1 //===-- MachineBlockPlacement.cpp - Basic Block Code Layout optimization --===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements basic block placement transformations using the CFG
11 // structure and branch probability estimates.
13 // The pass strives to preserve the structure of the CFG (that is, retain
14 // a topological ordering of basic blocks) in the absence of a *strong* signal
15 // to the contrary from probabilities. However, within the CFG structure, it
16 // attempts to choose an ordering which favors placing more likely sequences of
17 // blocks adjacent to each other.
19 // The algorithm works from the inner-most loop within a function outward, and
20 // at each stage walks through the basic blocks, trying to coalesce them into
21 // sequential chains where allowed by the CFG (or demanded by heavy
22 // probabilities). Finally, it walks the blocks in topological order, and the
23 // first time it reaches a chain of basic blocks, it schedules them in the
26 //===----------------------------------------------------------------------===//
28 #include "llvm/CodeGen/Passes.h"
29 #include "llvm/ADT/DenseMap.h"
30 #include "llvm/ADT/SmallPtrSet.h"
31 #include "llvm/ADT/SmallVector.h"
32 #include "llvm/ADT/Statistic.h"
33 #include "llvm/CodeGen/MachineBasicBlock.h"
34 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
35 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
36 #include "llvm/CodeGen/MachineDominators.h"
37 #include "llvm/CodeGen/MachineFunction.h"
38 #include "llvm/CodeGen/MachineFunctionPass.h"
39 #include "llvm/CodeGen/MachineLoopInfo.h"
40 #include "llvm/CodeGen/MachineModuleInfo.h"
41 #include "llvm/Support/Allocator.h"
42 #include "llvm/Support/CommandLine.h"
43 #include "llvm/Support/Debug.h"
44 #include "llvm/Target/TargetInstrInfo.h"
45 #include "llvm/Target/TargetLowering.h"
46 #include "llvm/Target/TargetSubtargetInfo.h"
50 #define DEBUG_TYPE "block-placement"
52 STATISTIC(NumCondBranches, "Number of conditional branches");
53 STATISTIC(NumUncondBranches, "Number of uncondittional branches");
54 STATISTIC(CondBranchTakenFreq,
55 "Potential frequency of taking conditional branches");
56 STATISTIC(UncondBranchTakenFreq,
57 "Potential frequency of taking unconditional branches");
59 static cl::opt<unsigned> AlignAllBlock("align-all-blocks",
60 cl::desc("Force the alignment of all "
61 "blocks in the function."),
62 cl::init(0), cl::Hidden);
64 // FIXME: Find a good default for this flag and remove the flag.
65 static cl::opt<unsigned> ExitBlockBias(
66 "block-placement-exit-block-bias",
67 cl::desc("Block frequency percentage a loop exit block needs "
68 "over the original exit to be considered the new exit."),
69 cl::init(0), cl::Hidden);
71 static cl::opt<bool> OutlineOptionalBranches(
72 "outline-optional-branches",
73 cl::desc("Put completely optional branches, i.e. branches with a common "
74 "post dominator, out of line."),
75 cl::init(false), cl::Hidden);
79 /// \brief Type for our function-wide basic block -> block chain mapping.
80 typedef DenseMap<MachineBasicBlock *, BlockChain *> BlockToChainMapType;
84 /// \brief A chain of blocks which will be laid out contiguously.
86 /// This is the datastructure representing a chain of consecutive blocks that
87 /// are profitable to layout together in order to maximize fallthrough
88 /// probabilities and code locality. We also can use a block chain to represent
89 /// a sequence of basic blocks which have some external (correctness)
90 /// requirement for sequential layout.
92 /// Chains can be built around a single basic block and can be merged to grow
93 /// them. They participate in a block-to-chain mapping, which is updated
94 /// automatically as chains are merged together.
96 /// \brief The sequence of blocks belonging to this chain.
98 /// This is the sequence of blocks for a particular chain. These will be laid
99 /// out in-order within the function.
100 SmallVector<MachineBasicBlock *, 4> Blocks;
102 /// \brief A handle to the function-wide basic block to block chain mapping.
104 /// This is retained in each block chain to simplify the computation of child
105 /// block chains for SCC-formation and iteration. We store the edges to child
106 /// basic blocks, and map them back to their associated chains using this
108 BlockToChainMapType &BlockToChain;
111 /// \brief Construct a new BlockChain.
113 /// This builds a new block chain representing a single basic block in the
114 /// function. It also registers itself as the chain that block participates
115 /// in with the BlockToChain mapping.
116 BlockChain(BlockToChainMapType &BlockToChain, MachineBasicBlock *BB)
117 : Blocks(1, BB), BlockToChain(BlockToChain), LoopPredecessors(0) {
118 assert(BB && "Cannot create a chain with a null basic block");
119 BlockToChain[BB] = this;
122 /// \brief Iterator over blocks within the chain.
123 typedef SmallVectorImpl<MachineBasicBlock *>::iterator iterator;
125 /// \brief Beginning of blocks within the chain.
126 iterator begin() { return Blocks.begin(); }
128 /// \brief End of blocks within the chain.
129 iterator end() { return Blocks.end(); }
131 /// \brief Merge a block chain into this one.
133 /// This routine merges a block chain into this one. It takes care of forming
134 /// a contiguous sequence of basic blocks, updating the edge list, and
135 /// updating the block -> chain mapping. It does not free or tear down the
136 /// old chain, but the old chain's block list is no longer valid.
137 void merge(MachineBasicBlock *BB, BlockChain *Chain) {
139 assert(!Blocks.empty());
141 // Fast path in case we don't have a chain already.
143 assert(!BlockToChain[BB]);
144 Blocks.push_back(BB);
145 BlockToChain[BB] = this;
149 assert(BB == *Chain->begin());
150 assert(Chain->begin() != Chain->end());
152 // Update the incoming blocks to point to this chain, and add them to the
154 for (MachineBasicBlock *ChainBB : *Chain) {
155 Blocks.push_back(ChainBB);
156 assert(BlockToChain[ChainBB] == Chain && "Incoming blocks not in chain");
157 BlockToChain[ChainBB] = this;
162 /// \brief Dump the blocks in this chain.
163 LLVM_DUMP_METHOD void dump() {
164 for (MachineBasicBlock *MBB : *this)
169 /// \brief Count of predecessors within the loop currently being processed.
171 /// This count is updated at each loop we process to represent the number of
172 /// in-loop predecessors of this chain.
173 unsigned LoopPredecessors;
178 class MachineBlockPlacement : public MachineFunctionPass {
179 /// \brief A typedef for a block filter set.
180 typedef SmallPtrSet<MachineBasicBlock *, 16> BlockFilterSet;
182 /// \brief A handle to the branch probability pass.
183 const MachineBranchProbabilityInfo *MBPI;
185 /// \brief A handle to the function-wide block frequency pass.
186 const MachineBlockFrequencyInfo *MBFI;
188 /// \brief A handle to the loop info.
189 const MachineLoopInfo *MLI;
191 /// \brief A handle to the target's instruction info.
192 const TargetInstrInfo *TII;
194 /// \brief A handle to the target's lowering info.
195 const TargetLoweringBase *TLI;
197 /// \brief A handle to the post dominator tree.
198 MachineDominatorTree *MDT;
200 /// \brief A set of blocks that are unavoidably execute, i.e. they dominate
201 /// all terminators of the MachineFunction.
202 SmallPtrSet<MachineBasicBlock *, 4> UnavoidableBlocks;
204 /// \brief Allocator and owner of BlockChain structures.
206 /// We build BlockChains lazily while processing the loop structure of
207 /// a function. To reduce malloc traffic, we allocate them using this
208 /// slab-like allocator, and destroy them after the pass completes. An
209 /// important guarantee is that this allocator produces stable pointers to
211 SpecificBumpPtrAllocator<BlockChain> ChainAllocator;
213 /// \brief Function wide BasicBlock to BlockChain mapping.
215 /// This mapping allows efficiently moving from any given basic block to the
216 /// BlockChain it participates in, if any. We use it to, among other things,
217 /// allow implicitly defining edges between chains as the existing edges
218 /// between basic blocks.
219 DenseMap<MachineBasicBlock *, BlockChain *> BlockToChain;
221 void markChainSuccessors(BlockChain &Chain, MachineBasicBlock *LoopHeaderBB,
222 SmallVectorImpl<MachineBasicBlock *> &BlockWorkList,
223 const BlockFilterSet *BlockFilter = nullptr);
224 MachineBasicBlock *selectBestSuccessor(MachineBasicBlock *BB,
226 const BlockFilterSet *BlockFilter);
228 selectBestCandidateBlock(BlockChain &Chain,
229 SmallVectorImpl<MachineBasicBlock *> &WorkList,
230 const BlockFilterSet *BlockFilter);
232 getFirstUnplacedBlock(MachineFunction &F, const BlockChain &PlacedChain,
233 MachineFunction::iterator &PrevUnplacedBlockIt,
234 const BlockFilterSet *BlockFilter);
235 void buildChain(MachineBasicBlock *BB, BlockChain &Chain,
236 SmallVectorImpl<MachineBasicBlock *> &BlockWorkList,
237 const BlockFilterSet *BlockFilter = nullptr);
238 MachineBasicBlock *findBestLoopTop(MachineLoop &L,
239 const BlockFilterSet &LoopBlockSet);
240 MachineBasicBlock *findBestLoopExit(MachineFunction &F, MachineLoop &L,
241 const BlockFilterSet &LoopBlockSet);
242 void buildLoopChains(MachineFunction &F, MachineLoop &L);
243 void rotateLoop(BlockChain &LoopChain, MachineBasicBlock *ExitingBB,
244 const BlockFilterSet &LoopBlockSet);
245 void buildCFGChains(MachineFunction &F);
248 static char ID; // Pass identification, replacement for typeid
249 MachineBlockPlacement() : MachineFunctionPass(ID) {
250 initializeMachineBlockPlacementPass(*PassRegistry::getPassRegistry());
253 bool runOnMachineFunction(MachineFunction &F) override;
255 void getAnalysisUsage(AnalysisUsage &AU) const override {
256 AU.addRequired<MachineBranchProbabilityInfo>();
257 AU.addRequired<MachineBlockFrequencyInfo>();
258 AU.addRequired<MachineDominatorTree>();
259 AU.addRequired<MachineLoopInfo>();
260 MachineFunctionPass::getAnalysisUsage(AU);
265 char MachineBlockPlacement::ID = 0;
266 char &llvm::MachineBlockPlacementID = MachineBlockPlacement::ID;
267 INITIALIZE_PASS_BEGIN(MachineBlockPlacement, "block-placement",
268 "Branch Probability Basic Block Placement", false, false)
269 INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
270 INITIALIZE_PASS_DEPENDENCY(MachineBlockFrequencyInfo)
271 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
272 INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
273 INITIALIZE_PASS_END(MachineBlockPlacement, "block-placement",
274 "Branch Probability Basic Block Placement", false, false)
277 /// \brief Helper to print the name of a MBB.
279 /// Only used by debug logging.
280 static std::string getBlockName(MachineBasicBlock *BB) {
282 raw_string_ostream OS(Result);
283 OS << "BB#" << BB->getNumber();
284 OS << " (derived from LLVM BB '" << BB->getName() << "')";
289 /// \brief Helper to print the number of a MBB.
291 /// Only used by debug logging.
292 static std::string getBlockNum(MachineBasicBlock *BB) {
294 raw_string_ostream OS(Result);
295 OS << "BB#" << BB->getNumber();
301 /// \brief Mark a chain's successors as having one fewer preds.
303 /// When a chain is being merged into the "placed" chain, this routine will
304 /// quickly walk the successors of each block in the chain and mark them as
305 /// having one fewer active predecessor. It also adds any successors of this
306 /// chain which reach the zero-predecessor state to the worklist passed in.
307 void MachineBlockPlacement::markChainSuccessors(
308 BlockChain &Chain, MachineBasicBlock *LoopHeaderBB,
309 SmallVectorImpl<MachineBasicBlock *> &BlockWorkList,
310 const BlockFilterSet *BlockFilter) {
311 // Walk all the blocks in this chain, marking their successors as having
312 // a predecessor placed.
313 for (MachineBasicBlock *MBB : Chain) {
314 // Add any successors for which this is the only un-placed in-loop
315 // predecessor to the worklist as a viable candidate for CFG-neutral
316 // placement. No subsequent placement of this block will violate the CFG
317 // shape, so we get to use heuristics to choose a favorable placement.
318 for (MachineBasicBlock *Succ : MBB->successors()) {
319 if (BlockFilter && !BlockFilter->count(Succ))
321 BlockChain &SuccChain = *BlockToChain[Succ];
322 // Disregard edges within a fixed chain, or edges to the loop header.
323 if (&Chain == &SuccChain || Succ == LoopHeaderBB)
326 // This is a cross-chain edge that is within the loop, so decrement the
327 // loop predecessor count of the destination chain.
328 if (SuccChain.LoopPredecessors > 0 && --SuccChain.LoopPredecessors == 0)
329 BlockWorkList.push_back(*SuccChain.begin());
334 /// \brief Select the best successor for a block.
336 /// This looks across all successors of a particular block and attempts to
337 /// select the "best" one to be the layout successor. It only considers direct
338 /// successors which also pass the block filter. It will attempt to avoid
339 /// breaking CFG structure, but cave and break such structures in the case of
340 /// very hot successor edges.
342 /// \returns The best successor block found, or null if none are viable.
344 MachineBlockPlacement::selectBestSuccessor(MachineBasicBlock *BB,
346 const BlockFilterSet *BlockFilter) {
347 const BranchProbability HotProb(4, 5); // 80%
349 MachineBasicBlock *BestSucc = nullptr;
350 // FIXME: Due to the performance of the probability and weight routines in
351 // the MBPI analysis, we manually compute probabilities using the edge
352 // weights. This is suboptimal as it means that the somewhat subtle
353 // definition of edge weight semantics is encoded here as well. We should
354 // improve the MBPI interface to efficiently support query patterns such as
356 uint32_t BestWeight = 0;
357 uint32_t WeightScale = 0;
358 uint32_t SumWeight = MBPI->getSumForBlock(BB, WeightScale);
359 DEBUG(dbgs() << "Attempting merge from: " << getBlockName(BB) << "\n");
360 for (MachineBasicBlock *Succ : BB->successors()) {
361 if (BlockFilter && !BlockFilter->count(Succ))
363 BlockChain &SuccChain = *BlockToChain[Succ];
364 if (&SuccChain == &Chain) {
365 DEBUG(dbgs() << " " << getBlockName(Succ) << " -> Already merged!\n");
368 if (Succ != *SuccChain.begin()) {
369 DEBUG(dbgs() << " " << getBlockName(Succ) << " -> Mid chain!\n");
373 uint32_t SuccWeight = MBPI->getEdgeWeight(BB, Succ);
374 BranchProbability SuccProb(SuccWeight / WeightScale, SumWeight);
376 // If we outline optional branches, look whether Succ is unavoidable, i.e.
377 // dominates all terminators of the MachineFunction. If it does, other
378 // successors must be optional. Don't do this for cold branches.
379 if (OutlineOptionalBranches && SuccProb > HotProb.getCompl() &&
380 UnavoidableBlocks.count(Succ) > 0)
383 // Only consider successors which are either "hot", or wouldn't violate
384 // any CFG constraints.
385 if (SuccChain.LoopPredecessors != 0) {
386 if (SuccProb < HotProb) {
387 DEBUG(dbgs() << " " << getBlockName(Succ) << " -> " << SuccProb
388 << " (prob) (CFG conflict)\n");
392 // Make sure that a hot successor doesn't have a globally more
393 // important predecessor.
394 BlockFrequency CandidateEdgeFreq =
395 MBFI->getBlockFreq(BB) * SuccProb * HotProb.getCompl();
396 bool BadCFGConflict = false;
397 for (MachineBasicBlock *Pred : Succ->predecessors()) {
398 if (Pred == Succ || (BlockFilter && !BlockFilter->count(Pred)) ||
399 BlockToChain[Pred] == &Chain)
401 BlockFrequency PredEdgeFreq =
402 MBFI->getBlockFreq(Pred) * MBPI->getEdgeProbability(Pred, Succ);
403 if (PredEdgeFreq >= CandidateEdgeFreq) {
404 BadCFGConflict = true;
408 if (BadCFGConflict) {
409 DEBUG(dbgs() << " " << getBlockName(Succ) << " -> " << SuccProb
410 << " (prob) (non-cold CFG conflict)\n");
415 DEBUG(dbgs() << " " << getBlockName(Succ) << " -> " << SuccProb
417 << (SuccChain.LoopPredecessors != 0 ? " (CFG break)" : "")
419 if (BestSucc && BestWeight >= SuccWeight)
422 BestWeight = SuccWeight;
427 /// \brief Select the best block from a worklist.
429 /// This looks through the provided worklist as a list of candidate basic
430 /// blocks and select the most profitable one to place. The definition of
431 /// profitable only really makes sense in the context of a loop. This returns
432 /// the most frequently visited block in the worklist, which in the case of
433 /// a loop, is the one most desirable to be physically close to the rest of the
434 /// loop body in order to improve icache behavior.
436 /// \returns The best block found, or null if none are viable.
437 MachineBasicBlock *MachineBlockPlacement::selectBestCandidateBlock(
438 BlockChain &Chain, SmallVectorImpl<MachineBasicBlock *> &WorkList,
439 const BlockFilterSet *BlockFilter) {
440 // Once we need to walk the worklist looking for a candidate, cleanup the
441 // worklist of already placed entries.
442 // FIXME: If this shows up on profiles, it could be folded (at the cost of
443 // some code complexity) into the loop below.
444 WorkList.erase(std::remove_if(WorkList.begin(), WorkList.end(),
445 [&](MachineBasicBlock *BB) {
446 return BlockToChain.lookup(BB) == &Chain;
450 MachineBasicBlock *BestBlock = nullptr;
451 BlockFrequency BestFreq;
452 for (MachineBasicBlock *MBB : WorkList) {
453 BlockChain &SuccChain = *BlockToChain[MBB];
454 if (&SuccChain == &Chain) {
455 DEBUG(dbgs() << " " << getBlockName(MBB) << " -> Already merged!\n");
458 assert(SuccChain.LoopPredecessors == 0 && "Found CFG-violating block");
460 BlockFrequency CandidateFreq = MBFI->getBlockFreq(MBB);
461 DEBUG(dbgs() << " " << getBlockName(MBB) << " -> ";
462 MBFI->printBlockFreq(dbgs(), CandidateFreq) << " (freq)\n");
463 if (BestBlock && BestFreq >= CandidateFreq)
466 BestFreq = CandidateFreq;
471 /// \brief Retrieve the first unplaced basic block.
473 /// This routine is called when we are unable to use the CFG to walk through
474 /// all of the basic blocks and form a chain due to unnatural loops in the CFG.
475 /// We walk through the function's blocks in order, starting from the
476 /// LastUnplacedBlockIt. We update this iterator on each call to avoid
477 /// re-scanning the entire sequence on repeated calls to this routine.
478 MachineBasicBlock *MachineBlockPlacement::getFirstUnplacedBlock(
479 MachineFunction &F, const BlockChain &PlacedChain,
480 MachineFunction::iterator &PrevUnplacedBlockIt,
481 const BlockFilterSet *BlockFilter) {
482 for (MachineFunction::iterator I = PrevUnplacedBlockIt, E = F.end(); I != E;
484 if (BlockFilter && !BlockFilter->count(I))
486 if (BlockToChain[I] != &PlacedChain) {
487 PrevUnplacedBlockIt = I;
488 // Now select the head of the chain to which the unplaced block belongs
489 // as the block to place. This will force the entire chain to be placed,
490 // and satisfies the requirements of merging chains.
491 return *BlockToChain[I]->begin();
497 void MachineBlockPlacement::buildChain(
498 MachineBasicBlock *BB, BlockChain &Chain,
499 SmallVectorImpl<MachineBasicBlock *> &BlockWorkList,
500 const BlockFilterSet *BlockFilter) {
502 assert(BlockToChain[BB] == &Chain);
503 MachineFunction &F = *BB->getParent();
504 MachineFunction::iterator PrevUnplacedBlockIt = F.begin();
506 MachineBasicBlock *LoopHeaderBB = BB;
507 markChainSuccessors(Chain, LoopHeaderBB, BlockWorkList, BlockFilter);
508 BB = *std::prev(Chain.end());
511 assert(BlockToChain[BB] == &Chain);
512 assert(*std::prev(Chain.end()) == BB);
514 // Look for the best viable successor if there is one to place immediately
516 MachineBasicBlock *BestSucc = selectBestSuccessor(BB, Chain, BlockFilter);
518 // If an immediate successor isn't available, look for the best viable
519 // block among those we've identified as not violating the loop's CFG at
520 // this point. This won't be a fallthrough, but it will increase locality.
522 BestSucc = selectBestCandidateBlock(Chain, BlockWorkList, BlockFilter);
526 getFirstUnplacedBlock(F, Chain, PrevUnplacedBlockIt, BlockFilter);
530 DEBUG(dbgs() << "Unnatural loop CFG detected, forcibly merging the "
531 "layout successor until the CFG reduces\n");
534 // Place this block, updating the datastructures to reflect its placement.
535 BlockChain &SuccChain = *BlockToChain[BestSucc];
536 // Zero out LoopPredecessors for the successor we're about to merge in case
537 // we selected a successor that didn't fit naturally into the CFG.
538 SuccChain.LoopPredecessors = 0;
539 DEBUG(dbgs() << "Merging from " << getBlockNum(BB) << " to "
540 << getBlockNum(BestSucc) << "\n");
541 markChainSuccessors(SuccChain, LoopHeaderBB, BlockWorkList, BlockFilter);
542 Chain.merge(BestSucc, &SuccChain);
543 BB = *std::prev(Chain.end());
546 DEBUG(dbgs() << "Finished forming chain for header block "
547 << getBlockNum(*Chain.begin()) << "\n");
550 /// \brief Find the best loop top block for layout.
552 /// Look for a block which is strictly better than the loop header for laying
553 /// out at the top of the loop. This looks for one and only one pattern:
554 /// a latch block with no conditional exit. This block will cause a conditional
555 /// jump around it or will be the bottom of the loop if we lay it out in place,
556 /// but if it it doesn't end up at the bottom of the loop for any reason,
557 /// rotation alone won't fix it. Because such a block will always result in an
558 /// unconditional jump (for the backedge) rotating it in front of the loop
559 /// header is always profitable.
561 MachineBlockPlacement::findBestLoopTop(MachineLoop &L,
562 const BlockFilterSet &LoopBlockSet) {
563 // Check that the header hasn't been fused with a preheader block due to
564 // crazy branches. If it has, we need to start with the header at the top to
565 // prevent pulling the preheader into the loop body.
566 BlockChain &HeaderChain = *BlockToChain[L.getHeader()];
567 if (!LoopBlockSet.count(*HeaderChain.begin()))
568 return L.getHeader();
570 DEBUG(dbgs() << "Finding best loop top for: " << getBlockName(L.getHeader())
573 BlockFrequency BestPredFreq;
574 MachineBasicBlock *BestPred = nullptr;
575 for (MachineBasicBlock *Pred : L.getHeader()->predecessors()) {
576 if (!LoopBlockSet.count(Pred))
578 DEBUG(dbgs() << " header pred: " << getBlockName(Pred) << ", "
579 << Pred->succ_size() << " successors, ";
580 MBFI->printBlockFreq(dbgs(), Pred) << " freq\n");
581 if (Pred->succ_size() > 1)
584 BlockFrequency PredFreq = MBFI->getBlockFreq(Pred);
585 if (!BestPred || PredFreq > BestPredFreq ||
586 (!(PredFreq < BestPredFreq) &&
587 Pred->isLayoutSuccessor(L.getHeader()))) {
589 BestPredFreq = PredFreq;
593 // If no direct predecessor is fine, just use the loop header.
595 return L.getHeader();
597 // Walk backwards through any straight line of predecessors.
598 while (BestPred->pred_size() == 1 &&
599 (*BestPred->pred_begin())->succ_size() == 1 &&
600 *BestPred->pred_begin() != L.getHeader())
601 BestPred = *BestPred->pred_begin();
603 DEBUG(dbgs() << " final top: " << getBlockName(BestPred) << "\n");
607 /// \brief Find the best loop exiting block for layout.
609 /// This routine implements the logic to analyze the loop looking for the best
610 /// block to layout at the top of the loop. Typically this is done to maximize
611 /// fallthrough opportunities.
613 MachineBlockPlacement::findBestLoopExit(MachineFunction &F, MachineLoop &L,
614 const BlockFilterSet &LoopBlockSet) {
615 // We don't want to layout the loop linearly in all cases. If the loop header
616 // is just a normal basic block in the loop, we want to look for what block
617 // within the loop is the best one to layout at the top. However, if the loop
618 // header has be pre-merged into a chain due to predecessors not having
619 // analyzable branches, *and* the predecessor it is merged with is *not* part
620 // of the loop, rotating the header into the middle of the loop will create
621 // a non-contiguous range of blocks which is Very Bad. So start with the
622 // header and only rotate if safe.
623 BlockChain &HeaderChain = *BlockToChain[L.getHeader()];
624 if (!LoopBlockSet.count(*HeaderChain.begin()))
627 BlockFrequency BestExitEdgeFreq;
628 unsigned BestExitLoopDepth = 0;
629 MachineBasicBlock *ExitingBB = nullptr;
630 // If there are exits to outer loops, loop rotation can severely limit
631 // fallthrough opportunites unless it selects such an exit. Keep a set of
632 // blocks where rotating to exit with that block will reach an outer loop.
633 SmallPtrSet<MachineBasicBlock *, 4> BlocksExitingToOuterLoop;
635 DEBUG(dbgs() << "Finding best loop exit for: " << getBlockName(L.getHeader())
637 for (MachineBasicBlock *MBB : L.getBlocks()) {
638 BlockChain &Chain = *BlockToChain[MBB];
639 // Ensure that this block is at the end of a chain; otherwise it could be
640 // mid-way through an inner loop or a successor of an analyzable branch.
641 if (MBB != *std::prev(Chain.end()))
644 // Now walk the successors. We need to establish whether this has a viable
645 // exiting successor and whether it has a viable non-exiting successor.
646 // We store the old exiting state and restore it if a viable looping
647 // successor isn't found.
648 MachineBasicBlock *OldExitingBB = ExitingBB;
649 BlockFrequency OldBestExitEdgeFreq = BestExitEdgeFreq;
650 bool HasLoopingSucc = false;
651 // FIXME: Due to the performance of the probability and weight routines in
652 // the MBPI analysis, we use the internal weights and manually compute the
653 // probabilities to avoid quadratic behavior.
654 uint32_t WeightScale = 0;
655 uint32_t SumWeight = MBPI->getSumForBlock(MBB, WeightScale);
656 for (MachineBasicBlock *Succ : MBB->successors()) {
657 if (Succ->isLandingPad())
661 BlockChain &SuccChain = *BlockToChain[Succ];
662 // Don't split chains, either this chain or the successor's chain.
663 if (&Chain == &SuccChain) {
664 DEBUG(dbgs() << " exiting: " << getBlockName(MBB) << " -> "
665 << getBlockName(Succ) << " (chain conflict)\n");
669 uint32_t SuccWeight = MBPI->getEdgeWeight(MBB, Succ);
670 if (LoopBlockSet.count(Succ)) {
671 DEBUG(dbgs() << " looping: " << getBlockName(MBB) << " -> "
672 << getBlockName(Succ) << " (" << SuccWeight << ")\n");
673 HasLoopingSucc = true;
677 unsigned SuccLoopDepth = 0;
678 if (MachineLoop *ExitLoop = MLI->getLoopFor(Succ)) {
679 SuccLoopDepth = ExitLoop->getLoopDepth();
680 if (ExitLoop->contains(&L))
681 BlocksExitingToOuterLoop.insert(MBB);
684 BranchProbability SuccProb(SuccWeight / WeightScale, SumWeight);
685 BlockFrequency ExitEdgeFreq = MBFI->getBlockFreq(MBB) * SuccProb;
686 DEBUG(dbgs() << " exiting: " << getBlockName(MBB) << " -> "
687 << getBlockName(Succ) << " [L:" << SuccLoopDepth << "] (";
688 MBFI->printBlockFreq(dbgs(), ExitEdgeFreq) << ")\n");
689 // Note that we bias this toward an existing layout successor to retain
690 // incoming order in the absence of better information. The exit must have
691 // a frequency higher than the current exit before we consider breaking
693 BranchProbability Bias(100 - ExitBlockBias, 100);
694 if (!ExitingBB || BestExitLoopDepth < SuccLoopDepth ||
695 ExitEdgeFreq > BestExitEdgeFreq ||
696 (MBB->isLayoutSuccessor(Succ) &&
697 !(ExitEdgeFreq < BestExitEdgeFreq * Bias))) {
698 BestExitEdgeFreq = ExitEdgeFreq;
703 // Restore the old exiting state, no viable looping successor was found.
704 if (!HasLoopingSucc) {
705 ExitingBB = OldExitingBB;
706 BestExitEdgeFreq = OldBestExitEdgeFreq;
710 // Without a candidate exiting block or with only a single block in the
711 // loop, just use the loop header to layout the loop.
712 if (!ExitingBB || L.getNumBlocks() == 1)
715 // Also, if we have exit blocks which lead to outer loops but didn't select
716 // one of them as the exiting block we are rotating toward, disable loop
717 // rotation altogether.
718 if (!BlocksExitingToOuterLoop.empty() &&
719 !BlocksExitingToOuterLoop.count(ExitingBB))
722 DEBUG(dbgs() << " Best exiting block: " << getBlockName(ExitingBB) << "\n");
726 /// \brief Attempt to rotate an exiting block to the bottom of the loop.
728 /// Once we have built a chain, try to rotate it to line up the hot exit block
729 /// with fallthrough out of the loop if doing so doesn't introduce unnecessary
730 /// branches. For example, if the loop has fallthrough into its header and out
731 /// of its bottom already, don't rotate it.
732 void MachineBlockPlacement::rotateLoop(BlockChain &LoopChain,
733 MachineBasicBlock *ExitingBB,
734 const BlockFilterSet &LoopBlockSet) {
738 MachineBasicBlock *Top = *LoopChain.begin();
739 bool ViableTopFallthrough = false;
740 for (MachineBasicBlock *Pred : Top->predecessors()) {
741 BlockChain *PredChain = BlockToChain[Pred];
742 if (!LoopBlockSet.count(Pred) &&
743 (!PredChain || Pred == *std::prev(PredChain->end()))) {
744 ViableTopFallthrough = true;
749 // If the header has viable fallthrough, check whether the current loop
750 // bottom is a viable exiting block. If so, bail out as rotating will
751 // introduce an unnecessary branch.
752 if (ViableTopFallthrough) {
753 MachineBasicBlock *Bottom = *std::prev(LoopChain.end());
754 for (MachineBasicBlock *Succ : Bottom->successors()) {
755 BlockChain *SuccChain = BlockToChain[Succ];
756 if (!LoopBlockSet.count(Succ) &&
757 (!SuccChain || Succ == *SuccChain->begin()))
762 BlockChain::iterator ExitIt =
763 std::find(LoopChain.begin(), LoopChain.end(), ExitingBB);
764 if (ExitIt == LoopChain.end())
767 std::rotate(LoopChain.begin(), std::next(ExitIt), LoopChain.end());
770 /// \brief Forms basic block chains from the natural loop structures.
772 /// These chains are designed to preserve the existing *structure* of the code
773 /// as much as possible. We can then stitch the chains together in a way which
774 /// both preserves the topological structure and minimizes taken conditional
776 void MachineBlockPlacement::buildLoopChains(MachineFunction &F,
778 // First recurse through any nested loops, building chains for those inner
780 for (MachineLoop *InnerLoop : L)
781 buildLoopChains(F, *InnerLoop);
783 SmallVector<MachineBasicBlock *, 16> BlockWorkList;
784 BlockFilterSet LoopBlockSet(L.block_begin(), L.block_end());
786 // First check to see if there is an obviously preferable top block for the
787 // loop. This will default to the header, but may end up as one of the
788 // predecessors to the header if there is one which will result in strictly
789 // fewer branches in the loop body.
790 MachineBasicBlock *LoopTop = findBestLoopTop(L, LoopBlockSet);
792 // If we selected just the header for the loop top, look for a potentially
793 // profitable exit block in the event that rotating the loop can eliminate
794 // branches by placing an exit edge at the bottom.
795 MachineBasicBlock *ExitingBB = nullptr;
796 if (LoopTop == L.getHeader())
797 ExitingBB = findBestLoopExit(F, L, LoopBlockSet);
799 BlockChain &LoopChain = *BlockToChain[LoopTop];
801 // FIXME: This is a really lame way of walking the chains in the loop: we
802 // walk the blocks, and use a set to prevent visiting a particular chain
804 SmallPtrSet<BlockChain *, 4> UpdatedPreds;
805 assert(LoopChain.LoopPredecessors == 0);
806 UpdatedPreds.insert(&LoopChain);
807 for (MachineBasicBlock *LoopBB : L.getBlocks()) {
808 BlockChain &Chain = *BlockToChain[LoopBB];
809 if (!UpdatedPreds.insert(&Chain).second)
812 assert(Chain.LoopPredecessors == 0);
813 for (MachineBasicBlock *ChainBB : Chain) {
814 assert(BlockToChain[ChainBB] == &Chain);
815 for (MachineBasicBlock *Pred : ChainBB->predecessors()) {
816 if (BlockToChain[Pred] == &Chain || !LoopBlockSet.count(Pred))
818 ++Chain.LoopPredecessors;
822 if (Chain.LoopPredecessors == 0)
823 BlockWorkList.push_back(*Chain.begin());
826 buildChain(LoopTop, LoopChain, BlockWorkList, &LoopBlockSet);
827 rotateLoop(LoopChain, ExitingBB, LoopBlockSet);
830 // Crash at the end so we get all of the debugging output first.
831 bool BadLoop = false;
832 if (LoopChain.LoopPredecessors) {
834 dbgs() << "Loop chain contains a block without its preds placed!\n"
835 << " Loop header: " << getBlockName(*L.block_begin()) << "\n"
836 << " Chain header: " << getBlockName(*LoopChain.begin()) << "\n";
838 for (MachineBasicBlock *ChainBB : LoopChain) {
839 dbgs() << " ... " << getBlockName(ChainBB) << "\n";
840 if (!LoopBlockSet.erase(ChainBB)) {
841 // We don't mark the loop as bad here because there are real situations
842 // where this can occur. For example, with an unanalyzable fallthrough
843 // from a loop block to a non-loop block or vice versa.
844 dbgs() << "Loop chain contains a block not contained by the loop!\n"
845 << " Loop header: " << getBlockName(*L.block_begin()) << "\n"
846 << " Chain header: " << getBlockName(*LoopChain.begin()) << "\n"
847 << " Bad block: " << getBlockName(ChainBB) << "\n";
851 if (!LoopBlockSet.empty()) {
853 for (MachineBasicBlock *LoopBB : LoopBlockSet)
854 dbgs() << "Loop contains blocks never placed into a chain!\n"
855 << " Loop header: " << getBlockName(*L.block_begin()) << "\n"
856 << " Chain header: " << getBlockName(*LoopChain.begin()) << "\n"
857 << " Bad block: " << getBlockName(LoopBB) << "\n";
859 assert(!BadLoop && "Detected problems with the placement of this loop.");
863 void MachineBlockPlacement::buildCFGChains(MachineFunction &F) {
864 // Ensure that every BB in the function has an associated chain to simplify
865 // the assumptions of the remaining algorithm.
866 SmallVector<MachineOperand, 4> Cond; // For AnalyzeBranch.
867 for (MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
868 MachineBasicBlock *BB = FI;
870 new (ChainAllocator.Allocate()) BlockChain(BlockToChain, BB);
871 // Also, merge any blocks which we cannot reason about and must preserve
872 // the exact fallthrough behavior for.
875 MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch.
876 if (!TII->AnalyzeBranch(*BB, TBB, FBB, Cond) || !FI->canFallThrough())
879 MachineFunction::iterator NextFI(std::next(FI));
880 MachineBasicBlock *NextBB = NextFI;
881 // Ensure that the layout successor is a viable block, as we know that
882 // fallthrough is a possibility.
883 assert(NextFI != FE && "Can't fallthrough past the last block.");
884 DEBUG(dbgs() << "Pre-merging due to unanalyzable fallthrough: "
885 << getBlockName(BB) << " -> " << getBlockName(NextBB)
887 Chain->merge(NextBB, nullptr);
893 if (OutlineOptionalBranches) {
894 // Find the nearest common dominator of all of F's terminators.
895 MachineBasicBlock *Terminator = nullptr;
896 for (MachineBasicBlock &MBB : F) {
897 if (MBB.succ_size() == 0) {
898 if (Terminator == nullptr)
901 Terminator = MDT->findNearestCommonDominator(Terminator, &MBB);
905 // MBBs dominating this common dominator are unavoidable.
906 UnavoidableBlocks.clear();
907 for (MachineBasicBlock &MBB : F) {
908 if (MDT->dominates(&MBB, Terminator)) {
909 UnavoidableBlocks.insert(&MBB);
914 // Build any loop-based chains.
915 for (MachineLoop *L : *MLI)
916 buildLoopChains(F, *L);
918 SmallVector<MachineBasicBlock *, 16> BlockWorkList;
920 SmallPtrSet<BlockChain *, 4> UpdatedPreds;
921 for (MachineBasicBlock &MBB : F) {
922 BlockChain &Chain = *BlockToChain[&MBB];
923 if (!UpdatedPreds.insert(&Chain).second)
926 assert(Chain.LoopPredecessors == 0);
927 for (MachineBasicBlock *ChainBB : Chain) {
928 assert(BlockToChain[ChainBB] == &Chain);
929 for (MachineBasicBlock *Pred : ChainBB->predecessors()) {
930 if (BlockToChain[Pred] == &Chain)
932 ++Chain.LoopPredecessors;
936 if (Chain.LoopPredecessors == 0)
937 BlockWorkList.push_back(*Chain.begin());
940 BlockChain &FunctionChain = *BlockToChain[&F.front()];
941 buildChain(&F.front(), FunctionChain, BlockWorkList);
944 typedef SmallPtrSet<MachineBasicBlock *, 16> FunctionBlockSetType;
947 // Crash at the end so we get all of the debugging output first.
948 bool BadFunc = false;
949 FunctionBlockSetType FunctionBlockSet;
950 for (MachineBasicBlock &MBB : F)
951 FunctionBlockSet.insert(&MBB);
953 for (MachineBasicBlock *ChainBB : FunctionChain)
954 if (!FunctionBlockSet.erase(ChainBB)) {
956 dbgs() << "Function chain contains a block not in the function!\n"
957 << " Bad block: " << getBlockName(ChainBB) << "\n";
960 if (!FunctionBlockSet.empty()) {
962 for (MachineBasicBlock *RemainingBB : FunctionBlockSet)
963 dbgs() << "Function contains blocks never placed into a chain!\n"
964 << " Bad block: " << getBlockName(RemainingBB) << "\n";
966 assert(!BadFunc && "Detected problems with the block placement.");
969 // Splice the blocks into place.
970 MachineFunction::iterator InsertPos = F.begin();
971 for (MachineBasicBlock *ChainBB : FunctionChain) {
972 DEBUG(dbgs() << (ChainBB == *FunctionChain.begin() ? "Placing chain "
974 << getBlockName(ChainBB) << "\n");
975 if (InsertPos != MachineFunction::iterator(ChainBB))
976 F.splice(InsertPos, ChainBB);
980 // Update the terminator of the previous block.
981 if (ChainBB == *FunctionChain.begin())
983 MachineBasicBlock *PrevBB = std::prev(MachineFunction::iterator(ChainBB));
985 // FIXME: It would be awesome of updateTerminator would just return rather
986 // than assert when the branch cannot be analyzed in order to remove this
989 MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch.
990 if (!TII->AnalyzeBranch(*PrevBB, TBB, FBB, Cond)) {
991 // The "PrevBB" is not yet updated to reflect current code layout, so,
992 // o. it may fall-through to a block without explict "goto" instruction
993 // before layout, and no longer fall-through it after layout; or
996 // AnalyzeBranch() may return erroneous value for FBB when these two
997 // situations take place. For the first scenario FBB is mistakenly set
998 // NULL; for the 2nd scenario, the FBB, which is expected to be NULL,
999 // is mistakenly pointing to "*BI".
1001 bool needUpdateBr = true;
1002 if (!Cond.empty() && (!FBB || FBB == ChainBB)) {
1003 PrevBB->updateTerminator();
1004 needUpdateBr = false;
1006 TBB = FBB = nullptr;
1007 if (TII->AnalyzeBranch(*PrevBB, TBB, FBB, Cond)) {
1008 // FIXME: This should never take place.
1009 TBB = FBB = nullptr;
1013 // If PrevBB has a two-way branch, try to re-order the branches
1014 // such that we branch to the successor with higher weight first.
1015 if (TBB && !Cond.empty() && FBB &&
1016 MBPI->getEdgeWeight(PrevBB, FBB) > MBPI->getEdgeWeight(PrevBB, TBB) &&
1017 !TII->ReverseBranchCondition(Cond)) {
1018 DEBUG(dbgs() << "Reverse order of the two branches: "
1019 << getBlockName(PrevBB) << "\n");
1020 DEBUG(dbgs() << " Edge weight: " << MBPI->getEdgeWeight(PrevBB, FBB)
1021 << " vs " << MBPI->getEdgeWeight(PrevBB, TBB) << "\n");
1022 DebugLoc dl; // FIXME: this is nowhere
1023 TII->RemoveBranch(*PrevBB);
1024 TII->InsertBranch(*PrevBB, FBB, TBB, Cond, dl);
1025 needUpdateBr = true;
1028 PrevBB->updateTerminator();
1032 // Fixup the last block.
1034 MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch.
1035 if (!TII->AnalyzeBranch(F.back(), TBB, FBB, Cond))
1036 F.back().updateTerminator();
1038 // Walk through the backedges of the function now that we have fully laid out
1039 // the basic blocks and align the destination of each backedge. We don't rely
1040 // exclusively on the loop info here so that we can align backedges in
1041 // unnatural CFGs and backedges that were introduced purely because of the
1042 // loop rotations done during this layout pass.
1043 if (F.getFunction()->hasFnAttribute(Attribute::OptimizeForSize))
1045 if (FunctionChain.begin() == FunctionChain.end())
1046 return; // Empty chain.
1048 const BranchProbability ColdProb(1, 5); // 20%
1049 BlockFrequency EntryFreq = MBFI->getBlockFreq(F.begin());
1050 BlockFrequency WeightedEntryFreq = EntryFreq * ColdProb;
1051 for (MachineBasicBlock *ChainBB : FunctionChain) {
1052 if (ChainBB == *FunctionChain.begin())
1055 // Don't align non-looping basic blocks. These are unlikely to execute
1056 // enough times to matter in practice. Note that we'll still handle
1057 // unnatural CFGs inside of a natural outer loop (the common case) and
1059 MachineLoop *L = MLI->getLoopFor(ChainBB);
1063 unsigned Align = TLI->getPrefLoopAlignment(L);
1065 continue; // Don't care about loop alignment.
1067 // If the block is cold relative to the function entry don't waste space
1069 BlockFrequency Freq = MBFI->getBlockFreq(ChainBB);
1070 if (Freq < WeightedEntryFreq)
1073 // If the block is cold relative to its loop header, don't align it
1074 // regardless of what edges into the block exist.
1075 MachineBasicBlock *LoopHeader = L->getHeader();
1076 BlockFrequency LoopHeaderFreq = MBFI->getBlockFreq(LoopHeader);
1077 if (Freq < (LoopHeaderFreq * ColdProb))
1080 // Check for the existence of a non-layout predecessor which would benefit
1081 // from aligning this block.
1082 MachineBasicBlock *LayoutPred =
1083 &*std::prev(MachineFunction::iterator(ChainBB));
1085 // Force alignment if all the predecessors are jumps. We already checked
1086 // that the block isn't cold above.
1087 if (!LayoutPred->isSuccessor(ChainBB)) {
1088 ChainBB->setAlignment(Align);
1092 // Align this block if the layout predecessor's edge into this block is
1093 // cold relative to the block. When this is true, other predecessors make up
1094 // all of the hot entries into the block and thus alignment is likely to be
1096 BranchProbability LayoutProb =
1097 MBPI->getEdgeProbability(LayoutPred, ChainBB);
1098 BlockFrequency LayoutEdgeFreq = MBFI->getBlockFreq(LayoutPred) * LayoutProb;
1099 if (LayoutEdgeFreq <= (Freq * ColdProb))
1100 ChainBB->setAlignment(Align);
1104 bool MachineBlockPlacement::runOnMachineFunction(MachineFunction &F) {
1105 // Check for single-block functions and skip them.
1106 if (std::next(F.begin()) == F.end())
1109 if (skipOptnoneFunction(*F.getFunction()))
1112 MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
1113 MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
1114 MLI = &getAnalysis<MachineLoopInfo>();
1115 TII = F.getSubtarget().getInstrInfo();
1116 TLI = F.getSubtarget().getTargetLowering();
1117 MDT = &getAnalysis<MachineDominatorTree>();
1118 assert(BlockToChain.empty());
1122 BlockToChain.clear();
1123 ChainAllocator.DestroyAll();
1126 // Align all of the blocks in the function to a specific alignment.
1127 for (MachineBasicBlock &MBB : F)
1128 MBB.setAlignment(AlignAllBlock);
1130 // We always return true as we have no way to track whether the final order
1131 // differs from the original order.
1136 /// \brief A pass to compute block placement statistics.
1138 /// A separate pass to compute interesting statistics for evaluating block
1139 /// placement. This is separate from the actual placement pass so that they can
1140 /// be computed in the absence of any placement transformations or when using
1141 /// alternative placement strategies.
1142 class MachineBlockPlacementStats : public MachineFunctionPass {
1143 /// \brief A handle to the branch probability pass.
1144 const MachineBranchProbabilityInfo *MBPI;
1146 /// \brief A handle to the function-wide block frequency pass.
1147 const MachineBlockFrequencyInfo *MBFI;
1150 static char ID; // Pass identification, replacement for typeid
1151 MachineBlockPlacementStats() : MachineFunctionPass(ID) {
1152 initializeMachineBlockPlacementStatsPass(*PassRegistry::getPassRegistry());
1155 bool runOnMachineFunction(MachineFunction &F) override;
1157 void getAnalysisUsage(AnalysisUsage &AU) const override {
1158 AU.addRequired<MachineBranchProbabilityInfo>();
1159 AU.addRequired<MachineBlockFrequencyInfo>();
1160 AU.setPreservesAll();
1161 MachineFunctionPass::getAnalysisUsage(AU);
1166 char MachineBlockPlacementStats::ID = 0;
1167 char &llvm::MachineBlockPlacementStatsID = MachineBlockPlacementStats::ID;
1168 INITIALIZE_PASS_BEGIN(MachineBlockPlacementStats, "block-placement-stats",
1169 "Basic Block Placement Stats", false, false)
1170 INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
1171 INITIALIZE_PASS_DEPENDENCY(MachineBlockFrequencyInfo)
1172 INITIALIZE_PASS_END(MachineBlockPlacementStats, "block-placement-stats",
1173 "Basic Block Placement Stats", false, false)
1175 bool MachineBlockPlacementStats::runOnMachineFunction(MachineFunction &F) {
1176 // Check for single-block functions and skip them.
1177 if (std::next(F.begin()) == F.end())
1180 MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
1181 MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
1183 for (MachineBasicBlock &MBB : F) {
1184 BlockFrequency BlockFreq = MBFI->getBlockFreq(&MBB);
1185 Statistic &NumBranches =
1186 (MBB.succ_size() > 1) ? NumCondBranches : NumUncondBranches;
1187 Statistic &BranchTakenFreq =
1188 (MBB.succ_size() > 1) ? CondBranchTakenFreq : UncondBranchTakenFreq;
1189 for (MachineBasicBlock *Succ : MBB.successors()) {
1190 // Skip if this successor is a fallthrough.
1191 if (MBB.isLayoutSuccessor(Succ))
1194 BlockFrequency EdgeFreq =
1195 BlockFreq * MBPI->getEdgeProbability(&MBB, Succ);
1197 BranchTakenFreq += EdgeFreq.getFrequency();