// structure and branch probability estimates.
//
// The pass strives to preserve the structure of the CFG (that is, retain
-// a topological ordering of basic blocks) in the absense of a *strong* signal
+// a topological ordering of basic blocks) in the absence of a *strong* signal
// to the contrary from probabilities. However, within the CFG structure, it
// attempts to choose an ordering which favors placing more likely sequences of
// blocks adjacent to each other.
//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "block-placement2"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
+#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
-#include "llvm/CodeGen/Passes.h"
#include "llvm/Support/Allocator.h"
+#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
-#include "llvm/Support/ErrorHandling.h"
-#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/PostOrderIterator.h"
-#include "llvm/ADT/SCCIterator.h"
-#include "llvm/ADT/SmallPtrSet.h"
-#include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
#include <algorithm>
using namespace llvm;
+#define DEBUG_TYPE "block-placement"
+
STATISTIC(NumCondBranches, "Number of conditional branches");
-STATISTIC(NumUncondBranches, "Number of uncondittional branches");
+STATISTIC(NumUncondBranches, "Number of unconditional branches");
STATISTIC(CondBranchTakenFreq,
"Potential frequency of taking conditional branches");
STATISTIC(UncondBranchTakenFreq,
"Potential frequency of taking unconditional branches");
-namespace {
-/// \brief A structure for storing a weighted edge.
-///
-/// This stores an edge and its weight, computed as the product of the
-/// frequency that the starting block is entered with the probability of
-/// a particular exit block.
-struct WeightedEdge {
- BlockFrequency EdgeFrequency;
- MachineBasicBlock *From, *To;
-
- bool operator<(const WeightedEdge &RHS) const {
- return EdgeFrequency < RHS.EdgeFrequency;
- }
-};
-}
+static cl::opt<unsigned> AlignAllBlock("align-all-blocks",
+ cl::desc("Force the alignment of all "
+ "blocks in the function."),
+ cl::init(0), cl::Hidden);
+
+static cl::opt<unsigned>
+ AlignAllLoops("align-all-loops",
+ cl::desc("Force the alignment of all loops in the function."),
+ cl::init(0), cl::Hidden);
+
+// FIXME: Find a good default for this flag and remove the flag.
+static cl::opt<unsigned> ExitBlockBias(
+ "block-placement-exit-block-bias",
+ cl::desc("Block frequency percentage a loop exit block needs "
+ "over the original exit to be considered the new exit."),
+ cl::init(0), cl::Hidden);
+
+static cl::opt<bool> OutlineOptionalBranches(
+ "outline-optional-branches",
+ cl::desc("Put completely optional branches, i.e. branches with a common "
+ "post dominator, out of line."),
+ cl::init(false), cl::Hidden);
+
+static cl::opt<unsigned> OutlineOptionalThreshold(
+ "outline-optional-threshold",
+ cl::desc("Don't outline optional branches that are a single block with an "
+ "instruction count below this threshold"),
+ cl::init(4), cl::Hidden);
+
+static cl::opt<unsigned> LoopToColdBlockRatio(
+ "loop-to-cold-block-ratio",
+ cl::desc("Outline loop blocks from loop chain if (frequency of loop) / "
+ "(frequency of block) is greater than this ratio"),
+ cl::init(5), cl::Hidden);
+
+static cl::opt<bool>
+ PreciseRotationCost("precise-rotation-cost",
+ cl::desc("Model the cost of loop rotation more "
+ "precisely by using profile data."),
+ cl::init(false), cl::Hidden);
+
+static cl::opt<unsigned> MisfetchCost(
+ "misfetch-cost",
+ cl::desc("Cost that models the probablistic risk of an instruction "
+ "misfetch due to a jump comparing to falling through, whose cost "
+ "is zero."),
+ cl::init(1), cl::Hidden);
+
+static cl::opt<unsigned> JumpInstCost("jump-inst-cost",
+ cl::desc("Cost of jump instructions."),
+ cl::init(1), cl::Hidden);
namespace {
class BlockChain;
///
/// This is the datastructure representing a chain of consecutive blocks that
/// are profitable to layout together in order to maximize fallthrough
-/// probabilities. We also can use a block chain to represent a sequence of
-/// basic blocks which have some external (correctness) requirement for
-/// sequential layout.
+/// probabilities and code locality. We also can use a block chain to represent
+/// a sequence of basic blocks which have some external (correctness)
+/// requirement for sequential layout.
///
-/// Eventually, the block chains will form a directed graph over the function.
-/// We provide an SCC-supporting-iterator in order to quicky build and walk the
-/// SCCs of block chains within a function.
-///
-/// The block chains also have support for calculating and caching probability
-/// information related to the chain itself versus other chains. This is used
-/// for ranking during the final layout of block chains.
+/// Chains can be built around a single basic block and can be merged to grow
+/// them. They participate in a block-to-chain mapping, which is updated
+/// automatically as chains are merged together.
class BlockChain {
/// \brief The sequence of blocks belonging to this chain.
///
/// function. It also registers itself as the chain that block participates
/// in with the BlockToChain mapping.
BlockChain(BlockToChainMapType &BlockToChain, MachineBasicBlock *BB)
- : Blocks(1, BB), BlockToChain(BlockToChain), LoopPredecessors(0) {
+ : Blocks(1, BB), BlockToChain(BlockToChain), LoopPredecessors(0) {
assert(BB && "Cannot create a chain with a null basic block");
BlockToChain[BB] = this;
}
/// \brief Iterator over blocks within the chain.
typedef SmallVectorImpl<MachineBasicBlock *>::iterator iterator;
- typedef SmallVectorImpl<MachineBasicBlock *>::reverse_iterator
- reverse_iterator;
/// \brief Beginning of blocks within the chain.
iterator begin() { return Blocks.begin(); }
- reverse_iterator rbegin() { return Blocks.rbegin(); }
/// \brief End of blocks within the chain.
iterator end() { return Blocks.end(); }
- reverse_iterator rend() { return Blocks.rend(); }
/// \brief Merge a block chain into this one.
///
// Update the incoming blocks to point to this chain, and add them to the
// chain structure.
- for (BlockChain::iterator BI = Chain->begin(), BE = Chain->end();
- BI != BE; ++BI) {
- Blocks.push_back(*BI);
- assert(BlockToChain[*BI] == Chain && "Incoming blocks not in chain");
- BlockToChain[*BI] = this;
+ for (MachineBasicBlock *ChainBB : *Chain) {
+ Blocks.push_back(ChainBB);
+ assert(BlockToChain[ChainBB] == Chain && "Incoming blocks not in chain");
+ BlockToChain[ChainBB] = this;
}
}
+#ifndef NDEBUG
+ /// \brief Dump the blocks in this chain.
+ LLVM_DUMP_METHOD void dump() {
+ for (MachineBasicBlock *MBB : *this)
+ MBB->dump();
+ }
+#endif // NDEBUG
+
/// \brief Count of predecessors within the loop currently being processed.
///
/// This count is updated at each loop we process to represent the number of
const TargetInstrInfo *TII;
/// \brief A handle to the target's lowering info.
- const TargetLowering *TLI;
+ const TargetLoweringBase *TLI;
+
+ /// \brief A handle to the post dominator tree.
+ MachineDominatorTree *MDT;
+
+ /// \brief A set of blocks that are unavoidably execute, i.e. they dominate
+ /// all terminators of the MachineFunction.
+ SmallPtrSet<MachineBasicBlock *, 4> UnavoidableBlocks;
/// \brief Allocator and owner of BlockChain structures.
///
- /// We build BlockChains lazily by merging together high probability BB
- /// sequences acording to the "Algo2" in the paper mentioned at the top of
- /// the file. To reduce malloc traffic, we allocate them using this slab-like
- /// allocator, and destroy them after the pass completes.
+ /// We build BlockChains lazily while processing the loop structure of
+ /// a function. To reduce malloc traffic, we allocate them using this
+ /// slab-like allocator, and destroy them after the pass completes. An
+ /// important guarantee is that this allocator produces stable pointers to
+ /// the chains.
SpecificBumpPtrAllocator<BlockChain> ChainAllocator;
/// \brief Function wide BasicBlock to BlockChain mapping.
/// between basic blocks.
DenseMap<MachineBasicBlock *, BlockChain *> BlockToChain;
- void markChainSuccessors(BlockChain &Chain,
- MachineBasicBlock *LoopHeaderBB,
+ void markChainSuccessors(BlockChain &Chain, MachineBasicBlock *LoopHeaderBB,
SmallVectorImpl<MachineBasicBlock *> &BlockWorkList,
- const BlockFilterSet *BlockFilter = 0);
+ const BlockFilterSet *BlockFilter = nullptr);
MachineBasicBlock *selectBestSuccessor(MachineBasicBlock *BB,
BlockChain &Chain,
const BlockFilterSet *BlockFilter);
- MachineBasicBlock *selectBestCandidateBlock(
- BlockChain &Chain, SmallVectorImpl<MachineBasicBlock *> &WorkList,
- const BlockFilterSet *BlockFilter);
- MachineBasicBlock *getFirstUnplacedBlock(
- MachineFunction &F,
- const BlockChain &PlacedChain,
- MachineFunction::iterator &PrevUnplacedBlockIt,
- const BlockFilterSet *BlockFilter);
+ MachineBasicBlock *
+ selectBestCandidateBlock(BlockChain &Chain,
+ SmallVectorImpl<MachineBasicBlock *> &WorkList,
+ const BlockFilterSet *BlockFilter);
+ MachineBasicBlock *
+ getFirstUnplacedBlock(MachineFunction &F, const BlockChain &PlacedChain,
+ MachineFunction::iterator &PrevUnplacedBlockIt,
+ const BlockFilterSet *BlockFilter);
void buildChain(MachineBasicBlock *BB, BlockChain &Chain,
SmallVectorImpl<MachineBasicBlock *> &BlockWorkList,
- const BlockFilterSet *BlockFilter = 0);
- void rotateLoop(MachineLoop &L, BlockChain &LoopChain,
- const BlockFilterSet &LoopBlockSet);
+ const BlockFilterSet *BlockFilter = nullptr);
+ MachineBasicBlock *findBestLoopTop(MachineLoop &L,
+ const BlockFilterSet &LoopBlockSet);
+ MachineBasicBlock *findBestLoopExit(MachineFunction &F, MachineLoop &L,
+ const BlockFilterSet &LoopBlockSet);
+ BlockFilterSet collectLoopBlockSet(MachineFunction &F, MachineLoop &L);
void buildLoopChains(MachineFunction &F, MachineLoop &L);
+ void rotateLoop(BlockChain &LoopChain, MachineBasicBlock *ExitingBB,
+ const BlockFilterSet &LoopBlockSet);
+ void rotateLoopWithProfile(BlockChain &LoopChain, MachineLoop &L,
+ const BlockFilterSet &LoopBlockSet);
void buildCFGChains(MachineFunction &F);
- void AlignLoops(MachineFunction &F);
public:
static char ID; // Pass identification, replacement for typeid
initializeMachineBlockPlacementPass(*PassRegistry::getPassRegistry());
}
- bool runOnMachineFunction(MachineFunction &F);
+ bool runOnMachineFunction(MachineFunction &F) override;
- void getAnalysisUsage(AnalysisUsage &AU) const {
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<MachineBranchProbabilityInfo>();
AU.addRequired<MachineBlockFrequencyInfo>();
+ AU.addRequired<MachineDominatorTree>();
AU.addRequired<MachineLoopInfo>();
MachineFunctionPass::getAnalysisUsage(AU);
}
-
- const char *getPassName() const { return "Block Placement"; }
};
}
char MachineBlockPlacement::ID = 0;
-INITIALIZE_PASS_BEGIN(MachineBlockPlacement, "block-placement2",
+char &llvm::MachineBlockPlacementID = MachineBlockPlacement::ID;
+INITIALIZE_PASS_BEGIN(MachineBlockPlacement, "block-placement",
"Branch Probability Basic Block Placement", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
INITIALIZE_PASS_DEPENDENCY(MachineBlockFrequencyInfo)
+INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
-INITIALIZE_PASS_END(MachineBlockPlacement, "block-placement2",
+INITIALIZE_PASS_END(MachineBlockPlacement, "block-placement",
"Branch Probability Basic Block Placement", false, false)
-FunctionPass *llvm::createMachineBlockPlacementPass() {
- return new MachineBlockPlacement();
-}
-
#ifndef NDEBUG
/// \brief Helper to print the name of a MBB.
///
static std::string getBlockName(MachineBasicBlock *BB) {
std::string Result;
raw_string_ostream OS(Result);
- OS << "BB#" << BB->getNumber()
- << " (derived from LLVM BB '" << BB->getName() << "')";
+ OS << "BB#" << BB->getNumber();
+ OS << " (derived from LLVM BB '" << BB->getName() << "')";
OS.flush();
return Result;
}
/// having one fewer active predecessor. It also adds any successors of this
/// chain which reach the zero-predecessor state to the worklist passed in.
void MachineBlockPlacement::markChainSuccessors(
- BlockChain &Chain,
- MachineBasicBlock *LoopHeaderBB,
+ BlockChain &Chain, MachineBasicBlock *LoopHeaderBB,
SmallVectorImpl<MachineBasicBlock *> &BlockWorkList,
const BlockFilterSet *BlockFilter) {
// Walk all the blocks in this chain, marking their successors as having
// a predecessor placed.
- for (BlockChain::iterator CBI = Chain.begin(), CBE = Chain.end();
- CBI != CBE; ++CBI) {
+ for (MachineBasicBlock *MBB : Chain) {
// Add any successors for which this is the only un-placed in-loop
// predecessor to the worklist as a viable candidate for CFG-neutral
// placement. No subsequent placement of this block will violate the CFG
// shape, so we get to use heuristics to choose a favorable placement.
- for (MachineBasicBlock::succ_iterator SI = (*CBI)->succ_begin(),
- SE = (*CBI)->succ_end();
- SI != SE; ++SI) {
- if (BlockFilter && !BlockFilter->count(*SI))
+ for (MachineBasicBlock *Succ : MBB->successors()) {
+ if (BlockFilter && !BlockFilter->count(Succ))
continue;
- BlockChain &SuccChain = *BlockToChain[*SI];
+ BlockChain &SuccChain = *BlockToChain[Succ];
// Disregard edges within a fixed chain, or edges to the loop header.
- if (&Chain == &SuccChain || *SI == LoopHeaderBB)
+ if (&Chain == &SuccChain || Succ == LoopHeaderBB)
continue;
// This is a cross-chain edge that is within the loop, so decrement the
/// very hot successor edges.
///
/// \returns The best successor block found, or null if none are viable.
-MachineBasicBlock *MachineBlockPlacement::selectBestSuccessor(
- MachineBasicBlock *BB, BlockChain &Chain,
- const BlockFilterSet *BlockFilter) {
+MachineBasicBlock *
+MachineBlockPlacement::selectBestSuccessor(MachineBasicBlock *BB,
+ BlockChain &Chain,
+ const BlockFilterSet *BlockFilter) {
const BranchProbability HotProb(4, 5); // 80%
- MachineBasicBlock *BestSucc = 0;
- // FIXME: Due to the performance of the probability and weight routines in
- // the MBPI analysis, we manually compute probabilities using the edge
- // weights. This is suboptimal as it means that the somewhat subtle
- // definition of edge weight semantics is encoded here as well. We should
- // improve the MBPI interface to effeciently support query patterns such as
- // this.
- uint32_t BestWeight = 0;
- uint32_t WeightScale = 0;
- uint32_t SumWeight = MBPI->getSumForBlock(BB, WeightScale);
- DEBUG(dbgs() << "Attempting merge from: " << getBlockName(BB) << "\n");
- for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
- SE = BB->succ_end();
- SI != SE; ++SI) {
- if (BlockFilter && !BlockFilter->count(*SI))
- continue;
- BlockChain &SuccChain = *BlockToChain[*SI];
- if (&SuccChain == &Chain) {
- DEBUG(dbgs() << " " << getBlockName(*SI) << " -> Already merged!\n");
- continue;
- }
- if (*SI != *SuccChain.begin()) {
- DEBUG(dbgs() << " " << getBlockName(*SI) << " -> Mid chain!\n");
- continue;
+ MachineBasicBlock *BestSucc = nullptr;
+ auto BestProb = BranchProbability::getZero();
+
+ // Adjust edge probabilities by excluding edges pointing to blocks that is
+ // either not in BlockFilter or is already in the current chain. Consider the
+ // following CFG:
+ //
+ // --->A
+ // | / \
+ // | B C
+ // | \ / \
+ // ----D E
+ //
+ // Assume A->C is very hot (>90%), and C->D has a 50% probability, then after
+ // A->C is chosen as a fall-through, D won't be selected as a successor of C
+ // due to CFG constraint (the probability of C->D is not greater than
+ // HotProb). If we exclude E that is not in BlockFilter when calculating the
+ // probability of C->D, D will be selected and we will get A C D B as the
+ // layout of this loop.
+ auto AdjustedSumProb = BranchProbability::getOne();
+ SmallVector<MachineBasicBlock *, 4> Successors;
+ for (MachineBasicBlock *Succ : BB->successors()) {
+ bool SkipSucc = false;
+ if (BlockFilter && !BlockFilter->count(Succ)) {
+ SkipSucc = true;
+ } else {
+ BlockChain *SuccChain = BlockToChain[Succ];
+ if (SuccChain == &Chain) {
+ DEBUG(dbgs() << " " << getBlockName(Succ)
+ << " -> Already merged!\n");
+ SkipSucc = true;
+ } else if (Succ != *SuccChain->begin()) {
+ DEBUG(dbgs() << " " << getBlockName(Succ) << " -> Mid chain!\n");
+ continue;
+ }
}
+ if (SkipSucc)
+ AdjustedSumProb -= MBPI->getEdgeProbability(BB, Succ);
+ else
+ Successors.push_back(Succ);
+ }
- uint32_t SuccWeight = MBPI->getEdgeWeight(BB, *SI);
- BranchProbability SuccProb(SuccWeight / WeightScale, SumWeight);
+ DEBUG(dbgs() << "Attempting merge from: " << getBlockName(BB) << "\n");
+ for (MachineBasicBlock *Succ : Successors) {
+ BranchProbability SuccProb;
+ uint32_t SuccProbN = MBPI->getEdgeProbability(BB, Succ).getNumerator();
+ uint32_t SuccProbD = AdjustedSumProb.getNumerator();
+ if (SuccProbN >= SuccProbD)
+ SuccProb = BranchProbability::getOne();
+ else
+ SuccProb = BranchProbability(SuccProbN, SuccProbD);
+
+ // If we outline optional branches, look whether Succ is unavoidable, i.e.
+ // dominates all terminators of the MachineFunction. If it does, other
+ // successors must be optional. Don't do this for cold branches.
+ if (OutlineOptionalBranches && SuccProb > HotProb.getCompl() &&
+ UnavoidableBlocks.count(Succ) > 0) {
+ auto HasShortOptionalBranch = [&]() {
+ for (MachineBasicBlock *Pred : Succ->predecessors()) {
+ // Check whether there is an unplaced optional branch.
+ if (Pred == Succ || (BlockFilter && !BlockFilter->count(Pred)) ||
+ BlockToChain[Pred] == &Chain)
+ continue;
+ // Check whether the optional branch has exactly one BB.
+ if (Pred->pred_size() > 1 || *Pred->pred_begin() != BB)
+ continue;
+ // Check whether the optional branch is small.
+ if (Pred->size() < OutlineOptionalThreshold)
+ return true;
+ }
+ return false;
+ };
+ if (!HasShortOptionalBranch())
+ return Succ;
+ }
// Only consider successors which are either "hot", or wouldn't violate
// any CFG constraints.
+ BlockChain &SuccChain = *BlockToChain[Succ];
if (SuccChain.LoopPredecessors != 0) {
if (SuccProb < HotProb) {
- DEBUG(dbgs() << " " << getBlockName(*SI) << " -> CFG conflict\n");
+ DEBUG(dbgs() << " " << getBlockName(Succ) << " -> " << SuccProb
+ << " (prob) (CFG conflict)\n");
continue;
}
- // Make sure that a hot successor doesn't have a globally more important
- // predecessor.
- BlockFrequency CandidateEdgeFreq
- = MBFI->getBlockFreq(BB) * SuccProb * HotProb.getCompl();
+ // Make sure that a hot successor doesn't have a globally more
+ // important predecessor.
+ auto RealSuccProb = MBPI->getEdgeProbability(BB, Succ);
+ BlockFrequency CandidateEdgeFreq =
+ MBFI->getBlockFreq(BB) * RealSuccProb * HotProb.getCompl();
bool BadCFGConflict = false;
- for (MachineBasicBlock::pred_iterator PI = (*SI)->pred_begin(),
- PE = (*SI)->pred_end();
- PI != PE; ++PI) {
- if (*PI == *SI || (BlockFilter && !BlockFilter->count(*PI)) ||
- BlockToChain[*PI] == &Chain)
+ for (MachineBasicBlock *Pred : Succ->predecessors()) {
+ if (Pred == Succ || (BlockFilter && !BlockFilter->count(Pred)) ||
+ BlockToChain[Pred] == &Chain)
continue;
- BlockFrequency PredEdgeFreq
- = MBFI->getBlockFreq(*PI) * MBPI->getEdgeProbability(*PI, *SI);
+ BlockFrequency PredEdgeFreq =
+ MBFI->getBlockFreq(Pred) * MBPI->getEdgeProbability(Pred, Succ);
if (PredEdgeFreq >= CandidateEdgeFreq) {
BadCFGConflict = true;
break;
}
}
if (BadCFGConflict) {
- DEBUG(dbgs() << " " << getBlockName(*SI)
- << " -> non-cold CFG conflict\n");
+ DEBUG(dbgs() << " " << getBlockName(Succ) << " -> " << SuccProb
+ << " (prob) (non-cold CFG conflict)\n");
continue;
}
}
- DEBUG(dbgs() << " " << getBlockName(*SI) << " -> " << SuccProb
+ DEBUG(dbgs() << " " << getBlockName(Succ) << " -> " << SuccProb
<< " (prob)"
<< (SuccChain.LoopPredecessors != 0 ? " (CFG break)" : "")
<< "\n");
- if (BestSucc && BestWeight >= SuccWeight)
+ if (BestSucc && BestProb >= SuccProb)
continue;
- BestSucc = *SI;
- BestWeight = SuccWeight;
+ BestSucc = Succ;
+ BestProb = SuccProb;
}
return BestSucc;
}
-namespace {
-/// \brief Predicate struct to detect blocks already placed.
-class IsBlockPlaced {
- const BlockChain &PlacedChain;
- const BlockToChainMapType &BlockToChain;
-
-public:
- IsBlockPlaced(const BlockChain &PlacedChain,
- const BlockToChainMapType &BlockToChain)
- : PlacedChain(PlacedChain), BlockToChain(BlockToChain) {}
-
- bool operator()(MachineBasicBlock *BB) const {
- return BlockToChain.lookup(BB) == &PlacedChain;
- }
-};
-}
-
/// \brief Select the best block from a worklist.
///
/// This looks through the provided worklist as a list of candidate basic
// FIXME: If this shows up on profiles, it could be folded (at the cost of
// some code complexity) into the loop below.
WorkList.erase(std::remove_if(WorkList.begin(), WorkList.end(),
- IsBlockPlaced(Chain, BlockToChain)),
+ [&](MachineBasicBlock *BB) {
+ return BlockToChain.lookup(BB) == &Chain;
+ }),
WorkList.end());
- MachineBasicBlock *BestBlock = 0;
+ MachineBasicBlock *BestBlock = nullptr;
BlockFrequency BestFreq;
- for (SmallVectorImpl<MachineBasicBlock *>::iterator WBI = WorkList.begin(),
- WBE = WorkList.end();
- WBI != WBE; ++WBI) {
- assert(!BlockFilter || BlockFilter->count(*WBI));
- BlockChain &SuccChain = *BlockToChain[*WBI];
+ for (MachineBasicBlock *MBB : WorkList) {
+ BlockChain &SuccChain = *BlockToChain[MBB];
if (&SuccChain == &Chain) {
- DEBUG(dbgs() << " " << getBlockName(*WBI)
- << " -> Already merged!\n");
+ DEBUG(dbgs() << " " << getBlockName(MBB) << " -> Already merged!\n");
continue;
}
assert(SuccChain.LoopPredecessors == 0 && "Found CFG-violating block");
- BlockFrequency CandidateFreq = MBFI->getBlockFreq(*WBI);
- DEBUG(dbgs() << " " << getBlockName(*WBI) << " -> " << CandidateFreq
- << " (freq)\n");
+ BlockFrequency CandidateFreq = MBFI->getBlockFreq(MBB);
+ DEBUG(dbgs() << " " << getBlockName(MBB) << " -> ";
+ MBFI->printBlockFreq(dbgs(), CandidateFreq) << " (freq)\n");
if (BestBlock && BestFreq >= CandidateFreq)
continue;
- BestBlock = *WBI;
+ BestBlock = MBB;
BestFreq = CandidateFreq;
}
return BestBlock;
const BlockFilterSet *BlockFilter) {
for (MachineFunction::iterator I = PrevUnplacedBlockIt, E = F.end(); I != E;
++I) {
- if (BlockFilter && !BlockFilter->count(I))
+ if (BlockFilter && !BlockFilter->count(&*I))
continue;
- if (BlockToChain[I] != &PlacedChain) {
+ if (BlockToChain[&*I] != &PlacedChain) {
PrevUnplacedBlockIt = I;
// Now select the head of the chain to which the unplaced block belongs
// as the block to place. This will force the entire chain to be placed,
// and satisfies the requirements of merging chains.
- return *BlockToChain[I]->begin();
+ return *BlockToChain[&*I]->begin();
}
}
- return 0;
+ return nullptr;
}
void MachineBlockPlacement::buildChain(
- MachineBasicBlock *BB,
- BlockChain &Chain,
+ MachineBasicBlock *BB, BlockChain &Chain,
SmallVectorImpl<MachineBasicBlock *> &BlockWorkList,
const BlockFilterSet *BlockFilter) {
assert(BB);
MachineBasicBlock *LoopHeaderBB = BB;
markChainSuccessors(Chain, LoopHeaderBB, BlockWorkList, BlockFilter);
- BB = *llvm::prior(Chain.end());
+ BB = *std::prev(Chain.end());
for (;;) {
assert(BB);
assert(BlockToChain[BB] == &Chain);
- assert(*llvm::prior(Chain.end()) == BB);
- MachineBasicBlock *BestSucc = 0;
+ assert(*std::prev(Chain.end()) == BB);
// Look for the best viable successor if there is one to place immediately
// after this block.
- BestSucc = selectBestSuccessor(BB, Chain, BlockFilter);
+ MachineBasicBlock *BestSucc = selectBestSuccessor(BB, Chain, BlockFilter);
// If an immediate successor isn't available, look for the best viable
// block among those we've identified as not violating the loop's CFG at
BestSucc = selectBestCandidateBlock(Chain, BlockWorkList, BlockFilter);
if (!BestSucc) {
- BestSucc = getFirstUnplacedBlock(F, Chain, PrevUnplacedBlockIt,
- BlockFilter);
+ BestSucc =
+ getFirstUnplacedBlock(F, Chain, PrevUnplacedBlockIt, BlockFilter);
if (!BestSucc)
break;
// Zero out LoopPredecessors for the successor we're about to merge in case
// we selected a successor that didn't fit naturally into the CFG.
SuccChain.LoopPredecessors = 0;
- DEBUG(dbgs() << "Merging from " << getBlockNum(BB)
- << " to " << getBlockNum(BestSucc) << "\n");
+ DEBUG(dbgs() << "Merging from " << getBlockNum(BB) << " to "
+ << getBlockNum(BestSucc) << "\n");
markChainSuccessors(SuccChain, LoopHeaderBB, BlockWorkList, BlockFilter);
Chain.merge(BestSucc, &SuccChain);
- BB = *llvm::prior(Chain.end());
- };
+ BB = *std::prev(Chain.end());
+ }
DEBUG(dbgs() << "Finished forming chain for header block "
<< getBlockNum(*Chain.begin()) << "\n");
}
-/// \brief Attempt to rotate loop chains ending in an unconditional backedge.
+/// \brief Find the best loop top block for layout.
///
-/// This is a very conservative attempt to rotate unconditional backedge jumps
-/// into fallthrough opportunities. It only attempts to perform the rotation
-/// when it is trivial to find a block within the loop which has a conditional
-/// loop exit. This block is then made the bottom of the chain, and the in-loop
-/// fallthrough block the top. That turns a conditional branch out of the loop
-/// into a conditional branch to the top of the loop while completely
-/// eliminitating an unconditional branch within the loop.
-void MachineBlockPlacement::rotateLoop(MachineLoop &L,
- BlockChain &LoopChain,
+/// Look for a block which is strictly better than the loop header for laying
+/// out at the top of the loop. This looks for one and only one pattern:
+/// a latch block with no conditional exit. This block will cause a conditional
+/// jump around it or will be the bottom of the loop if we lay it out in place,
+/// but if it it doesn't end up at the bottom of the loop for any reason,
+/// rotation alone won't fix it. Because such a block will always result in an
+/// unconditional jump (for the backedge) rotating it in front of the loop
+/// header is always profitable.
+MachineBasicBlock *
+MachineBlockPlacement::findBestLoopTop(MachineLoop &L,
const BlockFilterSet &LoopBlockSet) {
- MachineBasicBlock *Header = *L.block_begin();
- // Ensure that we have a chain of blocks which starts with the loop header.
- // Otherwise, rotating the blocks might break an analyzable branch.
- if (Header != *LoopChain.begin())
- return;
+ // Check that the header hasn't been fused with a preheader block due to
+ // crazy branches. If it has, we need to start with the header at the top to
+ // prevent pulling the preheader into the loop body.
+ BlockChain &HeaderChain = *BlockToChain[L.getHeader()];
+ if (!LoopBlockSet.count(*HeaderChain.begin()))
+ return L.getHeader();
+
+ DEBUG(dbgs() << "Finding best loop top for: " << getBlockName(L.getHeader())
+ << "\n");
+
+ BlockFrequency BestPredFreq;
+ MachineBasicBlock *BestPred = nullptr;
+ for (MachineBasicBlock *Pred : L.getHeader()->predecessors()) {
+ if (!LoopBlockSet.count(Pred))
+ continue;
+ DEBUG(dbgs() << " header pred: " << getBlockName(Pred) << ", "
+ << Pred->succ_size() << " successors, ";
+ MBFI->printBlockFreq(dbgs(), Pred) << " freq\n");
+ if (Pred->succ_size() > 1)
+ continue;
- // We only support rotating the loop chain as a unit, so look directly at the
- // back of the chain and check that it has a backedge.
- MachineBasicBlock *Latch = *llvm::prior(LoopChain.end());
- if (Latch == Header ||
- !Latch->isSuccessor(Header))
- return;
+ BlockFrequency PredFreq = MBFI->getBlockFreq(Pred);
+ if (!BestPred || PredFreq > BestPredFreq ||
+ (!(PredFreq < BestPredFreq) &&
+ Pred->isLayoutSuccessor(L.getHeader()))) {
+ BestPred = Pred;
+ BestPredFreq = PredFreq;
+ }
+ }
- // We need to analyze the branch and determine if rotating the loop will
- // completely remove a branch. We bail if the analysis fails or we don't find
- // an unconditional backedge.
- SmallVector<MachineOperand, 4> Cond;
- MachineBasicBlock *TBB = 0, *FBB = 0;
- if (TII->AnalyzeBranch(*Latch, TBB, FBB, Cond) || !TBB || FBB || !Cond.empty())
- return;
- assert(TBB == Header && "Found backedge that doesn't go to the header!");
-
- // Next we need to find a split point. This rotate algorithm is *very*
- // narrow, and it only tries to do the rotate when it can find a split point
- // which is an analyzable branch that exits the loop. Splitting there allows
- // us to form a fallthrough out of the loop and a conditional jump to the top
- // of the loop after rotation.
- MachineBasicBlock *NewBottom = 0, *NewTop = 0;
- BlockChain::iterator SplitIt = LoopChain.end();
- for (BlockChain::reverse_iterator I = llvm::next(LoopChain.rbegin()),
- E = LoopChain.rend();
- I != E; ++I) {
- Cond.clear();
- TBB = FBB = 0;
- if (TII->AnalyzeBranch(**I, TBB, FBB, Cond) || !TBB || Cond.empty())
+ // If no direct predecessor is fine, just use the loop header.
+ if (!BestPred)
+ return L.getHeader();
+
+ // Walk backwards through any straight line of predecessors.
+ while (BestPred->pred_size() == 1 &&
+ (*BestPred->pred_begin())->succ_size() == 1 &&
+ *BestPred->pred_begin() != L.getHeader())
+ BestPred = *BestPred->pred_begin();
+
+ DEBUG(dbgs() << " final top: " << getBlockName(BestPred) << "\n");
+ return BestPred;
+}
+
+/// \brief Find the best loop exiting block for layout.
+///
+/// This routine implements the logic to analyze the loop looking for the best
+/// block to layout at the top of the loop. Typically this is done to maximize
+/// fallthrough opportunities.
+MachineBasicBlock *
+MachineBlockPlacement::findBestLoopExit(MachineFunction &F, MachineLoop &L,
+ const BlockFilterSet &LoopBlockSet) {
+ // We don't want to layout the loop linearly in all cases. If the loop header
+ // is just a normal basic block in the loop, we want to look for what block
+ // within the loop is the best one to layout at the top. However, if the loop
+ // header has be pre-merged into a chain due to predecessors not having
+ // analyzable branches, *and* the predecessor it is merged with is *not* part
+ // of the loop, rotating the header into the middle of the loop will create
+ // a non-contiguous range of blocks which is Very Bad. So start with the
+ // header and only rotate if safe.
+ BlockChain &HeaderChain = *BlockToChain[L.getHeader()];
+ if (!LoopBlockSet.count(*HeaderChain.begin()))
+ return nullptr;
+
+ BlockFrequency BestExitEdgeFreq;
+ unsigned BestExitLoopDepth = 0;
+ MachineBasicBlock *ExitingBB = nullptr;
+ // If there are exits to outer loops, loop rotation can severely limit
+ // fallthrough opportunites unless it selects such an exit. Keep a set of
+ // blocks where rotating to exit with that block will reach an outer loop.
+ SmallPtrSet<MachineBasicBlock *, 4> BlocksExitingToOuterLoop;
+
+ DEBUG(dbgs() << "Finding best loop exit for: " << getBlockName(L.getHeader())
+ << "\n");
+ for (MachineBasicBlock *MBB : L.getBlocks()) {
+ BlockChain &Chain = *BlockToChain[MBB];
+ // Ensure that this block is at the end of a chain; otherwise it could be
+ // mid-way through an inner loop or a successor of an unanalyzable branch.
+ if (MBB != *std::prev(Chain.end()))
continue;
- // Swap things so that the in-loop successor is always in FBB or is an
- // implicit fallthrough.
- if (FBB && !LoopBlockSet.count(FBB))
- std::swap(TBB, FBB);
- // Check that we actually have a loop exit branch.
- // FIXME: We should probably just use the LoopInfo for this.
- if (!LoopBlockSet.count(TBB) && (!FBB || !LoopBlockSet.count(FBB))) {
- // This is a very arbitrary restriction, but it ensures we don't disrupt
- // the existing chain layout. We insist that the in-loop successor is
- // chained as a fallthrough successor (even if the branch hasn't been
- // updated to reflect that yet).
- if (FBB && FBB != *llvm::prior(I))
+
+ // Now walk the successors. We need to establish whether this has a viable
+ // exiting successor and whether it has a viable non-exiting successor.
+ // We store the old exiting state and restore it if a viable looping
+ // successor isn't found.
+ MachineBasicBlock *OldExitingBB = ExitingBB;
+ BlockFrequency OldBestExitEdgeFreq = BestExitEdgeFreq;
+ bool HasLoopingSucc = false;
+ for (MachineBasicBlock *Succ : MBB->successors()) {
+ if (Succ->isEHPad())
+ continue;
+ if (Succ == MBB)
+ continue;
+ BlockChain &SuccChain = *BlockToChain[Succ];
+ // Don't split chains, either this chain or the successor's chain.
+ if (&Chain == &SuccChain) {
+ DEBUG(dbgs() << " exiting: " << getBlockName(MBB) << " -> "
+ << getBlockName(Succ) << " (chain conflict)\n");
+ continue;
+ }
+
+ auto SuccProb = MBPI->getEdgeProbability(MBB, Succ);
+ if (LoopBlockSet.count(Succ)) {
+ DEBUG(dbgs() << " looping: " << getBlockName(MBB) << " -> "
+ << getBlockName(Succ) << " (" << SuccProb << ")\n");
+ HasLoopingSucc = true;
continue;
+ }
+
+ unsigned SuccLoopDepth = 0;
+ if (MachineLoop *ExitLoop = MLI->getLoopFor(Succ)) {
+ SuccLoopDepth = ExitLoop->getLoopDepth();
+ if (ExitLoop->contains(&L))
+ BlocksExitingToOuterLoop.insert(MBB);
+ }
+
+ BlockFrequency ExitEdgeFreq = MBFI->getBlockFreq(MBB) * SuccProb;
+ DEBUG(dbgs() << " exiting: " << getBlockName(MBB) << " -> "
+ << getBlockName(Succ) << " [L:" << SuccLoopDepth << "] (";
+ MBFI->printBlockFreq(dbgs(), ExitEdgeFreq) << ")\n");
+ // Note that we bias this toward an existing layout successor to retain
+ // incoming order in the absence of better information. The exit must have
+ // a frequency higher than the current exit before we consider breaking
+ // the layout.
+ BranchProbability Bias(100 - ExitBlockBias, 100);
+ if (!ExitingBB || SuccLoopDepth > BestExitLoopDepth ||
+ ExitEdgeFreq > BestExitEdgeFreq ||
+ (MBB->isLayoutSuccessor(Succ) &&
+ !(ExitEdgeFreq < BestExitEdgeFreq * Bias))) {
+ BestExitEdgeFreq = ExitEdgeFreq;
+ ExitingBB = MBB;
+ }
+ }
- NewBottom = *I;
- NewTop = *llvm::prior(I);
- SplitIt = I.base();
+ if (!HasLoopingSucc) {
+ // Restore the old exiting state, no viable looping successor was found.
+ ExitingBB = OldExitingBB;
+ BestExitEdgeFreq = OldBestExitEdgeFreq;
+ continue;
+ }
+ }
+ // Without a candidate exiting block or with only a single block in the
+ // loop, just use the loop header to layout the loop.
+ if (!ExitingBB || L.getNumBlocks() == 1)
+ return nullptr;
+
+ // Also, if we have exit blocks which lead to outer loops but didn't select
+ // one of them as the exiting block we are rotating toward, disable loop
+ // rotation altogether.
+ if (!BlocksExitingToOuterLoop.empty() &&
+ !BlocksExitingToOuterLoop.count(ExitingBB))
+ return nullptr;
+
+ DEBUG(dbgs() << " Best exiting block: " << getBlockName(ExitingBB) << "\n");
+ return ExitingBB;
+}
+
+/// \brief Attempt to rotate an exiting block to the bottom of the loop.
+///
+/// Once we have built a chain, try to rotate it to line up the hot exit block
+/// with fallthrough out of the loop if doing so doesn't introduce unnecessary
+/// branches. For example, if the loop has fallthrough into its header and out
+/// of its bottom already, don't rotate it.
+void MachineBlockPlacement::rotateLoop(BlockChain &LoopChain,
+ MachineBasicBlock *ExitingBB,
+ const BlockFilterSet &LoopBlockSet) {
+ if (!ExitingBB)
+ return;
+
+ MachineBasicBlock *Top = *LoopChain.begin();
+ bool ViableTopFallthrough = false;
+ for (MachineBasicBlock *Pred : Top->predecessors()) {
+ BlockChain *PredChain = BlockToChain[Pred];
+ if (!LoopBlockSet.count(Pred) &&
+ (!PredChain || Pred == *std::prev(PredChain->end()))) {
+ ViableTopFallthrough = true;
break;
}
}
- if (!NewBottom || !NewTop ||
- SplitIt == LoopChain.end() || SplitIt == LoopChain.begin())
+
+ // If the header has viable fallthrough, check whether the current loop
+ // bottom is a viable exiting block. If so, bail out as rotating will
+ // introduce an unnecessary branch.
+ if (ViableTopFallthrough) {
+ MachineBasicBlock *Bottom = *std::prev(LoopChain.end());
+ for (MachineBasicBlock *Succ : Bottom->successors()) {
+ BlockChain *SuccChain = BlockToChain[Succ];
+ if (!LoopBlockSet.count(Succ) &&
+ (!SuccChain || Succ == *SuccChain->begin()))
+ return;
+ }
+ }
+
+ BlockChain::iterator ExitIt =
+ std::find(LoopChain.begin(), LoopChain.end(), ExitingBB);
+ if (ExitIt == LoopChain.end())
return;
- assert(BlockToChain[NewBottom] == &LoopChain);
- assert(BlockToChain[NewTop] == &LoopChain);
- assert(*SplitIt == NewTop);
-
- // Rotate the chain and we're done.
- DEBUG(dbgs() << "Rotating loop headed by: " << getBlockName(Header) << "\n"
- << " new top: " << getBlockName(NewTop) << "\n"
- << " new bottom: " << getBlockName(NewBottom) << "\n");
- std::rotate(LoopChain.begin(), SplitIt, LoopChain.end());
+
+ std::rotate(LoopChain.begin(), std::next(ExitIt), LoopChain.end());
+}
+
+/// \brief Attempt to rotate a loop based on profile data to reduce branch cost.
+///
+/// With profile data, we can determine the cost in terms of missed fall through
+/// opportunities when rotating a loop chain and select the best rotation.
+/// Basically, there are three kinds of cost to consider for each rotation:
+/// 1. The possibly missed fall through edge (if it exists) from BB out of
+/// the loop to the loop header.
+/// 2. The possibly missed fall through edges (if they exist) from the loop
+/// exits to BB out of the loop.
+/// 3. The missed fall through edge (if it exists) from the last BB to the
+/// first BB in the loop chain.
+/// Therefore, the cost for a given rotation is the sum of costs listed above.
+/// We select the best rotation with the smallest cost.
+void MachineBlockPlacement::rotateLoopWithProfile(
+ BlockChain &LoopChain, MachineLoop &L, const BlockFilterSet &LoopBlockSet) {
+ auto HeaderBB = L.getHeader();
+ auto HeaderIter = std::find(LoopChain.begin(), LoopChain.end(), HeaderBB);
+ auto RotationPos = LoopChain.end();
+
+ BlockFrequency SmallestRotationCost = BlockFrequency::getMaxFrequency();
+
+ // A utility lambda that scales up a block frequency by dividing it by a
+ // branch probability which is the reciprocal of the scale.
+ auto ScaleBlockFrequency = [](BlockFrequency Freq,
+ unsigned Scale) -> BlockFrequency {
+ if (Scale == 0)
+ return 0;
+ // Use operator / between BlockFrequency and BranchProbability to implement
+ // saturating multiplication.
+ return Freq / BranchProbability(1, Scale);
+ };
+
+ // Compute the cost of the missed fall-through edge to the loop header if the
+ // chain head is not the loop header. As we only consider natural loops with
+ // single header, this computation can be done only once.
+ BlockFrequency HeaderFallThroughCost(0);
+ for (auto *Pred : HeaderBB->predecessors()) {
+ BlockChain *PredChain = BlockToChain[Pred];
+ if (!LoopBlockSet.count(Pred) &&
+ (!PredChain || Pred == *std::prev(PredChain->end()))) {
+ auto EdgeFreq =
+ MBFI->getBlockFreq(Pred) * MBPI->getEdgeProbability(Pred, HeaderBB);
+ auto FallThruCost = ScaleBlockFrequency(EdgeFreq, MisfetchCost);
+ // If the predecessor has only an unconditional jump to the header, we
+ // need to consider the cost of this jump.
+ if (Pred->succ_size() == 1)
+ FallThruCost += ScaleBlockFrequency(EdgeFreq, JumpInstCost);
+ HeaderFallThroughCost = std::max(HeaderFallThroughCost, FallThruCost);
+ }
+ }
+
+ // Here we collect all exit blocks in the loop, and for each exit we find out
+ // its hottest exit edge. For each loop rotation, we define the loop exit cost
+ // as the sum of frequencies of exit edges we collect here, excluding the exit
+ // edge from the tail of the loop chain.
+ SmallVector<std::pair<MachineBasicBlock *, BlockFrequency>, 4> ExitsWithFreq;
+ for (auto BB : LoopChain) {
+ auto LargestExitEdgeProb = BranchProbability::getZero();
+ for (auto *Succ : BB->successors()) {
+ BlockChain *SuccChain = BlockToChain[Succ];
+ if (!LoopBlockSet.count(Succ) &&
+ (!SuccChain || Succ == *SuccChain->begin())) {
+ auto SuccProb = MBPI->getEdgeProbability(BB, Succ);
+ LargestExitEdgeProb = std::max(LargestExitEdgeProb, SuccProb);
+ }
+ }
+ if (LargestExitEdgeProb > BranchProbability::getZero()) {
+ auto ExitFreq = MBFI->getBlockFreq(BB) * LargestExitEdgeProb;
+ ExitsWithFreq.emplace_back(BB, ExitFreq);
+ }
+ }
+
+ // In this loop we iterate every block in the loop chain and calculate the
+ // cost assuming the block is the head of the loop chain. When the loop ends,
+ // we should have found the best candidate as the loop chain's head.
+ for (auto Iter = LoopChain.begin(), TailIter = std::prev(LoopChain.end()),
+ EndIter = LoopChain.end();
+ Iter != EndIter; Iter++, TailIter++) {
+ // TailIter is used to track the tail of the loop chain if the block we are
+ // checking (pointed by Iter) is the head of the chain.
+ if (TailIter == LoopChain.end())
+ TailIter = LoopChain.begin();
+
+ auto TailBB = *TailIter;
+
+ // Calculate the cost by putting this BB to the top.
+ BlockFrequency Cost = 0;
+
+ // If the current BB is the loop header, we need to take into account the
+ // cost of the missed fall through edge from outside of the loop to the
+ // header.
+ if (Iter != HeaderIter)
+ Cost += HeaderFallThroughCost;
+
+ // Collect the loop exit cost by summing up frequencies of all exit edges
+ // except the one from the chain tail.
+ for (auto &ExitWithFreq : ExitsWithFreq)
+ if (TailBB != ExitWithFreq.first)
+ Cost += ExitWithFreq.second;
+
+ // The cost of breaking the once fall-through edge from the tail to the top
+ // of the loop chain. Here we need to consider three cases:
+ // 1. If the tail node has only one successor, then we will get an
+ // additional jmp instruction. So the cost here is (MisfetchCost +
+ // JumpInstCost) * tail node frequency.
+ // 2. If the tail node has two successors, then we may still get an
+ // additional jmp instruction if the layout successor after the loop
+ // chain is not its CFG successor. Note that the more frequently executed
+ // jmp instruction will be put ahead of the other one. Assume the
+ // frequency of those two branches are x and y, where x is the frequency
+ // of the edge to the chain head, then the cost will be
+ // (x * MisfetechCost + min(x, y) * JumpInstCost) * tail node frequency.
+ // 3. If the tail node has more than two successors (this rarely happens),
+ // we won't consider any additional cost.
+ if (TailBB->isSuccessor(*Iter)) {
+ auto TailBBFreq = MBFI->getBlockFreq(TailBB);
+ if (TailBB->succ_size() == 1)
+ Cost += ScaleBlockFrequency(TailBBFreq.getFrequency(),
+ MisfetchCost + JumpInstCost);
+ else if (TailBB->succ_size() == 2) {
+ auto TailToHeadProb = MBPI->getEdgeProbability(TailBB, *Iter);
+ auto TailToHeadFreq = TailBBFreq * TailToHeadProb;
+ auto ColderEdgeFreq = TailToHeadProb > BranchProbability(1, 2)
+ ? TailBBFreq * TailToHeadProb.getCompl()
+ : TailToHeadFreq;
+ Cost += ScaleBlockFrequency(TailToHeadFreq, MisfetchCost) +
+ ScaleBlockFrequency(ColderEdgeFreq, JumpInstCost);
+ }
+ }
+
+ DEBUG(dbgs() << "The cost of loop rotation by making " << getBlockNum(*Iter)
+ << " to the top: " << Cost.getFrequency() << "\n");
+
+ if (Cost < SmallestRotationCost) {
+ SmallestRotationCost = Cost;
+ RotationPos = Iter;
+ }
+ }
+
+ if (RotationPos != LoopChain.end()) {
+ DEBUG(dbgs() << "Rotate loop by making " << getBlockNum(*RotationPos)
+ << " to the top\n");
+ std::rotate(LoopChain.begin(), RotationPos, LoopChain.end());
+ }
+}
+
+/// \brief Collect blocks in the given loop that are to be placed.
+///
+/// When profile data is available, exclude cold blocks from the returned set;
+/// otherwise, collect all blocks in the loop.
+MachineBlockPlacement::BlockFilterSet
+MachineBlockPlacement::collectLoopBlockSet(MachineFunction &F, MachineLoop &L) {
+ BlockFilterSet LoopBlockSet;
+
+ // Filter cold blocks off from LoopBlockSet when profile data is available.
+ // Collect the sum of frequencies of incoming edges to the loop header from
+ // outside. If we treat the loop as a super block, this is the frequency of
+ // the loop. Then for each block in the loop, we calculate the ratio between
+ // its frequency and the frequency of the loop block. When it is too small,
+ // don't add it to the loop chain. If there are outer loops, then this block
+ // will be merged into the first outer loop chain for which this block is not
+ // cold anymore. This needs precise profile data and we only do this when
+ // profile data is available.
+ if (F.getFunction()->getEntryCount()) {
+ BlockFrequency LoopFreq(0);
+ for (auto LoopPred : L.getHeader()->predecessors())
+ if (!L.contains(LoopPred))
+ LoopFreq += MBFI->getBlockFreq(LoopPred) *
+ MBPI->getEdgeProbability(LoopPred, L.getHeader());
+
+ for (MachineBasicBlock *LoopBB : L.getBlocks()) {
+ auto Freq = MBFI->getBlockFreq(LoopBB).getFrequency();
+ if (Freq == 0 || LoopFreq.getFrequency() / Freq > LoopToColdBlockRatio)
+ continue;
+ LoopBlockSet.insert(LoopBB);
+ }
+ } else
+ LoopBlockSet.insert(L.block_begin(), L.block_end());
+
+ return LoopBlockSet;
}
/// \brief Forms basic block chains from the natural loop structures.
MachineLoop &L) {
// First recurse through any nested loops, building chains for those inner
// loops.
- for (MachineLoop::iterator LI = L.begin(), LE = L.end(); LI != LE; ++LI)
- buildLoopChains(F, **LI);
+ for (MachineLoop *InnerLoop : L)
+ buildLoopChains(F, *InnerLoop);
SmallVector<MachineBasicBlock *, 16> BlockWorkList;
- BlockFilterSet LoopBlockSet(L.block_begin(), L.block_end());
- BlockChain &LoopChain = *BlockToChain[L.getHeader()];
+ BlockFilterSet LoopBlockSet = collectLoopBlockSet(F, L);
+
+ // Check if we have profile data for this function. If yes, we will rotate
+ // this loop by modeling costs more precisely which requires the profile data
+ // for better layout.
+ bool RotateLoopWithProfile =
+ PreciseRotationCost && F.getFunction()->getEntryCount();
+
+ // First check to see if there is an obviously preferable top block for the
+ // loop. This will default to the header, but may end up as one of the
+ // predecessors to the header if there is one which will result in strictly
+ // fewer branches in the loop body.
+ // When we use profile data to rotate the loop, this is unnecessary.
+ MachineBasicBlock *LoopTop =
+ RotateLoopWithProfile ? L.getHeader() : findBestLoopTop(L, LoopBlockSet);
+
+ // If we selected just the header for the loop top, look for a potentially
+ // profitable exit block in the event that rotating the loop can eliminate
+ // branches by placing an exit edge at the bottom.
+ MachineBasicBlock *ExitingBB = nullptr;
+ if (!RotateLoopWithProfile && LoopTop == L.getHeader())
+ ExitingBB = findBestLoopExit(F, L, LoopBlockSet);
+
+ BlockChain &LoopChain = *BlockToChain[LoopTop];
// FIXME: This is a really lame way of walking the chains in the loop: we
// walk the blocks, and use a set to prevent visiting a particular chain
// twice.
SmallPtrSet<BlockChain *, 4> UpdatedPreds;
- for (MachineLoop::block_iterator BI = L.block_begin(),
- BE = L.block_end();
- BI != BE; ++BI) {
- BlockChain &Chain = *BlockToChain[*BI];
- if (!UpdatedPreds.insert(&Chain) || BI == L.block_begin())
+ assert(LoopChain.LoopPredecessors == 0);
+ UpdatedPreds.insert(&LoopChain);
+
+ for (MachineBasicBlock *LoopBB : LoopBlockSet) {
+ BlockChain &Chain = *BlockToChain[LoopBB];
+ if (!UpdatedPreds.insert(&Chain).second)
continue;
assert(Chain.LoopPredecessors == 0);
- for (BlockChain::iterator BCI = Chain.begin(), BCE = Chain.end();
- BCI != BCE; ++BCI) {
- assert(BlockToChain[*BCI] == &Chain);
- for (MachineBasicBlock::pred_iterator PI = (*BCI)->pred_begin(),
- PE = (*BCI)->pred_end();
- PI != PE; ++PI) {
- if (BlockToChain[*PI] == &Chain || !LoopBlockSet.count(*PI))
+ for (MachineBasicBlock *ChainBB : Chain) {
+ assert(BlockToChain[ChainBB] == &Chain);
+ for (MachineBasicBlock *Pred : ChainBB->predecessors()) {
+ if (BlockToChain[Pred] == &Chain || !LoopBlockSet.count(Pred))
continue;
++Chain.LoopPredecessors;
}
BlockWorkList.push_back(*Chain.begin());
}
- buildChain(*L.block_begin(), LoopChain, BlockWorkList, &LoopBlockSet);
- rotateLoop(L, LoopChain, LoopBlockSet);
+ buildChain(LoopTop, LoopChain, BlockWorkList, &LoopBlockSet);
+
+ if (RotateLoopWithProfile)
+ rotateLoopWithProfile(LoopChain, L, LoopBlockSet);
+ else
+ rotateLoop(LoopChain, ExitingBB, LoopBlockSet);
DEBUG({
// Crash at the end so we get all of the debugging output first.
<< " Loop header: " << getBlockName(*L.block_begin()) << "\n"
<< " Chain header: " << getBlockName(*LoopChain.begin()) << "\n";
}
- for (BlockChain::iterator BCI = LoopChain.begin(), BCE = LoopChain.end();
- BCI != BCE; ++BCI)
- if (!LoopBlockSet.erase(*BCI)) {
+ for (MachineBasicBlock *ChainBB : LoopChain) {
+ dbgs() << " ... " << getBlockName(ChainBB) << "\n";
+ if (!LoopBlockSet.erase(ChainBB)) {
// We don't mark the loop as bad here because there are real situations
// where this can occur. For example, with an unanalyzable fallthrough
// from a loop block to a non-loop block or vice versa.
dbgs() << "Loop chain contains a block not contained by the loop!\n"
<< " Loop header: " << getBlockName(*L.block_begin()) << "\n"
<< " Chain header: " << getBlockName(*LoopChain.begin()) << "\n"
- << " Bad block: " << getBlockName(*BCI) << "\n";
+ << " Bad block: " << getBlockName(ChainBB) << "\n";
}
+ }
if (!LoopBlockSet.empty()) {
BadLoop = true;
- for (BlockFilterSet::iterator LBI = LoopBlockSet.begin(),
- LBE = LoopBlockSet.end();
- LBI != LBE; ++LBI)
+ for (MachineBasicBlock *LoopBB : LoopBlockSet)
dbgs() << "Loop contains blocks never placed into a chain!\n"
<< " Loop header: " << getBlockName(*L.block_begin()) << "\n"
<< " Chain header: " << getBlockName(*LoopChain.begin()) << "\n"
- << " Bad block: " << getBlockName(*LBI) << "\n";
+ << " Bad block: " << getBlockName(LoopBB) << "\n";
}
assert(!BadLoop && "Detected problems with the placement of this loop.");
});
// the assumptions of the remaining algorithm.
SmallVector<MachineOperand, 4> Cond; // For AnalyzeBranch.
for (MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
- MachineBasicBlock *BB = FI;
- BlockChain *Chain
- = new (ChainAllocator.Allocate()) BlockChain(BlockToChain, BB);
+ MachineBasicBlock *BB = &*FI;
+ BlockChain *Chain =
+ new (ChainAllocator.Allocate()) BlockChain(BlockToChain, BB);
// Also, merge any blocks which we cannot reason about and must preserve
// the exact fallthrough behavior for.
for (;;) {
Cond.clear();
- MachineBasicBlock *TBB = 0, *FBB = 0; // For AnalyzeBranch.
+ MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch.
if (!TII->AnalyzeBranch(*BB, TBB, FBB, Cond) || !FI->canFallThrough())
break;
- MachineFunction::iterator NextFI(llvm::next(FI));
- MachineBasicBlock *NextBB = NextFI;
+ MachineFunction::iterator NextFI = std::next(FI);
+ MachineBasicBlock *NextBB = &*NextFI;
// Ensure that the layout successor is a viable block, as we know that
// fallthrough is a possibility.
assert(NextFI != FE && "Can't fallthrough past the last block.");
DEBUG(dbgs() << "Pre-merging due to unanalyzable fallthrough: "
<< getBlockName(BB) << " -> " << getBlockName(NextBB)
<< "\n");
- Chain->merge(NextBB, 0);
+ Chain->merge(NextBB, nullptr);
FI = NextFI;
BB = NextBB;
}
}
+ if (OutlineOptionalBranches) {
+ // Find the nearest common dominator of all of F's terminators.
+ MachineBasicBlock *Terminator = nullptr;
+ for (MachineBasicBlock &MBB : F) {
+ if (MBB.succ_size() == 0) {
+ if (Terminator == nullptr)
+ Terminator = &MBB;
+ else
+ Terminator = MDT->findNearestCommonDominator(Terminator, &MBB);
+ }
+ }
+
+ // MBBs dominating this common dominator are unavoidable.
+ UnavoidableBlocks.clear();
+ for (MachineBasicBlock &MBB : F) {
+ if (MDT->dominates(&MBB, Terminator)) {
+ UnavoidableBlocks.insert(&MBB);
+ }
+ }
+ }
+
// Build any loop-based chains.
- for (MachineLoopInfo::iterator LI = MLI->begin(), LE = MLI->end(); LI != LE;
- ++LI)
- buildLoopChains(F, **LI);
+ for (MachineLoop *L : *MLI)
+ buildLoopChains(F, *L);
SmallVector<MachineBasicBlock *, 16> BlockWorkList;
SmallPtrSet<BlockChain *, 4> UpdatedPreds;
- for (MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
- MachineBasicBlock *BB = &*FI;
- BlockChain &Chain = *BlockToChain[BB];
- if (!UpdatedPreds.insert(&Chain))
+ for (MachineBasicBlock &MBB : F) {
+ BlockChain &Chain = *BlockToChain[&MBB];
+ if (!UpdatedPreds.insert(&Chain).second)
continue;
assert(Chain.LoopPredecessors == 0);
- for (BlockChain::iterator BCI = Chain.begin(), BCE = Chain.end();
- BCI != BCE; ++BCI) {
- assert(BlockToChain[*BCI] == &Chain);
- for (MachineBasicBlock::pred_iterator PI = (*BCI)->pred_begin(),
- PE = (*BCI)->pred_end();
- PI != PE; ++PI) {
- if (BlockToChain[*PI] == &Chain)
+ for (MachineBasicBlock *ChainBB : Chain) {
+ assert(BlockToChain[ChainBB] == &Chain);
+ for (MachineBasicBlock *Pred : ChainBB->predecessors()) {
+ if (BlockToChain[Pred] == &Chain)
continue;
++Chain.LoopPredecessors;
}
BlockChain &FunctionChain = *BlockToChain[&F.front()];
buildChain(&F.front(), FunctionChain, BlockWorkList);
+#ifndef NDEBUG
typedef SmallPtrSet<MachineBasicBlock *, 16> FunctionBlockSetType;
+#endif
DEBUG({
// Crash at the end so we get all of the debugging output first.
bool BadFunc = false;
FunctionBlockSetType FunctionBlockSet;
- for (MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
- FunctionBlockSet.insert(FI);
+ for (MachineBasicBlock &MBB : F)
+ FunctionBlockSet.insert(&MBB);
- for (BlockChain::iterator BCI = FunctionChain.begin(),
- BCE = FunctionChain.end();
- BCI != BCE; ++BCI)
- if (!FunctionBlockSet.erase(*BCI)) {
+ for (MachineBasicBlock *ChainBB : FunctionChain)
+ if (!FunctionBlockSet.erase(ChainBB)) {
BadFunc = true;
dbgs() << "Function chain contains a block not in the function!\n"
- << " Bad block: " << getBlockName(*BCI) << "\n";
+ << " Bad block: " << getBlockName(ChainBB) << "\n";
}
if (!FunctionBlockSet.empty()) {
BadFunc = true;
- for (FunctionBlockSetType::iterator FBI = FunctionBlockSet.begin(),
- FBE = FunctionBlockSet.end();
- FBI != FBE; ++FBI)
+ for (MachineBasicBlock *RemainingBB : FunctionBlockSet)
dbgs() << "Function contains blocks never placed into a chain!\n"
- << " Bad block: " << getBlockName(*FBI) << "\n";
+ << " Bad block: " << getBlockName(RemainingBB) << "\n";
}
assert(!BadFunc && "Detected problems with the block placement.");
});
// Splice the blocks into place.
MachineFunction::iterator InsertPos = F.begin();
- for (BlockChain::iterator BI = FunctionChain.begin(),
- BE = FunctionChain.end();
- BI != BE; ++BI) {
- DEBUG(dbgs() << (BI == FunctionChain.begin() ? "Placing chain "
- : " ... ")
- << getBlockName(*BI) << "\n");
- if (InsertPos != MachineFunction::iterator(*BI))
- F.splice(InsertPos, *BI);
+ for (MachineBasicBlock *ChainBB : FunctionChain) {
+ DEBUG(dbgs() << (ChainBB == *FunctionChain.begin() ? "Placing chain "
+ : " ... ")
+ << getBlockName(ChainBB) << "\n");
+ if (InsertPos != MachineFunction::iterator(ChainBB))
+ F.splice(InsertPos, ChainBB);
else
++InsertPos;
// Update the terminator of the previous block.
- if (BI == FunctionChain.begin())
+ if (ChainBB == *FunctionChain.begin())
continue;
- MachineBasicBlock *PrevBB = llvm::prior(MachineFunction::iterator(*BI));
+ MachineBasicBlock *PrevBB = &*std::prev(MachineFunction::iterator(ChainBB));
// FIXME: It would be awesome of updateTerminator would just return rather
// than assert when the branch cannot be analyzed in order to remove this
// boiler plate.
Cond.clear();
- MachineBasicBlock *TBB = 0, *FBB = 0; // For AnalyzeBranch.
- if (!TII->AnalyzeBranch(*PrevBB, TBB, FBB, Cond))
- PrevBB->updateTerminator();
+ MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch.
+ if (!TII->AnalyzeBranch(*PrevBB, TBB, FBB, Cond)) {
+ // The "PrevBB" is not yet updated to reflect current code layout, so,
+ // o. it may fall-through to a block without explict "goto" instruction
+ // before layout, and no longer fall-through it after layout; or
+ // o. just opposite.
+ //
+ // AnalyzeBranch() may return erroneous value for FBB when these two
+ // situations take place. For the first scenario FBB is mistakenly set
+ // NULL; for the 2nd scenario, the FBB, which is expected to be NULL,
+ // is mistakenly pointing to "*BI".
+ //
+ bool needUpdateBr = true;
+ if (!Cond.empty() && (!FBB || FBB == ChainBB)) {
+ PrevBB->updateTerminator();
+ needUpdateBr = false;
+ Cond.clear();
+ TBB = FBB = nullptr;
+ if (TII->AnalyzeBranch(*PrevBB, TBB, FBB, Cond)) {
+ // FIXME: This should never take place.
+ TBB = FBB = nullptr;
+ }
+ }
+
+ // If PrevBB has a two-way branch, try to re-order the branches
+ // such that we branch to the successor with higher probability first.
+ if (TBB && !Cond.empty() && FBB &&
+ MBPI->getEdgeProbability(PrevBB, FBB) >
+ MBPI->getEdgeProbability(PrevBB, TBB) &&
+ !TII->ReverseBranchCondition(Cond)) {
+ DEBUG(dbgs() << "Reverse order of the two branches: "
+ << getBlockName(PrevBB) << "\n");
+ DEBUG(dbgs() << " Edge probability: "
+ << MBPI->getEdgeProbability(PrevBB, FBB) << " vs "
+ << MBPI->getEdgeProbability(PrevBB, TBB) << "\n");
+ DebugLoc dl; // FIXME: this is nowhere
+ TII->RemoveBranch(*PrevBB);
+ TII->InsertBranch(*PrevBB, FBB, TBB, Cond, dl);
+ needUpdateBr = true;
+ }
+ if (needUpdateBr)
+ PrevBB->updateTerminator();
+ }
}
// Fixup the last block.
Cond.clear();
- MachineBasicBlock *TBB = 0, *FBB = 0; // For AnalyzeBranch.
+ MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch.
if (!TII->AnalyzeBranch(F.back(), TBB, FBB, Cond))
F.back().updateTerminator();
-}
-/// \brief Recursive helper to align a loop and any nested loops.
-static void AlignLoop(MachineFunction &F, MachineLoop *L, unsigned Align) {
- // Recurse through nested loops.
- for (MachineLoop::iterator I = L->begin(), E = L->end(); I != E; ++I)
- AlignLoop(F, *I, Align);
+ // Walk through the backedges of the function now that we have fully laid out
+ // the basic blocks and align the destination of each backedge. We don't rely
+ // exclusively on the loop info here so that we can align backedges in
+ // unnatural CFGs and backedges that were introduced purely because of the
+ // loop rotations done during this layout pass.
+ // FIXME: Use Function::optForSize().
+ if (F.getFunction()->hasFnAttribute(Attribute::OptimizeForSize))
+ return;
+ if (FunctionChain.begin() == FunctionChain.end())
+ return; // Empty chain.
+
+ const BranchProbability ColdProb(1, 5); // 20%
+ BlockFrequency EntryFreq = MBFI->getBlockFreq(&F.front());
+ BlockFrequency WeightedEntryFreq = EntryFreq * ColdProb;
+ for (MachineBasicBlock *ChainBB : FunctionChain) {
+ if (ChainBB == *FunctionChain.begin())
+ continue;
- L->getTopBlock()->setAlignment(Align);
-}
+ // Don't align non-looping basic blocks. These are unlikely to execute
+ // enough times to matter in practice. Note that we'll still handle
+ // unnatural CFGs inside of a natural outer loop (the common case) and
+ // rotated loops.
+ MachineLoop *L = MLI->getLoopFor(ChainBB);
+ if (!L)
+ continue;
-/// \brief Align loop headers to target preferred alignments.
-void MachineBlockPlacement::AlignLoops(MachineFunction &F) {
- if (F.getFunction()->hasFnAttr(Attribute::OptimizeForSize))
- return;
+ if (AlignAllLoops) {
+ ChainBB->setAlignment(AlignAllLoops);
+ continue;
+ }
+
+ unsigned Align = TLI->getPrefLoopAlignment(L);
+ if (!Align)
+ continue; // Don't care about loop alignment.
+
+ // If the block is cold relative to the function entry don't waste space
+ // aligning it.
+ BlockFrequency Freq = MBFI->getBlockFreq(ChainBB);
+ if (Freq < WeightedEntryFreq)
+ continue;
+
+ // If the block is cold relative to its loop header, don't align it
+ // regardless of what edges into the block exist.
+ MachineBasicBlock *LoopHeader = L->getHeader();
+ BlockFrequency LoopHeaderFreq = MBFI->getBlockFreq(LoopHeader);
+ if (Freq < (LoopHeaderFreq * ColdProb))
+ continue;
+
+ // Check for the existence of a non-layout predecessor which would benefit
+ // from aligning this block.
+ MachineBasicBlock *LayoutPred =
+ &*std::prev(MachineFunction::iterator(ChainBB));
- unsigned Align = TLI->getPrefLoopAlignment();
- if (!Align)
- return; // Don't care about loop alignment.
+ // Force alignment if all the predecessors are jumps. We already checked
+ // that the block isn't cold above.
+ if (!LayoutPred->isSuccessor(ChainBB)) {
+ ChainBB->setAlignment(Align);
+ continue;
+ }
- for (MachineLoopInfo::iterator I = MLI->begin(), E = MLI->end(); I != E; ++I)
- AlignLoop(F, *I, Align);
+ // Align this block if the layout predecessor's edge into this block is
+ // cold relative to the block. When this is true, other predecessors make up
+ // all of the hot entries into the block and thus alignment is likely to be
+ // important.
+ BranchProbability LayoutProb =
+ MBPI->getEdgeProbability(LayoutPred, ChainBB);
+ BlockFrequency LayoutEdgeFreq = MBFI->getBlockFreq(LayoutPred) * LayoutProb;
+ if (LayoutEdgeFreq <= (Freq * ColdProb))
+ ChainBB->setAlignment(Align);
+ }
}
bool MachineBlockPlacement::runOnMachineFunction(MachineFunction &F) {
// Check for single-block functions and skip them.
- if (llvm::next(F.begin()) == F.end())
+ if (std::next(F.begin()) == F.end())
+ return false;
+
+ if (skipOptnoneFunction(*F.getFunction()))
return false;
MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
MLI = &getAnalysis<MachineLoopInfo>();
- TII = F.getTarget().getInstrInfo();
- TLI = F.getTarget().getTargetLowering();
+ TII = F.getSubtarget().getInstrInfo();
+ TLI = F.getSubtarget().getTargetLowering();
+ MDT = &getAnalysis<MachineDominatorTree>();
assert(BlockToChain.empty());
buildCFGChains(F);
- AlignLoops(F);
BlockToChain.clear();
ChainAllocator.DestroyAll();
+ if (AlignAllBlock)
+ // Align all of the blocks in the function to a specific alignment.
+ for (MachineBasicBlock &MBB : F)
+ MBB.setAlignment(AlignAllBlock);
+
// We always return true as we have no way to track whether the final order
// differs from the original order.
return true;
///
/// A separate pass to compute interesting statistics for evaluating block
/// placement. This is separate from the actual placement pass so that they can
-/// be computed in the absense of any placement transformations or when using
+/// be computed in the absence of any placement transformations or when using
/// alternative placement strategies.
class MachineBlockPlacementStats : public MachineFunctionPass {
/// \brief A handle to the branch probability pass.
initializeMachineBlockPlacementStatsPass(*PassRegistry::getPassRegistry());
}
- bool runOnMachineFunction(MachineFunction &F);
+ bool runOnMachineFunction(MachineFunction &F) override;
- void getAnalysisUsage(AnalysisUsage &AU) const {
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<MachineBranchProbabilityInfo>();
AU.addRequired<MachineBlockFrequencyInfo>();
AU.setPreservesAll();
MachineFunctionPass::getAnalysisUsage(AU);
}
-
- const char *getPassName() const { return "Block Placement Stats"; }
};
}
char MachineBlockPlacementStats::ID = 0;
+char &llvm::MachineBlockPlacementStatsID = MachineBlockPlacementStats::ID;
INITIALIZE_PASS_BEGIN(MachineBlockPlacementStats, "block-placement-stats",
"Basic Block Placement Stats", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
INITIALIZE_PASS_END(MachineBlockPlacementStats, "block-placement-stats",
"Basic Block Placement Stats", false, false)
-FunctionPass *llvm::createMachineBlockPlacementStatsPass() {
- return new MachineBlockPlacementStats();
-}
-
bool MachineBlockPlacementStats::runOnMachineFunction(MachineFunction &F) {
// Check for single-block functions and skip them.
- if (llvm::next(F.begin()) == F.end())
+ if (std::next(F.begin()) == F.end())
return false;
MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
- for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) {
- BlockFrequency BlockFreq = MBFI->getBlockFreq(I);
- Statistic &NumBranches = (I->succ_size() > 1) ? NumCondBranches
- : NumUncondBranches;
- Statistic &BranchTakenFreq = (I->succ_size() > 1) ? CondBranchTakenFreq
- : UncondBranchTakenFreq;
- for (MachineBasicBlock::succ_iterator SI = I->succ_begin(),
- SE = I->succ_end();
- SI != SE; ++SI) {
+ for (MachineBasicBlock &MBB : F) {
+ BlockFrequency BlockFreq = MBFI->getBlockFreq(&MBB);
+ Statistic &NumBranches =
+ (MBB.succ_size() > 1) ? NumCondBranches : NumUncondBranches;
+ Statistic &BranchTakenFreq =
+ (MBB.succ_size() > 1) ? CondBranchTakenFreq : UncondBranchTakenFreq;
+ for (MachineBasicBlock *Succ : MBB.successors()) {
// Skip if this successor is a fallthrough.
- if (I->isLayoutSuccessor(*SI))
+ if (MBB.isLayoutSuccessor(Succ))
continue;
- BlockFrequency EdgeFreq = BlockFreq * MBPI->getEdgeProbability(I, *SI);
+ BlockFrequency EdgeFreq =
+ BlockFreq * MBPI->getEdgeProbability(&MBB, Succ);
++NumBranches;
BranchTakenFreq += EdgeFreq.getFrequency();
}
return false;
}
-
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