Lazy deserialization of the declaration chains associated with

identifiers from a precompiled header.

This patch changes the primary name lookup method for entities within
a precompiled header. Previously, we would load all of the names of
declarations at translation unit scope into a large DenseMap (inside
the TranslationUnitDecl's DeclContext), and then perform a special
"last resort" lookup into this DeclContext when we knew there was a
PCH file (see Sema::LookupName). Now, when we see an identifier named
for the first time, we load all of the declarations with that name
that are visible from the translation unit into the IdentifierInfo's
chain of declarations. Thus, the explicit "look into the translation
unit's DeclContext" code is gone, and Sema effectively uses the same
IdentifierInfo-based name lookup mechanism whether we are using a PCH
file or not. 

This approach should help PCH scale with the size of the input program
rather than the size of the PCH file. The "Hello, World!" application
with Carbon.h as a PCH file now loads 20% of the identifiers in the
PCH file rather than 85% of the identifiers. 

90% of the 20% of identifiers loaded are actually loaded when we
deserialize the preprocessor state. The next step is to make the
preprocessor load macros lazily, which should drastically reduce the
number of types, declarations, and identifiers loaded for "Hello,
World".



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@69737 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 34 insertions, 4 deletions

diff --git a/include/clang/Basic/IdentifierTable.h b/include/clang/Basic/IdentifierTable.h
index d4f680494e..3156bbc4e9 100644
--- a/include/clang/Basic/IdentifierTable.h
+++ b/include/clang/Basic/IdentifierTable.h
@@ -229,7 +229,7 @@ private:
 };
 
 /// IdentifierInfoLookup - An abstract class used by IdentifierTable that
-///  provides an interface for for performing lookups from strings
+///  provides an interface for performing lookups from strings
 /// (const char *) to IdentiferInfo objects.
 class IdentifierInfoLookup {
 public:
@@ -260,6 +260,11 @@ public:
   IdentifierTable(const LangOptions &LangOpts,
                   IdentifierInfoLookup* externalLookup = 0);
   
+  /// \brief Set the external identifier lookup mechanism.
+  void setExternalIdentifierLookup(IdentifierInfoLookup *IILookup) {
+    ExternalLookup = IILookup;
+  }
+
   llvm::BumpPtrAllocator& getAllocator() {
     return HashTable.getAllocator();
   }
@@ -295,6 +300,34 @@ public:
     return *II;
   }
   
+  /// \brief Creates a new IdentifierInfo from the given string.
+  ///
+  /// This is a lower-level version of get() that requires that this
+  /// identifier not be known previously and that does not consult an
+  /// external source for identifiers. In particular, external
+  /// identifier sources can use this routine to build IdentifierInfo
+  /// nodes and then introduce additional information about those
+  /// identifiers.
+  IdentifierInfo &CreateIdentifierInfo(const char *NameStart, 
+                                       const char *NameEnd) {
+    llvm::StringMapEntry<IdentifierInfo*> &Entry =
+      HashTable.GetOrCreateValue(NameStart, NameEnd);
+    
+    IdentifierInfo *II = Entry.getValue();
+    assert(!II && "IdentifierInfo already exists");
+    
+    // Lookups failed, make a new IdentifierInfo.
+    void *Mem = getAllocator().Allocate<IdentifierInfo>();
+    II = new (Mem) IdentifierInfo();
+    Entry.setValue(II);
+
+    // Make sure getName() knows how to find the IdentifierInfo
+    // contents.
+    II->Entry = &Entry;
+
+    return *II;
+  }
+
   IdentifierInfo &get(const char *Name) {
     return get(Name, Name+strlen(Name));
   }
@@ -304,14 +337,11 @@ public:
     return get(NameBytes, NameBytes+Name.size());
   }
 
-private:
   typedef HashTableTy::const_iterator iterator;
   typedef HashTableTy::const_iterator const_iterator;
   
   iterator begin() const { return HashTable.begin(); }
   iterator end() const   { return HashTable.end(); }
-public:
-  
   unsigned size() const { return HashTable.size(); }
   
   /// PrintStats - Print some statistics to stderr that indicate how well the