[clang-cl] Don't emit dllexport inline functions etc. from pch files (PR37801)

With MSVC, PCH files are created along with an object file that needs to
be linked into the final library or executable. That object file
contains the code generated when building the headers. In particular, it
will include definitions of inline dllexport functions, and because they
are emitted in this object file, other files using the PCH do not need
to emit them. See the bug for an example.

This patch makes clang-cl match MSVC's behaviour in this regard, causing
significant compile-time savings when building dlls using precompiled
headers.

For example, in a 64-bit optimized shared library build of Chromium with
PCH, it reduces the binary size and compile time of
stroke_opacity_custom.obj from 9315564 bytes to 3659629 bytes and 14.6
to 6.63 s. The wall-clock time of building blink_core.dll goes from
38m41s to 22m33s. ("user" time goes from 1979m to 1142m).

Differential Revision: https://reviews.llvm.org/D48426

llvm-svn: 335466

1 files changed, 11 insertions, 4 deletions

diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 1e3a098b09e..7d5b521d4d9 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -1458,16 +1458,23 @@ void ASTWriter::WriteControlBlock(Preprocessor &PP, ASTContext &Context,
   MetadataAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 16)); // Clang min.
   MetadataAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // Relocatable
   MetadataAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // Timestamps
+  MetadataAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // PCHHasObjectFile
   MetadataAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // Errors
   MetadataAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Blob)); // SVN branch/tag
   unsigned MetadataAbbrevCode = Stream.EmitAbbrev(std::move(MetadataAbbrev));
   assert((!WritingModule || isysroot.empty()) &&
          "writing module as a relocatable PCH?");
   {
-    RecordData::value_type Record[] = {METADATA, VERSION_MAJOR, VERSION_MINOR,
-                                       CLANG_VERSION_MAJOR, CLANG_VERSION_MINOR,
-                                       !isysroot.empty(), IncludeTimestamps,
-                                       ASTHasCompilerErrors};
+    RecordData::value_type Record[] = {
+        METADATA,
+        VERSION_MAJOR,
+        VERSION_MINOR,
+        CLANG_VERSION_MAJOR,
+        CLANG_VERSION_MINOR,
+        !isysroot.empty(),
+        IncludeTimestamps,
+        Context.getLangOpts().BuildingPCHWithObjectFile,
+        ASTHasCompilerErrors};
     Stream.EmitRecordWithBlob(MetadataAbbrevCode, Record,
                               getClangFullRepositoryVersion());
   }