DebugInfo: Let -gdwarf use the toolchain default DWARF version, instead of hardcoded/aliased to -gdwarf-4

Author: dwblaikie

clang/include/clang/Driver/Options.td

@@ -1972,6 +1972,10 @@ def ggdb2 : Flag<["-"], "ggdb2">, Group<ggdbN_Group>;
 def ggdb3 : Flag<["-"], "ggdb3">, Group<ggdbN_Group>;
 def glldb : Flag<["-"], "glldb">, Group<gTune_Group>;
 def gsce : Flag<["-"], "gsce">, Group<gTune_Group>;
+// Equivalent to our default dwarf version. Forces usual dwarf emission when
+// CodeView is enabled.
+def gdwarf : Flag<["-"], "gdwarf">, Group<g_Group>,
+  HelpText<"Generate source-level debug information with the default dwarf version">;
 def gdwarf_2 : Flag<["-"], "gdwarf-2">, Group<g_Group>,
   HelpText<"Generate source-level debug information with dwarf version 2">;
 def gdwarf_3 : Flag<["-"], "gdwarf-3">, Group<g_Group>,
@@ -1989,10 +1993,6 @@ def gcodeview_ghash : Flag<["-"], "gcodeview-ghash">,
   Flags<[CC1Option, CoreOption]>;
 def gno_codeview_ghash : Flag<["-"], "gno-codeview-ghash">, Flags<[CoreOption]>;
 
-// Equivalent to our default dwarf version. Forces usual dwarf emission when
-// CodeView is enabled.
-def gdwarf : Flag<["-"], "gdwarf">, Alias<gdwarf_4>, Flags<[CoreOption]>;
-
 def gfull : Flag<["-"], "gfull">, Group<g_Group>;
 def gused : Flag<["-"], "gused">, Group<g_Group>;
 def gstabs : Joined<["-"], "gstabs">, Group<g_Group>, Flags<[Unsupported]>;

clang/lib/Driver/ToolChains/Clang.cpp

@@ -3198,9 +3198,9 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D,
   }
 
   // If a -gdwarf argument appeared, remember it.
-  const Arg *GDwarfN =
-          Args.getLastArg(options::OPT_gdwarf_2, options::OPT_gdwarf_3,
-                          options::OPT_gdwarf_4, options::OPT_gdwarf_5);
+  const Arg *GDwarfN = Args.getLastArg(
+      options::OPT_gdwarf_2, options::OPT_gdwarf_3, options::OPT_gdwarf_4,
+      options::OPT_gdwarf_5, options::OPT_gdwarf);
   bool EmitDwarf = false;
   if (GDwarfN) {
     if (checkDebugInfoOption(GDwarfN, Args, D, TC))
@@ -3231,6 +3231,7 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D,
   if (EmitDwarf) {
     // Start with the platform default DWARF version
     DWARFVersion = TC.GetDefaultDwarfVersion();
+    assert(DWARFVersion && "toolchain default DWARF version must be nonzero");
 
     // Override with a user-specified DWARF version
     if (GDwarfN)

clang/test/CodeGen/dwarf-version.c

@@ -14,6 +14,7 @@
 // RUN: %clang -target powerpc-unknown-openbsd -g -S -emit-llvm -o - %s | FileCheck %s --check-prefix=VER2
 // RUN: %clang -target powerpc-unknown-freebsd -g -S -emit-llvm -o - %s | FileCheck %s --check-prefix=VER2
 // RUN: %clang -target i386-pc-solaris -g -S -emit-llvm -o - %s | FileCheck %s --check-prefix=VER2
+// RUN: %clang -target i386-pc-solaris -gdwarf -S -emit-llvm -o - %s | FileCheck %s --check-prefix=VER2
 
 // Check which debug info formats we use on Windows. By default, in an MSVC
 // environment, we should use codeview. You can enable dwarf, which implicitly