 MachineBasicBlock* Water, CPUser &U,
930 unsigned &Growth) {
931 unsigned CPEOffset = BBInfo[Water->getNumber()].postOffset();
932 unsigned NextBlockOffset;
933 Align NextBlockAlignment;
934 MachineFunction::const_iterator NextBlock = ++Water->getIterator();
935 if (NextBlock == MF->end()) {
936 NextBlockOffset = BBInfo[Water->getNumber()].postOffset();
937 NextBlockAlignment = Align(1);
938 } else {
939 NextBlockOffset = BBInfo[NextBlock->getNumber()].Offset;
940 NextBlockAlignment = NextBlock->getAlignment();
941 }
942 unsigned Size = U.CPEMI->getOperand(i: 2).getImm();
943 unsigned CPEEnd = CPEOffset + Size;
944
945 // The CPE may be able to hide in the alignment padding before the next
946 // block. It may also cause more padding to be required if it is more aligned
947 // that the next block.
948 if (CPEEnd > NextBlockOffset) {
949 Growth = CPEEnd - NextBlockOffset;
950 // Compute the padding that would go at the end of the CPE to align the next
951 // block.
952 Growth += offsetToAlignment(Value: CPEEnd, Alignment: NextBlockAlignment);
953
954 // If the CPE is to be inserted before the instruction, that will raise
955 // the offset of the instruction. Also account for unknown alignment padding
956 // in blocks between CPE and the user.
957 if (CPEOffset < UserOffset)
958 UserOffset += Growth;
959 } else
960 // CPE fits in existing padding.
961 Growth = 0;
962
963 return isOffsetInRange(UserOffset, TrialOffset: CPEOffset, U);
964}
965
966/// isCPEntryInRange - Returns true if the distance between specific MI and
967/// specific ConstPool entry instruction can fit in MI's displacement field.
968bool MipsConstantIslands::isCPEntryInRange
969 (MachineInstr *MI, unsigned UserOffset,
970 MachineInstr *CPEMI, unsigned MaxDisp,
971 bool NegOk, bool DoDump) {
972 unsigned CPEOffset = getOffsetOf(MI: CPEMI);
973
974 if (DoDump) {
975 LLVM_DEBUG({
976 unsigned Block = MI->getParent()->getNumber();
977 const BasicBlockInfo &BBI = BBInfo[Block];
978 dbgs() << "User of CPE#" << CPEMI->getOperand(0).getImm()
979 << " max delta=" << MaxDisp
980 << format(" insn address=%#x", UserOffset) << " in "
981 << printMBBReference(*MI->getParent()) << ": "
982 << format("%#x-%x\t", BBI.Offset, BBI.postOffset()) << *MI
983 << format("CPE address=%#x offset=%+d: ", CPEOffset,
984 int(CPEOffset - UserOffset));
985 });
986 }
987
988 return isOffsetInRange(UserOffset, TrialOffset: CPEOffset, MaxDisp, NegativeOK: NegOk);
989}
990
991#ifndef NDEBUG
992/// BBIsJumpedOver - Return true of the specified basic block's only predecessor
993/// unconditionally branches to its only successor.
994static bool BBIsJumpedOver(MachineBasicBlock *MBB) {
995 if (MBB->pred_size() != 1 || MBB->succ_size() != 1)
996 return false;
997 MachineBasicBlock *Succ = *MBB->succ_begin();
998 MachineBasicBlock *Pred = *MBB->pred_begin();
999 MachineInstr *PredMI = &Pred->back();
1000 if (PredMI->getOpcode() == Mips::Bimm16)
1001 return PredMI->getOperand(0).getMBB() == Succ;
1002 return false;
1003}
1004#endif
1005
1006void MipsConstantIslands::adjustBBOffsetsAfter(MachineBasicBlock *BB) {
1007 unsigned BBNum = BB->getNumber();
1008 for(unsigned i = BBNum + 1, e = MF->getNumBlockIDs(); i < e; ++i) {
1009 // Get the offset and known bits at the end of the layout predecessor.
1010 // Include the alignment of the current block.
1011 unsigned Offset = BBInfo[i - 1].Offset + BBInfo[i - 1].Size;
1012 BBInfo[i].Offset = Offset;
1013 }
1014}
1015
1016/// decrementCPEReferenceCount - find the constant pool entry with index CPI
1017/// and instruction CPEMI, and decrement its refcount. If the refcount
1018/// becomes 0 remove the entry and instruction. Returns true if we removed
1019/// the entry, false if we didn't.
1020bool MipsConstantIslands::decrementCPEReferenceCount(unsigned CPI,
1021 MachineInstr *CPEMI) {
1022 // Find the old entry. Eliminate it if it is no longer used.
1023 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI);
1024 assert(CPE && "Unexpected!");
1025 if (--CPE->RefCount == 0) {
1026 removeDeadCPEMI(CPEMI);
1027 CPE->CPEMI = nullptr;
1028 --NumCPEs;
1029 return true;
1030 }
1031 return false;
1032}
1033
1034/// LookForCPEntryInRange - see if the currently referenced CPE is in range;
1035/// if not, see if an in-range clone of the CPE is in range, and if so,
1036/// change the data structures so the user references the clone. Returns:
1037/// 0 = no existing entry found
1038/// 1 = entry found, and there were no code insertions or deletions
1039/// 2 = entry found, and there were code insertions or deletions
1040int MipsConstantIslands::findInRangeCPEntry(CPUser& U, unsigned UserOffset)
1041{
1042 MachineInstr *UserMI = U.MI;
1043 MachineInstr *CPEMI = U.CPEMI;
1044
1045 // Check to see if the CPE is already in-range.
1046 if (isCPEntryInRange(MI: UserMI, UserOffset, CPEMI, MaxDisp: U.getMaxDisp(), NegOk: U.NegOk,
1047 DoDump: true)) {
1048 LLVM_DEBUG(dbgs() << "In range\n");
1049 return 1;
1050 }
1051
1052 // No. Look for previously created clones of the CPE that are in range.
1053 unsigned CPI = CPEMI->getOperand(i: 1).getIndex();
1054 std::vector<CPEntry> &CPEs = CPEntries[CPI];
1055 for (CPEntry &CPE : CPEs) {
1056 // We already tried this one
1057 if (CPE.CPEMI == CPEMI)
1058 continue;
1059 // Removing CPEs can leave empty entries, skip
1060 if (CPE.CPEMI == nullptr)
1061 continue;
1062 if (isCPEntryInRange(MI: UserMI, UserOffset, CPEMI: CPE.CPEMI, MaxDisp: U.getMaxDisp(),
1063 NegOk: U.NegOk)) {
1064 LLVM_DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" << CPE.CPI
1065 << "\n");
1066 // Point the CPUser node to the replacement
1067 U.CPEMI = CPE.CPEMI;
1068 // Change the CPI in the instruction operand to refer to the clone.
1069 for (MachineOperand &MO : UserMI->operands())
1070 if (MO.isCPI()) {
1071 MO.setIndex(CPE.CPI);
1072 break;
1073 }
1074 // Adjust the refcount of the clone...
1075 CPE.RefCount++;
1076 // ...and the original. If we didn't remove the old entry, none of the
1077 // addresses changed, so we don't need another pass.
1078 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1;
1079 }
1080 }
1081 return 0;
1082}
1083
1084/// LookForCPEntryInRange - see if the currently referenced CPE is in range;
1085/// This version checks if the longer form of the instruction can be used to
1086/// to satisfy things.
1087/// if not, see if an in-range clone of the CPE is in range, and if so,
1088/// change the data structures so the user references the clone. Returns:
1089/// 0 = no existing entry found
1090/// 1 = entry found, and there were no code insertions or deletions
1091/// 2 = entry found, and there were code insertions or deletions
1092int MipsConstantIslands::findLongFormInRangeCPEntry
1093 (CPUser& U, unsigned UserOffset)
1094{
1095 MachineInstr *UserMI = U.MI;
1096 MachineInstr *CPEMI = U.CPEMI;
1097
1098 // Check to see if the CPE is already in-range.
1099 if (isCPEntryInRange(MI: UserMI, UserOffset, CPEMI,
1100 MaxDisp: U.getLongFormMaxDisp(), NegOk: U.NegOk,
1101 DoDump: true)) {
1102 LLVM_DEBUG(dbgs() << "In range\n");
1103 UserMI->setDesc(TII->get(Opcode: U.getLongFormOpcode()));
1104 U.setMaxDisp(U.getLongFormMaxDisp());
1105 return 2; // instruction is longer length now
1106 }
1107
1108 // No. Look for previously created clones of the CPE that are in range.
1109 unsigned CPI = CPEMI->getOperand(i: 1).getIndex();
1110 std::vector<CPEntry> &CPEs = CPEntries[CPI];
1111 for (CPEntry &CPE : CPEs) {
1112 // We already tried this one
1113 if (CPE.CPEMI == CPEMI)
1114 continue;
1115 // Removing CPEs can leave empty entries, skip
1116 if (CPE.CPEMI == nullptr)
1117 continue;
1118 if (isCPEntryInRange(MI: UserMI, UserOffset, CPEMI: CPE.CPEMI, MaxDisp: U.getLongFormMaxDisp(),
1119 NegOk: U.NegOk)) {
1120 LLVM_DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" << CPE.CPI
1121 << "\n");
1122 // Point the CPUser node to the replacement
1123 U.CPEMI = CPE.CPEMI;
1124 // Change the CPI in the instruction operand to refer to the clone.
1125 for (MachineOperand &MO : UserMI->operands())
1126 if (MO.isCPI()) {
1127 MO.setIndex(CPE.CPI);
1128 break;
1129 }
1130 // Adjust the refcount of the clone...
1131 CPE.RefCount++;
1132 // ...and the original. If we didn't remove the old entry, none of the
1133 // addresses changed, so we don't need another pass.
1134 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1;
1135 }
1136 }
1137 return 0;
1138}
1139
1140/// getUnconditionalBrDisp - Returns the maximum displacement that can fit in
1141/// the specific unconditional branch instruction.
1142static inline unsigned getUnconditionalBrDisp(int Opc) {
1143 switch (Opc) {
1144 case Mips::Bimm16:
1145 return ((1<<10)-1)*2;
1146 case Mips::BimmX16:
1147 return ((1<<16)-1)*2;
1148 default:
1149 break;
1150 }
1151 return ((1<<16)-1)*2;
1152}
1153
1154/// findAvailableWater - Look for an existing entry in the WaterList in which
1155/// we can place the CPE referenced from U so it's within range of U's MI.
1156/// Returns true if found, false if not. If it returns true, WaterIter
1157/// is set to the WaterList entry.
1158/// To ensure that this pass
1159/// terminates, the CPE location for a particular CPUser is only allowed to
1160/// move to a lower address, so search backward from the end of the list and
1161/// prefer the first water that is in range.
1162bool MipsConstantIslands::findAvailableWater(CPUser &U, unsigned UserOffset,
1163 water_iterator &WaterIter) {
1164 if (WaterList.empty())
1165 return false;
1166
1167 unsigned BestGrowth = ~0u;
1168 for (water_iterator IP = std::prev(x: WaterList.end()), B = WaterList.begin();;
1169 --IP) {
1170 MachineBasicBlock* WaterBB = *IP;
1171 // Check if water is in range and is either at a lower address than the
1172 // current "high water mark" or a new water block that was created since
1173 // the previous iteration by inserting an unconditional branch. In the
1174 // latter case, we want to allow resetting the high water mark back to
1175 // this new water since we haven't seen it before. Inserting branches
1176 // should be relatively uncommon and when it does happen, we want to be
1177 // sure to take advantage of it for all the CPEs near that block, so that
1178 // we don't insert more branches than necessary.
1179 unsigned Growth;
1180 if (isWaterInRange(UserOffset, Water: WaterBB, U, Growth) &&
1181 (WaterBB->getNumber() < U.HighWaterMark->getNumber() ||
1182 NewWaterList.count(Ptr: WaterBB)) && Growth < BestGrowth) {
1183 // This is the least amount of required padding seen so far.
1184 BestGrowth = Growth;
1185 WaterIter = IP;
1186 LLVM_DEBUG(dbgs() << "Found water after " << printMBBReference(*WaterBB)
1187 << " Growth=" << Growth << '\n');
1188
1189 // Keep looking unless it is perfect.
1190 if (BestGrowth == 0)
1191 return true;
1192 }
1193 if (IP == B)
1194 break;
1195 }
1196 return BestGrowth != ~0u;
1197}
1198
1199/// createNewWater - No existing WaterList entry will work for
1200/// CPUsers[CPUserIndex], so create a place to put the CPE. The end of the
1201/// block is used if in range, and the conditional branch munged so control
1202/// flow is correct. Otherwise the block is split to create a hole with an
1203/// unconditional branch around it. In either case NewMBB is set to a
1204/// block following which the new island can be inserted (the WaterList
1205/// is not adjusted).
1206void MipsConstantIslands::createNewWater(unsigned CPUserIndex,
1207 unsigned UserOffset,
1208 MachineBasicBlock *&NewMBB) {
1209 CPUser &U = CPUsers[CPUserIndex];
1210 MachineInstr *UserMI = U.MI;
1211 MachineInstr *CPEMI = U.CPEMI;
1212 MachineBasicBlock *UserMBB = UserMI->getParent();
1213 const BasicBlockInfo &UserBBI = BBInfo[UserMBB->getNumber()];
1214
1215 // If the block does not end in an unconditional branch already, and if the
1216 // end of the block is within range, make new water there.
1217 if (BBHasFallthrough(MBB: UserMBB)) {
1218 // Size of branch to insert.
1219 unsigned Delta = 2;
1220 // Compute the offset where the CPE will begin.
1221 unsigned CPEOffset = UserBBI.postOffset() + Delta;
1222
1223 if (isOffsetInRange(UserOffset, TrialOffset: CPEOffset, U)) {
1224 LLVM_DEBUG(dbgs() << "Split at end of " << printMBBReference(*UserMBB)
1225 << format(", expected CPE offset %#x\n", CPEOffset));
1226 NewMBB = &*++UserMBB->getIterator();
1227 // Add an unconditional branch from UserMBB to fallthrough block. Record
1228 // it for branch lengthening; this new branch will not get out of range,
1229 // but if the preceding conditional branch is out of range, the targets
1230 // will be exchanged, and the altered branch may be out of range, so the
1231 // machinery has to know about it.
1232 int UncondBr = Mips::Bimm16;
1233 BuildMI(BB: UserMBB, MIMD: DebugLoc(), MCID: TII->get(Opcode: UncondBr)).addMBB(MBB: NewMBB);
1234 unsigned MaxDisp = getUnconditionalBrDisp(Opc: UncondBr);
1235 ImmBranches.push_back(x: ImmBranch(&UserMBB->back(),
1236 MaxDisp, false, UncondBr));
1237 BBInfo[UserMBB->getNumber()].Size += Delta;
1238 adjustBBOffsetsAfter(BB: UserMBB);
1239 return;
1240 }
1241 }
1242
1243 // What a big block. Find a place within the block to split it.
1244
1245 // Try to split the block so it's fully aligned. Compute the latest split
1246 // point where we can add a 4-byte branch instruction, and then align to
1247 // Align which is the largest possible alignment in the function.
1248 const Align Align = MF->getAlignment();
1249 unsigned BaseInsertOffset = UserOffset + U.getMaxDisp();
1250 LLVM_DEBUG(dbgs() << format("Split in middle of big block before %#x",
1251 BaseInsertOffset));
1252
1253 // The 4 in the following is for the unconditional branch we'll be inserting
1254 // Alignment of the island is handled
1255 // inside isOffsetInRange.
1256 BaseInsertOffset -= 4;
1257
1258 LLVM_DEBUG(dbgs() << format(", adjusted to %#x", BaseInsertOffset)
1259 << " la=" << Log2(Align) << '\n');
1260
1261 // This could point off the end of the block if we've already got constant
1262 // pool entries following this block; only the last one is in the water list.
1263 // Back past any possible branches (allow for a conditional and a maximally
1264 // long unconditional).
1265 if (BaseInsertOffset + 8 >= UserBBI.postOffset()) {
1266 BaseInsertOffset = UserBBI.postOffset() - 8;
1267 LLVM_DEBUG(dbgs() << format("Move inside block: %#x\n", BaseInsertOffset));
1268 }
1269 unsigned EndInsertOffset = BaseInsertOffset + 4 +
1270 CPEMI->getOperand(i: 2).getImm();
1271 MachineBasicBlock::iterator MI = UserMI;
1272 ++MI;
1273 unsigned CPUIndex = CPUserIndex+1;
1274 unsigned NumCPUsers = CPUsers.size();
1275 //MachineInstr *LastIT = 0;
1276 for (unsigned Offset = UserOffset + TII->getInstSizeInBytes(MI: *UserMI);
1277 Offset < BaseInsertOffset;
1278 Offset += TII->getInstSizeInBytes(MI: *MI), MI = std::next(x: MI)) {
1279 assert(MI != UserMBB->end() && "Fell off end of block");
1280 if (CPUIndex < NumCPUsers && CPUsers[CPUIndex].MI == MI) {
1281 CPUser &U = CPUsers[CPUIndex];
1282 if (!isOffsetInRange(UserOffset: Offset, TrialOffset: EndInsertOffset, U)) {
1283 // Shift intertion point by one unit of alignment so it is within reach.
1284 BaseInsertOffset -= Align.value();
1285 EndInsertOffset -= Align.value();
1286 }
1287 // This is overly conservative, as we don't account for CPEMIs being
1288 // reused within the block, but it doesn't matter much. Also assume CPEs
1289 // are added in order with alignment padding. We may eventually be able
1290 // to pack the aligned CPEs better.
1291 EndInsertOffset += U.CPEMI->getOperand(i: 2).getImm();
1292 CPUIndex++;
1293 }
1294 }
1295
1296 NewMBB = splitBlockBeforeInstr(MI&: *--MI);
1297}
1298
1299/// handleConstantPoolUser - Analyze the specified user, checking to see if it
1300/// is out-of-range. If so, pick up the constant pool value and move it some
1301/// place in-range. Return true if we changed any addresses (thus must run
1302/// another pass of branch lengthening), false otherwise.
1303bool MipsConstantIslands::handleConstantPoolUser(unsigned CPUserIndex) {
1304 CPUser &U = CPUsers[CPUserIndex];
1305 MachineInstr *UserMI = U.MI;
1306 MachineInstr *CPEMI = U.CPEMI;
1307 unsigned CPI = CPEMI->getOperand(i: 1).getIndex();
1308 unsigned Size = CPEMI->getOperand(i: 2).getImm();
1309 // Compute this only once, it's expensive.
1310 unsigned UserOffset = getUserOffset(U);
1311
1312 // See if the current entry is within range, or there is a clone of it
1313 // in range.
1314 int result = findInRangeCPEntry(U, UserOffset);
1315 if (result==1) return false;
1316 else if (result==2) return true;
1317
1318 // Look for water where we can place this CPE.
1319 MachineBasicBlock *NewIsland = MF->CreateMachineBasicBlock();
1320 MachineBasicBlock *NewMBB;
1321 water_iterator IP;
1322 if (findAvailableWater(U, UserOffset, WaterIter&: IP)) {
1323 LLVM_DEBUG(dbgs() << "Found water in range\n");
1324 MachineBasicBlock *WaterBB = *IP;
1325
1326 // If the original WaterList entry was "new water" on this iteration,
1327 // propagate that to the new island. This is just keeping NewWaterList
1328 // updated to match the WaterList, which will be updated below.
1329 if (NewWaterList.erase(Ptr: WaterBB))
1330 NewWaterList.insert(Ptr: NewIsland);
1331
1332 // The new CPE goes before the following block (NewMBB).
1333 NewMBB = &*++WaterBB->getIterator();
1334 } else {
1335 // No water found.
1336 // we first see if a longer form of the instrucion could have reached
1337 // the constant. in that case we won't bother to split
1338 if (!NoLoadRelaxation) {
1339 result = findLongFormInRangeCPEntry(U, UserOffset);
1340 if (result != 0) return true;
1341 }
1342 LLVM_DEBUG(dbgs() << "No water found\n");
1343 createNewWater(CPUserIndex, UserOffset, NewMBB);
1344
1345 // splitBlockBeforeInstr adds to WaterList, which is important when it is
1346 // called while handling branches so that the water will be seen on the
1347 // next iteration for constant pools, but in this context, we don't want
1348 // it. Check for this so it will be removed from the WaterList.
1349 // Also remove any entry from NewWaterList.
1350 MachineBasicBlock *WaterBB = &*--NewMBB->getIterator();
1351 IP = llvm::find(Range&: WaterList, Val: WaterBB);
1352 if (IP != WaterList.end())
1353 NewWaterList.erase(Ptr: WaterBB);
1354
1355 // We are adding new water. Update NewWaterList.
1356 NewWaterList.insert(Ptr: NewIsland);
1357 }
1358
1359 // Remove the original WaterList entry; we want subsequent insertions in
1360 // this vicinity to go after the one we're about to insert. This
1361 // considerably reduces the number of times we have to move the same CPE
1362 // more than once and is also important to ensure the algorithm terminates.
1363 if (IP != WaterList.end())
1364 WaterList.erase(position: IP);
1365
1366 // Okay, we know we can put an island before NewMBB now, do it!
1367 MF->insert(MBBI: NewMBB->getIterator(), MBB: NewIsland);
1368
1369 // Update internal data structures to account for the newly inserted MBB.
1370 updateForInsertedWaterBlock(NewBB: NewIsland);
1371
1372 // Decrement the old entry, and remove it if refcount becomes 0.
1373 decrementCPEReferenceCount(CPI, CPEMI);
1374
1375 // No existing clone of this CPE is within range.
1376 // We will be generating a new clone. Get a UID for it.
1377 unsigned ID = createPICLabelUId();
1378
1379 // Now that we have an island to add the CPE to, clone the original CPE and
1380 // add it to the island.
1381 U.HighWaterMark = NewIsland;
1382 U.CPEMI = BuildMI(BB: NewIsland, MIMD: DebugLoc(), MCID: TII->get(Opcode: Mips::CONSTPOOL_ENTRY))
1383 .addImm(Val: ID).addConstantPoolIndex(Idx: CPI).addImm(Val: Size);
1384 CPEntries[CPI].push_back(x: CPEntry(U.CPEMI, ID, 1));
1385 ++NumCPEs;
1386
1387 // Mark the basic block as aligned as required by the const-pool entry.
1388 NewIsland->setAlignment(getCPEAlign(CPEMI: *U.CPEMI));
1389
1390 // Increase the size of the island block to account for the new entry.
1391 BBInfo[NewIsland->getNumber()].Size += Size;
1392 adjustBBOffsetsAfter(BB: &*--NewIsland->getIterator());
1393
1394 // Finally, change the CPI in the instruction operand to be ID.
1395 for (MachineOperand &MO : UserMI->operands())
1396 if (MO.isCPI()) {
1397 MO.setIndex(ID);
1398 break;
1399 }
1400
1401 LLVM_DEBUG(
1402 dbgs() << " Moved CPE to #" << ID << " CPI=" << CPI
1403 << format(" offset=%#x\n", BBInfo[NewIsland->getNumber()].Offset));
1404
1405 return true;
1406}
1407
1408/// removeDeadCPEMI - Remove a dead constant pool entry instruction. Update
1409/// sizes and offsets of impacted basic blocks.
1410void MipsConstantIslands::removeDeadCPEMI(MachineInstr *CPEMI) {
1411 MachineBasicBlock *CPEBB = CPEMI->getParent();
1412 unsigned Size = CPEMI->getOperand(i: 2).getImm();
1413 CPEMI->eraseFromParent();
1414 BBInfo[CPEBB->getNumber()].Size -= Size;
1415 // All succeeding offsets have the current size value added in, fix this.
1416 if (CPEBB->empty()) {
1417 BBInfo[CPEBB->getNumber()].Size = 0;
1418
1419 // This block no longer needs to be aligned.
1420 CPEBB->setAlignment(Align(1));
1421 } else {
1422 // Entries are sorted by descending alignment, so realign from the front.
1423 CPEBB->setAlignment(getCPEAlign(CPEMI: *CPEBB->begin()));
1424 }
1425
1426 adjustBBOffsetsAfter(BB: 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?
1432}
1433
1434/// removeUnusedCPEntries - Remove constant pool entries whose refcounts
1435/// are zero.
1436bool MipsConstantIslands::removeUnusedCPEntries() {
1437 unsigned MadeChange = false;
1438 for (std::vector<CPEntry> &CPEs : CPEntries) {
1439 for (CPEntry &CPE : CPEs) {
1440 if (CPE.RefCount == 0 && CPE.CPEMI) {
1441 removeDeadCPEMI(CPEMI: CPE.CPEMI);
1442 CPE.CPEMI = nullptr;
1443 MadeChange = true;
1444 }
1445 }
1446 }
1447 return MadeChange;
1448}
1449
1450/// isBBInRange - Returns true if the distance between specific MI and
1451/// specific BB can fit in MI's displacement field.
1452bool MipsConstantIslands::isBBInRange
1453 (MachineInstr *MI,MachineBasicBlock *DestBB, unsigned MaxDisp) {
1454 unsigned PCAdj = 4;
1455 unsigned BrOffset = getOffsetOf(MI) + PCAdj;
1456 unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset;
1457
1458 LLVM_DEBUG(dbgs() << "Branch of destination " << printMBBReference(*DestBB)
1459 << " from " << printMBBReference(*MI->getParent())
1460 << " max delta=" << MaxDisp << " from " << getOffsetOf(MI)
1461 << " to " << DestOffset << " offset "
1462 << int(DestOffset - BrOffset) << "\t" << *MI);
1463
1464 if (BrOffset <= DestOffset) {
1465 // Branch before the Dest.
1466 if (DestOffset-BrOffset <= MaxDisp)
1467 return true;
1468 } else {
1469 if (BrOffset-DestOffset <= MaxDisp)
1470 return true;
1471 }
1472 return false;
1473}
1474
1475/// fixupImmediateBr - Fix up an immediate branch whose destination is too far
1476/// away to fit in its displacement field.
1477bool MipsConstantIslands::fixupImmediateBr(ImmBranch &Br) {
1478 MachineInstr *MI = Br.MI;
1479 unsigned TargetOperand = branchTargetOperand(MI);
1480 MachineBasicBlock *DestBB = MI->getOperand(i: TargetOperand).getMBB();
1481
1482 // Check to see if the DestBB is already in-range.
1483 if (isBBInRange(MI, DestBB, MaxDisp: Br.MaxDisp))
1484 return false;
1485
1486 if (!Br.isCond)
1487 return fixupUnconditionalBr(Br);
1488 return fixupConditionalBr(Br);
1489}
1490
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.
1495bool
1496MipsConstantIslands::fixupUnconditionalBr(ImmBranch &Br) {
1497 MachineInstr *MI = Br.MI;
1498 MachineBasicBlock *MBB = MI->getParent();
1499 MachineBasicBlock *DestBB = MI->getOperand(i: 0).getMBB();
1500 // Use BL to implement far jump.
1501 unsigned BimmX16MaxDisp = ((1 << 16)-1) * 2;
1502 if (isBBInRange(MI, DestBB, MaxDisp: BimmX16MaxDisp)) {
1503 Br.MaxDisp = BimmX16MaxDisp;
1504 MI->setDesc(TII->get(Opcode: Mips::BimmX16));
1505 }
1506 else {
1507 // need to give the math a more careful look here
1508 // this is really a segment address and not
1509 // a PC relative address. FIXME. But I think that
1510 // just reducing the bits by 1 as I've done is correct.
1511 // The basic block we are branching too much be longword aligned.
1512 // we know that RA is saved because we always save it right now.
1513 // this requirement will be relaxed later but we also have an alternate
1514 // way to implement this that I will implement that does not need jal.
1515 // We should have a way to back out this alignment restriction
1516 // if we "can" later. but it is not harmful.
1517 //
1518 DestBB->setAlignment(Align(4));
1519 Br.MaxDisp = ((1<<24)-1) * 2;
1520 MI->setDesc(TII->get(Opcode: Mips::JalB16));
1521 }
1522 BBInfo[MBB->getNumber()].Size += 2;
1523 adjustBBOffsetsAfter(BB: MBB);
1524 HasFarJump = true;
1525 ++NumUBrFixed;
1526
1527 LLVM_DEBUG(dbgs() << " Changed B to long jump " << *MI);
1528
1529 return true;
1530}
1531
1532/// fixupConditionalBr - Fix up a conditional branch whose destination is too
1533/// far away to fit in its displacement field. It is converted to an inverse
1534/// conditional branch + an unconditional branch to the destination.
1535bool
1536MipsConstantIslands::fixupConditionalBr(ImmBranch &Br) {
1537 MachineInstr *MI = Br.MI;
1538 unsigned TargetOperand = branchTargetOperand(MI);
1539 MachineBasicBlock *DestBB = MI->getOperand(i: TargetOperand).getMBB();
1540 unsigned Opcode = MI->getOpcode();
1541 unsigned LongFormOpcode = longformBranchOpcode(Opcode);
1542 unsigned LongFormMaxOff = branchMaxOffsets(Opcode: LongFormOpcode);
1543
1544 // Check to see if the DestBB is already in-range.
1545 if (isBBInRange(MI, DestBB, MaxDisp: LongFormMaxOff)) {
1546 Br.MaxDisp = LongFormMaxOff;
1547 MI->setDesc(TII->get(Opcode: LongFormOpcode));
1548 return true;
1549 }
1550
1551 // Add an unconditional branch to the destination and invert the branch
1552 // condition to jump over it:
1553 // bteqz L1
1554 // =>
1555 // bnez L2
1556 // b L1
1557 // L2:
1558
1559 // If the branch is at the end of its MBB and that has a fall-through block,
1560 // direct the updated conditional branch to the fall-through block. Otherwise,
1561 // split the MBB before the next instruction.
1562 MachineBasicBlock *MBB = MI->getParent();
1563 MachineInstr *BMI = &MBB->back();
1564 bool NeedSplit = (BMI != MI) || !BBHasFallthrough(MBB);
1565 unsigned OppositeBranchOpcode = TII->getOppositeBranchOpc(Opc: Opcode);
1566
1567 ++NumCBrFixed;
1568 if (BMI != MI) {
1569 if (std::next(x: MachineBasicBlock::iterator(MI)) == std::prev(x: MBB->end()) &&
1570 BMI->isUnconditionalBranch()) {
1571 // Last MI in the BB is an unconditional branch. Can we simply invert the
1572 // condition and swap destinations:
1573 // beqz L1
1574 // b L2
1575 // =>
1576 // bnez L2
1577 // b L1
1578 unsigned BMITargetOperand = branchTargetOperand(MI: BMI);
1579 MachineBasicBlock *NewDest =
1580 BMI->getOperand(i: BMITargetOperand).getMBB();
1581 if (isBBInRange(MI, DestBB: NewDest, MaxDisp: Br.MaxDisp)) {
1582 LLVM_DEBUG(
1583 dbgs() << " Invert Bcc condition and swap its destination with "
1584 << *BMI);
1585 MI->setDesc(TII->get(Opcode: OppositeBranchOpcode));
1586 BMI->getOperand(i: BMITargetOperand).setMBB(DestBB);
1587 MI->getOperand(i: TargetOperand).setMBB(NewDest);
1588 return true;
1589 }
1590 }
1591 }
1592
1593 if (NeedSplit) {
1594 splitBlockBeforeInstr(MI&: *MI);
1595 // No need for the branch to the next block. We're adding an unconditional
1596 // branch to the destination.
1597 int delta = TII->getInstSizeInBytes(MI: MBB->back());
1598 BBInfo[MBB->getNumber()].Size -= delta;
1599 MBB->back().eraseFromParent();
1600 // BBInfo[SplitBB].Offset is wrong temporarily, fixed below
1601 }
1602 MachineBasicBlock *NextBB = &*++MBB->getIterator();
1603
1604 LLVM_DEBUG(dbgs() << " Insert B to " << printMBBReference(*DestBB)
1605 << " also invert condition and change dest. to "
1606 << printMBBReference(*NextBB) << "\n");
1607
1608 // Insert a new conditional branch and a new unconditional branch.
1609 // Also update the ImmBranch as well as adding a new entry for the new branch.
1610 if (MI->getNumExplicitOperands() == 2) {
1611 BuildMI(BB: MBB, MIMD: DebugLoc(), MCID: TII->get(Opcode: OppositeBranchOpcode))
1612 .addReg(RegNo: MI->getOperand(i: 0).getReg())
1613 .addMBB(MBB: NextBB);
1614 } else {
1615 BuildMI(BB: MBB, MIMD: DebugLoc(), MCID: TII->get(Opcode: OppositeBranchOpcode))
1616 .addMBB(MBB: NextBB);
1617 }
1618 Br.MI = &MBB->back();
1619 BBInfo[MBB->getNumber()].Size += TII->getInstSizeInBytes(MI: MBB->back());
1620 BuildMI(BB: MBB, MIMD: DebugLoc(), MCID: TII->get(Opcode: Br.UncondBr)).addMBB(MBB: DestBB);
1621 BBInfo[MBB->getNumber()].Size += TII->getInstSizeInBytes(MI: MBB->back());
1622 unsigned MaxDisp = getUnconditionalBrDisp(Opc: Br.UncondBr);
1623 ImmBranches.push_back(x: ImmBranch(&MBB->back(), MaxDisp, false, Br.UncondBr));
1624
1625 // Remove the old conditional branch. It may or may not still be in MBB.
1626 BBInfo[MI->getParent()->getNumber()].Size -= TII->getInstSizeInBytes(MI: *MI);
1627 MI->eraseFromParent();
1628 adjustBBOffsetsAfter(BB: MBB);
1629 return true;
1630}
1631
1632void MipsConstantIslands::prescanForConstants() {
1633 unsigned J = 0;
1634 (void)J;
1635 for (MachineBasicBlock &B : *MF) {
1636 for (MachineBasicBlock::instr_iterator I = B.instr_begin(),
1637 EB = B.instr_end();
1638 I != EB; ++I) {
1639 switch(I->getDesc().getOpcode()) {
1640 case Mips::LwConstant32: {
1641 PrescannedForConstants = true;
1642 LLVM_DEBUG(dbgs() << "constant island constant " << *I << "\n");
1643 J = I->getNumOperands();
1644 LLVM_DEBUG(dbgs() << "num operands " << J << "\n");
1645 MachineOperand& Literal = I->getOperand(i: 1);
1646 if (Literal.isImm()) {
1647 int64_t V = Literal.getImm();
1648 LLVM_DEBUG(dbgs() << "literal " << V << "\n");
1649 Type *Int32Ty =
1650 Type::getInt32Ty(C&: MF->getFunction().getContext());
1651 const Constant *C = ConstantInt::get(Ty: Int32Ty, V);
1652 unsigned index = MCP->getConstantPoolIndex(C, Alignment: Align(4));
1653 I->getOperand(i: 2).ChangeToImmediate(ImmVal: index);
1654 LLVM_DEBUG(dbgs() << "constant island constant " << *I << "\n");
1655 I->setDesc(TII->get(Opcode: Mips::LwRxPcTcp16));
1656 I->removeOperand(OpNo: 1);
1657 I->removeOperand(OpNo: 1);
1658 I->addOperand(Op: MachineOperand::CreateCPI(Idx: index, Offset: 0));
1659 I->addOperand(Op: MachineOperand::CreateImm(Val: 4));
1660 }
1661 break;
1662 }
1663 default:
1664 break;
1665 }
1666 }
1667 }
1668}
1669
1670/// Returns a pass that converts branches to long branches.
1671FunctionPass *llvm::createMipsConstantIslandPass() {
1672 return new MipsConstantIslands();
1673}
1674