[clang][DebugInfo] Add DW_AT_default_value support for template template parameters

[Michael137]

Summary

After this patch, in the following snippet:

template <typename T> Foo {};

template <template <typename T> class CT = Foo> Bar {};

Bar<> b;

The debug-info entry for the CT template parameter will have
a DW_AT_default_value (true) attached to it.

[dblaikie]

clang/lib/CodeGen/CGDebugInfo.cpp

2095–2097 ↗

(On Diff #482680)

Could we pull this snipped out and do it before the switch - so we don't have to repeat it for each different kind of template parameter type?

[Michael137]

clang/lib/CodeGen/CGDebugInfo.cpp

2095–2097 ↗

(On Diff #482680)

yup makes sense!

[Michael137]

• Remove now redundant isSubstitutedDefaultArgument call

[dblaikie]

Looks good to me - we'd usually split the LLVM part from the Clang part, but I don't think we have fine grained unit tests for DIBuilder (could you check - if we do, then the LLVM part should go separately, with unit test coverage, then the Clang part can go in that uses it) & /maybe/ it's worth having a default value for the IsDefault argument, so any existing callers aren't broken, but I don't feel strongly about it if it all works, the number of external callers is probably quite small/not a big deal.

(if you do split up the clang/llvm parts into separate commits, no need to send them as separate reviews - you can commit them directly)

[Michael137]

• Rebase

[Michael137]

• Split out LLVM changes into separate commit

llvm/include/llvm/IR/DIBuilder.h

public:
     createTemplateValueParameter(DIScope *Scope, StringRef Name, DIType *Ty,
                                  bool IsDefault, Constant *Val);
 
     /// Create debugging information for a template template parameter.
     /// \param Scope        Scope in which this type is defined.
     /// \param Name         Value parameter name.
     /// \param Ty           Parameter type.
     /// \param Val          The fully qualified name of the template.
-    DITemplateValueParameter *createTemplateTemplateParameter(DIScope *Scope,
-                                                              StringRef Name,
-                                                              DIType *Ty,
-                                                              StringRef Val);
+    /// \param IsDefault    Parameter is default or not.
+    DITemplateValueParameter *
+    createTemplateTemplateParameter(DIScope *Scope, StringRef Name, DIType *Ty,
+                                    StringRef Val, bool IsDefault = false);
 
     /// Create debugging information for a template parameter pack.
     /// \param Scope        Scope in which this type is defined.
     /// \param Name         Value parameter name.
     /// \param Ty           Parameter type.
     /// \param Val          An array of types in the pack.
     DITemplateValueParameter *createTemplateParameterPack(DIScope *Scope,
                                                           StringRef Name,

llvm/lib/IR/DIBuilder.cpp

DIBuilder::createTemplateValueParameter(DIScope *Context, StringRef Name,
                                         Constant *Val) {
   return createTemplateValueParameterHelper(
       VMContext, dwarf::DW_TAG_template_value_parameter, Context, Name, Ty,
       isDefault, getConstantOrNull(Val));
 }
 
 DITemplateValueParameter *
 DIBuilder::createTemplateTemplateParameter(DIScope *Context, StringRef Name,
-                                           DIType *Ty, StringRef Val) {
+                                           DIType *Ty, StringRef Val,
+                                           bool IsDefault) {
   return createTemplateValueParameterHelper(
       VMContext, dwarf::DW_TAG_GNU_template_template_param, Context, Name, Ty,
-      false, MDString::get(VMContext, Val));
+      IsDefault, MDString::get(VMContext, Val));
 }
 
 DITemplateValueParameter *
 DIBuilder::createTemplateParameterPack(DIScope *Context, StringRef Name,
                                        DIType *Ty, DINodeArray Val) {
   return createTemplateValueParameterHelper(
       VMContext, dwarf::DW_TAG_GNU_template_parameter_pack, Context, Name, Ty,
       false, Val.get());