[clang] Add -fdebug-default-version for specifying the default DWARF version

This flag decouples specifying the DWARF version from enabling/disabling
DWARF in general (or the gN level - gmlt/limited/standalone, etc) while
still allowing existing -gdwarf-N flags to override this default.

Patch by Caroline Tice!

Differential Revision: https://reviews.llvm.org/D69822

3 files changed, 30 insertions, 1 deletions

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 17cb4816e61..008742aca57 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3335,7 +3335,6 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D,
   // This avoids having to monkey around further in cc1 other than to disable
   // codeview if not running in a Windows environment. Perhaps even that
   // decision should be made in the driver as well though.
-  unsigned DWARFVersion = 0;
   llvm::DebuggerKind DebuggerTuning = TC.getDefaultDebuggerTuning();
 
   bool SplitDWARFInlining =
@@ -3418,11 +3417,18 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D,
     }
   }
 
+  unsigned DWARFVersion = 0;
+  unsigned DefaultDWARFVersion = ParseDebugDefaultVersion(TC, Args);
   if (EmitDwarf) {
     // Start with the platform default DWARF version
     DWARFVersion = TC.GetDefaultDwarfVersion();
     assert(DWARFVersion && "toolchain default DWARF version must be nonzero");
 
+    // If the user specified a default DWARF version, that takes precedence
+    // over the platform default.
+    if (DefaultDWARFVersion)
+      DWARFVersion = DefaultDWARFVersion;
+
     // Override with a user-specified DWARF version
     if (GDwarfN)
       if (auto ExplicitVersion = DwarfVersionNum(GDwarfN->getSpelling()))
@@ -6354,6 +6360,11 @@ void ClangAs::ConstructJob(Compilation &C, const JobAction &JA,
     if (WantDebug)
       DwarfVersion = DwarfVersionNum(A->getSpelling());
   }
+
+  unsigned DefaultDwarfVersion = ParseDebugDefaultVersion(getToolChain(), Args);
+  if (DwarfVersion == 0)
+    DwarfVersion = DefaultDwarfVersion;
+
   if (DwarfVersion == 0)
     DwarfVersion = getToolChain().GetDefaultDwarfVersion();
 
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 10743559e04..709ddaae4ab 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -1138,6 +1138,21 @@ unsigned tools::ParseFunctionAlignment(const ToolChain &TC,
   return Value ? llvm::Log2_32_Ceil(std::min(Value, 65536u)) : Value;
 }
 
+unsigned tools::ParseDebugDefaultVersion(const ToolChain &TC,
+                                         const ArgList &Args) {
+  const Arg *A = Args.getLastArg(options::OPT_fdebug_default_version);
+
+  if (!A)
+    return 0;
+
+  unsigned Value = 0;
+  if (StringRef(A->getValue()).getAsInteger(10, Value) || Value > 5 ||
+      Value < 2)
+    TC.getDriver().Diag(diag::err_drv_invalid_int_value)
+        << A->getAsString(Args) << A->getValue();
+  return Value;
+}
+
 void tools::AddAssemblerKPIC(const ToolChain &ToolChain, const ArgList &Args,
                              ArgStringList &CmdArgs) {
   llvm::Reloc::Model RelocationModel;
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.h b/clang/lib/Driver/ToolChains/CommonArgs.h
index 79468e6b892..cf1ce14249e 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.h
+++ b/clang/lib/Driver/ToolChains/CommonArgs.h
@@ -68,6 +68,9 @@ ParsePICArgs(const ToolChain &ToolChain, const llvm::opt::ArgList &Args);
 unsigned ParseFunctionAlignment(const ToolChain &TC,
                                 const llvm::opt::ArgList &Args);
 
+unsigned ParseDebugDefaultVersion(const ToolChain &TC,
+                                  const llvm::opt::ArgList &Args);
+
 void AddAssemblerKPIC(const ToolChain &ToolChain,
                       const llvm::opt::ArgList &Args,
                       llvm::opt::ArgStringList &CmdArgs);