Use the AST on-disk hash table for name lookup inside a DeclContext.

*Huge* improvement over the amount of deserializing that we do for C++ lookup.
e.g, if he have the Carbon header precompiled and include it on a file containing this:

int x;

these are the before/after stats:

BEFORE:

*** AST File Statistics:
  578 stat cache hits
  4 stat cache misses
  548/30654 source location entries read (1.787695%)
  15907/16501 types read (96.400223%)
  53525/59955 declarations read (89.275291%)
  33993/43525 identifiers read (78.099945%)
  41516/51891 statements read (80.006165%)
  77/5317 macros read (1.448185%)
  0/6335 lexical declcontexts read (0.000000%)
  1/5424 visible declcontexts read (0.018437%)

AFTER using the on-disk table:

*** AST File Statistics:
  578 stat cache hits
  4 stat cache misses
  548/30654 source location entries read (1.787695%)
  10/16501 types read (0.060602%)
  9/59955 declarations read (0.015011%)
  161/43525 identifiers read (0.369902%)
  20/51891 statements read (0.038542%)
  6/5317 macros read (0.112846%)
  0/6335 lexical declcontexts read (0.000000%)
  2/5424 visible declcontexts read (0.036873%)

There's only one issue affecting mostly the precompiled preambles which I will address soon.

llvm-svn: 111636

1 files changed, 6 insertions, 0 deletions

diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 016f4d3c738..a5d2ce21c21 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -1086,6 +1086,12 @@ void ASTWriter::WriteDeclsBlockAbbrevs() {
   Abv->Add(BitCodeAbbrevOp(serialization::DECL_CONTEXT_LEXICAL));
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Blob));
   DeclContextLexicalAbbrev = Stream.EmitAbbrev(Abv);
+
+  Abv = new BitCodeAbbrev();
+  Abv->Add(BitCodeAbbrevOp(serialization::DECL_CONTEXT_VISIBLE));
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 32));
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Blob));
+  DeclContextVisibleLookupAbbrev = Stream.EmitAbbrev(Abv);
 }
 
 /// isRequiredDecl - Check if this is a "required" Decl, which must be seen by