[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

2 files changed, 8 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index 01d018fdde3..3b1fd76638e 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -92,9 +92,6 @@
 using namespace llvm;
 using namespace llvm::codeview;
 
-static cl::opt<bool> EmitDebugGlobalHashes("emit-codeview-ghash-section",
-                                           cl::ReallyHidden, cl::init(false));
-
 static CPUType mapArchToCVCPUType(Triple::ArchType Type) {
   switch (Type) {
   case Triple::ArchType::x86:
@@ -125,6 +122,11 @@ CodeViewDebug::CodeViewDebug(AsmPrinter *AP)
 
   TheCPU =
       mapArchToCVCPUType(Triple(MMI->getModule()->getTargetTriple()).getArch());
+
+  // Check if we should emit type record hashes.
+  ConstantInt *GH = mdconst::extract_or_null<ConstantInt>(
+      MMI->getModule()->getModuleFlag("CodeViewGHash"));
+  EmitDebugGlobalHashes = GH && !GH->isZero();
 }
 
 StringRef CodeViewDebug::getFullFilepath(const DIFile *File) {
diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
index ef0f0c3635e..e85de5235aa 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
@@ -54,6 +54,9 @@ class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
   BumpPtrAllocator Allocator;
   codeview::GlobalTypeTableBuilder TypeTable;
 
+  /// Whether to emit type record hashes into .debug$H.
+  bool EmitDebugGlobalHashes = false;
+
   /// The codeview CPU type used by the translation unit.
   codeview::CPUType TheCPU;