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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133184 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 113 insertions, 0 deletions

diff --git a/lib/CodeGen/MachineBranchProbabilityInfo.cpp b/lib/CodeGen/MachineBranchProbabilityInfo.cpp
new file mode 100644
index 0000000000..c13fa6bc53
--- /dev/null
+++ b/lib/CodeGen/MachineBranchProbabilityInfo.cpp
@@ -0,0 +1,113 @@
+//===- MachineBranchProbabilityInfo.cpp - Machine Branch Probability Info -===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This analysis uses probability info stored in Machine Basic Blocks.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Instructions.h"
+#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+INITIALIZE_PASS_BEGIN(MachineBranchProbabilityInfo, "machine-branch-prob",
+                      "Machine Branch Probability Analysis", false, true)
+INITIALIZE_PASS_END(MachineBranchProbabilityInfo, "machine-branch-prob",
+                    "Machine Branch Probability Analysis", false, true)
+
+char MachineBranchProbabilityInfo::ID = 0;
+
+uint32_t MachineBranchProbabilityInfo::
+getSumForBlock(MachineBasicBlock *MBB) const {
+  uint32_t Sum = 0;
+
+  for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
+       E = MBB->succ_end(); I != E; ++I) {
+    MachineBasicBlock *Succ = *I;
+    uint32_t Weight = getEdgeWeight(MBB, Succ);
+    uint32_t PrevSum = Sum;
+
+    Sum += Weight;
+    assert(Sum > PrevSum); (void) PrevSum;
+  }
+
+  return Sum;
+}
+
+uint32_t
+MachineBranchProbabilityInfo::getEdgeWeight(MachineBasicBlock *Src,
+                                            MachineBasicBlock *Dst) const {
+  uint32_t Weight = Src->getSuccWeight(Dst);
+  if (!Weight)
+    return DEFAULT_WEIGHT;
+  return Weight;
+}
+
+bool MachineBranchProbabilityInfo::isEdgeHot(MachineBasicBlock *Src,
+                                             MachineBasicBlock *Dst) const {
+  // Hot probability is at least 4/5 = 80%
+  uint32_t Weight = getEdgeWeight(Src, Dst);
+  uint32_t Sum = getSumForBlock(Src);
+
+  // FIXME: Implement BranchProbability::compare then change this code to
+  // compare this BranchProbability against a static "hot" BranchProbability.
+  return (uint64_t)Weight * 5 > (uint64_t)Sum * 4;
+}
+
+MachineBasicBlock *
+MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
+  uint32_t Sum = 0;
+  uint32_t MaxWeight = 0;
+  MachineBasicBlock *MaxSucc = 0;
+
+  for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
+       E = MBB->succ_end(); I != E; ++I) {
+    MachineBasicBlock *Succ = *I;
+    uint32_t Weight = getEdgeWeight(MBB, Succ);
+    uint32_t PrevSum = Sum;
+
+    Sum += Weight;
+    assert(Sum > PrevSum); (void) PrevSum;
+
+    if (Weight > MaxWeight) {
+      MaxWeight = Weight;
+      MaxSucc = Succ;
+    }
+  }
+
+  // FIXME: Use BranchProbability::compare.
+  if ((uint64_t)MaxWeight * 5 >= (uint64_t)Sum * 4)
+    return MaxSucc;
+
+  return 0;
+}
+
+BranchProbability
+MachineBranchProbabilityInfo::getEdgeProbability(MachineBasicBlock *Src,
+                                                 MachineBasicBlock *Dst) const {
+  uint32_t N = getEdgeWeight(Src, Dst);
+  uint32_t D = getSumForBlock(Src);
+
+  return BranchProbability(N, D);
+}
+
+raw_ostream &MachineBranchProbabilityInfo::
+printEdgeProbability(raw_ostream &OS, MachineBasicBlock *Src,
+                     MachineBasicBlock *Dst) const {
+
+  const BranchProbability Prob = getEdgeProbability(Src, Dst);
+  OS << "edge MBB#" << Src->getNumber() << " -> MBB#" << Dst->getNumber()
+     << " probability is "  << Prob 
+     << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
+
+  return OS;
+}