[Driver] Set the default win32-macho debug format to DWARF

rdar://53267670

Differential Revision: https://reviews.llvm.org/D65116

llvm-svn: 366744

Author: vedantk

clang/lib/Driver/ToolChains/MSVC.h

@@ -78,10 +78,12 @@ class LLVM_LIBRARY_VISIBILITY MSVCToolChain : public ToolChain {
   bool isPIEDefault() const override;
   bool isPICDefaultForced() const override;
 
-  /// Set CodeView as the default debug info format. Users can use -gcodeview
-  /// and -gdwarf to override the default.
+  /// Set CodeView as the default debug info format for non-MachO binary
+  /// formats, and to DWARF otherwise. Users can use -gcodeview and -gdwarf to
+  /// override the default.
   codegenoptions::DebugInfoFormat getDefaultDebugFormat() const override {
-    return codegenoptions::DIF_CodeView;
+    return getTriple().isOSBinFormatMachO() ? codegenoptions::DIF_DWARF
+                                            : codegenoptions::DIF_CodeView;
   }
 
   /// Set the debugger tuning to "default", since we're definitely not tuning

clang/test/Misc/win32-macho.c

@@ -1,2 +1,5 @@
 // Check that basic use of win32-macho targets works.
 // RUN: %clang -fsyntax-only -target x86_64-pc-win32-macho %s
+
+// RUN: %clang -fsyntax-only -target x86_64-pc-win32-macho -g %s -### 2>&1 | FileCheck %s -check-prefix=DEBUG-INFO
+// DEBUG-INFO: -dwarf-version={{.*}}