Modules: Use hash of PCM content for SIGNATURE

Change ASTFileSignature from a random 32-bit number to the hash of the
PCM content.

  - Move definition ASTFileSignature to Basic/Module.h so Module and
    ASTSourceDescriptor can use it.

  - Change the signature from uint64_t to std::array<uint32_t,5>.

  - Stop using (saving/reading) the size and modification time of PCM
    files when there is a valid SIGNATURE.

  - Add UNHASHED_CONTROL_BLOCK, and use it to store the SIGNATURE record
    and other records that shouldn't affect the hash.  Because implicit
    modules reuses the same file for multiple levels of -Werror, this
    includes DIAGNOSTIC_OPTIONS and DIAG_PRAGMA_MAPPINGS.

This helps to solve a PCH + implicit Modules dependency issue: PCH files
are handled by the external build system, whereas implicit modules are
handled by internal compiler build system.  This prevents invalidating a
PCH when the compiler overwrites a PCM file with the same content
(modulo the diagnostic differences).

Design and original patch by Manman Ren!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@297655 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 2 insertions, 1 deletions

diff --git a/include/clang/Frontend/PCHContainerOperations.h b/include/clang/Frontend/PCHContainerOperations.h
index d323fb3e8b..f9a73508d7 100644
--- a/include/clang/Frontend/PCHContainerOperations.h
+++ b/include/clang/Frontend/PCHContainerOperations.h
@@ -10,6 +10,7 @@
 #ifndef LLVM_CLANG_PCH_CONTAINER_OPERATIONS_H
 #define LLVM_CLANG_PCH_CONTAINER_OPERATIONS_H
 
+#include "clang/Basic/Module.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/Support/MemoryBuffer.h"
@@ -29,7 +30,7 @@ class DiagnosticsEngine;
 class CompilerInstance;
 
 struct PCHBuffer {
-  uint64_t Signature;
+  ASTFileSignature Signature;
   llvm::SmallVector<char, 0> Data;
   bool IsComplete;
 };