Re-implement caching for the linkage calculation of declarations.

My previous attempt at solving the compile-time problem with many
redeclarations of the same entity cached both linkage and visibility,
while this patch only tackles linkage. There are several reasons for
this difference:

  - Linkage is a language concept, and is evaluated many times during
    semantic analysis and codegen, while visibility is only a
    code-generation concept that is evaluated only once per (unique)
    declaration. Hence, we *must* optimize linkage calculations but
    don't need to optimize visibility computation.
  - Once we know the linkage of a declaration, subsequent
    redeclarations can't change that linkage. Hence, cache
    invalidation is far simpler than for visibility, where a later
    redeclaration can completely change the visibility.
  - We have 3 spare bits in Decl to store the linkage cache, so the
    cache doesn't increase the size of declarations. With the
    visibility+linkage cache, NamedDecl got larger.

llvm-svn: 121023

1 files changed, 2 insertions, 2 deletions

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index adbf3bff3c3..7053f404e43 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -384,7 +384,7 @@ 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++]);
@@ -651,7 +651,7 @@ 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++]);