[ORC] Change handling for SymbolStringPtr tombstones and empty keys.

SymbolStringPtr used to use nullptr as its empty value and (since it performed
ref-count operations on any non-nullptr) a pointer to a special pool-entry
instance as its tombstone.

This commit changes the scheme to use two invalid pointer values as the empty
and tombstone values, and broadens the ref-count guard to prevent ref-counting
operations from being performed on these pointers. This should improve the
performance of SymbolStringPtrs used in DenseMaps/DenseSets, as ref counting
operations will no longer be performed on the tombstone.

llvm-svn: 360925

1 files changed, 0 insertions, 2 deletions

diff --git a/llvm/lib/ExecutionEngine/Orc/Core.cpp b/llvm/lib/ExecutionEngine/Orc/Core.cpp
index 674b44501ac..bbc5a3e8dab 100644
--- a/llvm/lib/ExecutionEngine/Orc/Core.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/Core.cpp
@@ -133,8 +133,6 @@ struct PrintSymbolMapElemsMatchingCLOpts {
 namespace llvm {
 namespace orc {
 
-SymbolStringPool::PoolMapEntry SymbolStringPtr::Tombstone(0);
-
 char FailedToMaterialize::ID = 0;
 char SymbolsNotFound::ID = 0;
 char SymbolsCouldNotBeRemoved::ID = 0;