Fix a quadratic algorithm in MachineBranchProbabilityInfo.

The getSumForBlock function was quadratic in the number of successors
because getSuccWeight would perform a linear search for an already known
iterator.

This patch was originally committed as r161460, but reverted again
because of assertion failures. Now that duplicate Machine CFG edges have
been eliminated, this works properly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162233 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 16 insertions, 9 deletions

diff --git a/lib/CodeGen/MachineBasicBlock.cpp b/lib/CodeGen/MachineBasicBlock.cpp
index fa6b450..cf13dbd 100644
--- a/lib/CodeGen/MachineBasicBlock.cpp
+++ b/lib/CodeGen/MachineBasicBlock.cpp
@@ -942,12 +942,11 @@ MachineBasicBlock::findDebugLoc(instr_iterator MBBI) {
 
 /// getSuccWeight - Return weight of the edge from this block to MBB.
 ///
-uint32_t MachineBasicBlock::getSuccWeight(const MachineBasicBlock *succ) const {
+uint32_t MachineBasicBlock::getSuccWeight(const_succ_iterator Succ) const {
   if (Weights.empty())
     return 0;
 
-  const_succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
-  return *getWeightIterator(I);
+  return *getWeightIterator(Succ);
 }
 
 /// getWeightIterator - Return wight iterator corresonding to the I successor
diff --git a/lib/CodeGen/MachineBranchProbabilityInfo.cpp b/lib/CodeGen/MachineBranchProbabilityInfo.cpp
index 0cc1af0..4479211 100644
--- a/lib/CodeGen/MachineBranchProbabilityInfo.cpp
+++ b/lib/CodeGen/MachineBranchProbabilityInfo.cpp
@@ -38,7 +38,7 @@ getSumForBlock(const MachineBasicBlock *MBB, uint32_t &Scale) const {
   Scale = 1;
   for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
        E = MBB->succ_end(); I != E; ++I) {
-    uint32_t Weight = getEdgeWeight(MBB, *I);
+    uint32_t Weight = getEdgeWeight(MBB, I);
     Sum += Weight;
   }
 
@@ -53,22 +53,30 @@ getSumForBlock(const MachineBasicBlock *MBB, uint32_t &Scale) const {
   Sum = 0;
   for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
        E = MBB->succ_end(); I != E; ++I) {
-    uint32_t Weight = getEdgeWeight(MBB, *I);
+    uint32_t Weight = getEdgeWeight(MBB, I);
     Sum += Weight / Scale;
   }
   assert(Sum <= UINT32_MAX);
   return Sum;
 }
 
-uint32_t
-MachineBranchProbabilityInfo::getEdgeWeight(const MachineBasicBlock *Src,
-                                            const 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;
 }
 
+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(MachineBasicBlock *Src,
                                              MachineBasicBlock *Dst) const {
   // Hot probability is at least 4/5 = 80%
@@ -82,7 +90,7 @@ MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
   MachineBasicBlock *MaxSucc = 0;
   for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
        E = MBB->succ_end(); I != E; ++I) {
-    uint32_t Weight = getEdgeWeight(MBB, *I);
+    uint32_t Weight = getEdgeWeight(MBB, I);
     if (Weight > MaxWeight) {
       MaxWeight = Weight;
       MaxSucc = *I;