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.

llvm-svn: 162233

1 files changed, 2 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
index fa6b4502c4a..cf13dbdab6b 100644
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/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