Revamp the SourceManager to separate the representation of parsed

source locations from source locations loaded from an AST/PCH file.

Previously, loading an AST/PCH file involved carefully pre-allocating
space at the beginning of the source manager for the source locations
and FileIDs that correspond to the prefix, and then appending the
source locations/FileIDs used for parsing the remaining translation
unit. This design forced us into loading PCH files early, as a prefix,
whic has become a rather significant limitation.

This patch splits the SourceManager space into two parts: for source
location "addresses", the lower values (growing upward) are used to
describe parsed code, while upper values (growing downward) are used
for source locations loaded from AST/PCH files. Similarly, positive
FileIDs are used to describe parsed code while negative FileIDs are
used to file/macro locations loaded from AST/PCH files. As a result,
we can load PCH/AST files even during parsing, making various
improvemnts in the future possible, e.g., teaching #include <foo.h> to
look for and load <foo.h.gch> if it happens to be already available.

This patch was originally written by Sebastian Redl, then brought
forward to the modern age by Jonathan Turner, and finally
polished/finished by me to be committed.

llvm-svn: 135484

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index c58e3af5089..d9535735b5c 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -42,7 +42,7 @@
 using namespace clang;
 
 CompilerInstance::CompilerInstance()
-  : Invocation(new CompilerInvocation()) {
+  : Invocation(new CompilerInvocation()), ModuleManager(0) {
 }
 
 CompilerInstance::~CompilerInstance() {
@@ -275,6 +275,7 @@ void CompilerInstance::createPCHExternalASTSource(llvm::StringRef Path,
                                           getPreprocessor(), getASTContext(),
                                           DeserializationListener,
                                           Preamble));
+  ModuleManager = static_cast<ASTReader*>(Source.get());
   getASTContext().setExternalSource(Source);
 }