Module Debugging: Use a nonzero DWO id for precompiled headers.

PCH files don't have a module signature and LLVM uses a nonzero DWO id as
an indicator for skeleton / module CUs. This change pins the DWO id for PCH
files to a known constant value.
The correct long-term solution here is to implement a module signature
that is an actual dterministic hash (at the moment module signatures are
just random nonzero numbers) and then enable this for PCH files as well.

<rdar://problem/24290667>

llvm-svn: 258507

1 files changed, 5 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/ObjectFilePCHContainerOperations.cpp b/clang/lib/CodeGen/ObjectFilePCHContainerOperations.cpp
index cd17832554d..2178ec21c7a 100644
--- a/clang/lib/CodeGen/ObjectFilePCHContainerOperations.cpp
+++ b/clang/lib/CodeGen/ObjectFilePCHContainerOperations.cpp
@@ -219,7 +219,11 @@ public:
 
     M->setTargetTriple(Ctx.getTargetInfo().getTriple().getTriple());
     M->setDataLayout(Ctx.getTargetInfo().getDataLayoutString());
-    Builder->getModuleDebugInfo()->setDwoId(Buffer->Signature);
+
+    // PCH files don't have a signature field in the control block,
+    // but LLVM detects DWO CUs by looking for a non-zero DWO id.
+    uint64_t Signature = Buffer->Signature ? Buffer->Signature : ~1U;
+    Builder->getModuleDebugInfo()->setDwoId(Signature);
 
     // Finalize the Builder.
     if (Builder)