1 files changed, 477 insertions, 0 deletions
diff --git a/lib/CodeGen/MachineTraceMetrics.cpp b/lib/CodeGen/MachineTraceMetrics.cpp
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+//===- lib/CodeGen/MachineTraceMetrics.cpp ----------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "early-ifcvt"
+#include "MachineTraceMetrics.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/ADT/PostOrderIterator.h"
+
+using namespace llvm;
+
+char MachineTraceMetrics::ID = 0;
+char &llvm::MachineTraceMetricsID = MachineTraceMetrics::ID;
+
+INITIALIZE_PASS_BEGIN(MachineTraceMetrics,
+                  "machine-trace-metrics", "Machine Trace Metrics", false, true)
+INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
+INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
+INITIALIZE_PASS_END(MachineTraceMetrics,
+                  "machine-trace-metrics", "Machine Trace Metrics", false, true)
+
+MachineTraceMetrics::MachineTraceMetrics()
+  : MachineFunctionPass(ID), TII(0), TRI(0), MRI(0), Loops(0) {
+  std::fill(Ensembles, array_endof(Ensembles), (Ensemble*)0);
+}
+
+void MachineTraceMetrics::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.setPreservesAll();
+  AU.addRequired<MachineBranchProbabilityInfo>();
+  AU.addRequired<MachineLoopInfo>();
+  MachineFunctionPass::getAnalysisUsage(AU);
+}
+
+bool MachineTraceMetrics::runOnMachineFunction(MachineFunction &MF) {
+  TII = MF.getTarget().getInstrInfo();
+  TRI = MF.getTarget().getRegisterInfo();
+  MRI = &MF.getRegInfo();
+  Loops = &getAnalysis<MachineLoopInfo>();
+  unsigned NumBlocks = MF.getNumBlockIDs();
+  BlockInfo.resize(NumBlocks);
+  return false;
+}
+
+void MachineTraceMetrics::releaseMemory() {
+  BlockInfo.clear();
+  for (unsigned i = 0; i != TS_NumStrategies; ++i) {
+    delete Ensembles[i];
+    Ensembles[i] = 0;
+  }
+}
+
+//===----------------------------------------------------------------------===//
+//                          Fixed block information
+//===----------------------------------------------------------------------===//
+//
+// The number of instructions in a basic block and the CPU resources used by
+// those instructions don't depend on any given trace strategy.
+
+/// Is MI an instruction that should be considered free because it will likely
+/// be eliminated by later passes?
+static bool isFree(const MachineInstr *MI) {
+  switch(MI->getOpcode()) {
+  default: return false;
+  case TargetOpcode::PHI:
+  case TargetOpcode::PROLOG_LABEL:
+  case TargetOpcode::EH_LABEL:
+  case TargetOpcode::GC_LABEL:
+  case TargetOpcode::KILL:
+  case TargetOpcode::EXTRACT_SUBREG:
+  case TargetOpcode::INSERT_SUBREG:
+  case TargetOpcode::IMPLICIT_DEF:
+  case TargetOpcode::SUBREG_TO_REG:
+  case TargetOpcode::COPY_TO_REGCLASS:
+  case TargetOpcode::DBG_VALUE:
+  case TargetOpcode::REG_SEQUENCE:
+  case TargetOpcode::COPY:
+    return true;
+  }
+}
+
+/// Compute the resource usage in basic block MBB.
+const MachineTraceMetrics::FixedBlockInfo*
+MachineTraceMetrics::getResources(const MachineBasicBlock *MBB) {
+  assert(MBB && "No basic block");
+  FixedBlockInfo *FBI = &BlockInfo[MBB->getNumber()];
+  if (FBI->hasResources())
+    return FBI;
+
+  // Compute resource usage in the block.
+  // FIXME: Compute per-functional unit counts.
+  FBI->HasCalls = false;
+  unsigned InstrCount = 0;
+  for (MachineBasicBlock::const_iterator I = MBB->begin(), E = MBB->end();
+       I != E; ++I) {
+    const MachineInstr *MI = I;
+    if (isFree(MI))
+      continue;
+    ++InstrCount;
+    if (MI->isCall())
+      FBI->HasCalls = true;
+  }
+  FBI->InstrCount = InstrCount;
+  return FBI;
+}
+
+//===----------------------------------------------------------------------===//
+//                         Ensemble utility functions
+//===----------------------------------------------------------------------===//
+
+MachineTraceMetrics::Ensemble::Ensemble(MachineTraceMetrics *ct)
+  : CT(*ct) {
+  BlockInfo.resize(CT.BlockInfo.size());
+}
+
+// Virtual destructor serves as an anchor.
+MachineTraceMetrics::Ensemble::~Ensemble() {}
+
+MachineLoop*
+MachineTraceMetrics::Ensemble::getLoopFor(const MachineBasicBlock *MBB) {
+  return CT.Loops->getLoopFor(MBB);
+}
+
+// Update resource-related information in the TraceBlockInfo for MBB.
+// Only update resources related to the trace above MBB.
+void MachineTraceMetrics::Ensemble::
+computeDepthResources(const MachineBasicBlock *MBB) {
+  TraceBlockInfo *TBI = &BlockInfo[MBB->getNumber()];
+
+  // Compute resources from trace above. The top block is simple.
+  if (!TBI->Pred) {
+    TBI->InstrDepth = 0;
+    return;
+  }
+
+  // Compute from the block above. A post-order traversal ensures the
+  // predecessor is always computed first.
+  TraceBlockInfo *PredTBI = &BlockInfo[TBI->Pred->getNumber()];
+  assert(PredTBI->hasValidDepth() && "Trace above has not been computed yet");
+  const FixedBlockInfo *PredFBI = CT.getResources(TBI->Pred);
+  TBI->InstrDepth = PredTBI->InstrDepth + PredFBI->InstrCount;
+}
+
+// Update resource-related information in the TraceBlockInfo for MBB.
+// Only update resources related to the trace below MBB.
+void MachineTraceMetrics::Ensemble::
+computeHeightResources(const MachineBasicBlock *MBB) {
+  TraceBlockInfo *TBI = &BlockInfo[MBB->getNumber()];
+
+  // Compute resources for the current block.
+  TBI->InstrHeight = CT.getResources(MBB)->InstrCount;
+
+  // The trace tail is done.
+  if (!TBI->Succ)
+    return;
+
+  // Compute from the block below. A post-order traversal ensures the
+  // predecessor is always computed first.
+  TraceBlockInfo *SuccTBI = &BlockInfo[TBI->Succ->getNumber()];
+  assert(SuccTBI->hasValidHeight() && "Trace below has not been computed yet");
+  TBI->InstrHeight += SuccTBI->InstrHeight;
+}
+
+// Check if depth resources for MBB are valid and return the TBI.
+// Return NULL if the resources have been invalidated.
+const MachineTraceMetrics::TraceBlockInfo*
+MachineTraceMetrics::Ensemble::
+getDepthResources(const MachineBasicBlock *MBB) const {
+  const TraceBlockInfo *TBI = &BlockInfo[MBB->getNumber()];
+  return TBI->hasValidDepth() ? TBI : 0;
+}
+
+// Check if height resources for MBB are valid and return the TBI.
+// Return NULL if the resources have been invalidated.
+const MachineTraceMetrics::TraceBlockInfo*
+MachineTraceMetrics::Ensemble::
+getHeightResources(const MachineBasicBlock *MBB) const {
+  const TraceBlockInfo *TBI = &BlockInfo[MBB->getNumber()];
+  return TBI->hasValidHeight() ? TBI : 0;
+}
+
+//===----------------------------------------------------------------------===//
+//                         Trace Selection Strategies
+//===----------------------------------------------------------------------===//
+//
+// A trace selection strategy is implemented as a sub-class of Ensemble. The
+// trace through a block B is computed by two DFS traversals of the CFG
+// starting from B. One upwards, and one downwards. During the upwards DFS,
+// pickTracePred() is called on the post-ordered blocks. During the downwards
+// DFS, pickTraceSucc() is called in a post-order.
+//
+
+// MinInstrCountEnsemble - Pick the trace that executes the least number of
+// instructions.
+namespace {
+class MinInstrCountEnsemble : public MachineTraceMetrics::Ensemble {
+  const char *getName() { return "MinInstr"; }
+  const MachineBasicBlock *pickTracePred(const MachineBasicBlock*);
+  const MachineBasicBlock *pickTraceSucc(const MachineBasicBlock*);
+
+public:
+  MinInstrCountEnsemble(MachineTraceMetrics *ct)
+    : MachineTraceMetrics::Ensemble(ct) {}
+};
+}
+
+// Select the preferred predecessor for MBB.
+const MachineBasicBlock*
+MinInstrCountEnsemble::pickTracePred(const MachineBasicBlock *MBB) {
+  if (MBB->pred_empty())
+    return 0;
+  MachineLoop *CurLoop = getLoopFor(MBB);
+  // Don't leave loops, and never follow back-edges.
+  if (CurLoop && MBB == CurLoop->getHeader())
+    return 0;
+  unsigned CurCount = CT.getResources(MBB)->InstrCount;
+  const MachineBasicBlock *Best = 0;
+  unsigned BestDepth = 0;
+  for (MachineBasicBlock::const_pred_iterator
+       I = MBB->pred_begin(), E = MBB->pred_end(); I != E; ++I) {
+    const MachineBasicBlock *Pred = *I;
+    const MachineTraceMetrics::TraceBlockInfo *PredTBI =
+      getDepthResources(Pred);
+    // Ignore invalidated predecessors. This never happens on the first scan,
+    // but if we rejected this predecessor earlier, it won't be revalidated.
+    if (!PredTBI)
+      continue;
+    // Don't consider predecessors in other loops.
+    if (getLoopFor(Pred) != CurLoop)
+      continue;
+    // Pick the predecessor that would give this block the smallest InstrDepth.
+    unsigned Depth = PredTBI->InstrDepth + CurCount;
+    if (!Best || Depth < BestDepth)
+      Best = Pred, BestDepth = Depth;
+  }
+  return Best;
+}
+
+// Select the preferred successor for MBB.
+const MachineBasicBlock*
+MinInstrCountEnsemble::pickTraceSucc(const MachineBasicBlock *MBB) {
+  if (MBB->pred_empty())
+    return 0;
+  MachineLoop *CurLoop = getLoopFor(MBB);
+  const MachineBasicBlock *Best = 0;
+  unsigned BestHeight = 0;
+  for (MachineBasicBlock::const_succ_iterator
+       I = MBB->succ_begin(), E = MBB->succ_end(); I != E; ++I) {
+    const MachineBasicBlock *Succ = *I;
+    const MachineTraceMetrics::TraceBlockInfo *SuccTBI =
+      getHeightResources(Succ);
+    // Ignore invalidated successors.
+    if (!SuccTBI)
+      continue;
+    // Don't consider back-edges.
+    if (CurLoop && Succ == CurLoop->getHeader())
+      continue;
+    // Don't consider successors in other loops.
+    if (getLoopFor(Succ) != CurLoop)
+      continue;
+    // Pick the successor that would give this block the smallest InstrHeight.
+    unsigned Height = SuccTBI->InstrHeight;
+    if (!Best || Height < BestHeight)
+      Best = Succ, BestHeight = Height;
+  }
+  return Best;
+}
+
+// Get an Ensemble sub-class for the requested trace strategy.
+MachineTraceMetrics::Ensemble *
+MachineTraceMetrics::getEnsemble(MachineTraceMetrics::Strategy strategy) {
+  assert(strategy < TS_NumStrategies && "Invalid trace strategy enum");
+  Ensemble *&E = Ensembles[strategy];
+  if (E)
+    return E;
+
+  // Allocate new Ensemble on demand.
+  switch (strategy) {
+  case TS_MinInstrCount: return (E = new MinInstrCountEnsemble(this));
+  default: llvm_unreachable("Invalid trace strategy enum");
+  }
+}
+
+void MachineTraceMetrics::invalidate(const MachineBasicBlock *MBB) {
+  DEBUG(dbgs() << "Invalidate traces through BB#" << MBB->getNumber() << '\n');
+  BlockInfo[MBB->getNumber()].invalidate();
+  for (unsigned i = 0; i != TS_NumStrategies; ++i)
+    if (Ensembles[i])
+      Ensembles[i]->invalidate(MBB);
+}
+
+//===----------------------------------------------------------------------===//
+//                               Trace building
+//===----------------------------------------------------------------------===//
+//
+// Traces are built by two CFG traversals. To avoid recomputing too much, use a
+// set abstraction that confines the search to the current loop, and doesn't
+// revisit blocks.
+
+namespace {
+struct LoopBounds {
+  MutableArrayRef<MachineTraceMetrics::TraceBlockInfo> Blocks;
+  const MachineLoopInfo *Loops;
+  const MachineLoop *CurLoop;
+  bool Downward;
+  LoopBounds(MutableArrayRef<MachineTraceMetrics::TraceBlockInfo> blocks,
+             const MachineLoopInfo *loops, const MachineLoop *curloop)
+    : Blocks(blocks), Loops(loops), CurLoop(curloop), Downward(false) {}
+};
+}
+
+// Specialize po_iterator_storage in order to prune the post-order traversal so
+// it is limited to the current loop and doesn't traverse the loop back edges.
+namespace llvm {
+template<>
+class po_iterator_storage<LoopBounds, true> {
+  LoopBounds &LB;
+public:
+  po_iterator_storage(LoopBounds &lb) : LB(lb) {}
+  void finishPostorder(const MachineBasicBlock*) {}
+
+  bool insertEdge(const MachineBasicBlock *From, const MachineBasicBlock *To) {
+    // Skip already visited To blocks.
+    MachineTraceMetrics::TraceBlockInfo &TBI = LB.Blocks[To->getNumber()];
+    if (LB.Downward ? TBI.hasValidHeight() : TBI.hasValidDepth())
+      return false;
+    // Don't follow CurLoop backedges.
+    if (LB.CurLoop && (LB.Downward ? To : From) == LB.CurLoop->getHeader())
+      return false;
+    // Don't leave CurLoop.
+    if (LB.Loops->getLoopFor(To) != LB.CurLoop)
+      return false;
+    // This is a new block. The PO traversal will compute height/depth
+    // resources, causing us to reject new edges to To. This only works because
+    // we reject back-edges, so the CFG is cycle-free.
+    return true;
+  }
+};
+}
+
+/// Compute the trace through MBB.
+void MachineTraceMetrics::Ensemble::computeTrace(const MachineBasicBlock *MBB) {
+  DEBUG(dbgs() << "Computing " << getName() << " trace through BB#"
+               << MBB->getNumber() << '\n');
+  // Set up loop bounds for the backwards post-order traversal.
+  LoopBounds Bounds(BlockInfo, CT.Loops, getLoopFor(MBB));
+
+  // Run an upwards post-order search for the trace start.
+  Bounds.Downward = false;
+  typedef ipo_ext_iterator<const MachineBasicBlock*, LoopBounds> UpwardPO;
+  for (UpwardPO I = ipo_ext_begin(MBB, Bounds), E = ipo_ext_end(MBB, Bounds);
+       I != E; ++I) {
+    DEBUG(dbgs() << "  pred for BB#" << I->getNumber() << ": ");
+    TraceBlockInfo &TBI = BlockInfo[I->getNumber()];
+    // All the predecessors have been visited, pick the preferred one.
+    TBI.Pred = pickTracePred(*I);
+    DEBUG({
+      if (TBI.Pred)
+        dbgs() << "BB#" << TBI.Pred->getNumber() << '\n';
+      else
+        dbgs() << "null\n";
+    });
+    // The trace leading to I is now known, compute the depth resources.
+    computeDepthResources(*I);
+  }
+
+  // Run a downwards post-order search for the trace end.
+  Bounds.Downward = true;
+  typedef po_ext_iterator<const MachineBasicBlock*, LoopBounds> DownwardPO;
+  for (DownwardPO I = po_ext_begin(MBB, Bounds), E = po_ext_end(MBB, Bounds);
+       I != E; ++I) {
+    DEBUG(dbgs() << "  succ for BB#" << I->getNumber() << ": ");
+    TraceBlockInfo &TBI = BlockInfo[I->getNumber()];
+    // All the successors have been visited, pick the preferred one.
+    BlockInfo[I->getNumber()].Succ = pickTraceSucc(*I);
+    DEBUG({
+      if (TBI.Pred)
+        dbgs() << "BB#" << TBI.Succ->getNumber() << '\n';
+      else
+        dbgs() << "null\n";
+    });
+    // The trace leaving I is now known, compute the height resources.
+    computeHeightResources(*I);
+  }
+}
+
+/// Invalidate traces through BadMBB.
+void
+MachineTraceMetrics::Ensemble::invalidate(const MachineBasicBlock *BadMBB) {
+  SmallVector<const MachineBasicBlock*, 16> WorkList;
+  TraceBlockInfo &BadTBI = BlockInfo[BadMBB->getNumber()];
+
+  // Invalidate height resources of blocks above MBB.
+  if (BadTBI.hasValidHeight()) {
+    BadTBI.invalidateHeight();
+    WorkList.push_back(BadMBB);
+    do {
+      const MachineBasicBlock *MBB = WorkList.pop_back_val();
+      DEBUG(dbgs() << "Invalidate BB#" << MBB->getNumber() << ' ' << getName()
+            << " height.\n");
+      // Find any MBB predecessors that have MBB as their preferred successor.
+      // They are the only ones that need to be invalidated.
+      for (MachineBasicBlock::const_pred_iterator
+           I = MBB->pred_begin(), E = MBB->pred_end(); I != E; ++I) {
+        TraceBlockInfo &TBI = BlockInfo[(*I)->getNumber()];
+        if (TBI.hasValidHeight() && TBI.Succ == MBB) {
+          TBI.invalidateHeight();
+          WorkList.push_back(*I);
+        }
+      }
+    } while (!WorkList.empty());
+  }
+
+  // Invalidate depth resources of blocks below MBB.
+  if (BadTBI.hasValidDepth()) {
+    BadTBI.invalidateDepth();
+    WorkList.push_back(BadMBB);
+    do {
+      const MachineBasicBlock *MBB = WorkList.pop_back_val();
+      DEBUG(dbgs() << "Invalidate BB#" << MBB->getNumber() << ' ' << getName()
+            << " depth.\n");
+      // Find any MBB successors that have MBB as their preferred predecessor.
+      // They are the only ones that need to be invalidated.
+      for (MachineBasicBlock::const_succ_iterator
+           I = MBB->succ_begin(), E = MBB->succ_end(); I != E; ++I) {
+        TraceBlockInfo &TBI = BlockInfo[(*I)->getNumber()];
+        if (TBI.hasValidDepth() && TBI.Pred == MBB) {
+          TBI.invalidateDepth();
+          WorkList.push_back(*I);
+        }
+      }
+    } while (!WorkList.empty());
+  }
+}
+
+
+MachineTraceMetrics::Trace
+MachineTraceMetrics::Ensemble::getTrace(const MachineBasicBlock *MBB) {
+  // FIXME: Check cache tags, recompute as needed.
+  computeTrace(MBB);
+  return Trace(*this, BlockInfo[MBB->getNumber()]);
+}
+
+void MachineTraceMetrics::Trace::print(raw_ostream &OS) const {
+  OS << TE.getName() << " trace:";
+  if (TBI.hasValidHeight() && TBI.hasValidDepth())
+    OS << ' ' << getInstrCount() << " instrs.";
+
+  const MachineTraceMetrics::TraceBlockInfo *Block = &TBI;
+  OS << "\n *";
+  while (Block->hasValidDepth() && Block->Pred) {
+    unsigned Num = Block->Pred->getNumber();
+    OS << " <- BB#" << Num;
+    Block = &TE.BlockInfo[Num];
+  }
+
+  Block = &TBI;
+  OS << "\n *";
+  while (Block->hasValidHeight() && Block->Succ) {
+    unsigned Num = Block->Succ->getNumber();
+    OS << " -> BB#" << Num;
+    Block = &TE.BlockInfo[Num];
+  }
+  OS << '\n';
+}