Optimize MachineBasicBlock::getSymbol by caching the symbol. Since the symbol

name computation is expensive, this helps save about 25% of the time spent in
this function.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180049 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineBasicBlock.h

@@ -71,7 +71,6 @@ class MachineBasicBlock : public ilist_node<MachineBasicBlock> {
   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).
@@ -96,6 +95,10 @@ class MachineBasicBlock : public ilist_node<MachineBasicBlock> {
   /// target of an indirect branch.
   bool AddressTaken;
 
+  /// \brief since getSymbol is a relatively heavy-weight operation, the symbol
+  /// is only computed once and is cached.
+  mutable MCSymbol *CachedMCSymbol;
+
   // Intrusive list support
   MachineBasicBlock() {}