[modules] In C++, stop serializing and deserializing a list of declarations in

the identifier table. This is redundant, since the TU-scope lookups are also
serialized as part of the TU DeclContext, and wasteful in a number of ways. We
still emit the decls for PCH / preamble builds, since for those we want
identical results, not merely semantically equivalent ones.

llvm-svn: 242855

1 files changed, 19 insertions, 7 deletions

diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index 3fd1f21ba3f..99b945597bc 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -378,7 +378,7 @@ void LookupResult::resolveKind() {
   // Don't do any extra resolution if we've already resolved as ambiguous.
   if (ResultKind == Ambiguous) return;
 
-  llvm::SmallPtrSet<NamedDecl*, 16> Unique;
+  llvm::SmallDenseMap<NamedDecl*, unsigned, 16> Unique;
   llvm::SmallPtrSet<QualType, 16> UniqueTypes;
 
   bool Ambiguous = false;
@@ -414,14 +414,26 @@ void LookupResult::resolveKind() {
       }
     }
 
-    if (!Unique.insert(D).second) {
+    auto UniqueResult = Unique.insert(std::make_pair(D, I));
+    if (!UniqueResult.second) {
       // If it's not unique, pull something off the back (and
       // continue at this index).
-      // FIXME: This is wrong. We need to take the more recent declaration in
-      // order to get the right type, default arguments, etc. We also need to
-      // prefer visible declarations to hidden ones (for redeclaration lookup
-      // in modules builds).
-      Decls[I] = Decls[--N];
+      auto ExistingI = UniqueResult.first->second;
+      auto *Existing = Decls[ExistingI]->getUnderlyingDecl();
+      for (Decl *Prev = Decls[I]->getUnderlyingDecl()->getPreviousDecl(); /**/;
+           Prev = Prev->getPreviousDecl()) {
+        if (Prev == Existing) {
+          // Existing result is older. Replace it with the new one.
+          Decls[ExistingI] = Decls[I];
+          Decls[I] = Decls[--N];
+          break;
+        }
+        if (!Prev) {
+          // New decl is older. Keep the existing one.
+          Decls[I] = Decls[--N];
+          break;
+        }
+      }
       continue;
     }