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, 11 deletions

diff --git a/llvm/lib/IR/ConstantsContext.h b/llvm/lib/IR/ConstantsContext.h
index e87e23128fc..2f8c9c447d4 100644
--- a/llvm/lib/IR/ConstantsContext.h
+++ b/llvm/lib/IR/ConstantsContext.h
@@ -15,7 +15,7 @@
 #ifndef LLVM_LIB_IR_CONSTANTSCONTEXT_H
 #define LLVM_LIB_IR_CONSTANTSCONTEXT_H
 
-#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/Hashing.h"
 #include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/Instructions.h"
@@ -584,26 +584,25 @@ private:
   };
 
 public:
-  typedef DenseMap<ConstantClass *, char, MapInfo> MapTy;
+  typedef DenseSet<ConstantClass *, MapInfo> MapTy;
 
 private:
   MapTy Map;
 
 public:
-  typename MapTy::iterator map_begin() { return Map.begin(); }
-  typename MapTy::iterator map_end() { return Map.end(); }
+  typename MapTy::iterator begin() { return Map.begin(); }
+  typename MapTy::iterator end() { return Map.end(); }
 
   void freeConstants() {
     for (auto &I : Map)
-      // Asserts that use_empty().
-      delete I.first;
+      delete I; // Asserts that use_empty().
   }
 private:
   ConstantClass *create(TypeClass *Ty, ValType V, LookupKeyHashed &HashKey) {
     ConstantClass *Result = V.create(Ty);
 
     assert(Result->getType() == Ty && "Type specified is not correct!");
-    Map.insert_as(std::make_pair(Result, '\0'), HashKey);
+    Map.insert_as(Result, HashKey);
 
     return Result;
   }
@@ -621,7 +620,7 @@ public:
     if (I == Map.end())
       Result = create(Ty, V, Lookup);
     else
-      Result = I->first;
+      Result = *I;
     assert(Result && "Unexpected nullptr");
 
     return Result;
@@ -631,7 +630,7 @@ public:
   void remove(ConstantClass *CP) {
     typename MapTy::iterator I = Map.find(CP);
     assert(I != Map.end() && "Constant not found in constant table!");
-    assert(I->first == CP && "Didn't find correct element?");
+    assert(*I == CP && "Didn't find correct element?");
     Map.erase(I);
   }
 
@@ -645,7 +644,7 @@ public:
 
     auto I = Map.find_as(Lookup);
     if (I != Map.end())
-      return I->first;
+      return *I;
 
     // Update to the new value.  Optimize for the case when we have a single
     // operand that we're changing, but handle bulk updates efficiently.
@@ -659,7 +658,7 @@ public:
         if (CP->getOperand(I) == From)
           CP->setOperand(I, To);
     }
-    Map.insert_as(std::make_pair(CP, '\0'), Lookup);
+    Map.insert_as(CP, Lookup);
     return nullptr;
   }