X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FMachineBranchProbabilityInfo.cpp;h=6fbc2be70486ad3ff2059ebae14fa9aa1edd56f2;hb=33966cf988cb9db5c8f839bf8b8509f12db4a529;hp=987403796f44e8696943be43f994062f17b51e95;hpb=91bbe237167bf84ce41d01eff3c028ff2b10be26;p=oota-llvm.git

diff --git a/lib/CodeGen/MachineBranchProbabilityInfo.cpp b/lib/CodeGen/MachineBranchProbabilityInfo.cpp
index 987403796f4..6fbc2be7048 100644
--- a/lib/CodeGen/MachineBranchProbabilityInfo.cpp
+++ b/lib/CodeGen/MachineBranchProbabilityInfo.cpp
@@ -11,9 +11,9 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/Instructions.h"
 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/IR/Instructions.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -26,34 +26,60 @@ INITIALIZE_PASS_END(MachineBranchProbabilityInfo, "machine-branch-prob",
 
 char MachineBranchProbabilityInfo::ID = 0;
 
-uint32_t MachineBranchProbabilityInfo::
-getSumForBlock(MachineBasicBlock *MBB) const {
-  uint32_t Sum = 0;
+void MachineBranchProbabilityInfo::anchor() { }
 
+uint32_t MachineBranchProbabilityInfo::
+getSumForBlock(const MachineBasicBlock *MBB, uint32_t &Scale) const {
+  // First we compute the sum with 64-bits of precision, ensuring that cannot
+  // overflow by bounding the number of weights considered. Hopefully no one
+  // actually needs 2^32 successors.
+  assert(MBB->succ_size() < UINT32_MAX);
+  uint64_t Sum = 0;
+  Scale = 1;
   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;
-
+    uint32_t Weight = getEdgeWeight(MBB, I);
     Sum += Weight;
-    assert(Sum > PrevSum); (void) PrevSum;
   }
 
+  // If the computed sum fits in 32-bits, we're done.
+  if (Sum <= UINT32_MAX)
+    return Sum;
+
+  // Otherwise, compute the scale necessary to cause the weights to fit, and
+  // re-sum with that scale applied.
+  assert((Sum / UINT32_MAX) < UINT32_MAX);
+  Scale = (Sum / UINT32_MAX) + 1;
+  Sum = 0;
+  for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
+       E = MBB->succ_end(); I != E; ++I) {
+    uint32_t Weight = getEdgeWeight(MBB, I);
+    Sum += Weight / Scale;
+  }
+  assert(Sum <= UINT32_MAX);
   return Sum;
 }
 
-uint32_t
-MachineBranchProbabilityInfo::getEdgeWeight(MachineBasicBlock *Src,
-                                            MachineBasicBlock *Dst) const {
+uint32_t MachineBranchProbabilityInfo::
+getEdgeWeight(const MachineBasicBlock *Src,
+              MachineBasicBlock::const_succ_iterator Dst) const {
   uint32_t Weight = Src->getSuccWeight(Dst);
   if (!Weight)
     return DEFAULT_WEIGHT;
   return Weight;
 }
 
-bool MachineBranchProbabilityInfo::isEdgeHot(MachineBasicBlock *Src,
-                                             MachineBasicBlock *Dst) const {
+uint32_t MachineBranchProbabilityInfo::
+getEdgeWeight(const MachineBasicBlock *Src,
+              const MachineBasicBlock *Dst) const {
+  // This is a linear search. Try to use the const_succ_iterator version when
+  // possible.
+  return getEdgeWeight(Src, std::find(Src->succ_begin(), Src->succ_end(), Dst));
+}
+
+bool
+MachineBranchProbabilityInfo::isEdgeHot(const MachineBasicBlock *Src,
+                                        const MachineBasicBlock *Dst) const {
   // Hot probability is at least 4/5 = 80%
   // FIXME: Compare against a static "hot" BranchProbability.
   return getEdgeProbability(Src, Dst) > BranchProbability(4, 5);
@@ -61,47 +87,39 @@ bool MachineBranchProbabilityInfo::isEdgeHot(MachineBasicBlock *Src,
 
 MachineBasicBlock *
 MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
-  uint32_t Sum = 0;
   uint32_t MaxWeight = 0;
-  MachineBasicBlock *MaxSucc = 0;
-
+  MachineBasicBlock *MaxSucc = nullptr;
   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;
-
+    uint32_t Weight = getEdgeWeight(MBB, I);
     if (Weight > MaxWeight) {
       MaxWeight = Weight;
-      MaxSucc = Succ;
+      MaxSucc = *I;
     }
   }
 
-  if (BranchProbability(MaxWeight, Sum) >= BranchProbability(4, 5))
+  if (getEdgeProbability(MBB, MaxSucc) >= BranchProbability(4, 5))
     return MaxSucc;
 
-  return 0;
+  return nullptr;
 }
 
-BranchProbability
-MachineBranchProbabilityInfo::getEdgeProbability(MachineBasicBlock *Src,
-                                                 MachineBasicBlock *Dst) const {
-  uint32_t N = getEdgeWeight(Src, Dst);
-  uint32_t D = getSumForBlock(Src);
+BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
+    const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
+  uint32_t Scale = 1;
+  uint32_t D = getSumForBlock(Src, Scale);
+  uint32_t N = getEdgeWeight(Src, Dst) / Scale;
 
   return BranchProbability(N, D);
 }
 
-raw_ostream &MachineBranchProbabilityInfo::
-printEdgeProbability(raw_ostream &OS, MachineBasicBlock *Src,
-                     MachineBasicBlock *Dst) const {
+raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability(
+    raw_ostream &OS, const MachineBasicBlock *Src,
+    const MachineBasicBlock *Dst) const {
 
   const BranchProbability Prob = getEdgeProbability(Src, Dst);
   OS << "edge MBB#" << Src->getNumber() << " -> MBB#" << Dst->getNumber()
-     << " probability is "  << Prob 
+     << " probability is " << Prob
      << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
 
   return OS;