[AST] Squeeze some bits in LinkageComputer::QueryType

Replace the pair std::pair<const NamedDecl *, unsigned> where the
unsigned represents an LVComputationKind by a PointerIntPair.
This saves a pointer per entry in the map LinkageComputer::CachedLinkageInfo.

Differential Revision: https://reviews.llvm.org/D52268

Reviewed by: rjmccall, george.burgess.iv, erichkeane



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@342973 91177308-0d34-0410-b5e6-96231b3b80d8

lib/AST/Linkage.h

@@ -20,6 +20,7 @@
 #include "clang/AST/Type.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/Optional.h"
+#include "llvm/ADT/PointerIntPair.h"
 
 namespace clang {
 /// Kinds of LV computation.  The linkage side of the computation is
@@ -36,6 +37,8 @@ struct LVComputationKind {
   /// in computing linkage.
   unsigned IgnoreAllVisibility : 1;
 
+  enum { NumLVComputationKindBits = 3 };
+
   explicit LVComputationKind(NamedDecl::ExplicitVisibilityKind EK)
       : ExplicitKind(EK), IgnoreExplicitVisibility(false),
         IgnoreAllVisibility(false) {}
@@ -78,12 +81,14 @@ class LinkageComputer {
   // using C = Foo<B, B>;
   // using D = Foo<C, C>;
   //
-  // The unsigned represents an LVComputationKind.
-  using QueryType = std::pair<const NamedDecl *, unsigned>;
+  // The integer represents an LVComputationKind.
+  using QueryType =
+      llvm::PointerIntPair<const NamedDecl *,
+                           LVComputationKind::NumLVComputationKindBits>;
   llvm::SmallDenseMap<QueryType, LinkageInfo, 8> CachedLinkageInfo;
 
   static QueryType makeCacheKey(const NamedDecl *ND, LVComputationKind Kind) {
-    return std::make_pair(ND, Kind.toBits());
+    return QueryType(ND, Kind.toBits());
   }
 
   llvm::Optional<LinkageInfo> lookup(const NamedDecl *ND,