[codeview] Expose -gcodeview-ghash for global type hashing

Summary:
Experience has shown that the functionality is useful. It makes linking
optimized clang with debug info for me a lot faster, 20s to 13s. The
type merging phase of PDB writing goes from 10s to 3s.

This removes the LLVM cl::opt and replaces it with a metadata flag.

After this change, users can do the following to use ghash:
- add -gcodeview-ghash to compiler flags
- replace /DEBUG with /DEBUG:GHASH in linker flags

Reviewers: zturner, hans, thakis, takuto.ikuta

Subscribers: aprantl, hiraditya, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D54370

llvm-svn: 347072

1 files changed, 8 insertions, 1 deletions

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index b2d0ae7f1de..dd79e8ee868 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3198,9 +3198,16 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D,
       CmdArgs.push_back("-gembed-source");
   }
 
-  if (EmitCodeView)
+  if (EmitCodeView) {
     CmdArgs.push_back("-gcodeview");
 
+    // Emit codeview type hashes if requested.
+    if (Args.hasFlag(options::OPT_gcodeview_ghash,
+                     options::OPT_gno_codeview_ghash, false)) {
+      CmdArgs.push_back("-gcodeview-ghash");
+    }
+  }
+
   RenderDebugEnablingArgs(Args, CmdArgs, DebugInfoKind, DWARFVersion,
                           DebuggerTuning);