Introduce MachineBranchProbabilityInfo class, which has similar API to

BranchProbabilityInfo (expect setEdgeWeight which is not available here).
Branch Weights are kept in MachineBasicBlocks. To turn off this analysis
set -use-mbpi=false.

llvm-svn: 133184

Author: Jakub Staszak

Diff for: llvm/include/llvm/Analysis/BranchProbabilityInfo.h

@@ -25,6 +25,11 @@ class raw_ostream;
 class BranchProbabilityInfo : public FunctionPass {
 
   // Default weight value. Used when we don't have information about the edge.
+  // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
+  // the successors have a weight yet. But it doesn't make sense when providing
+  // weight to an edge that may have siblings with non-zero weights. This can
+  // be handled various ways, but it's probably fine for an edge with unknown
+  // weight to just "inherit" the non-zero weight of an adjacent successor.
   static const uint32_t DEFAULT_WEIGHT = 16;
 
   typedef std::pair<BasicBlock *, BasicBlock *> Edge;

Diff for: llvm/include/llvm/CodeGen/FunctionLoweringInfo.h

@@ -24,6 +24,7 @@
 #ifndef NDEBUG
 #include "llvm/ADT/SmallSet.h"
 #endif
+#include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/CodeGen/ValueTypes.h"
 #include "llvm/CodeGen/ISDOpcodes.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
@@ -57,7 +58,7 @@ class FunctionLoweringInfo {
   const Function *Fn;
   MachineFunction *MF;
   MachineRegisterInfo *RegInfo;
-
+  BranchProbabilityInfo *BPI;
   /// CanLowerReturn - true iff the function's return value can be lowered to
   /// registers.
   bool CanLowerReturn;

Diff for: llvm/include/llvm/CodeGen/MachineBasicBlock.h

@@ -16,6 +16,7 @@
 
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/ADT/GraphTraits.h"
+#include "llvm/Support/DataTypes.h"
 #include <functional>
 
 namespace llvm {
@@ -27,6 +28,7 @@ class MCSymbol;
 class SlotIndexes;
 class StringRef;
 class raw_ostream;
+class MachineBranchProbabilityInfo;
 
 template <>
 struct ilist_traits<MachineInstr> : public ilist_default_traits<MachineInstr> {
@@ -63,12 +65,19 @@ class MachineBasicBlock : public ilist_node<MachineBasicBlock> {
   const BasicBlock *BB;
   int Number;
   MachineFunction *xParent;
-  
+
   /// Predecessors/Successors - Keep track of the predecessor / successor
   /// basicblocks.
   std::vector<MachineBasicBlock *> Predecessors;
   std::vector<MachineBasicBlock *> Successors;
 
+
+  /// Weights - Keep track of the weights to the successors. This vector
+  /// has the same order as Successors, or it is empty if we don't use it
+  /// (disable optimization).
+  std::vector<uint32_t> Weights;
+  typedef std::vector<uint32_t>::iterator weight_iterator;
+
   /// LiveIns - Keep track of the physical registers that are livein of
   /// the basicblock.
   std::vector<unsigned> LiveIns;
@@ -244,11 +253,13 @@ class MachineBasicBlock : public ilist_node<MachineBasicBlock> {
   void updateTerminator();
 
   // Machine-CFG mutators
-  
+
   /// addSuccessor - Add succ as a successor of this MachineBasicBlock.
-  /// The Predecessors list of succ is automatically updated.
+  /// The Predecessors list of succ is automatically updated. WEIGHT
+  /// parameter is stored in Weights list and it may be used by
+  /// MachineBranchProbabilityInfo analysis to calculate branch probability.
   ///
-  void addSuccessor(MachineBasicBlock *succ);
+  void addSuccessor(MachineBasicBlock *succ, uint32_t weight = 0);
 
   /// removeSuccessor - Remove successor from the successors list of this
   /// MachineBasicBlock. The Predecessors list of succ is automatically updated.
@@ -260,7 +271,12 @@ class MachineBasicBlock : public ilist_node<MachineBasicBlock> {
   /// updated.  Return the iterator to the element after the one removed.
   ///
   succ_iterator removeSuccessor(succ_iterator I);
-  
+
+  /// replaceSuccessor - Replace successor OLD with NEW and update weight info.
+  ///
+  void replaceSuccessor(MachineBasicBlock *Old, MachineBasicBlock *New);
+
+
   /// transferSuccessors - Transfers all the successors from MBB to this
   /// machine basic block (i.e., copies all the successors fromMBB and
   /// remove all the successors from fromMBB).
@@ -396,8 +412,22 @@ class MachineBasicBlock : public ilist_node<MachineBasicBlock> {
   /// getSymbol - Return the MCSymbol for this basic block.
   ///
   MCSymbol *getSymbol() const;
-  
-private:   // Methods used to maintain doubly linked list of blocks...
+
+
+private:
+  /// getWeightIterator - Return weight iterator corresponding to the I
+  /// successor iterator.
+  weight_iterator getWeightIterator(succ_iterator I);
+
+  friend class MachineBranchProbabilityInfo;
+
+  /// getSuccWeight - Return weight of the edge from this block to MBB. This
+  /// method should NOT be called directly, but by using getEdgeWeight method
+  /// from MachineBranchProbabilityInfo class.
+  uint32_t getSuccWeight(MachineBasicBlock *succ);
+
+
+  // Methods used to maintain doubly linked list of blocks...
   friend struct ilist_traits<MachineBasicBlock>;
 
   // Machine-CFG mutators

Diff for: llvm/include/llvm/CodeGen/MachineBranchProbabilityInfo.h

@@ -0,0 +1,77 @@
+
+//==- MachineBranchProbabilityInfo.h - Machine Branch Probability Analysis -==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass is used to evaluate branch probabilties on machine basic blocks.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
+#define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
+
+#include "llvm/Pass.h"
+#include "llvm/Support/BranchProbability.h"
+#include <climits>
+
+namespace llvm {
+
+class raw_ostream;
+
+class MachineBranchProbabilityInfo : public ImmutablePass {
+
+  // Default weight value. Used when we don't have information about the edge.
+  // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
+  // the successors have a weight yet. But it doesn't make sense when providing
+  // weight to an edge that may have siblings with non-zero weights. This can
+  // be handled various ways, but it's probably fine for an edge with unknown
+  // weight to just "inherit" the non-zero weight of an adjacent successor.
+  static const uint32_t DEFAULT_WEIGHT = 16;
+
+  // Get sum of the block successors' weights.
+  uint32_t getSumForBlock(MachineBasicBlock *MBB) const;
+
+public:
+  static char ID;
+
+  MachineBranchProbabilityInfo() : ImmutablePass(ID) {
+    PassRegistry &Registry = *PassRegistry::getPassRegistry();
+    initializeMachineBranchProbabilityInfoPass(Registry);
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const {
+    AU.setPreservesAll();
+  }
+
+  // Return edge weight. If we don't have any informations about it - return
+  // DEFAULT_WEIGHT.
+  uint32_t getEdgeWeight(MachineBasicBlock *Src, MachineBasicBlock *Dst) const;
+
+  // A 'Hot' edge is an edge which probability is >= 80%.
+  bool isEdgeHot(MachineBasicBlock *Src, MachineBasicBlock *Dst) const;
+
+  // Return a hot successor for the block BB or null if there isn't one.
+  MachineBasicBlock *getHotSucc(MachineBasicBlock *MBB) const;
+
+  // Return a probability as a fraction between 0 (0% probability) and
+  // 1 (100% probability), however the value is never equal to 0, and can be 1
+  // only iff SRC block has only one successor.
+  BranchProbability getEdgeProbability(MachineBasicBlock *Src,
+                                       MachineBasicBlock *Dst) const;
+
+  // Print value between 0 (0% probability) and 1 (100% probability),
+  // however the value is never equal to 0, and can be 1 only iff SRC block
+  // has only one successor.
+  raw_ostream &printEdgeProbability(raw_ostream &OS, MachineBasicBlock *Src,
+                                    MachineBasicBlock *Dst) const;
+};
+
+}
+
+
+#endif

Diff for: llvm/include/llvm/InitializePasses.h

@@ -144,6 +144,7 @@ void initializeLowerIntrinsicsPass(PassRegistry&);
 void initializeLowerInvokePass(PassRegistry&);
 void initializeLowerSetJmpPass(PassRegistry&);
 void initializeLowerSwitchPass(PassRegistry&);
+void initializeMachineBranchProbabilityInfoPass(PassRegistry&);
 void initializeMachineCSEPass(PassRegistry&);
 void initializeMachineDominatorTreePass(PassRegistry&);
 void initializeMachineLICMPass(PassRegistry&);

Diff for: llvm/lib/Analysis/BranchProbabilityInfo.cpp

@@ -348,8 +348,8 @@ getEdgeProbability(BasicBlock *Src, BasicBlock *Dst) const {
 raw_ostream &
 BranchProbabilityInfo::printEdgeProbability(raw_ostream &OS, BasicBlock *Src,
                                             BasicBlock *Dst) const {
-  BranchProbability Prob = getEdgeProbability(Src, Dst);
 
+  const BranchProbability Prob = getEdgeProbability(Src, Dst);
   OS << "edge " << Src->getNameStr() << " -> " << Dst->getNameStr()
      << " probability is " << Prob
      << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");

Diff for: llvm/lib/CodeGen/CMakeLists.txt

@@ -33,6 +33,7 @@ add_llvm_library(LLVMCodeGen
   LocalStackSlotAllocation.cpp
   LowerSubregs.cpp
   MachineBasicBlock.cpp
+  MachineBranchProbabilityInfo.cpp
   MachineCSE.cpp
   MachineDominators.cpp
   MachineFunction.cpp

Diff for: llvm/lib/CodeGen/MachineBasicBlock.cpp

@@ -339,25 +339,64 @@ void MachineBasicBlock::updateTerminator() {
   }
 }
 
-void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) {
-  Successors.push_back(succ);
-  succ->addPredecessor(this);
-}
+void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ, uint32_t weight) {
+
+  // If we see non-zero value for the first time it means we actually use Weight
+  // list, so we fill all Weights with 0's.
+  if (weight != 0 && Weights.empty())
+    Weights.resize(Successors.size());
+
+  if (weight != 0 || !Weights.empty())
+    Weights.push_back(weight);
+
+   Successors.push_back(succ);
+   succ->addPredecessor(this);
+ }
 
 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
   succ->removePredecessor(this);
   succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
   assert(I != Successors.end() && "Not a current successor!");
+
+  // If Weight list is empty it means we don't use it (disabled optimization).
+  if (!Weights.empty()) {
+    weight_iterator WI = getWeightIterator(I);
+    Weights.erase(WI);
+  }
+
   Successors.erase(I);
 }
 
 MachineBasicBlock::succ_iterator
 MachineBasicBlock::removeSuccessor(succ_iterator I) {
   assert(I != Successors.end() && "Not a current successor!");
+
+  // If Weight list is empty it means we don't use it (disabled optimization).
+  if (!Weights.empty()) {
+    weight_iterator WI = getWeightIterator(I);
+    Weights.erase(WI);
+  }
+
   (*I)->removePredecessor(this);
   return Successors.erase(I);
 }
 
+void MachineBasicBlock::replaceSuccessor(MachineBasicBlock *Old,
+                                         MachineBasicBlock *New) {
+  uint32_t weight = 0;
+  succ_iterator SI = std::find(Successors.begin(), Successors.end(), Old);
+
+  // If Weight list is empty it means we don't use it (disabled optimization).
+  if (!Weights.empty()) {
+    weight_iterator WI = getWeightIterator(SI);
+    weight = *WI;
+  }
+
+  // Update the successor information.
+  removeSuccessor(SI);
+  addSuccessor(New, weight);
+}
+
 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
   Predecessors.push_back(pred);
 }
@@ -374,7 +413,14 @@ void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
 
   while (!fromMBB->succ_empty()) {
     MachineBasicBlock *Succ = *fromMBB->succ_begin();
-    addSuccessor(Succ);
+    uint32_t weight = 0;
+
+
+    // If Weight list is empty it means we don't use it (disabled optimization).
+    if (!fromMBB->Weights.empty())
+      weight = *fromMBB->Weights.begin();
+
+    addSuccessor(Succ, weight);
     fromMBB->removeSuccessor(Succ);
   }
 }
@@ -637,8 +683,7 @@ void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
   }
 
   // Update the successor information.
-  removeSuccessor(Old);
-  addSuccessor(New);
+  replaceSuccessor(Old, New);
 }
 
 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
@@ -720,6 +765,23 @@ MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
   return DL;
 }
 
+/// getSuccWeight - Return weight of the edge from this block to MBB.
+///
+uint32_t MachineBasicBlock::getSuccWeight(MachineBasicBlock *succ) {
+  succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
+  return *getWeightIterator(I);
+}
+
+/// getWeightIterator - Return wight iterator corresonding to the I successor
+/// iterator
+MachineBasicBlock::weight_iterator MachineBasicBlock::
+getWeightIterator(MachineBasicBlock::succ_iterator I) {
+  assert(Weights.size() == Successors.size() && "Async weight list!");
+  size_t index = std::distance(Successors.begin(), I);
+  assert(index < Weights.size() && "Not a current successor!");
+  return Weights.begin() + index;
+}
+
 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
                           bool t) {
   OS << "BB#" << MBB->getNumber();