Implement caching for the linkage and visibility calculations of

declarations.

The motivation for this patch is that linkage/visibility computations
are linear in the number of redeclarations of an entity, and we've run
into a case where a single translation unit has > 6500 redeclarations
of the same (unused!) external variable. Since each redeclaration
involves a linkage check, the resulting quadratic behavior makes Clang
slow to a crawl. With this change, a simple test with 512
redeclarations of a variable syntax-checks ~20x faster than
before.

That said, I hate this change, and will probably end up reverting it
in a few hours. Reasons to hate it:
  - It makes NamedDecl larger, since we don't have enough free bits in
  Decl to squeeze in the extra information about caching.
  - There are way too many places where we need to invalidate this
  cache, because the visibility of a declaration can change due to
  redeclarations (!). Despite self-hosting and passing the testsuite,
  I have no confidence that I've found all of places where this cache
  needs to be invalidated.

llvm-svn: 120808

1 files changed, 2 insertions, 2 deletions

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index b1e46a623e4..c21dfc2b1f1 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -383,7 +383,7 @@ void ASTDeclReader::VisitFunctionDecl(FunctionDecl *FD) {
   // FunctionDecl's body is handled last at ASTDeclReader::Visit,
   // after everything else is read.
 
-  FD->setStorageClass((StorageClass)Record[Idx++]);
+  FD->SClass = (StorageClass)Record[Idx++];
   FD->setStorageClassAsWritten((StorageClass)Record[Idx++]);
   FD->setInlineSpecified(Record[Idx++]);
   FD->setVirtualAsWritten(Record[Idx++]);
@@ -650,7 +650,7 @@ void ASTDeclReader::VisitIndirectFieldDecl(IndirectFieldDecl *FD) {
 void ASTDeclReader::VisitVarDecl(VarDecl *VD) {
   VisitDeclaratorDecl(VD);
   VisitRedeclarable(VD);
-  VD->setStorageClass((StorageClass)Record[Idx++]);
+  VD->SClass = (StorageClass)Record[Idx++];
   VD->setStorageClassAsWritten((StorageClass)Record[Idx++]);
   VD->setThreadSpecified(Record[Idx++]);
   VD->setCXXDirectInitializer(Record[Idx++]);