1 //===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the Evan Cheng and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the machine instruction level if-conversion pass.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "ifcvt"
15 #include "llvm/Function.h"
16 #include "llvm/CodeGen/Passes.h"
17 #include "llvm/CodeGen/MachineModuleInfo.h"
18 #include "llvm/CodeGen/MachineFunctionPass.h"
19 #include "llvm/Target/TargetInstrInfo.h"
20 #include "llvm/Target/TargetLowering.h"
21 #include "llvm/Target/TargetMachine.h"
22 #include "llvm/Support/CommandLine.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/ADT/DepthFirstIterator.h"
25 #include "llvm/ADT/Statistic.h"
29 // Hidden options for help debugging.
30 cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
31 cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
32 cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
33 cl::opt<bool> DisableSimple("disable-ifcvt-simple",
34 cl::init(false), cl::Hidden);
35 cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
36 cl::init(false), cl::Hidden);
37 cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
38 cl::init(false), cl::Hidden);
39 cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
40 cl::init(false), cl::Hidden);
41 cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
42 cl::init(false), cl::Hidden);
43 cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
44 cl::init(false), cl::Hidden);
45 cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
46 cl::init(false), cl::Hidden);
49 STATISTIC(NumSimple, "Number of simple if-conversions performed");
50 STATISTIC(NumSimpleFalse, "Number of simple (F) if-conversions performed");
51 STATISTIC(NumTriangle, "Number of triangle if-conversions performed");
52 STATISTIC(NumTriangleRev, "Number of triangle (R) if-conversions performed");
53 STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
54 STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
55 STATISTIC(NumDiamonds, "Number of diamond if-conversions performed");
56 STATISTIC(NumIfConvBBs, "Number of if-converted blocks");
59 class IfConverter : public MachineFunctionPass {
61 ICNotClassfied, // BB data valid, but not classified.
62 ICSimple, // BB is entry of an one split, no rejoin sub-CFG.
63 ICSimpleFalse, // Same as ICSimple, but on the false path.
64 ICTriangle, // BB is entry of a triangle sub-CFG.
65 ICTriangleRev, // Same as ICTriangle, but true path rev condition.
66 ICTriangleFalse, // Same as ICTriangle, but on the false path.
67 ICTriangleFRev, // Same as ICTriangleFalse, but false path rev condition.
68 ICDiamond // BB is entry of a diamond sub-CFG.
71 /// BBInfo - One per MachineBasicBlock, this is used to cache the result
72 /// if-conversion feasibility analysis. This includes results from
73 /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
74 /// classification, and common tail block of its successors (if it's a
75 /// diamond shape), its size, whether it's predicable, and whether any
76 /// instruction can clobber the 'would-be' predicate.
78 /// Kind - Type of block. See BBICKind.
79 /// IsDone - True if BB is not to be considered for ifcvt.
80 /// IsBeingAnalyzed - True if BB is currently being analyzed.
81 /// IsAnalyzed - True if BB has been analyzed (info is still valid).
82 /// IsEnqueued - True if BB has been enqueued to be ifcvt'ed.
83 /// IsBrAnalyzable - True if AnalyzeBranch() returns false.
84 /// HasFallThrough - True if BB may fallthrough to the following BB.
85 /// IsUnpredicable - True if BB is known to be unpredicable.
86 /// ClobbersPredicate- True if BB would modify the predicate (e.g. has
88 /// NonPredSize - Number of non-predicated instructions.
89 /// BB - Corresponding MachineBasicBlock.
90 /// TrueBB / FalseBB- See AnalyzeBranch().
91 /// BrCond - Conditions for end of block conditional branches.
92 /// Predicate - Predicate used in the BB.
96 bool IsBeingAnalyzed : 1;
99 bool IsBrAnalyzable : 1;
100 bool HasFallThrough : 1;
101 bool IsUnpredicable : 1;
102 bool ClobbersPred : 1;
103 unsigned NonPredSize;
104 MachineBasicBlock *BB;
105 MachineBasicBlock *TrueBB;
106 MachineBasicBlock *FalseBB;
107 MachineBasicBlock *TailBB;
108 std::vector<MachineOperand> BrCond;
109 std::vector<MachineOperand> Predicate;
110 BBInfo() : Kind(ICNotClassfied), IsDone(false), IsBeingAnalyzed(false),
111 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
112 HasFallThrough(false), IsUnpredicable(false),
113 ClobbersPred(false), NonPredSize(0),
114 BB(0), TrueBB(0), FalseBB(0), TailBB(0) {}
117 /// Roots - Basic blocks that do not have successors. These are the starting
118 /// points of Graph traversal.
119 std::vector<MachineBasicBlock*> Roots;
121 /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
122 /// basic block number.
123 std::vector<BBInfo> BBAnalysis;
125 const TargetLowering *TLI;
126 const TargetInstrInfo *TII;
130 IfConverter() : MachineFunctionPass((intptr_t)&ID) {}
132 virtual bool runOnMachineFunction(MachineFunction &MF);
133 virtual const char *getPassName() const { return "If converter"; }
136 bool ReverseBranchCondition(BBInfo &BBI);
137 bool ValidSimple(BBInfo &TrueBBI) const;
138 bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
139 bool FalseBranch = false) const;
140 bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const;
141 void ScanInstructions(BBInfo &BBI);
142 BBInfo &AnalyzeBlock(MachineBasicBlock *BB);
143 bool FeasibilityAnalysis(BBInfo &BBI, std::vector<MachineOperand> &Cond,
144 bool isTriangle = false, bool RevBranch = false);
145 bool AttemptRestructuring(BBInfo &BBI);
146 bool AnalyzeBlocks(MachineFunction &MF,
147 std::vector<BBInfo*> &Candidates);
148 void ReTryPreds(MachineBasicBlock *BB);
149 void RemoveExtraEdges(BBInfo &BBI);
150 bool IfConvertSimple(BBInfo &BBI);
151 bool IfConvertTriangle(BBInfo &BBI);
152 bool IfConvertDiamond(BBInfo &BBI);
153 void PredicateBlock(BBInfo &BBI,
154 std::vector<MachineOperand> &Cond,
155 bool IgnoreTerm = false);
156 void MergeBlocks(BBInfo &TrueBBI, BBInfo &FalseBBI);
158 // blockAlwaysFallThrough - Block ends without a terminator.
159 bool blockAlwaysFallThrough(BBInfo &BBI) const {
160 return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
163 // IfcvtCandidateCmp - Used to sort if-conversion candidates.
164 static bool IfcvtCandidateCmp(BBInfo* C1, BBInfo* C2){
165 // Favor diamond over triangle, etc.
166 return (unsigned)C1->Kind < (unsigned)C2->Kind;
169 char IfConverter::ID = 0;
172 FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
174 bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
175 TLI = MF.getTarget().getTargetLowering();
176 TII = MF.getTarget().getInstrInfo();
177 if (!TII) return false;
179 static int FnNum = -1;
180 DOUT << "\nIfcvt: function (" << ++FnNum << ") \'"
181 << MF.getFunction()->getName() << "\'";
183 if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
184 DOUT << " skipped\n";
190 BBAnalysis.resize(MF.getNumBlockIDs());
192 // Look for root nodes, i.e. blocks without successors.
193 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
194 if (I->succ_size() == 0)
197 std::vector<BBInfo*> Candidates;
199 while (IfCvtLimit == -1 || (int)NumIfConvBBs < IfCvtLimit) {
200 // Do an intial analysis for each basic block and finding all the potential
201 // candidates to perform if-convesion.
202 bool Change = AnalyzeBlocks(MF, Candidates);
203 while (!Candidates.empty()) {
204 BBInfo &BBI = *Candidates.back();
205 Candidates.pop_back();
207 // If the block has been evicted out of the queue or it has already been
208 // marked dead (due to it being predicated), then skip it.
209 if (!BBI.IsEnqueued || BBI.IsDone)
214 default: assert(false && "Unexpected!");
217 case ICSimpleFalse: {
218 bool isFalse = BBI.Kind == ICSimpleFalse;
219 if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
220 DOUT << "Ifcvt (Simple" << (BBI.Kind == ICSimpleFalse ? " false" : "")
221 << "): BB#" << BBI.BB->getNumber() << " ("
222 << ((BBI.Kind == ICSimpleFalse)
223 ? BBI.FalseBB->getNumber() : BBI.TrueBB->getNumber()) << ") ";
224 RetVal = IfConvertSimple(BBI);
225 DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
227 if (isFalse) NumSimpleFalse++;
233 case ICTriangleFalse:
234 case ICTriangleFRev: {
235 bool isFalse = BBI.Kind == ICTriangleFalse;
236 bool isRev = (BBI.Kind == ICTriangleRev || BBI.Kind == ICTriangleFRev);
237 if (DisableTriangle && !isFalse && !isRev) break;
238 if (DisableTriangleR && !isFalse && isRev) break;
239 if (DisableTriangleF && isFalse && !isRev) break;
240 if (DisableTriangleFR && isFalse && isRev) break;
241 DOUT << "Ifcvt (Triangle";
246 DOUT << "): BB#" << BBI.BB->getNumber() << " (T:"
247 << BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber()
249 RetVal = IfConvertTriangle(BBI);
250 DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
253 if (isRev) NumTriangleFRev++;
254 else NumTriangleFalse++;
256 if (isRev) NumTriangleRev++;
263 if (DisableDiamond) break;
264 DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
265 << BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber();
267 DOUT << "," << BBI.TailBB->getNumber() ;
269 RetVal = IfConvertDiamond(BBI);
270 DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
271 if (RetVal) NumDiamonds++;
276 if (IfCvtLimit != -1 && (int)NumIfConvBBs >= IfCvtLimit)
282 MadeChange |= Change;
291 static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
292 MachineBasicBlock *TrueBB) {
293 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
294 E = BB->succ_end(); SI != E; ++SI) {
295 MachineBasicBlock *SuccBB = *SI;
296 if (SuccBB != TrueBB)
302 bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
303 if (!TII->ReverseBranchCondition(BBI.BrCond)) {
304 TII->RemoveBranch(*BBI.BB);
305 TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
306 std::swap(BBI.TrueBB, BBI.FalseBB);
312 /// getNextBlock - Returns the next block in the function blocks ordering. If
313 /// it is the end, returns NULL.
314 static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
315 MachineFunction::iterator I = BB;
316 MachineFunction::iterator E = BB->getParent()->end();
322 /// ValidSimple - Returns true if the 'true' block (along with its
323 /// predecessor) forms a valid simple shape for ifcvt.
324 bool IfConverter::ValidSimple(BBInfo &TrueBBI) const {
325 if (TrueBBI.IsBeingAnalyzed)
328 return !blockAlwaysFallThrough(TrueBBI) &&
329 TrueBBI.BrCond.size() == 0 && TrueBBI.BB->pred_size() == 1;
332 /// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
333 /// with their common predecessor) forms a valid triangle shape for ifcvt.
334 bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
335 bool FalseBranch) const {
336 if (TrueBBI.IsBeingAnalyzed)
339 if (TrueBBI.BB->pred_size() != 1)
342 MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
343 if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
344 MachineFunction::iterator I = TrueBBI.BB;
345 if (++I == TrueBBI.BB->getParent()->end())
349 return TExit && TExit == FalseBBI.BB;
352 /// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
353 /// with their common predecessor) forms a valid diamond shape for ifcvt.
354 bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const {
355 if (TrueBBI.IsBeingAnalyzed || FalseBBI.IsBeingAnalyzed)
358 MachineBasicBlock *TT = TrueBBI.TrueBB;
359 MachineBasicBlock *FT = FalseBBI.TrueBB;
361 if (!TT && blockAlwaysFallThrough(TrueBBI))
362 TT = getNextBlock(TrueBBI.BB);
363 if (!FT && blockAlwaysFallThrough(FalseBBI))
364 FT = getNextBlock(FalseBBI.BB);
367 if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
369 // FIXME: Allow false block to have an early exit?
370 return (TrueBBI.BB->pred_size() == 1 &&
371 FalseBBI.BB->pred_size() == 1 &&
372 !TrueBBI.FalseBB && !FalseBBI.FalseBB);
375 /// ScanInstructions - Scan all the instructions in the block to determine if
376 /// the block is predicable. In most cases, that means all the instructions
377 /// in the block has M_PREDICABLE flag. Also checks if the block contains any
378 /// instruction which can clobber a predicate (e.g. condition code register).
379 /// If so, the block is not predicable unless it's the last instruction.
380 void IfConverter::ScanInstructions(BBInfo &BBI) {
384 // First analyze the end of BB branches.
385 BBI.TrueBB = BBI.FalseBB;
388 !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
389 BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
391 if (BBI.BrCond.size()) {
392 // No false branch. This BB must end with a conditional branch and a
395 BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
396 assert(BBI.FalseBB && "Expected to find the fallthrough block!");
399 // Then scan all the instructions.
401 BBI.ClobbersPred = false;
402 bool SeenCondBr = false;
403 for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
405 const TargetInstrDescriptor *TID = I->getInstrDescriptor();
406 bool isPredicated = TII->isPredicated(I);
407 bool isCondBr = BBI.IsBrAnalyzable &&
408 (TID->Flags & M_BRANCH_FLAG) != 0 && (TID->Flags & M_BARRIER_FLAG) == 0;
410 if (!isPredicated && !isCondBr)
413 if (BBI.ClobbersPred && !isPredicated) {
414 // Predicate modification instruction should end the block (except for
415 // already predicated instructions and end of block branches).
419 // Conditional branches is not predicable. But it may be eliminated.
423 // Predicate may have been modified, the subsequent (currently)
424 // unpredocated instructions cannot be correctly predicated.
425 BBI.IsUnpredicable = true;
429 if (TID->Flags & M_CLOBBERS_PRED)
430 BBI.ClobbersPred = true;
432 if (!I->isPredicable()) {
433 BBI.IsUnpredicable = true;
439 /// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
440 /// predicated by the specified predicate.
441 bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
442 std::vector<MachineOperand> &Pred,
443 bool isTriangle, bool RevBranch) {
444 // Forget about it if it's unpredicable.
445 if (BBI.IsUnpredicable)
448 // If the block is dead, or it is going to be the entry block of a sub-CFG
449 // that will be if-converted, then it cannot be predicated.
450 if (BBI.IsDone || BBI.IsEnqueued)
453 // Check predication threshold.
454 if (BBI.NonPredSize == 0 || BBI.NonPredSize > TLI->getIfCvtBlockSizeLimit())
457 // If it is already predicated, check if its predicate subsumes the new
459 if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
462 if (BBI.BrCond.size()) {
466 // Test predicate subsumsion.
467 std::vector<MachineOperand> RevPred(Pred);
468 std::vector<MachineOperand> Cond(BBI.BrCond);
470 if (TII->ReverseBranchCondition(Cond))
473 if (TII->ReverseBranchCondition(RevPred) ||
474 !TII->SubsumesPredicate(Cond, RevPred))
481 /// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
482 /// the specified block. Record its successors and whether it looks like an
483 /// if-conversion candidate.
484 IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
485 BBInfo &BBI = BBAnalysis[BB->getNumber()];
487 if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
491 BBI.IsBeingAnalyzed = true;
492 BBI.Kind = ICNotClassfied;
494 ScanInstructions(BBI);
496 // Unanalyable or ends with fallthrough or unconditional branch.
497 if (!BBI.IsBrAnalyzable || BBI.BrCond.size() == 0) {
498 BBI.IsBeingAnalyzed = false;
499 BBI.IsAnalyzed = true;
503 // Do not ifcvt if either path is a back edge to the entry block.
504 if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
505 BBI.IsBeingAnalyzed = false;
506 BBI.IsAnalyzed = true;
510 BBInfo &TrueBBI = AnalyzeBlock(BBI.TrueBB);
511 BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB);
513 if (TrueBBI.IsDone && FalseBBI.IsDone) {
514 BBI.IsBeingAnalyzed = false;
515 BBI.IsAnalyzed = true;
519 std::vector<MachineOperand> RevCond(BBI.BrCond);
520 bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
522 if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI) &&
523 !(TrueBBI.ClobbersPred && FalseBBI.ClobbersPred) &&
524 FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
525 FeasibilityAnalysis(FalseBBI, RevCond)) {
533 // Note TailBB can be empty.
534 BBI.Kind = ICDiamond;
535 BBI.TailBB = TrueBBI.TrueBB;
537 // FIXME: Consider duplicating if BB is small.
538 if (ValidTriangle(TrueBBI, FalseBBI) &&
539 FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
547 BBI.Kind = ICTriangle;
548 } else if (ValidTriangle(TrueBBI, FalseBBI, true) &&
549 FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
550 BBI.Kind = ICTriangleRev;
551 } else if (ValidSimple(TrueBBI) &&
552 FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
553 // Simple (split, no rejoin):
561 } else if (CanRevCond) {
562 // Try the other path...
563 if (ValidTriangle(FalseBBI, TrueBBI) &&
564 FeasibilityAnalysis(FalseBBI, RevCond, true)) {
565 BBI.Kind = ICTriangleFalse;
566 } else if (ValidTriangle(FalseBBI, TrueBBI, true) &&
567 FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
568 BBI.Kind = ICTriangleFRev;
569 } else if (ValidSimple(FalseBBI) &&
570 FeasibilityAnalysis(FalseBBI, RevCond)) {
571 BBI.Kind = ICSimpleFalse;
576 BBI.IsBeingAnalyzed = false;
577 BBI.IsAnalyzed = true;
581 /// AttemptRestructuring - Restructure the sub-CFG rooted in the given block to
582 /// expose more if-conversion opportunities. e.g.
604 bool IfConverter::AttemptRestructuring(BBInfo &BBI) {
608 /// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
609 /// candidates. It returns true if any CFG restructuring is done to expose more
610 /// if-conversion opportunities.
611 bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
612 std::vector<BBInfo*> &Candidates) {
614 std::set<MachineBasicBlock*> Visited;
615 for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
616 for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
617 E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
618 MachineBasicBlock *BB = *I;
619 BBInfo &BBI = AnalyzeBlock(BB);
625 case ICTriangleFalse:
628 Candidates.push_back(&BBI);
631 Change |= AttemptRestructuring(BBI);
637 // Sort to favor more complex ifcvt scheme.
638 std::stable_sort(Candidates.begin(), Candidates.end(), IfcvtCandidateCmp);
643 /// canFallThroughTo - Returns true either if ToBB is the next block after BB or
644 /// that all the intervening blocks are empty (given BB can fall through to its
646 static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
647 MachineFunction::iterator I = BB;
648 MachineFunction::iterator TI = ToBB;
649 MachineFunction::iterator E = BB->getParent()->end();
651 if (I == E || !I->empty())
656 /// ReTryPreds - Invalidate predecessor BB info so it would be re-analyzed
657 /// to determine if it can be if-converted.
658 void IfConverter::ReTryPreds(MachineBasicBlock *BB) {
659 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
660 E = BB->pred_end(); PI != E; ++PI) {
661 BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
662 if (!PBBI.IsDone && PBBI.Kind == ICNotClassfied) {
663 assert(PBBI.IsEnqueued && "Unexpected");
664 PBBI.IsAnalyzed = false;
669 /// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
671 static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
672 const TargetInstrInfo *TII) {
673 std::vector<MachineOperand> NoCond;
674 TII->InsertBranch(*BB, ToBB, NULL, NoCond);
677 /// RemoveExtraEdges - Remove true / false edges if either / both are no longer
679 void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
680 MachineBasicBlock *TBB = NULL, *FBB = NULL;
681 std::vector<MachineOperand> Cond;
682 bool isAnalyzable = !TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond);
683 bool CanFallthrough = isAnalyzable && (TBB == NULL || FBB == NULL);
684 if (BBI.TrueBB && BBI.BB->isSuccessor(BBI.TrueBB))
685 if (!(BBI.TrueBB == TBB || BBI.TrueBB == FBB ||
686 (CanFallthrough && getNextBlock(BBI.BB) == BBI.TrueBB)))
687 BBI.BB->removeSuccessor(BBI.TrueBB);
688 if (BBI.FalseBB && BBI.BB->isSuccessor(BBI.FalseBB))
689 if (!(BBI.FalseBB == TBB || BBI.FalseBB == FBB ||
690 (CanFallthrough && getNextBlock(BBI.BB) == BBI.FalseBB)))
691 BBI.BB->removeSuccessor(BBI.FalseBB);
694 /// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
696 bool IfConverter::IfConvertSimple(BBInfo &BBI) {
697 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
698 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
699 BBInfo *CvtBBI = &TrueBBI;
700 BBInfo *NextBBI = &FalseBBI;
702 std::vector<MachineOperand> Cond(BBI.BrCond);
703 if (BBI.Kind == ICSimpleFalse) {
704 std::swap(CvtBBI, NextBBI);
705 TII->ReverseBranchCondition(Cond);
708 PredicateBlock(*CvtBBI, Cond);
710 // Merge converted block into entry block.
711 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
712 MergeBlocks(BBI, *CvtBBI);
714 bool IterIfcvt = true;
715 if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
716 InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
717 BBI.HasFallThrough = false;
718 // Now ifcvt'd block will look like this:
725 // We cannot further ifcvt this block because the unconditional branch
726 // will have to be predicated on the new condition, that will not be
727 // available if cmp executes.
731 RemoveExtraEdges(BBI);
733 // Update block info. BB can be iteratively if-converted.
737 CvtBBI->IsDone = true;
739 // FIXME: Must maintain LiveIns.
743 /// IfConvertTriangle - If convert a triangle sub-CFG.
745 bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
746 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
747 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
748 BBInfo *CvtBBI = &TrueBBI;
749 BBInfo *NextBBI = &FalseBBI;
751 std::vector<MachineOperand> Cond(BBI.BrCond);
752 if (BBI.Kind == ICTriangleFalse || BBI.Kind == ICTriangleFRev) {
753 std::swap(CvtBBI, NextBBI);
754 TII->ReverseBranchCondition(Cond);
756 if (BBI.Kind == ICTriangleRev || BBI.Kind == ICTriangleFRev) {
757 ReverseBranchCondition(*CvtBBI);
758 // BB has been changed, modify its predecessors (except for this
759 // one) so they don't get ifcvt'ed based on bad intel.
760 for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
761 E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
762 MachineBasicBlock *PBB = *PI;
765 BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
767 PBBI.IsEnqueued = false;
771 // Predicate the 'true' block after removing its branch.
772 TrueBBI.NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
773 PredicateBlock(*CvtBBI, Cond);
775 // If 'true' block has a 'false' successor, add an exit branch to it.
776 bool HasEarlyExit = CvtBBI->FalseBB != NULL;
778 std::vector<MachineOperand> RevCond(CvtBBI->BrCond);
779 if (TII->ReverseBranchCondition(RevCond))
780 assert(false && "Unable to reverse branch condition!");
781 TII->InsertBranch(*CvtBBI->BB, CvtBBI->FalseBB, NULL, RevCond);
784 // Now merge the entry of the triangle with the true block.
785 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
786 MergeBlocks(BBI, *CvtBBI);
788 // Merge in the 'false' block if the 'false' block has no other
789 // predecessors. Otherwise, add a unconditional branch from to 'false'.
790 bool FalseBBDead = false;
791 bool IterIfcvt = true;
792 bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
793 if (!isFallThrough) {
794 // Only merge them if the true block does not fallthrough to the false
795 // block. By not merging them, we make it possible to iteratively
797 if (!HasEarlyExit && NextBBI->BB->pred_size() == 1) {
798 MergeBlocks(BBI, *NextBBI);
801 InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
802 BBI.HasFallThrough = false;
804 // Mixed predicated and unpredicated code. This cannot be iteratively
809 RemoveExtraEdges(BBI);
811 // Update block info. BB can be iteratively if-converted.
815 CvtBBI->IsDone = true;
817 NextBBI->IsDone = true;
819 // FIXME: Must maintain LiveIns.
823 /// IfConvertDiamond - If convert a diamond sub-CFG.
825 bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
826 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
827 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
829 SmallVector<MachineInstr*, 2> Dups;
831 // No common merge block. Check if the terminators (e.g. return) are
832 // the same or predicable.
833 MachineBasicBlock::iterator TT = BBI.TrueBB->getFirstTerminator();
834 MachineBasicBlock::iterator FT = BBI.FalseBB->getFirstTerminator();
835 while (TT != BBI.TrueBB->end() && FT != BBI.FalseBB->end()) {
836 if (TT->isIdenticalTo(FT))
837 Dups.push_back(TT); // Will erase these later.
838 else if (!TT->isPredicable() && !FT->isPredicable())
839 return false; // Can't if-convert. Abort!
844 // One of the two pathes have more terminators, make sure they are
846 while (TT != BBI.TrueBB->end()) {
847 if (!TT->isPredicable()) {
848 return false; // Can't if-convert. Abort!
852 while (FT != BBI.FalseBB->end()) {
853 if (!FT->isPredicable()) {
854 return false; // Can't if-convert. Abort!
860 // Remove the duplicated instructions from the 'true' block.
861 for (unsigned i = 0, e = Dups.size(); i != e; ++i) {
862 Dups[i]->eraseFromParent();
863 --TrueBBI.NonPredSize;
866 // Merge the 'true' and 'false' blocks by copying the instructions
867 // from the 'false' block to the 'true' block. That is, unless the true
868 // block would clobber the predicate, in that case, do the opposite.
869 BBInfo *BBI1 = &TrueBBI;
870 BBInfo *BBI2 = &FalseBBI;
871 std::vector<MachineOperand> RevCond(BBI.BrCond);
872 TII->ReverseBranchCondition(RevCond);
873 std::vector<MachineOperand> *Cond1 = &BBI.BrCond;
874 std::vector<MachineOperand> *Cond2 = &RevCond;
875 // Check the 'true' and 'false' blocks if either isn't ended with a branch.
876 // Either the block fallthrough to another block or it ends with a
877 // return. If it's the former, add a branch to its successor.
878 bool NeedBr1 = !BBI1->TrueBB && BBI1->BB->succ_size();
879 bool NeedBr2 = !BBI2->TrueBB && BBI2->BB->succ_size();
881 if ((TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred) ||
882 (!TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred &&
883 NeedBr1 && !NeedBr2)) {
884 std::swap(BBI1, BBI2);
885 std::swap(Cond1, Cond2);
886 std::swap(NeedBr1, NeedBr2);
889 // Predicate the 'true' block after removing its branch.
890 BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
891 PredicateBlock(*BBI1, *Cond1);
893 // Add an early exit branch if needed.
895 TII->InsertBranch(*BBI1->BB, *BBI1->BB->succ_begin(), NULL, *Cond1);
897 // Predicate the 'false' block.
898 PredicateBlock(*BBI2, *Cond2, true);
900 // Add an unconditional branch from 'false' to to 'false' successor if it
901 // will not be the fallthrough block.
902 if (NeedBr2 && !NeedBr1) {
903 // If BBI2 isn't going to be merged in, then the existing fallthrough
904 // or branch is fine.
905 if (!canFallThroughTo(BBI.BB, *BBI2->BB->succ_begin())) {
906 InsertUncondBranch(BBI2->BB, *BBI2->BB->succ_begin(), TII);
907 BBI2->HasFallThrough = false;
911 // Keep them as two separate blocks if there is an early exit.
913 MergeBlocks(*BBI1, *BBI2);
915 // Remove the conditional branch from entry to the blocks.
916 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
918 // Merge the combined block into the entry of the diamond.
919 MergeBlocks(BBI, *BBI1);
921 // 'True' and 'false' aren't combined, see if we need to add a unconditional
922 // branch to the 'false' block.
923 if (NeedBr1 && !canFallThroughTo(BBI.BB, BBI2->BB)) {
924 InsertUncondBranch(BBI.BB, BBI2->BB, TII);
925 BBI1->HasFallThrough = false;
928 // If the if-converted block fallthrough or unconditionally branch into the
929 // tail block, and the tail block does not have other predecessors, then
930 // fold the tail block in as well.
931 BBInfo *CvtBBI = NeedBr1 ? BBI2 : &BBI;
933 BBI.TailBB->pred_size() == 1 && CvtBBI->BB->succ_size() == 1) {
934 CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
935 BBInfo TailBBI = BBAnalysis[BBI.TailBB->getNumber()];
936 MergeBlocks(*CvtBBI, TailBBI);
937 TailBBI.IsDone = true;
940 RemoveExtraEdges(BBI);
942 // Update block info.
943 BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
945 // FIXME: Must maintain LiveIns.
949 /// PredicateBlock - Predicate every instruction in the block with the specified
950 /// condition. If IgnoreTerm is true, skip over all terminator instructions.
951 void IfConverter::PredicateBlock(BBInfo &BBI,
952 std::vector<MachineOperand> &Cond,
954 for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
956 if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
958 if (TII->isPredicated(I))
960 if (!TII->PredicateInstruction(I, Cond)) {
961 cerr << "Unable to predicate " << *I << "!\n";
967 std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
972 /// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
974 void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
975 ToBBI.BB->splice(ToBBI.BB->end(),
976 FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
978 // Redirect all branches to FromBB to ToBB.
979 std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
980 FromBBI.BB->pred_end());
981 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
982 MachineBasicBlock *Pred = Preds[i];
983 if (Pred == ToBBI.BB)
985 Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
988 std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
989 FromBBI.BB->succ_end());
990 MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
991 MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
993 for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
994 MachineBasicBlock *Succ = Succs[i];
995 // Fallthrough edge can't be transferred.
996 if (Succ == FallThrough)
998 FromBBI.BB->removeSuccessor(Succ);
999 if (!ToBBI.BB->isSuccessor(Succ))
1000 ToBBI.BB->addSuccessor(Succ);
1003 // Now FromBBI always fall through to the next block!
1005 FromBBI.BB->addSuccessor(NBB);
1007 ToBBI.NonPredSize += FromBBI.NonPredSize;
1008 FromBBI.NonPredSize = 0;
1010 ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1011 ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1013 std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1014 std::back_inserter(ToBBI.Predicate));
1015 FromBBI.Predicate.clear();