Represent sentinel slot indexes with a null pointer.

This is much faster than using a pointer to a ManagedStatic object accessed with
a function call. The greedy register allocator is 5% faster overall just from
the SlotIndex default constructor savings.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126925 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SlotIndexes.cpp

@@ -13,45 +13,14 @@
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
-#include "llvm/Support/ManagedStatic.h"
 #include "llvm/Target/TargetInstrInfo.h"
 
 using namespace llvm;
 
-
-// Yep - these are thread safe. See the header for details. 
-namespace {
-
-
-  class EmptyIndexListEntry : public IndexListEntry {
-  public:
-    EmptyIndexListEntry() : IndexListEntry(EMPTY_KEY) {}
-  };
-
-  class TombstoneIndexListEntry : public IndexListEntry {
-  public:
-    TombstoneIndexListEntry() : IndexListEntry(TOMBSTONE_KEY) {}
-  };
-
-  // The following statics are thread safe. They're read only, and you
-  // can't step from them to any other list entries.
-  ManagedStatic<EmptyIndexListEntry> IndexListEntryEmptyKey;
-  ManagedStatic<TombstoneIndexListEntry> IndexListEntryTombstoneKey;
-}
-
 char SlotIndexes::ID = 0;
 INITIALIZE_PASS(SlotIndexes, "slotindexes",
                 "Slot index numbering", false, false)
 
-IndexListEntry* IndexListEntry::getEmptyKeyEntry() {
-  return &*IndexListEntryEmptyKey;
-}
-
-IndexListEntry* IndexListEntry::getTombstoneKeyEntry() {
-  return &*IndexListEntryTombstoneKey;
-}
-
-
 void SlotIndexes::getAnalysisUsage(AnalysisUsage &au) const {
   au.setPreservesAll();
   MachineFunctionPass::getAnalysisUsage(au);