[clang][DebugInfo] Attach DW_AT_default_value to template arg metadata regardless of DwarfVersion

[Michael137]

Summary

Summary

Starting with DWARFv5, DW_AT_default_value can be used to indicate
that a template argument has a default value. With this patch Clang
will attach the attribute to the debug metadata regardless of version.

In a follow-up patch we will change llvm to emit this attribute in
earlier versions of DWARF, unless compiling with -gstrict-dwarf.

Details

• Previously the DwarfVersion check in CGDebugInfo was inconsistent:

For non-type template arguments we attached the attribute to the debug
metadata in DWARFv5 only. Whereas for type template arguments we didn't
have such a version restriction. With this patch we attach the attribute
regardless of DWARF version (and instead offload the check to the AsmPrinter
in a future patch).

[Michael137]

• Fix test formatting

[dblaikie]

(This should be committed in two parts - the LLVM part first, then the Clang part - since they can be separated, they should be - but happy to review it altogether)

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

1856 ↗

(On Diff #482419)

Maybe this could be a more general function? It could take a version and then have a general name "isCompatibleWithVersion(X)" and be used for other strict DWARF+version checks?

1857–1858 ↗

(On Diff #482419)

You can drop these - there's tons of non-null assumptions throughout the codebase, most aren't asserted.

[Michael137]

• Split clang and llvm changes

[Michael137]

In D139928#3992233, @dblaikie wrote:

(This should be committed in two parts - the LLVM part first, then the Clang part - since they can be separated, they should be - but happy to review it altogether)

Split the review: https://reviews.llvm.org/D139953

Updated the version check to be a bit more general.

[dblaikie]

Looks good, thanks!

clang/lib/CodeGen/CGDebugInfo.cpp

case TemplateArgument::Type: {
                 templateType->getDefaultArgument() == TA.getAsType();
 
       TemplateParams.push_back(DBuilder.createTemplateTypeParameter(
           TheCU, Name, TTy, defaultParameter));
 
     } break;
     case TemplateArgument::Integral: {
       llvm::DIType *TTy = getOrCreateType(TA.getIntegralType(), Unit);
-      if (Args.TList && CGM.getCodeGenOpts().DwarfVersion >= 5)
+      if (Args.TList)
         if (auto *templateType = dyn_cast_or_null<NonTypeTemplateParmDecl>(
                 Args.TList->getParam(i)))
           if (templateType->hasDefaultArgument() &&
               !templateType->getDefaultArgument()->isValueDependent())
             defaultParameter = llvm::APSInt::isSameValue(
                 templateType->getDefaultArgument()->EvaluateKnownConstInt(
                     CGM.getContext()),
                 TA.getAsIntegral());

clang/test/CodeGenCXX/debug-info-template-parameter.cpp

 // Test for DebugInfo for Defaulted parameters for C++ templates
 // Supported: -O0, standalone DI
 
 // RUN: %clang_cc1 -emit-llvm %std_cxx11-14 -dwarf-version=5 -triple x86_64 %s -O0 -disable-llvm-passes -debug-info-kind=standalone -o - | FileCheck %s --check-prefixes=CHECK,PRE17
 // RUN: %clang_cc1 -emit-llvm %std_cxx17- -dwarf-version=5 -triple x86_64 %s -O0 -disable-llvm-passes -debug-info-kind=standalone -o - | FileCheck %s --check-prefixes=CHECK,CXX17
+// RUN: %clang_cc1 -emit-llvm %std_cxx17- -dwarf-version=4 -triple x86_64 %s -O0 -disable-llvm-passes -debug-info-kind=standalone -o - | FileCheck %s --check-prefixes=CHECK,CXX17
 
 // CHECK: DILocalVariable(name: "f1", {{.*}}, type: ![[TEMPLATE_TYPE:[0-9]+]]
 // CHECK: [[TEMPLATE_TYPE]] = {{.*}}!DICompositeType({{.*}}, templateParams: ![[F1_TYPE:[0-9]+]]
 // CHECK: [[F1_TYPE]] = !{![[FIRST:[0-9]+]], ![[SECOND:[0-9]+]], ![[THIRD:[0-9]+]], ![[FORTH:[0-9]+]]}
 // CHECK: [[FIRST]] = !DITemplateTypeParameter(name: "T", type: !{{[0-9]*}})
 // CHECK: [[SECOND]] = !DITemplateValueParameter(name: "i", type: !{{[0-9]*}}, value: i32 6)
 // PRE17: [[THIRD]] = !DITemplateValueParameter(name: "b", type: !{{[0-9]*}}, value: i8 0)
 // CXX17: [[THIRD]] = !DITemplateValueParameter(name: "b", type: !{{[0-9]*}}, value: i1 false)