[llvm] r369395 - [CodeGen] Add a pass to do block predication on SSA machine IR.

Roman Lebedev via llvm-commits llvm-commits at lists.llvm.org
Tue Aug 20 08:54:24 PDT 2019


Where did the tests go?

On Tue, Aug 20, 2019 at 6:53 PM Thomas Raoux via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
>
> Author: thomasraoux
> Date: Tue Aug 20 08:54:59 2019
> New Revision: 369395
>
> URL: http://llvm.org/viewvc/llvm-project?rev=369395&view=rev
> Log:
>     [CodeGen] Add a pass to do block predication on SSA machine IR.
>
>     For targets requiring aggressive scheduling and/or software pipeline we need to
>     apply predication before preRA scheduling. This adds a pass re-using the early
>     if-cvt infrastructure but generating predicated instructions instead of
>     speculatively executing instructions. It allows doing if conversion on blocks
>     containing instructions with side-effects. The pass re-use the target hook from
>     postRA if-conversion to let the target decide on the heuristic to apply.
>
>     Differential Revision: https://reviews.llvm.org/D66190
>
> Modified:
>     llvm/trunk/include/llvm/CodeGen/Passes.h
>     llvm/trunk/include/llvm/InitializePasses.h
>     llvm/trunk/lib/CodeGen/CodeGen.cpp
>     llvm/trunk/lib/CodeGen/EarlyIfConversion.cpp
>
> Modified: llvm/trunk/include/llvm/CodeGen/Passes.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/Passes.h?rev=369395&r1=369394&r2=369395&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/CodeGen/Passes.h (original)
> +++ llvm/trunk/include/llvm/CodeGen/Passes.h Tue Aug 20 08:54:59 2019
> @@ -226,6 +226,10 @@ namespace llvm {
>    /// inserting cmov instructions.
>    extern char &EarlyIfConverterID;
>
> +  /// EarlyIfPredicator - This pass performs if-conversion on SSA form by
> +  /// predicating if/else block and insert select at the join point.
> +  extern char &EarlyIfPredicatorID;
> +
>    /// This pass performs instruction combining using trace metrics to estimate
>    /// critical-path and resource depth.
>    extern char &MachineCombinerID;
>
> Modified: llvm/trunk/include/llvm/InitializePasses.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/InitializePasses.h?rev=369395&r1=369394&r2=369395&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/InitializePasses.h (original)
> +++ llvm/trunk/include/llvm/InitializePasses.h Tue Aug 20 08:54:59 2019
> @@ -132,6 +132,7 @@ void initializeDwarfEHPreparePass(PassRe
>  void initializeEarlyCSELegacyPassPass(PassRegistry&);
>  void initializeEarlyCSEMemSSALegacyPassPass(PassRegistry&);
>  void initializeEarlyIfConverterPass(PassRegistry&);
> +void initializeEarlyIfPredicatorPass(PassRegistry &);
>  void initializeEarlyMachineLICMPass(PassRegistry&);
>  void initializeEarlyTailDuplicatePass(PassRegistry&);
>  void initializeEdgeBundlesPass(PassRegistry&);
>
> Modified: llvm/trunk/lib/CodeGen/CodeGen.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/CodeGen.cpp?rev=369395&r1=369394&r2=369395&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/CodeGen.cpp (original)
> +++ llvm/trunk/lib/CodeGen/CodeGen.cpp Tue Aug 20 08:54:59 2019
> @@ -28,6 +28,7 @@ void llvm::initializeCodeGen(PassRegistr
>    initializeDetectDeadLanesPass(Registry);
>    initializeDwarfEHPreparePass(Registry);
>    initializeEarlyIfConverterPass(Registry);
> +  initializeEarlyIfPredicatorPass(Registry);
>    initializeEarlyMachineLICMPass(Registry);
>    initializeEarlyTailDuplicatePass(Registry);
>    initializeExpandMemCmpPassPass(Registry);
>
> Modified: llvm/trunk/lib/CodeGen/EarlyIfConversion.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/EarlyIfConversion.cpp?rev=369395&r1=369394&r2=369395&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/EarlyIfConversion.cpp (original)
> +++ llvm/trunk/lib/CodeGen/EarlyIfConversion.cpp Tue Aug 20 08:54:59 2019
> @@ -25,6 +25,7 @@
>  #include "llvm/CodeGen/MachineDominators.h"
>  #include "llvm/CodeGen/MachineFunction.h"
>  #include "llvm/CodeGen/MachineFunctionPass.h"
> +#include "llvm/CodeGen/MachineInstr.h"
>  #include "llvm/CodeGen/MachineLoopInfo.h"
>  #include "llvm/CodeGen/MachineRegisterInfo.h"
>  #include "llvm/CodeGen/MachineTraceMetrics.h"
> @@ -140,6 +141,18 @@ private:
>    /// speculated.
>    bool canSpeculateInstrs(MachineBasicBlock *MBB);
>
> +  /// Return true if all non-terminator instructions in MBB can be safely
> +  /// predicated.
> +  bool canPredicateInstrs(MachineBasicBlock *MBB);
> +
> +  /// Scan through instruction dependencies and update InsertAfter array.
> +  /// Return false if any dependency is incompatible with if conversion.
> +  bool InstrDependenciesAllowIfConv(MachineInstr *I);
> +
> +  /// Predicate all instructions of the basic block with current condition
> +  /// except for terminators. Reverse the condition if ReversePredicate is set.
> +  void PredicateBlock(MachineBasicBlock *MBB, bool ReversePredicate);
> +
>    /// Find a valid insertion point in Head.
>    bool findInsertionPoint();
>
> @@ -163,11 +176,14 @@ public:
>
>    /// canConvertIf - If the sub-CFG headed by MBB can be if-converted,
>    /// initialize the internal state, and return true.
> -  bool canConvertIf(MachineBasicBlock *MBB);
> +  /// If predicate is set try to predicate the block otherwise try to
> +  /// speculatively execute it.
> +  bool canConvertIf(MachineBasicBlock *MBB, bool Predicate = false);
>
>    /// convertIf - If-convert the last block passed to canConvertIf(), assuming
>    /// it is possible. Add any erased blocks to RemovedBlocks.
> -  void convertIf(SmallVectorImpl<MachineBasicBlock*> &RemovedBlocks);
> +  void convertIf(SmallVectorImpl<MachineBasicBlock *> &RemovedBlocks,
> +                 bool Predicate = false);
>  };
>  } // end anonymous namespace
>
> @@ -225,37 +241,112 @@ bool SSAIfConv::canSpeculateInstrs(Machi
>      }
>
>      // Check for any dependencies on Head instructions.
> -    for (const MachineOperand &MO : I->operands()) {
> -      if (MO.isRegMask()) {
> -        LLVM_DEBUG(dbgs() << "Won't speculate regmask: " << *I);
> -        return false;
> -      }
> -      if (!MO.isReg())
> -        continue;
> -      Register Reg = MO.getReg();
> +    if (!InstrDependenciesAllowIfConv(&(*I)))
> +      return false;
> +  }
> +  return true;
> +}
>
> -      // Remember clobbered regunits.
> -      if (MO.isDef() && Register::isPhysicalRegister(Reg))
> -        for (MCRegUnitIterator Units(Reg, TRI); Units.isValid(); ++Units)
> -          ClobberedRegUnits.set(*Units);
> +/// Check that there is no dependencies preventing if conversion.
> +///
> +/// If instruction uses any values that are defined in the head basic block,
> +/// the defining instructions are added to InsertAfter.
> +bool SSAIfConv::InstrDependenciesAllowIfConv(MachineInstr *I) {
> +  for (const MachineOperand &MO : I->operands()) {
> +    if (MO.isRegMask()) {
> +      LLVM_DEBUG(dbgs() << "Won't speculate regmask: " << *I);
> +      return false;
> +    }
> +    if (!MO.isReg())
> +      continue;
> +    Register Reg = MO.getReg();
>
> -      if (!MO.readsReg() || !Register::isVirtualRegister(Reg))
> -        continue;
> -      MachineInstr *DefMI = MRI->getVRegDef(Reg);
> -      if (!DefMI || DefMI->getParent() != Head)
> -        continue;
> -      if (InsertAfter.insert(DefMI).second)
> -        LLVM_DEBUG(dbgs() << printMBBReference(*MBB) << " depends on "
> -                          << *DefMI);
> -      if (DefMI->isTerminator()) {
> -        LLVM_DEBUG(dbgs() << "Can't insert instructions below terminator.\n");
> -        return false;
> -      }
> +    // Remember clobbered regunits.
> +    if (MO.isDef() && Register::isPhysicalRegister(Reg))
> +      for (MCRegUnitIterator Units(Reg, TRI); Units.isValid(); ++Units)
> +        ClobberedRegUnits.set(*Units);
> +
> +    if (!MO.readsReg() || !Register::isVirtualRegister(Reg))
> +      continue;
> +    MachineInstr *DefMI = MRI->getVRegDef(Reg);
> +    if (!DefMI || DefMI->getParent() != Head)
> +      continue;
> +    if (InsertAfter.insert(DefMI).second)
> +      LLVM_DEBUG(dbgs() << printMBBReference(*I->getParent()) << " depends on "
> +                        << *DefMI);
> +    if (DefMI->isTerminator()) {
> +      LLVM_DEBUG(dbgs() << "Can't insert instructions below terminator.\n");
> +      return false;
> +    }
> +  }
> +  return true;
> +}
> +
> +/// canPredicateInstrs - Returns true if all the instructions in MBB can safely
> +/// be predicates. The terminators are not considered.
> +///
> +/// If instructions use any values that are defined in the head basic block,
> +/// the defining instructions are added to InsertAfter.
> +///
> +/// Any clobbered regunits are added to ClobberedRegUnits.
> +///
> +bool SSAIfConv::canPredicateInstrs(MachineBasicBlock *MBB) {
> +  // Reject any live-in physregs. It's probably CPSR/EFLAGS, and very hard to
> +  // get right.
> +  if (!MBB->livein_empty()) {
> +    LLVM_DEBUG(dbgs() << printMBBReference(*MBB) << " has live-ins.\n");
> +    return false;
> +  }
> +
> +  unsigned InstrCount = 0;
> +
> +  // Check all instructions, except the terminators. It is assumed that
> +  // terminators never have side effects or define any used register values.
> +  for (MachineBasicBlock::iterator I = MBB->begin(),
> +                                   E = MBB->getFirstTerminator();
> +       I != E; ++I) {
> +    if (I->isDebugInstr())
> +      continue;
> +
> +    if (++InstrCount > BlockInstrLimit && !Stress) {
> +      LLVM_DEBUG(dbgs() << printMBBReference(*MBB) << " has more than "
> +                        << BlockInstrLimit << " instructions.\n");
> +      return false;
>      }
> +
> +    // There shouldn't normally be any phis in a single-predecessor block.
> +    if (I->isPHI()) {
> +      LLVM_DEBUG(dbgs() << "Can't predicate: " << *I);
> +      return false;
> +    }
> +
> +    // Check that instruction is predicable and that it is not already
> +    // predicated.
> +    if (!TII->isPredicable(*I) || TII->isPredicated(*I)) {
> +      return false;
> +    }
> +
> +    // Check for any dependencies on Head instructions.
> +    if (!InstrDependenciesAllowIfConv(&(*I)))
> +      return false;
>    }
>    return true;
>  }
>
> +// Apply predicate to all instructions in the machine block.
> +void SSAIfConv::PredicateBlock(MachineBasicBlock *MBB, bool ReversePredicate) {
> +  auto Condition = Cond;
> +  if (ReversePredicate)
> +    TII->reverseBranchCondition(Condition);
> +  // Terminators don't need to be predicated as they will be removed.
> +  for (MachineBasicBlock::iterator I = MBB->begin(),
> +                                   E = MBB->getFirstTerminator();
> +       I != E; ++I) {
> +    if (I->isDebugInstr())
> +      continue;
> +    TII->PredicateInstruction(*I, Condition);
> +  }
> +}
>
>  /// Find an insertion point in Head for the speculated instructions. The
>  /// insertion point must be:
> @@ -337,7 +428,7 @@ bool SSAIfConv::findInsertionPoint() {
>  /// canConvertIf - analyze the sub-cfg rooted in MBB, and return true if it is
>  /// a potential candidate for if-conversion. Fill out the internal state.
>  ///
> -bool SSAIfConv::canConvertIf(MachineBasicBlock *MBB) {
> +bool SSAIfConv::canConvertIf(MachineBasicBlock *MBB, bool Predicate) {
>    Head = MBB;
>    TBB = FBB = Tail = nullptr;
>
> @@ -378,8 +469,9 @@ bool SSAIfConv::canConvertIf(MachineBasi
>    }
>
>    // This is a triangle or a diamond.
> -  // If Tail doesn't have any phis, there must be side effects.
> -  if (Tail->empty() || !Tail->front().isPHI()) {
> +  // Skip if we cannot predicate and there are no phis skip as there must be
> +  // side effects that can only be handled with predication.
> +  if (!Predicate && (Tail->empty() || !Tail->front().isPHI())) {
>      LLVM_DEBUG(dbgs() << "No phis in tail.\n");
>      return false;
>    }
> @@ -437,10 +529,17 @@ bool SSAIfConv::canConvertIf(MachineBasi
>    // Check that the conditional instructions can be speculated.
>    InsertAfter.clear();
>    ClobberedRegUnits.reset();
> -  if (TBB != Tail && !canSpeculateInstrs(TBB))
> -    return false;
> -  if (FBB != Tail && !canSpeculateInstrs(FBB))
> -    return false;
> +  if (Predicate) {
> +    if (TBB != Tail && !canPredicateInstrs(TBB))
> +      return false;
> +    if (FBB != Tail && !canPredicateInstrs(FBB))
> +      return false;
> +  } else {
> +    if (TBB != Tail && !canSpeculateInstrs(TBB))
> +      return false;
> +    if (FBB != Tail && !canSpeculateInstrs(FBB))
> +      return false;
> +  }
>
>    // Try to find a valid insertion point for the speculated instructions in the
>    // head basic block.
> @@ -521,7 +620,8 @@ void SSAIfConv::rewritePHIOperands() {
>  ///
>  /// Any basic blocks erased will be added to RemovedBlocks.
>  ///
> -void SSAIfConv::convertIf(SmallVectorImpl<MachineBasicBlock*> &RemovedBlocks) {
> +void SSAIfConv::convertIf(SmallVectorImpl<MachineBasicBlock *> &RemovedBlocks,
> +                          bool Predicate) {
>    assert(Head && Tail && TBB && FBB && "Call canConvertIf first.");
>
>    // Update statistics.
> @@ -531,11 +631,16 @@ void SSAIfConv::convertIf(SmallVectorImp
>      ++NumDiamondsConv;
>
>    // Move all instructions into Head, except for the terminators.
> -  if (TBB != Tail)
> +  if (TBB != Tail) {
> +    if (Predicate)
> +      PredicateBlock(TBB, /*ReversePredicate=*/false);
>      Head->splice(InsertionPoint, TBB, TBB->begin(), TBB->getFirstTerminator());
> -  if (FBB != Tail)
> +  }
> +  if (FBB != Tail) {
> +    if (Predicate)
> +      PredicateBlock(FBB, /*ReversePredicate=*/true);
>      Head->splice(InsertionPoint, FBB, FBB->begin(), FBB->getFirstTerminator());
> -
> +  }
>    // Are there extra Tail predecessors?
>    bool ExtraPreds = Tail->pred_size() != 2;
>    if (ExtraPreds)
> @@ -587,7 +692,6 @@ void SSAIfConv::convertIf(SmallVectorImp
>    LLVM_DEBUG(dbgs() << *Head);
>  }
>
> -
>  //===----------------------------------------------------------------------===//
>  //                           EarlyIfConverter Pass
>  //===----------------------------------------------------------------------===//
> @@ -613,8 +717,6 @@ public:
>
>  private:
>    bool tryConvertIf(MachineBasicBlock*);
> -  void updateDomTree(ArrayRef<MachineBasicBlock*> Removed);
> -  void updateLoops(ArrayRef<MachineBasicBlock*> Removed);
>    void invalidateTraces();
>    bool shouldConvertIf();
>  };
> @@ -642,32 +744,36 @@ void EarlyIfConverter::getAnalysisUsage(
>    MachineFunctionPass::getAnalysisUsage(AU);
>  }
>
> +namespace {
>  /// Update the dominator tree after if-conversion erased some blocks.
> -void EarlyIfConverter::updateDomTree(ArrayRef<MachineBasicBlock*> Removed) {
> +void updateDomTree(MachineDominatorTree *DomTree, const SSAIfConv &IfConv,
> +                   ArrayRef<MachineBasicBlock *> Removed) {
>    // convertIf can remove TBB, FBB, and Tail can be merged into Head.
>    // TBB and FBB should not dominate any blocks.
>    // Tail children should be transferred to Head.
>    MachineDomTreeNode *HeadNode = DomTree->getNode(IfConv.Head);
> -  for (unsigned i = 0, e = Removed.size(); i != e; ++i) {
> -    MachineDomTreeNode *Node = DomTree->getNode(Removed[i]);
> +  for (auto B : Removed) {
> +    MachineDomTreeNode *Node = DomTree->getNode(B);
>      assert(Node != HeadNode && "Cannot erase the head node");
>      while (Node->getNumChildren()) {
>        assert(Node->getBlock() == IfConv.Tail && "Unexpected children");
>        DomTree->changeImmediateDominator(Node->getChildren().back(), HeadNode);
>      }
> -    DomTree->eraseNode(Removed[i]);
> +    DomTree->eraseNode(B);
>    }
>  }
>
>  /// Update LoopInfo after if-conversion.
> -void EarlyIfConverter::updateLoops(ArrayRef<MachineBasicBlock*> Removed) {
> +void updateLoops(MachineLoopInfo *Loops,
> +                 ArrayRef<MachineBasicBlock *> Removed) {
>    if (!Loops)
>      return;
>    // If-conversion doesn't change loop structure, and it doesn't mess with back
>    // edges, so updating LoopInfo is simply removing the dead blocks.
> -  for (unsigned i = 0, e = Removed.size(); i != e; ++i)
> -    Loops->removeBlock(Removed[i]);
> +  for (auto B : Removed)
> +    Loops->removeBlock(B);
>  }
> +} // namespace
>
>  /// Invalidate MachineTraceMetrics before if-conversion.
>  void EarlyIfConverter::invalidateTraces() {
> @@ -783,8 +889,8 @@ bool EarlyIfConverter::tryConvertIf(Mach
>      SmallVector<MachineBasicBlock*, 4> RemovedBlocks;
>      IfConv.convertIf(RemovedBlocks);
>      Changed = true;
> -    updateDomTree(RemovedBlocks);
> -    updateLoops(RemovedBlocks);
> +    updateDomTree(DomTree, IfConv, RemovedBlocks);
> +    updateLoops(Loops, RemovedBlocks);
>    }
>    return Changed;
>  }
> @@ -811,6 +917,135 @@ bool EarlyIfConverter::runOnMachineFunct
>
>    bool Changed = false;
>    IfConv.runOnMachineFunction(MF);
> +
> +  // Visit blocks in dominator tree post-order. The post-order enables nested
> +  // if-conversion in a single pass. The tryConvertIf() function may erase
> +  // blocks, but only blocks dominated by the head block. This makes it safe to
> +  // update the dominator tree while the post-order iterator is still active.
> +  for (auto DomNode : post_order(DomTree))
> +    if (tryConvertIf(DomNode->getBlock()))
> +      Changed = true;
> +
> +  return Changed;
> +}
> +
> +//===----------------------------------------------------------------------===//
> +//                           EarlyIfPredicator Pass
> +//===----------------------------------------------------------------------===//
> +
> +namespace {
> +class EarlyIfPredicator : public MachineFunctionPass {
> +  const TargetInstrInfo *TII;
> +  const TargetRegisterInfo *TRI;
> +  TargetSchedModel SchedModel;
> +  MachineRegisterInfo *MRI;
> +  MachineDominatorTree *DomTree;
> +  MachineLoopInfo *Loops;
> +  SSAIfConv IfConv;
> +
> +public:
> +  static char ID;
> +  EarlyIfPredicator() : MachineFunctionPass(ID) {}
> +  void getAnalysisUsage(AnalysisUsage &AU) const override;
> +  bool runOnMachineFunction(MachineFunction &MF) override;
> +  StringRef getPassName() const override { return "Early If-predicator"; }
> +
> +protected:
> +  bool tryConvertIf(MachineBasicBlock *);
> +  bool shouldConvertIf();
> +};
> +} // end anonymous namespace
> +
> +#undef DEBUG_TYPE
> +#define DEBUG_TYPE "early-if-predicator"
> +
> +char EarlyIfPredicator::ID = 0;
> +char &llvm::EarlyIfPredicatorID = EarlyIfPredicator::ID;
> +
> +INITIALIZE_PASS_BEGIN(EarlyIfPredicator, DEBUG_TYPE, "Early If Predicator",
> +                      false, false)
> +INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
> +INITIALIZE_PASS_END(EarlyIfPredicator, DEBUG_TYPE, "Early If Predicator", false,
> +                    false)
> +
> +void EarlyIfPredicator::getAnalysisUsage(AnalysisUsage &AU) const {
> +  AU.addRequired<MachineDominatorTree>();
> +  AU.addPreserved<MachineDominatorTree>();
> +  AU.addRequired<MachineLoopInfo>();
> +  AU.addPreserved<MachineLoopInfo>();
> +  MachineFunctionPass::getAnalysisUsage(AU);
> +}
> +
> +/// Apply the target heuristic to decide if the transformation is profitable.
> +bool EarlyIfPredicator::shouldConvertIf() {
> +  if (IfConv.isTriangle()) {
> +    MachineBasicBlock &IfBlock =
> +        (IfConv.TBB == IfConv.Tail) ? *IfConv.FBB : *IfConv.TBB;
> +
> +    unsigned ExtraPredCost = 0;
> +    unsigned Cycles = 0;
> +    for (MachineInstr &I : IfBlock) {
> +      unsigned NumCycles = SchedModel.computeInstrLatency(&I, false);
> +      if (NumCycles > 1)
> +        Cycles += NumCycles - 1;
> +      ExtraPredCost += TII->getPredicationCost(I);
> +    }
> +
> +    return TII->isProfitableToIfCvt(IfBlock, Cycles, ExtraPredCost,
> +                                    BranchProbability::getUnknown());
> +  }
> +  unsigned TExtra = 0;
> +  unsigned FExtra = 0;
> +  unsigned TCycle = 0;
> +  unsigned FCycle = 0;
> +  for (MachineInstr &I : *IfConv.TBB) {
> +    unsigned NumCycles = SchedModel.computeInstrLatency(&I, false);
> +    if (NumCycles > 1)
> +      TCycle += NumCycles - 1;
> +    TExtra += TII->getPredicationCost(I);
> +  }
> +  for (MachineInstr &I : *IfConv.FBB) {
> +    unsigned NumCycles = SchedModel.computeInstrLatency(&I, false);
> +    if (NumCycles > 1)
> +      FCycle += NumCycles - 1;
> +    FExtra += TII->getPredicationCost(I);
> +  }
> +  return TII->isProfitableToIfCvt(*IfConv.TBB, TCycle, TExtra, *IfConv.FBB,
> +                                  FCycle, FExtra,
> +                                  BranchProbability::getUnknown());
> +}
> +
> +/// Attempt repeated if-conversion on MBB, return true if successful.
> +///
> +bool EarlyIfPredicator::tryConvertIf(MachineBasicBlock *MBB) {
> +  bool Changed = false;
> +  while (IfConv.canConvertIf(MBB, /*Predicate*/ true) && shouldConvertIf()) {
> +    // If-convert MBB and update analyses.
> +    SmallVector<MachineBasicBlock *, 4> RemovedBlocks;
> +    IfConv.convertIf(RemovedBlocks, /*Predicate*/ true);
> +    Changed = true;
> +    updateDomTree(DomTree, IfConv, RemovedBlocks);
> +    updateLoops(Loops, RemovedBlocks);
> +  }
> +  return Changed;
> +}
> +
> +bool EarlyIfPredicator::runOnMachineFunction(MachineFunction &MF) {
> +  LLVM_DEBUG(dbgs() << "********** EARLY IF-PREDICATOR **********\n"
> +                    << "********** Function: " << MF.getName() << '\n');
> +  if (skipFunction(MF.getFunction()))
> +    return false;
> +
> +  const TargetSubtargetInfo &STI = MF.getSubtarget();
> +  TII = STI.getInstrInfo();
> +  TRI = STI.getRegisterInfo();
> +  MRI = &MF.getRegInfo();
> +  SchedModel.init(&STI);
> +  DomTree = &getAnalysis<MachineDominatorTree>();
> +  Loops = getAnalysisIfAvailable<MachineLoopInfo>();
> +
> +  bool Changed = false;
> +  IfConv.runOnMachineFunction(MF);
>
>    // Visit blocks in dominator tree post-order. The post-order enables nested
>    // if-conversion in a single pass. The tryConvertIf() function may erase
>
>
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