IR: Use DenseSet instead of DenseMap for ConstantUniqueMap; NFC

Use a DenseSet instead of a DenseMap for constants in LLVMContextImpl.
Last time I looked at this was some time before r223588, when
DenseSet<V> had no advantage over DenseMap<V,char>.  After r223588,
there's a 50% memory savings.

This is all mechanical.  There were little bits of missing API from
DenseSet so I added the trivial implementations:

  - iterator::operator++(int)
  - template <class LookupKeyT> insert_as(ValueTy, LookupKeyT)

There should be no functionality change, just reduced memory consumption
(this wasn't on a profile or anything; just a cleanup I stumbled on).

llvm-svn: 265577

1 files changed, 10 insertions, 32 deletions

diff --git a/llvm/lib/IR/LLVMContextImpl.cpp b/llvm/lib/IR/LLVMContextImpl.cpp
index 9fe189329b0..d5d9038d1e9 100644
--- a/llvm/lib/IR/LLVMContextImpl.cpp
+++ b/llvm/lib/IR/LLVMContextImpl.cpp
@@ -48,26 +48,6 @@ LLVMContextImpl::LLVMContextImpl(LLVMContext &C)
   NamedStructTypesUniqueID = 0;
 }
 
-namespace {
-struct DropReferences {
-  // Takes the value_type of a ConstantUniqueMap's internal map, whose 'second'
-  // is a Constant*.
-  template <typename PairT> void operator()(const PairT &P) {
-    P.second->dropAllReferences();
-  }
-};
-
-// Temporary - drops pair.first instead of second.
-struct DropFirst {
-  // Takes the value_type of a ConstantUniqueMap's internal map, whose 'second'
-  // is a Constant*.
-  template<typename PairT>
-  void operator()(const PairT &P) {
-    P.first->dropAllReferences();
-  }
-};
-}
-
 LLVMContextImpl::~LLVMContextImpl() {
   // NOTE: We need to delete the contents of OwnedModules, but Module's dtor
   // will call LLVMContextImpl::removeModule, thus invalidating iterators into
@@ -99,14 +79,14 @@ LLVMContextImpl::~LLVMContextImpl() {
 #include "llvm/IR/Metadata.def"
 
   // Free the constants.
-  std::for_each(ExprConstants.map_begin(), ExprConstants.map_end(),
-                DropFirst());
-  std::for_each(ArrayConstants.map_begin(), ArrayConstants.map_end(),
-                DropFirst());
-  std::for_each(StructConstants.map_begin(), StructConstants.map_end(),
-                DropFirst());
-  std::for_each(VectorConstants.map_begin(), VectorConstants.map_end(),
-                DropFirst());
+  for (auto *I : ExprConstants)
+    I->dropAllReferences();
+  for (auto *I : ArrayConstants)
+    I->dropAllReferences();
+  for (auto *I : StructConstants)
+    I->dropAllReferences();
+  for (auto *I : VectorConstants)
+    I->dropAllReferences();
   ExprConstants.freeConstants();
   ArrayConstants.freeConstants();
   StructConstants.freeConstants();
@@ -165,10 +145,8 @@ void LLVMContextImpl::dropTriviallyDeadConstantArrays() {
   do {
     Changed = false;
 
-    for (auto I = ArrayConstants.map_begin(), E = ArrayConstants.map_end();
-         I != E; ) {
-      auto *C = I->first;
-      I++;
+    for (auto I = ArrayConstants.begin(), E = ArrayConstants.end(); I != E;) {
+      auto *C = *I++;
       if (C->use_empty()) {
         Changed = true;
         C->destroyConstant();