Reuse a technique (pioneered for BasicBlocks) of superposing ilist with

its sentinel. This is quite a win when a function really has a basic block.                  
When the function is just a declaration (and stays so) the old way did not
allocate a sentinel. So this change is most beneficial when the ratio of
function definition to declaration is high. I.e. linkers etc. Incidentally  
these are the most resource demanding applications, so I expect that the
reduced malloc traffic, locality and space savings outweigh the cost of
addition of two pointers to Function.

llvm-svn: 65776

2 files changed, 8 insertions, 10 deletions

diff --git a/llvm/include/llvm/Function.h b/llvm/include/llvm/Function.h
index ee53252b954..bdae9cd02f5 100644
--- a/llvm/include/llvm/Function.h
+++ b/llvm/include/llvm/Function.h
@@ -32,12 +32,17 @@ class FunctionType;
 template<> struct ilist_traits<BasicBlock>
   : public SymbolTableListTraits<BasicBlock, Function> {
 
-  // createSentinel is used to create a node that marks the end of the list...
-  static BasicBlock *createSentinel();
-  static void destroySentinel(BasicBlock *BB) { delete BB; }
+  // createSentinel is used to get hold of the node that marks the end of the
+  // list... (same trick used here as in ilist_traits<Instruction>)
+  BasicBlock *createSentinel() const {
+    return const_cast<BasicBlock*>(static_cast<const BasicBlock*>(&Sentinel));
+  }
+  static void destroySentinel(BasicBlock*) {}
   static iplist<BasicBlock> &getList(Function *F);
   static ValueSymbolTable *getSymTab(Function *ItemParent);
   static int getListOffset();
+private:
+  ilist_node<BasicBlock> Sentinel;
 };
 
 template<> struct ilist_traits<Argument>
diff --git a/llvm/lib/VMCore/Function.cpp b/llvm/lib/VMCore/Function.cpp
index cff4457a418..fefe082cb4e 100644
--- a/llvm/lib/VMCore/Function.cpp
+++ b/llvm/lib/VMCore/Function.cpp
@@ -22,13 +22,6 @@
 #include "llvm/ADT/StringExtras.h"
 using namespace llvm;
 
-BasicBlock *ilist_traits<BasicBlock>::createSentinel() {
-  BasicBlock *Ret = BasicBlock::Create();
-  // This should not be garbage monitored.
-  LeakDetector::removeGarbageObject(Ret);
-  return Ret;
-}
-
 iplist<BasicBlock> &ilist_traits<BasicBlock>::getList(Function *F) {
   return F->getBasicBlockList();
 }