Update LLVM to r90226.

1 files changed, 249 insertions, 0 deletions

diff --git a/lib/CodeGen/TailDuplication.cpp b/lib/CodeGen/TailDuplication.cpp
new file mode 100644
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+++ b/lib/CodeGen/TailDuplication.cpp
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+//===-- TailDuplication.cpp - Duplicate blocks into predecessors' tails ---===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass duplicates basic blocks ending in unconditional branches into
+// the tails of their predecessors.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "tailduplication"
+#include "llvm/Function.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/Statistic.h"
+using namespace llvm;
+
+STATISTIC(NumTailDups  , "Number of tail duplicated blocks");
+STATISTIC(NumInstrDups , "Additional instructions due to tail duplication");
+STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
+
+// Heuristic for tail duplication.
+static cl::opt<unsigned>
+TailDuplicateSize("tail-dup-size",
+                  cl::desc("Maximum instructions to consider tail duplicating"),
+                  cl::init(2), cl::Hidden);
+
+namespace {
+  /// TailDuplicatePass - Perform tail duplication.
+  class TailDuplicatePass : public MachineFunctionPass {
+    const TargetInstrInfo *TII;
+    MachineModuleInfo *MMI;
+
+  public:
+    static char ID;
+    explicit TailDuplicatePass() : MachineFunctionPass(&ID) {}
+
+    virtual bool runOnMachineFunction(MachineFunction &MF);
+    virtual const char *getPassName() const { return "Tail Duplication"; }
+
+  private:
+    bool TailDuplicateBlocks(MachineFunction &MF);
+    bool TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF);
+    void RemoveDeadBlock(MachineBasicBlock *MBB);
+  };
+
+  char TailDuplicatePass::ID = 0;
+}
+
+FunctionPass *llvm::createTailDuplicatePass() {
+  return new TailDuplicatePass();
+}
+
+bool TailDuplicatePass::runOnMachineFunction(MachineFunction &MF) {
+  TII = MF.getTarget().getInstrInfo();
+  MMI = getAnalysisIfAvailable<MachineModuleInfo>();
+
+  bool MadeChange = false;
+  bool MadeChangeThisIteration = true;
+  while (MadeChangeThisIteration) {
+    MadeChangeThisIteration = false;
+    MadeChangeThisIteration |= TailDuplicateBlocks(MF);
+    MadeChange |= MadeChangeThisIteration;
+  }
+
+  return MadeChange;
+}
+
+/// TailDuplicateBlocks - Look for small blocks that are unconditionally
+/// branched to and do not fall through. Tail-duplicate their instructions
+/// into their predecessors to eliminate (dynamic) branches.
+bool TailDuplicatePass::TailDuplicateBlocks(MachineFunction &MF) {
+  bool MadeChange = false;
+
+  for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) {
+    MachineBasicBlock *MBB = I++;
+
+    // Only duplicate blocks that end with unconditional branches.
+    if (MBB->canFallThrough())
+      continue;
+
+    MadeChange |= TailDuplicate(MBB, MF);
+
+    // If it is dead, remove it.
+    if (MBB->pred_empty()) {
+      NumInstrDups -= MBB->size();
+      RemoveDeadBlock(MBB);
+      MadeChange = true;
+      ++NumDeadBlocks;
+    }
+  }
+  return MadeChange;
+}
+
+/// TailDuplicate - If it is profitable, duplicate TailBB's contents in each
+/// of its predecessors.
+bool TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB,
+                                        MachineFunction &MF) {
+  // Don't try to tail-duplicate single-block loops.
+  if (TailBB->isSuccessor(TailBB))
+    return false;
+
+  // Set the limit on the number of instructions to duplicate, with a default
+  // of one less than the tail-merge threshold. When optimizing for size,
+  // duplicate only one, because one branch instruction can be eliminated to
+  // compensate for the duplication.
+  unsigned MaxDuplicateCount;
+  if (!TailBB->empty() && TailBB->back().getDesc().isIndirectBranch())
+    // If the target has hardware branch prediction that can handle indirect
+    // branches, duplicating them can often make them predictable when there
+    // are common paths through the code.  The limit needs to be high enough
+    // to allow undoing the effects of tail merging.
+    MaxDuplicateCount = 20;
+  else if (MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize))
+    MaxDuplicateCount = 1;
+  else
+    MaxDuplicateCount = TailDuplicateSize;
+
+  // Check the instructions in the block to determine whether tail-duplication
+  // is invalid or unlikely to be profitable.
+  unsigned i = 0;
+  bool HasCall = false;
+  for (MachineBasicBlock::iterator I = TailBB->begin();
+       I != TailBB->end(); ++I, ++i) {
+    // Non-duplicable things shouldn't be tail-duplicated.
+    if (I->getDesc().isNotDuplicable()) return false;
+    // Don't duplicate more than the threshold.
+    if (i == MaxDuplicateCount) return false;
+    // Remember if we saw a call.
+    if (I->getDesc().isCall()) HasCall = true;
+  }
+  // Heuristically, don't tail-duplicate calls if it would expand code size,
+  // as it's less likely to be worth the extra cost.
+  if (i > 1 && HasCall)
+    return false;
+
+  // Iterate through all the unique predecessors and tail-duplicate this
+  // block into them, if possible. Copying the list ahead of time also
+  // avoids trouble with the predecessor list reallocating.
+  bool Changed = false;
+  SmallSetVector<MachineBasicBlock *, 8> Preds(TailBB->pred_begin(),
+                                               TailBB->pred_end());
+  for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
+       PE = Preds.end(); PI != PE; ++PI) {
+    MachineBasicBlock *PredBB = *PI;
+
+    assert(TailBB != PredBB &&
+           "Single-block loop should have been rejected earlier!");
+    if (PredBB->succ_size() > 1) continue;
+
+    MachineBasicBlock *PredTBB, *PredFBB;
+    SmallVector<MachineOperand, 4> PredCond;
+    if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
+      continue;
+    if (!PredCond.empty())
+      continue;
+    // EH edges are ignored by AnalyzeBranch.
+    if (PredBB->succ_size() != 1)
+      continue;
+    // Don't duplicate into a fall-through predecessor (at least for now).
+    if (PredBB->isLayoutSuccessor(TailBB) && PredBB->canFallThrough())
+      continue;
+
+    DEBUG(errs() << "\nTail-duplicating into PredBB: " << *PredBB
+                 << "From Succ: " << *TailBB);
+
+    // Remove PredBB's unconditional branch.
+    TII->RemoveBranch(*PredBB);
+    // Clone the contents of TailBB into PredBB.
+    for (MachineBasicBlock::iterator I = TailBB->begin(), E = TailBB->end();
+         I != E; ++I) {
+      MachineInstr *NewMI = MF.CloneMachineInstr(I);
+      PredBB->insert(PredBB->end(), NewMI);
+    }
+    NumInstrDups += TailBB->size() - 1; // subtract one for removed branch
+
+    // Update the CFG.
+    PredBB->removeSuccessor(PredBB->succ_begin());
+    assert(PredBB->succ_empty() &&
+           "TailDuplicate called on block with multiple successors!");
+    for (MachineBasicBlock::succ_iterator I = TailBB->succ_begin(),
+         E = TailBB->succ_end(); I != E; ++I)
+       PredBB->addSuccessor(*I);
+
+    Changed = true;
+    ++NumTailDups;
+  }
+
+  // If TailBB was duplicated into all its predecessors except for the prior
+  // block, which falls through unconditionally, move the contents of this
+  // block into the prior block.
+  MachineBasicBlock &PrevBB = *prior(MachineFunction::iterator(TailBB));
+  MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
+  SmallVector<MachineOperand, 4> PriorCond;
+  bool PriorUnAnalyzable =
+    TII->AnalyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, true);
+  // This has to check PrevBB->succ_size() because EH edges are ignored by
+  // AnalyzeBranch.
+  if (!PriorUnAnalyzable && PriorCond.empty() && !PriorTBB &&
+      TailBB->pred_size() == 1 && PrevBB.succ_size() == 1 &&
+      !TailBB->hasAddressTaken()) {
+    DEBUG(errs() << "\nMerging into block: " << PrevBB
+          << "From MBB: " << *TailBB);
+    PrevBB.splice(PrevBB.end(), TailBB, TailBB->begin(), TailBB->end());
+    PrevBB.removeSuccessor(PrevBB.succ_begin());;
+    assert(PrevBB.succ_empty());
+    PrevBB.transferSuccessors(TailBB);
+    Changed = true;
+  }
+
+  return Changed;
+}
+
+/// RemoveDeadBlock - Remove the specified dead machine basic block from the
+/// function, updating the CFG.
+void TailDuplicatePass::RemoveDeadBlock(MachineBasicBlock *MBB) {
+  assert(MBB->pred_empty() && "MBB must be dead!");
+  DEBUG(errs() << "\nRemoving MBB: " << *MBB);
+
+  // Remove all successors.
+  while (!MBB->succ_empty())
+    MBB->removeSuccessor(MBB->succ_end()-1);
+
+  // If there are any labels in the basic block, unregister them from
+  // MachineModuleInfo.
+  if (MMI && !MBB->empty()) {
+    for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
+         I != E; ++I) {
+      if (I->isLabel())
+        // The label ID # is always operand #0, an immediate.
+        MMI->InvalidateLabel(I->getOperand(0).getImm());
+    }
+  }
+
+  // Remove the block.
+  MBB->eraseFromParent();
+}
+